NOVEMBER, 1928 25 CENTS

(AEG. U. S. PATENT OFF.)

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A MAGAZINE OF NATIONAL CIRCULATION > COVERING THE ENTIRE FIELD

MAGNAVOX ebynamiesPEAKERS1111111.1111111-

glre vtristocratBeautiful butt burl walnutcabinet finished in two tones.For 4 -Battery Operation . $60For AC Operation . . . . $70

gra 'BeverlyGracefully proportioned cabinetfinished in light mahogany.For A -Battery Operation . $30For AC Operation $60

Other floor and table models up to $175Uniu only DC $30; AC $40. DYAMI C

"MAC," leader of the famousbroadcaaing "Haywire Orrbe.ary"

LAIagnavox Dynamic reproductionis infinitely finer . . . richer, fuller, morerealistic . . . Those who wince at distortedmusic or who must strain to hear otherspeakers welcome the beauty and generousvolume of Magnavox. That's why fourteenleading radio set manufacturers havechosen it for built-in equipment.

YAVO2CCOMPAY,r

Oakland, California Chicago, Illinois206

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RADIO1.stabli,lied 1917

Published Monthli by the Pacific Radio Publishing CO.ARTHUR H. HAI LORAN, H. W. DICKOW,

Editor Business Manager

P. S. LUCAS, A. I. RIVETT,Associate Editor Draughtsman

FRANK C. JONES, Technical AdviserEntered as second-class matter at Post Office at

San Francisco, Calif.Copyright 1928 by the Pacific Radio Publishing Co.

Address all communications to

PACIFIC RADIO PUBLISHING COMPANYPacific Building, San Francisco, California

VOL. X NOVEMBER, 1928 No II

CONTENTSRADIOTORIAL COMMENT 17

SHORT-WAVE TRANSATLANTICRADIOTELEPHONE SERVICE ..... _19

By S. R. WintersSIMPLIFIED REACTANCE

CALCULATIONS 20By Arthur Hobart

WHAT IS AN UNDERGROUNDANTENNA? /1

By G. M. BestSTANDARD FREQUENCY

TRANSMISSIONS 22

ELECTRIC PHONOGRAPH PICK-UP UNITS 23

By Francis ChurchillRADIO PICTURE TRANSMISSION

AND RECEPTION 25By John P. Arnold

RADIO AIDS AIR RACES 30By Wallace S. Wiggins

BATTERY CHARGING WITHA SYNC 31

By G. F. LampkinA COMPLETE TUBE TESTING

SET - 33By Clinton Osborne

THE MARSHALL SHORT-WAVERECEIVER 34

By S. R. WintersTECHNICAL BRIEFS 37

THE COMMERCIAL BRASS -POUNDER 39

By P. S. LucasA PRACTICAL "B" ELIMINATOR

FOR SHIP USE 39By R. M. Hughes

AN ALL -SHORT-WAVERECEIVER 41

By A. Binneweg, Jr.A SELECTIVE SHORT-WAVE

RECEIVER 42By R. Wm. Tanner

INSIDE STORIES OF FACTORY -BUILT RECEIVERS 43

FORECAST FOR DECEMBER ISSUEJ. Garrick Eisenberg has a helpful

article on "Some Service Considerations."G. F. Lainpkin describes the constrneth.of a crystal -controlled transmitter. "Melt-ing Precious Metals by Radio," is Illus-trated and described in detail. John P.Arnold has some more interesting infor-mation on radio transmission and rc cep-tion of pictures. Circuit diagrams anddescriptions are given of several new a.c.factory -built receivers. Articles necussarily omitted from the November issue,but definitely scheduled for December are"A Short -Wave Superheterodyne," by R.Wm. Tanner; "Impedance of R. F.Chokes," by Glenn L. Browning; and"Experimenting with the Grid Leak." byL. W. Hatry. In "Technical Briefs" willbe found a circuit for adapting a 45 k.c.superheterodyne to the use of a.c. tubes.Frank C. Jones, who is better known asFrancis Churchill, discusses the volumecontrol methods used in a.c. receivers.

2

"You Can Forget the Condensers-If They Are DUBILIERS"

Type PL 1120 especiallydesigned for the Thor-darson types 11-180 andR-280 Power Compacts.used with 171 typetubes and the 280 typetube Rectifier or theElkon E-80 metallicRectifier. Price $15.50

Thereis

No Substitute for QualityNo amount of lurid claims bynimble -penned advertising writ-ers will take the place of qualityin the final analysis-the opera-tion in your power supply.

Ever since the advent of Radio,Dubilier has been the manufac-turers' standard-and the set -builders' stand-by. Built in everyDubilier Condenser is a factor ofsafety which is your safeguard foryears of service without failure.

Dubilier Light Socket Aerial-"A Moulded Bakelite Product"Bring in programs with a mini-mum of interference. Do awaywith the unsightly and troublecausing outside aerial and light-ning arrestor. Simply attach tothe set and plug into the nearestlight socket. Uses no current.Sold by all good dealers on a 5day, money -back basis. Price$1.50.

Write to Dept. 20 for free catalog

DubilierCONDENSER CORPORATION

10 East43rd Street

Reg. U.S. Pet. Off.

New YorkCity

Six Issues for $1.00AVE money. Get the next 6 issues of "RADIO"

.) for one dollar-fifty cents less than they cost ifpurchased from a news dealer. The next six issues of"RADIO" will be better than ever. Let us mail themagazine to your address, starting with the Novemberissue, out on October 25th.

Mail coupon now. Attacha dollar bill, check, moneyorder or $1.00 in stamps

and mail NOW.

Name

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Tell them you saw it in RADIO

A NEW CATALOGJOT Off THE PRESS

Wholesale pricesrr HIS big new catalog heralds a new era in radio. Never before

have you been offered such variety-such quality-such ster-ling value in radio as you are now offered in this large new catalog.In it, wholesale prices are not a myth- but actual reality. Youwill marvel that such merchandise, comprising everything that isnew and worthwhile in radio can be offered at such prices. Hereyou will find high quality that is not high priced. If you are inter-ested in radio you cannot afford to be without the Allied Catalog.

SET BUILDERS!Set Builders, Amateurs and so called "Hams" will delightin the unusual variety-and remarkable values that areoffered in standard kits and parts. Tremendous stocks-real organization-prompt shipping service all combineto make Allied your ideal source of supply.

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What Allied offers you!

A.C.ELECTRIC SETSAllied offers you a new-completeline of A -C Receivers, available ineither chassis form or in a widevariety of beautiful console models.Prices range from $32.95 to $199.00.Dollar for dollar they stand out asone of the season's leading receiv-ers. Engineered to unusual perfec-tion they offer you features foundonly in the highest priced sets.

Allied Service will prove a revelation to you in what radio servicecan really be. Allied Executives backed by years of training in radioare practical men. They know radio. Their vast experience has builtup around them an organization trained to serve. Months of efforthave built up here a tremendous reserve of stock that makes forprompt shipments; and this stock is new stock comprising the sea-sons pick of such prominent manufacturers as Silver -Marshall,Tyrman, Aero, Hammerlund-Roberts, etc.

You Profit When You Buy RightBuying right is half the battle. From the small set builder to thelarge dealer, your success depends upon gauging the public pulse ofradio and in buying right. Everything that is new in radio-theitems the radio public is now demanding are here, ready for yourcall. Write now -the catalog is free for the asking.

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Allied RadioCORPORA -T -10N

711 W. LAKE ST. Dept. E-2 CHICAGO, ILL.

4

The broadcast ofthe ArmyNarygame last year seasenjoyed by hon.tireds of thousandsof fanse!! over thecountry.

Phillips Carlinbroadros flagat one of thebig footballgames.

The Big Game Comes Over.BETTER-CLEARER

MILLIONS of enthusiastic football fans arelistening this fall to the play by play broad-

casts of America's greatest games. They areexperiencing almost as keen enjoyment as ifthey were sitting in the stands. The voice ofthe announcer comes to them clearly and dis-tinctly because their receiving sets are Alumi-num equipped.

Leading radio manufacturers are using Alu-minum extensively for shielding, for conden-ser blades and frames, for chasses, sub -panels,front panels and for many other parts-be-cause Aluminum so ideally meets the variedconditions that radio design presents.

It combines remarkable shielding proper-ties, high electrical conductivity, great strengthand extreme lightness.

Examine the set you contemplate buying.If it is Aluminum equipped you may rest as-sured that the manufacturer has done every-thing in his power to give you the finest pos-sible reception.

And if you are building a receiving set useAluminum for finest results.

We will gladly send you the booklet, "Alumi-num For Radio," which explains the variedradio uses to which Aluminum is adapted.

ALUMINUM COMPANY OF AMERICAALUMINUM IN EVERY COMMERCIAL FORM

2463 Oliver BuildingPittsburgh, Ps. ALUMINU

Offices in 19 PrincipalAmerican Cities

ALUMINUM`We mark of Quality in Radio

'Fell them pill say% it in RA1)10

Faradon Capacitors are specified as standard equipmentwhere electrostatic condenser long life and durability isessential.Faradon Capacitor marks quality. Keep this in mindwhen considering a new set, kit or replacement parts.

WIRELESS SPECIALTY APPARATUS CO.Jamaica Plain, Boston, Mass., U. S. A.

Established 1907

Electrostatic Condensers for All Purposes

Tell them you saw it in RADIO

Hereis a Real

DYNAMICSpeaker Amplifier

:x7

Nothing else like it on the marketRemler Audio Transformers are Different

Because They are Designed for Dynamic SpeakersNO HUM from this super power amplifier and B

eliminator-even with the husky "250" powertube. Remler has so thoroughly engineered this poweramplifier that the hum is eliminated. By scientificplacing of parts and by skillful engineering Remlermakes it so simple for you to assemble this amplifierthat you are assured in advance of complete success.The new Remler audio transformer in the last stage-designed especially for the dynamic loud speaker andthe new Remler output transformer-the only one ofits kind available-allows you to get the most out ofa dynamic speaker for the FIRST time. There is no

other output transformer like it on the market.Nothing just as good. It's a brute in size and a sure-fire performer. It delivers better and purer tonalqualities to the loud speaker than any other knownamplifying device. You will marvel at the fidelity ofreproduction. You have never heard anything like itbefore. Only Remler gives you this modern up to dateequipment. This amplifier is known as the No. 950.The metal base goes with the kit. Everything isincluded-even the screws, nuts, wire and a simplediagram of connections.

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The NewREMLER29

ARECEIVER that looksas good as it works.

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A Professional JobHERE is a receiver for the most discriminating fan. It

can be assembled in a few hours. Simple, explicitwiring charts and instructions make it a pleasure to assemblethis new kit-the best of any we have seen this season. Metalchassis with all holes punched. Beautiful escutcheon plate.The illustration fails to do justice to this new "29" RemlerSUPER. Acknowledged by engineers as the finest thing inradio for the season.

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UNITED RADIO SUPPLIES CO.1062A Howard Street, San Francisco, Calif.

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UNITED RADIO SUPPLIES CO.1062A Howard St., San Francisco, Calif.

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Tell them you saw it in RADIO

DESIGNEDTO RENDERUTMOST INSERVICE

Frost VolumeControl

Gives complete, stepless andwonderfully smooth controlof volume and oscillation.Wearproof roller contactarm, Bakelite case and dustcover. $2.00 and $2.25.

FrostGem

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A Complete Line That Was BuiltFor Your Specific Requirements

Frost -Radio offers you the finest and most complete line of radio partsavailable. This great line was designed and built with the specific require.ments of the set builder in mind. Consequently, when you go to your dealerand order these parts you are sure of obtaining the very finest on the market,built by engineers with many years of experience in radio parts manufacture.Obviously, your receiver will give better, finer and much more dependableresults when you use these superior parts made by Frost -Radio.

Frost Volume ControlWith D.C. Switch

Equipped with sturdy Ger-man silver switch mountedon Bakelite panel, and withswitch points fitted withsterling silver contacts,this Volume Control givesquick operation, positive -locking off position andsaves space. For batteryoperated sets. $2.25.

Fit std. outletbox. Brush brassor Bakeliteplates. $1.00to $3.00.

Frost Gem Rheostats

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Frost ApprovedA.C. Switch

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250 volts, 3 ampUnderwriters' ap-proved. 75c.

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PRICED TOGIVE YOU

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Frost Volume ControlWith A.C. Switch

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ancer

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Slide back the braid 1,

soldering, then slip braidhack over soldered joint.No. 18 double cotton cov-ered, impregnated wire,tinned. 50 ft. roll, 80c.

Mail Coupon Below For Our Complete 16 Page CatalogFrost Blocking Condensers

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New York City CHICAGO San Francisco

HERE'S A BOOK THATYOU SHOULD SEND

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HERBERT H. FROST, INC.160 North La Salle Street, Chicago.-tnd me your new Frost Data Book, containing.,nd facts about tour complete line of parts. I

valuable radio informationenclose 10c.

I My Name

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(Are you a professional set builder,

Frost Heavy Duty FilterCondensers

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Tell them you saw it in RADIO

HFLIST PRICE

$195.00

The Marvelous New Screen Grid

ISOTONE radiophonograph

America's Finest Custom Built Receiver33 Modern Improvements

1. ABSOLUTE ONE SPOT OPERATION, 450 KILOCYCLES2. PERFECT PHONOGRAPH RECORD REPRODUCTION3. OPTIONAL, LOOP OR ANTENNA OPERATION4. PERFECT 8 KILOCYCLE SELECTIVITY5. EXTREME SENSITIVITY, UNLIMITED RANGE6. A.C. POWER SUPPLY OR BATTERY OPERATION7. THREE STAGE SCREENED GRID AMPLIFIER8. EXQUISITE TONE QUALITY FIVE POWER TUBES9. COMPLETE CONSTRUCTION IN ONE HOUR

10. NEW SIGNAL STATIC BALANCE CONTROL11. MANUALLY TUNED R.F. AMPLIFIER STAGES12. THREE STAGE PUSH PULL AUDIO AMPLIFIER13. SPECIAL AUDIO FREQUENCY FILTER14. AUTOMATIC TUBE BALLASTING CONTROL15. MEASURED GAIN OF 85 PER STAGE16. OPERATES ALL DYNAMIC LOUD SPEAKERS17. DUAL PHONO RADIO VOLUME CONTROL18. LABORATORY ASSEMBLED AND MATCHED UNITS19. BUILT IN MICROPHONE TRANSFORMER20. ABSOLUTE STABILITY -CANNOT SQUEAL OR HOWL21. CONSECUTIVE NUMERICAL DIALING22. BEAUTIFUL GOLD DIALS -WALNUT PANEL AND

KNOBS23. COMPLETE INTER UNIT SHIELDING24. VELVET SMOOTH -LINE DRIVEN DIALS25. AUTOMATIC TUBE DISCONNECTING SWITCH26. COMPLETELY SHIELDED -INVISIBLE WIRING27. CADMIUM PLATED STEEL SUPPORTING BASES28. PYRALIN DIFFUSED DIAL ILLUMINATION29. BUREAU OF STANDARD SHIELDING 24 GAUGE30. NEW TYPE LOUD SPEAKER IMPEDANCE31. SPRING SUSPENDED TUBE SOCKETS32. SPECIALLY DESIGNED TANK CONDENSERS33. NEW MIXER BALANCING PADDER

AND MANY OTHER MODERN IMPROVEMENTS

Isotonic Screened Grid AmplifierOperating frequency 450 kilocycles allowing absolute one spotoperation. Extremely sensitive, having a measured gain of 65per stage under actual operating conditions. Absolutely stable,cannot squeal or howl. Arranged for sub panel mounting andsold completely assembled and wired Overall

Unlimited Range. This excellent instrument employs practically everynew engineering feature known to radio science. The

range of the Isotone is almost unlimited. The three -stage screened grid amplifier having theunusually high gain of sixty-five per stage can be hand tuned by the operator which results in ',erectly balanced instrument. The 450 kilocycle amplifier allows absolute one spot tuning.

Perfect Selectivity Actual laboratory tests have shown that an Isotonecan be tuned so that it will select an eight kilocycle

band. This is undoubtedly the highest attainment in selectivity which has been obtained upto this time. Local station interference will never trouble the owner of an Isotone.

Exquisite Tone Quality. Five power tubes are used in the receiverwhich are responsible for the unsurpassed

tonal quality of the instrument. An automatic tube ballasting system eliminates all voltagesurges and phonograph records can be played through the three -stage push pull amplifier bysimply throwing the control knob on the front of the panel. The instrument operates per-fectly with a standard 180 volt B unit and a battery or with the new Isotonic model 5 ABCpower supply.

Easy to Construct.

The Isotone can be completely constructed and wiredby anyone in less than one hour. The factory as-

sembled and wired Isotonic units which make up the instrument are individually laboratorytested and are unconditionally guaranteed to be mechanically and electrically perfect. TheIsotone kit comes absolutely complete with all instructions. Nothing else to buy. Requires3 CX322, 3 CX312A, 2 CX371A, 2 CX30IA tubes.

size 119f," long, 5 wise, sue high. $ 60Requires 3 UX222 and I UX112A tbs. Price List Price, Less TubesHFL Audio Amplifier List

Three stage push pull, with built in microphone transformerand audio filter. Operates all dynamic speakers. All instru-ments and wiring perfectly shielded. Arranged for sub panelmounting and sold separately completely assembled and wired.Overall dimensions 11%" long, 5 %" wide.6.42" high. Uses 2 UX112A and 2 UX171Atubes. Price

HFL ABC Power UnitThis perfect device was designed especially for the Model IfIsotone. It is absolutely tree of A.C. hum, voltage surgesand motor boating. Oversize condenser sections, having anunusually high breakdown rating allowing perfect low notereproduction in the receiver. The Model 5 supplies A voltage8 volts at 2% amperes -Plate voltages 45-90-135 and 180and C Biasing voltages of 40 and variable 0 to 15 volts.Mounted on a satin finished Cadmium plated steel base withsteel cover. Unconditionally guaranteed against breakdownsand to operate perfectly with the Model 10 Iso-IOW` Iteeri,er. size 11" long, 10" wide, !41" 9high. !tequila, 1 UX 280 tube for operation. Price

Immediate Deliveries8 Hour Mail Order Service

Radio Dealers Supply ServiceWholesale Division of

'FibirDA211.1.6 ;

ELECTRIC COMPANY"The House of a Million Radio Parts"

1452 Market Street San Francisco, Calif.

HFL Audio Amplifier $55

$195.00

HFL Screen Grid Unit $60

HFLABCPowerSupply

Model 5$95.00

HFLAUDIOTRANSFORMER

FIFNEVER before has any receiver possessed such

selectivity and unlimited power. Imagine perfectseparations on every wave channel. Absolute 10 kilo-cycle splits-right alongside of the most powerfullocals in the country.

You can choose your station with an Isotone andyou can get that station. You can get it clear and youcan get it without the annoying overlapping swishesthat ordinarily ruin long distance reception.The H F L Isotone is the supreme radio achievement. Webelieve that no other receiver in the country can show anactual radio frequency gain of 65 per stage consistent withabsolute 10 kilocycle band selection.Nothing has been sacrificed to obtain this unprecedented efficiency.The instrument is beauty to behold. The three -stage push-pull audioamplifier produces tone quality that isa revelation. There is choice of radioor phonograph reproduction. A mas-ter control switch-automatic ballast.ing systems-hand-tuned filter trans-formers-these and over 25 other newfeatures play their part in making theIsotone the greatest radio receiver ofall time.

Write to the factory for complete in-formation and an eight -page bookletgiving circuits and all technical data.

Can beConstructedby AnyoneThere is nothing complicated about the construction of anISOTONE. Each of the three units is assembled, wired andlaboratory tested at our factory. All you have to do in orderto reproduce these wonderful results for yourself is to take astandard kit of ISOTONE parts and assemble the instrumentwith a few nuts, bolts and only ten wires. There is nothingto go wrong. Each piece fits together with absolute precision,and in less than an hour you can realize what is acclaimedby women as the most beautiful receiver of the day-andadmitted, beyond a question of doubt, byradio engineers as the most efficient radiophonograph ever designed.

HIGH FREQUENCYLABORATORIES

Office R. 28 N. Sheldon St.

CHICAGO, ILL.

FREE

Model 10ISOTONE70 Stationsin one eveningAn amazing demonstrationof ultra selectivity and extremedistance range.

Id

Shields removed to show construction

Absolute GuaranteeEvery ISOTONE kit and each ISOTONIC unit is fullyguaranteed. All H. F. L. items must be mechanically andelectrically perfect. Each instruments must test up to thestandard set by our laboratories. Any unit that does notoperate perfectly will be immediately replaced at no charge.No arguments-no lengthy correspondence-your ISOTONEmust be right or we will make it right. Our guarantee givesyou absolute protection. BUILD YOUR ISOTONE NOWand have the fincst receiver in your neighborhood. Send forfull particulars TODAY.

The Coupon Brings Complete Information

CircuitDiagramAnd AllInformation

gairL

HIGH FREQUENCY LABORATORIESOffice R, 28 North Sheldon Street,Chicago, Illinois.

Gentlemen,-Without obligation, please send complete in-formation on the ISOTONE receiver and the ISOTONICA. C. power supply.

Name

Address

City

Tell them you saw it in RADIO

State(Please print plainly)

- - - _ - - -

OUT -SELLING ALL

Single Dial ControlVerniers for long distance tuning

"De Luxe Model"SARGENT-RAYMENT SEVEN

Uses Four Screen Grid Tubes, Detector, and Two Audio

A Station for Every Dial DegreeTHAT is the average performance of the Sargent-Rayment

Seven over the entire dial. Tuning from slightly over 200meters up to 550 meters, this receiver will, under average

night-time conditions, receive 100 stations per evening.

The outstanding performance of this receiver is due to verycareful design throughout. Four stages of screen grid tubeamplification are used. Each stage is completely isolated byheavy aluminum shielding. Lap Shield joints are used to insureagainst any possibility of having the slightest leakage from stageto stage. Each screen grid, plate and filament wire is by-passedand nine radio frequency chokes are used to prevent inter -coupling. As a result, the set is not critical to operate and doesnot oscillate at any wave length. Even with the full powerturned on at 200 meters the receiver is fully stable.

THE ANTENNA CIRCUIT

An entirely new type of antenna circuit is used. This inputcircuit at once assures fine selectivity and good sensitivity, andat the same time it is so connected that antenna capacity does notaffect the setting of the gang condenser. Thus, although theantenna is sharply tuned, it is not necessary to compensate forchanges in wave length. This is a special feature released forthe first time in this set.

The full power of four screen grid tubes gives a degree ofsensitivity that has never before been attained in anything thathas been placed on the radio market. No suppressors or othercounteracting devices are used to prevent oscillation, so that thefull amplification of each tube becomes useful. As a result, thereceiver will produce a louder signal on a distant station thanany other set that can be put up against it, and the selectivity,which is 10 kilocycle in most cases, enables the owner to get longdistance reception during the early evening hours when all thelocal stations are on.

A Guarantee by the DesignersSome very broad claims have been made in our adver-

tising of the Sargent-Rayment Seven. Were it not for thefact that this set is unique in design these claims could notrightly be made. The Sargent-Rayment Seven has beenthoroughly tested under the most adverse conditions and isunconditionally guaranteed to do everything claimed in ouradvertising. In case anyone desiring to purchase one of thesesets is in doubt about this point, we will be glad to arrangeso that that person can obtain the set on a ten day moneyback trial basis.

We are perfectly willing to stake our professional repute.tions as radio designers on this circuit and will leave it tothe judgment of the radio fans at the end of the seasonwhether or not any misleading statements have been made.

(Signed) E. M. SARGENT, L. C. RAYMENT

I23

4

5

6

7

Seven Outstanding FeaturesTen kilocycle selectivity all over the wave band.

More power, more amplification, more sensitivity than everbefore available in any receiver.

All present distance records smashed. Sets a new standard.

Efficient all over the wave band. Plenty of power on thelong waves.

Tone quality unsurpassed. Uses the latest audio transformers.210 or 250 tube can be used in last stage if desired.

Tuning controlled by handsome, illuminated revolving drum.Only one control for master selector. Fine tuning verniersavailable for use when wanted.

Requires no cabinet. Finished in grained aluminum with blackand white trimmings, or in brown, crackle, crystalline lacquer.

THE OTHER KITS!Dealers

"Built Like a Battleship"NOTE THE CONSTRUCTION

The above illustrates a top view of the receiver with the cover removed, givingan idea of how substantially this set is built. It shows the complete isolation ofeach radio frequency stage, the single drum control on gang condensers and thespacing and angling of the coils to prevent feed hack. This is a triumph in radioset construction and at the Radio Shows at which it has been exhibited it hasattracted widespread attention and comment.

THE AUDIO SYSTEMThe audio system employed in the Sargent-Rayment Seven is noted for its

of tone. The small -sized Clough transformers Nos. 255, 256 and 251 havebeen purposely selected because they do not over -emphasize the base notes at theexpense of the high ones. More powerful transformers could have been selected,but as the set contains plenty of radio frequency power a distinct gain was madeby choosing the less powerful but clearer small transformers.

WHAT FINISH DO YOU LIKE?The Sargent-Rayment Seven is supplied in two finishes. For the dyed-in-the-wool

radio fan there is a standard grained aluminum finish, while for those who prefer adarker set which will better harmonize with living room furnishings we are preparedto supply the usual brown, crackle, crystalline finish. The set can be obtained eitherbuilt up or in kit form, with finish desired at the prices given below. The modelsare identical in every respect except for the finish.

The De Luxe model is put out exclusively by Radio Constructors Corporationand can only be bought from us or from jobbers listed on this page. All parts aremanufactured by Silver -Marshall and the De Luxe Finish is applied by us.

We especially recommend this model. It is unexcelled in appearance and har-monizes with all furnishings.

PRICES-FOR THE COMPLETE KITThe SM-710 Sargent-Rayment Seven Kit is complete in every respect. All parts

are inspected at the Silver -Marshall factory for both electrical and mechanical defectsand are fully guaranteed by both Silver -Marshall and by Radio Constructors Corpora-tion to be in first-class condition. Everything is carefully packed to withstand ship-ment. Coniplete instructions for assembling and wiring the kit are included. Theseinstructions are so explicit and so well illustrated that the novice will have no difficultyin following them.

All hardware, screws, nuts, washers, brackets-everything necessary to build theset-is included. There is nothing additional to be bought. The kit includes even the"cabinet."No. 710 Standard Model, Grained Aluminum Finish, Code Word "Mercury" $130.00No. 810 De Luxe Model, Brown, Crackle Crystalline Finish, Code Word

"Venus" $140.00

FOR THE BUILT-UP SETThe completely built, wired, and tested Sargent-Rayment Seven receiver is care-

fully packed in a specially cushioned packing case. It exceeds the parcel post sizelimits and hence must be shipped by express. Full instructions for connecting theset to the power supply and operating it are included.No. 711 Standard Model. Code Word "Neptune" $150.00No. 811 De Luxe Model, Code Word "Jupiter" $160.00

IMMEDIATE DELIVERY

RADIO CONSTRUCTORS357 Twelfth Street

Please send me at once full details regarding theSargent-Rayment Seven. I am a dealer or professionalset builder and buy my supplies from the jobbers listedbelow.

These jobbers can supply youwith either the kit or built-up set

WASHINGTONWEDEL CO.,

520 Second Ave., Seattle, Wash.HARPER-MEGGEE, Inc.,

4th at Blanchard St., Seattle, Wash.INLAND RADIO CO.,

922 West First, Spokane, Wash.HARPER MEGGEE & CO., INC.,

South 214 Howard St., Spokane, Wash.OREGON

STUBBS ELECTRIC CO.,75 6th St., Portland, Ore.

UNIVERSAL SPECIALTIES CO.,40 N. Ninth St., Portland, Ore.

SOUTHERN CALIFORNIAHERBERT H. HORN CO.,

1629 S. Hill St., Los Angeles, Calif.C. C. LAWTON,

1125 Wall St., Los Angeles, Calif.RADIO SUPPLY CO.,

912 S. Broadway, Los Angeles, Calif.RADIO MFRS. SUPPLY CO.,

1000 S. Broadway, Los Angeles, Calif.RADIO MFRS. SUPPLY CO.,

Long Beach, Calif.MODERN ELECTRIC CO.,

308 West Center St., Anaheim, Calif.SUNSET ELECTRIC CO.,

1141 1st St.. San Diego, Calif.WILLIAMS AND KLENTZ,

409 5th St., Santa Ana. Calif.NORTHERN CALIFORNIA

ELECTRIC SUPPLY CO.,370 11th St.. Oakland. Calif.

ELECTRIC SUPPLY CO.,Room 250, Chronicle Bldg., San Francisco.

COAST RADIO SUPPLY CO.,648 Howard St., San Francisco, Calif.

GILSON ELEC. SUPPLY CO.,1106 Madison St., Oakland, Calif.

KIMBALL-UPSON CO.,607 K St., Sacramento. Calif.

OFFENBACH ELECTRIC CO.,1432 Market St., San Francisco, Calif.

PACIFIC RADIO SALES CO.,357 Twelfth St.. Oakland, Calif.

COLORADOVREELAND RADIO CORP.,

1639 Tremont St., Denver, Colo.NEW MEXICO

PACKARD SERVICE STATION,417 West Gold Ave., Albuquerque, N. M.

UTAHINTERMOUNTAIN ELECTRIC CO.,

43 East 4th South. Salt Lake City, Utah.LUND RADIO CO.,

Fairview, Utah.NEVADA

RENO MOTOR SUPPI.Y CO.,Reno, NesMME MMMEM

DEALERS-SET BUILDERSGet established now in your community as head-quarters for the SargentRayment Seven. Fill inthe attached coupon and send it to us for fullinformation.

III IN II III Radio Constructors Corporation,

1111 357 Twelfth Street,Oakland, Calif.

CORPORATIONOakland, Calif.

Name

Address

City and State

Name of Jobber

Name of Jobber

INV

$130FOR ALL PARTS 6' CABINET

The KITFor those who want to buildtheir own receiver we offerthe Sargent-Rayment SevenKit, complete with aluminumcabinet, as illustrated, for thesurprisingly low price of$130.00. The kit forms itsown cabinet when assembledand gives the set a beautifulappearance. If you don't likethe aluminum cabinet as pic-tured on this page, we cansupply a "De Luxe" cabinet--the same cabinet exactlyas shown excepting that acoating of dark brown crys-talline is applied to the alum-inum, giving the set theappearance of the factorysets now on the market withcrystalline finishes. Thisfinish costs you $10.00 extra.All parts for this kit areguaranteed. Complete wiringdiagrams and instructions forassembly go with each kit.You can't go wrong. Im-mediate deliveries guaran-teed. Positively no delays.

6

$ 1 5 0The cabinet goes with the kit at $130.00. Aluminum, grainedfinish. Brown crackle lacquer finish $10.00 additional.

110."--

Sargent-RaymentReceiver Out -performs All Others

OUTSELLING everything in the kitfield, the new Sargent-Rayment 7 is

piling up sales records that exceeded ourfondest expectations. No wonder-thereis nothing to compare with it for DXrange - selectivity - tone and simplicity.A single dial control set. Verniers neededfor extreme long distance reception only.We predict that this receiver will sell inlarger quantities than all other kits com-bined. It is our leader. We always have astock on hand-kits and completely builtand wired receivers, ready to operate.Shipments made on same day your orderreaches us. Positively no delays.

64 Clear ChannelsOn November I 1 th the new wave allocations were made effective.For the first time in years the DX fan can now get his money'sworth out of a DX receiver. You can choose from six Eastern sta-tions nightly, if you live on the Pacific Coast-and from six Westernstations nightly if you live in the East-and be assured of no inter-ference wi:hin 10 kilocycles or more. All told, there ere 64channels throughout the Uni:ed States that are fairly clear of inter-ference and heterodynes. Cash in on the greatest DX season inradio. Get your 10 KC Sargent-Rayment receiver right now andget in on the sport. Why be content to listen to a separate localstation when the Sargent-Rayment receiver enables you to bring in100 stations during an evening? Stations 1000 miles away poundthrough like locals. The tone quality is SUPERB.

FOR THE ASSEMBLED SET

The SETCompletely assembled, wiredand tested on the air for ex-treme long distance recep-tion. Perfectly balanced for10 KC selectivity and thor-oughly inspected by com-petent engineers who special-ize solely on the constructionof this set. When a complete-ly wired Sargent Receiverleaves our establishmentyou have three guaranteesto protect you-one from theinventors, another from theconstructors and a final guar-antee by ourselves. The com-pletely assembled job sells for$150.00 in the aluminumsatin finished cabinet, as pic-tured. The De Luxe finish(brown crystalline) costs

are in stock for shipment onthe same day your orderreaches us. Send $40.00 to-day-balance c.o.d.-get ourspecial discounts to dealersand set builders. Order now'

A. C. OPERATION WITHOUT HUMRECENT developments in power units makes it possible for us to offer you the new Knapp Dry A PowerSupp:r. a guaranteed power unit which has been given a thorough test and is positively unequaled for reli-ability and sure-fire per'os man( e. No hum whatsoever. This Knapp A Power unit and a good B eliminatorwill make your Sargent-Rayment receiver an AC operated instrument free from annoying AC hum. You willget better tone quality-longer life from tubes and nothing to worry about. Price for the Knapp "A" is $37.50.Immediate shipment from stock. Na delays. We guarantee this power unit without reserve. There is nosatisfactory substitute for it.

Immediate Deliveries. 4 -Hour Mail Order Servicer - -I SET BUILDERS AND DEALERS-RADIO DEALERS SUPPLY SERVICE

II OFFENBACH ELECTRIC COMPANYI 1452 Nlarket Street,

San Francisco, Calif.I Send me

IV- .SM-710 Sargent-Rayment Kit, unwired,

I V

List $130.00.

SM-710 Sargent-Rayment Set, completely, II Brown Crystalline Finish-$10.00 Extra

wired, List $150.00.

I

Wholesale Division of

I for which I attach a deposit of $40.00, the balance to Ibe paid for C. 0. D. upon receipt of shipment.

Name.. 111

IStreet and Number I

1 City state111"mom. iii NW ii imil NM mil mm =h.

12 Ttll them you saw it in RADIO

Send the couponnow for yourSargent. RaymentSeven kit, or com-pletely wired re-ceiver. Telegraphorders promptlyfilled. Mail orderservice to all partsof the world. Alltubes and access-ories can be pur-chased from us atregular dealer dis-counts.

ORDER DIRECT FROMRadio Dealers Supply Service

Wholesale Division of

rEti6AELECTRIC COMPANY

"The House of a Million Radio Parts"

1452 Market Street San Francisco, California

CTANDING guard at the door of tone,L./ Thordarson audio and power transform-ers do their part in making real musical in-struments of hundreds of thousands of radioreceivers annually.

Leading receiver manufacturers are wellaware of the important relationship betweenthe choice of transformers and the musicalcharacteristics of their instruments. No won-der, then, that the majority of manufacturersof quality radio receivers have turned toThordarson as the logical transformer source.

When buying your receiver, insist onThordarson amplification and power supply.The set manufacturer who uses Thordarsontransformers can be depended upon to havethe balance of his receiver in keeping withthis high standard of performance.

Custom set builders will find Thordarsontransformers to meet every radio need

at their nearest parts dealer.

DIORDARSONILA DITFLAN S FORMER'S

SUPREME IN MUSICAL PERFORMANCE -

Tell them you saw it in RADIO

New JensenModel 6 Cabinet

In size and appearance thenew Model 6 Jensen Cabinetis ideally suited for use in themost artistically furnishedliving room or music room.Jensen Dynamic Speakers aremade in types to operate with110 volt A. C. house current,6 volt storage battery, "A"eliminator or trickle charger,110 volt D. C. house currentand 90 tont° volt D. C. cu rrentas provided by many of thelate model radio sets. Thesensitivity of the instrumentsis the same in any case.

Jensen DynamicSpeakerUnits maybe quickly andeasily installed inradio or phono-graph consolecabinets. Theymay be operatedwith the samecurrent supply asusedfor the radioreceiver or electricphonograph.Prices for theUnits for consolecabinet instal-lation range from

$40.00 to $55.00.

Jensen Dynamics Will Build Sales For YouSHREWD dealers know that radio sets sell best

when they sound best. These dealers areincreasing their set sales and dynamic speakersales every day by using Jensen Dynamics fordemonstration. It is Jensen reproduction "trueas the original" which provides this distinctselling advantage. It is the absolutely true,

en4endependable reproduction ofthe entire musical scalewhich accounts for the vastpublic preference for Jensentone quality. And the newdistinctive cabinets in which

Jensen units are enclosed is the final featurewhich clinches sales. Console cabinets sell bettertoo when they are Jensen equipped.All types of Jensen Dynamic Speakers are nowready for delivery to the trade. Dealers, jobbersand manufacturers are invited to write forparticulars and an immediate source of supply.

Jensen Radio Manufacturing Co.212 9th Street, OAKLAND, CALIF. 338 N. Kedzie Avenue, CHICAGO, ILL.

JENSEN PATENTS ALLOWED AND PENDINGLicensed under Lek, °phone and Magnavox

DriViinfIt SPEAKER

14 Tell them you saw it in RADIO

MIK 1List Price $135.00

Without Tubes

Bring the games to thecrowd-and they'll

welcome yourmessage.

PAM 16 or 17List Price $125.00

Without Tubes

Where Crowds Assemble --Use the Voice of a Samson

YOU can reproduce with great volume any radio music on the air or recreate thebest recorded music by using a PAM 16 or 17. For the radio music connectPAM to detector tube of any radio set or to a tuning unit, and for recordedmusic connect it to a magnetic phonograph pick up.

You can make announcements before,during or after the game if you use aSamson MIK 1 (a 2 -stage entirely ACoperated microphone input amplifier)which uses the same high grade trans-formers we have supplied many of thiscountry's better broadcast stations.

Main Office: Canton, Mass.Manufacturers Since 1882

For even greater volume use the PAM19 or 20 which has approximately 21/2times the undistorted output of thePAM 16 or 17.Send for illustrated bulletin RB1 describ-ing these units and other items showingwhy "PAM AMPLIFIERS are a SoundInvestment."

ClePir-'017aTiffe Factories at Cantonand Watertown, Mass.

Tell than you saw it in RAM() Is

........ . .

SIMPLIFYINGPOWER PLANT CONSTRUCTION

,/1 UniversalVoltage Separator

TRUVOLTDIVIDER

THE Truvolt Divider offers the radio en-gineer or builder of eliminators for the

first time a complete wire wound resistanceunit so arranged with five adjustable contactsthat all required voltages may be obtainedwith any set or eliminator combination.

This device removes the guesswork andsaves time and trouble in constructing an

FILL OUT

AND MAIL

THIS

COUPON

U. S. Patent 1,676.869and Patents Pending

eliminator. By dividing the filter voltage intousable values, it eliminates the necessity ofmathematical calculations. It does away witha great deal of wiring and the need of reg-ulator tubes.

The Truvolt Divider is not only flexible toall receiver current conditions, but it is pos-sible, because of its inherent design, to cali-brate the adjustable contacts. By the use oftables or graphs, the Divider may be adjustedto give the desired voltages without the useof a high resistance voltmeter.

Case made of genuine bakelite. Can bemounted on baseboard or sub -panel, or usedas the front panel of a metal cabinet, at thesame time providing binding posts for allB and C Voltages. PRICE $12.50.

Electrad specializes in a full line ofControls for all Radio Purposes, includingTelevision.

Write for Free Truvolt Divider Bookletgiving Full Information.

ELECT RAD[en them w saw it in RADIO

RADIOVOLUME X NO\ 1 \ IBER, 192 No. 11

ckadiotorial Comment

nOLMCAL speeches may simultaneously beeither the most or the least obnoxious kind

of radio advertising-depending upon the po-litical beliefs of the listener.

When a man ceases to criticize the radio con-ditions in his locality, he has lost his interest inradio. Then there is really something the mat-ter with it.

Radio applause cards, once as numberless asthe buffalos of the great plains, are now asnearly extinct. Advertising is killing them.

Good radio humor is the best of the twice-told tales. For if it "gets over" from a radiostudio it will register where the teller is pres-ent. And it is always clean.

Television will soon add "synchronize" tothe slang dictionary. Its meaning requires nodefinition, as applied to an individual, for any-one who has watched or manipulated a receiverscreen.

* * *

ARADIO operator has always been judgedlargely upon his proficiency in sending and

receiving code. Wire telegraph operators wereonce valued likewise. So also was a bookkeepergauged on his ability to add, and a typesetter by

his speed and accuracy as a hand compositor.But nowadays type is set on a linotype machine,adding is done with an adding machine, andtelegraph messages are sent and received bymeans of machine printers. Eventually, also,the great bulk of radio traffic will be sent byphotoradio.

In each of these cases the operator has grad-uated to higher duties which require more tech-nical knowledge and which command higherpay. The world is rapidly approaching thepoint where it will be difficult to find men tocope with the modern machines which are beingcreated. Radio, in particular, is a new field andis destined to great progress. The radio operator

who keeps in step with this progress is also de-stined to a great future.

* *

SOS is a signal for a broadcast station tocease transmitting. No matter how trivial

or how important its program, whether a jazzrequest number or an address by the Presidentof the United States, it must give way to thedistress call. This was absolutely necessary toprevent interference in the old days of sparktransmitters. But with the use of continuous

waves from vacuum tube transmitters it is asneedless as a hitching post for automobiles. Nobroadcast station on 545 meters or under needcause any interference on 600 meters. The por-tion of this law which requires a broadcast sta-tion to maintain continuous watch on 600 metersis virtually a dead letter. In view of the prog-ress which has been made since the law waspassed, it should now be wiped off the statute

books. Aside from the unnecessary annoyancethat it may cause broadcast listeners it may cause

a direct financial loss to a station which is broad-

casting a sponsored program.* *

MHE subject uppermost in broadcast discus-sion today is the probable effect of the Fed-

eral Radio Commission's order that nine -tenthsof the stations change their wavelengths onArmistice Day. At first glance it might appearthat in this new deal just as much satisfactionwould have been created by dealing five hands,

one to each zone, from a well -shuffled deck of

cards.Yet a little analysis shows that the deck has

been carefully stacked in an endeavor to im-prove reception conditions for the listener. So,

aside from the temporary inconvenience ofchanging the logs or dial markings of most ofthe stations ordinarily heard, the average listenerwill probably hear his favorite stations to betteradvantage than he did last winter.

RADIO FOR NOVEMBER, 192817

To understand the plan upon which the newallocations are based, it is necessary to know

that there are ninety-six channels or highwaysin the broadcast spectrum between 550 and 1500kilocycles. Each of these channels is ten kilo-cycles wide, the modulating or sound frequen-cies extending for five kilocycles on both sidesof the station's carrier frequency. Incidentally,since the station frequencies are designated inmultiples of ten so as to give this ten kilocycleseparation, it is more convenient and less con-fusing to omit the final cipher and to designatethe channels by numbers from 55 to 150, cor-responding to 550 to 1500 kilocycles.

Naturally a collision occurs whenever two ormore stations are radiating energy into the samechannel at the same time. If the stations arevery powerful and are not given sufficient geo-graphical separation, these collisions or hetero-dynes will be heard as a high-pitched singingnote, especially where the receiver is locatedbetween the interfering stations.

Of the ninety-six channels, six are assignedexclusively to Canada, leaving ninety channelsfor the use of six hundred and twenty-four sta-tions in the United States and Alaska, an averageof nearly seven stations per channel.

Heretofore, no station has occupied a clearchannel unless the other stations assigned to itswavelength were not broadcasting. For instance,due to the difference in time, some Pacific Coaststations could be heard without heterodyningonly after their Eastern channel -sharers hadshut down. But as a general rule no station wasfree from a heterodyne whistle during someperiod of its operation. What could the Com-mission do to remedy the trouble?

* * *

THERE were two answers to the problem ofpreventing collisions on the radio high-

ways: one to reduce the number of stationswhich employ them, and the other to reducethe time that some of the stations operate, thusallowing two or more stations to use the samechannel during different periods, much as athrifty landlord used one set of beds to accom-modate three shifts of miners in the early daysof the gold rushes. The Radio Commissionadopted the latter plan.

Forty channels were cleared, eight in eachzone. One-fourth of these were assigned ex-

clusively for the use of single stations. On theother three -fourths, two or more stations arelimited in time so that they do not operate simul-taneously. Most of them are high -power stations.Consequently, during the night hours, thereshould be little or no interference on nearlyone-half the dial. According to the Commis-sion's original order the clear channels are Nos.64 to 87 inclusive (excepting 78) and channels97 to 119 inclusive (excepting 101 and 112).Subsequent allocations may slightly changethese figures. This should revive interest inlong distance reception on these channels.

Of the remaining fifty channels, four are as-signed for simultaneous use in not less than twozones, thirty-five for not more than three zones,five for all zones for stations whose power doesnot exceed 1000 watts, and six for all zones forpower not over 100 watts. The last two classi-fications cover 317 stations. Thus more thanhalf the number of stations are accommodatedon eleven channels and nearly a fourth of themare found on three local service channels, num-ber 120 with 52, 121 with 45, and 131 with 51stations.

These allocations, as well as this interpreta-tion thereof, are somewhat tentative and manyof them will be changed, if the number of pro-tests is any criterion. But zone assignments ofpower and particular frequencies cannot begreatly altered because of the interdependenceof the entire set-up.

* * *

NOTHER revolutionary order which will bebitterly opposed by the stations, and as

heartily approved by the majority of listeners,is that prohibiting the broadcasting of chainprograms from more than one station for morethan one hour a day where the chain stationsare within three hundred miles of each other.

So the eleventh of November will probablymark the beginning of the end of much of theinterference that the listener has endured formany months. But in the meantime active hos-tilities are in progress between station and sta-tion and between stations and the Commission.Many stations and communities are up in armsagainst what they consider unjust discrimina-tion. Consequently, even if Armistice Daybrings an armistice in this radio warfare, itwill leave many hard feelings to be softened bysubsequent peace negotiations.

18 RADIO FOR NOVEMBER, 1928

The Short -Wave Trans -Atlantic Radiophone

R,,,, 1.:1R radiotelephone service onshort waves between the UnitedStates and England is soon to be

in effect. This is a departure in thattwo-way communication is to be at-tempted on short waves, instead of thelong waves by means of which the serv-ice was introduced. The Bell Tele-phone Laboratories, Inc., recently erectedbuildings and installed short-wave re-

ceiving equipment at Netcong, NewJersey, and the British Postoffice hascompleted a short-wave transmitting sta-tion in Scotland.

The radiotelephone calls between thiscountry and Great Britain now average30 a day, and occasionally the number ofinternational radio conversations mayreach 60 within twenty-four hours. Toaccommodate this increasing traffic aswell as to determine the suitability of

short waves for regular, dependablelong-distance communication, the duplex,two-way system has been constructed inthe two respective countries. Untilquite recently England had no short-wave transmitting station for communi-cation with the United States. The newshort-wave receiming station at Netcong,New Jersey, is a mate for the recentlybuilt English high -frequency transmit-ting station.

The use of a radiotelephone for de-pendable communication over a distanceexceeding 3000 miles requires the ap-plication of three pairs of short wave-lengths. The vagaries of short wavesare such as to require different fre-quencies for effective operation at vary-ing periods of the day and night. For

By S. R. WINTERS

example, in the two-way trans -Atlanticradiotelephone service one wavelengthwill be used during daylight hours, adifferent wavelength will be employedfor night service, and still a third wavechannel of a frequency at variance withthe other two will be necessary for ef-fective communication when a portionof the signal path is shrouded in dark-

sideband transmission and working bothways on one wavelength are not nowpracticable commercially on short waves,contend engineers of the Bell System.The voice -operated devices, however, areemployed in connection with two slightlydifferent wavelengths, one of which isused for eastbound speech and the otherfor westbound conversation.

Short -Wave Telephone Transmitting Station at Deal, N. 1.

ness and the other part illuminated bydaylight.

In this particular, the short-wave serv-ice differs essentially from that of long -wave radiotelephone com-munication. At present, in the use oflong wavelengths, two-way operation iseffected on a single wavelength by meansof the single-sideband method of trans-mission and voice -operated relays. Thisarrangement permits of telephone cur-rents traveling in but one direction onthe circuit at any given moment. Single -

Short -Wave Receiving Station at Netcong, N.

The short-wave transmitting stationof the Bell Telephone Laboratories is

located at Deal, New Jersey-occupyingthe grounds and housed in the buildingoriginally dedicated to the innovation ofexchanging radiotelephone communica-tions between shore and ship stations,about ten years ago. This is fitting thatthe same location should mark the in-auguration of two such signal achieve-ments in the art of radiotelephony. Theship -to -shore experiments were con-

ducted from 1919 to 1922. Quite re-cently, a marine -service company in Cali-fornia inaugurated a regular radiotele-phone service hourly between the LosAngeles harbor and a fleet of steamersand tugboats operating in the southernCalifornia waters.

The New Jersey short-wave trans-mitter for trans -Atlantic communicationis subject to quartz -crystal control, athin slab of this mineral-encased in aconstant temperature cabinet-governsthe transmitting frequency or wavelengthwith remarkable precision. The shift-ing from one wavelength to another inthe variable frequency operating sched-ule is effected in less than ten minutes.This change in operating wavelengthsmerely requires the substitution of oneslab of quartz crystal for another of dif-ferent thickness and the insertion of dif-ferent inductance units in the output cir-cuits of the high -frequency amplifier.These changes in operating conditionsare not only dictated by variations in dayand night periods but by seasonal de -

RADIO FOR NOVEMBER, 1928 19

mands-the change from summer towinter or vice versa, for example.

The short-wave receiving station atNetcong, New Jersey, is an absolutelynew link in the radio and telephone com-munication chains of the Bell System-the buildings having been recentlyerected and the equipment newly in-stalled. Both stations are linked by landwires with communication headquarters

Transmitting Equipment

of the Bell Telephone Laboratories at24 Walker Street, New York City. Atthis point, the two one-way circuits con-verge and are thus transformed into atwo-way circuit for connection throughthe long-distance switchboard to the linesof the Bell System.

This new undertaking of establishingtwo-way radio communication betweenAmerica and England on short -waves

Speech -Input Monitoring Panel at Trans-mitting Station

should further contribute to our knowl-edge of a band of frequencies whichradio amateurs discovered as havinggreat intrinsic value. Already, the one-way trans -Atlantic communication hasdisclosed that static or atmospheric dis-turbances discriminate against Ion?, waves

SIMPLIFIED FORMULAS FORREACTANCE

By ARTHUR HOBART

DELIGHTFUL simplification can bemade in radio's most fundamentalequation, which says that the total

reactance of a series circuit is equal tothe difference between the inductive re-actance and the capacitive reactance.

It is ordinarily expressed as X=wL-1/wC, where X is the reactance inohms, w is 2711, f being the frequency incycles per second, L is the inductance ofthe coil and C the capacity of the con-denser. The circuit is resonant whenwL,l/wC,the reactance then being zeroand the impedance to the flow of analternating current being equal solely tothe resistance of the circuit.

But the prodigious labor involved incalculating a resonance curve with thisformula may be greatly lessened bysimplifying it to meet the conditionsfound in practice. As the circuit con-ditions are constant when it has beentuned to resonance for a given frequency,the only variable is the non -resonantfrequency, for which the impedance is tobe found.

Thus it is common practice to use a170 microhenry coil with a .0905 micro-farad condenser to cover the broadcastband from 550 to 1500 kilocycles. Afrequent problem is to determine theproportionate interference that may becaused by a carrier wave in a channelclose to that to which the circuit is tuned.The reactance to the tuned frequencyis zero and that to the interferingfrequency is approximately X=47rLdwhen d is the difference in megacyclesbetween the two frequencies and L isexpressed in microhenries.

The value of this approximation canbest be illustrated by a typical problem.Assume that a circuit consisting of a 170microhenry coil and a .0005 mfd. con-denser is tuned to 1003 k.c., i.e. X=0at 1000 k.c. What is its reactance to990 k.c.?

By the standard formula it is firstnecessary to find the L C value of thecircuit, either from a published table orfrom the formula L C.-1/( 211)2,which in this case is .02532. From thisfind C as .02532÷170-=.000149 mfd.Then X = 6.28 X .990 X 17(1-1

in favor of short waves for such long-distance service. Short waves, it hasalso been found, do not travel so nearlyin a bee -line to their destination as dothe long wavelengths. The exact pathof short waves, however, remains to bedefined and charted. Our knowledge ofthe skip effect and the fading of signalswhen employing short waves should becontributed to measurably by this reg-ular radio service for spanning the At-lantic Ocean.

20RADIO FOR NOVEMBER, 1928

(6.28 X .990 X .000149) = 1057.4-1079.0=21.6 ohms.

By the approximate formula X =4-ff X 170 X .01=21.4 ohms, and howmuch easier it is to check the correctnessof your work!

For a 5 -ohm circuit tuned to 1000 k.c.,the impedance is 5 ohms to 1000 k.c., andV 52+21 A2 = 22 ohms to 990 k.c., or4.4 times greater. So, for equal signalinput, the 1000 k.c. signal is 4.4 strongerthan the 990 k.c. signal at the circuitoutput, or the 990 k.c. signal is less thanone-fourth as strong as the 1000 k.c.signal.

The method whereby this approxima-tion, and also a very simple exact equa-tion for reactance, may be derived isan interesting exercise. At the resonantfrequency fR, the inductive reactance isequal to the capacitive reactance,-27rf RL =1/274 RC, whence L C1 / (24R) 2 and 2771=1/(27/R2C). Atany frequency f, X = 27rfL - 1/274C=

(2irf)2 L C-1 (274120'0'27rf C (27

2771Cf2-fR2 27rL(

27rfR2CfLet f=fR±d, f2=fR27_4_-2fRd+d-./2_/R2 2fitd d2= d ( ±2fR+d)

So X=27rLd("=-2f R-4-4) and if d/fRfR d

is small, X.4irLd.As an example of the use of the exact

formula, consider a circuit tuned to 1500k.c., using a 170 microhenry coil. Whatis the reactance to 1510 and 1490 k.c.?

27rL -= 6.2832 X 170 = 1068.124, d,fR=1.5.

X=1068.124X.01 (-0-1-.01)1.5±.01

=10.68X 1.993 or -10.68 X 2.0066So the reactance to 1510 k.c. is 21.28ohms and to 1490 k.c. is 21.43 ohms. Bythe approximate method, X=21.4 ohmsfor either case. The magnitude of theerror introduced by this approximation isabout ± d/2f R, which is negligible inmost practical cases.

An equation of almost equal simplicitycan be developed for a parallel or non -

resonant circuit. Assuming that the lossesdue to resistance are small, and conse-quently neglecting R, the reactance X ofa parallel circuit is wL/(1-w2LC).Adopting the same method and notationas in the case of series reactance, this canbe successively reduced to

-27rLfR2 1±d/ffed (-1:21-d/fR) or

irr-f112approximately X_d

This method is much simpler and easierthan the usual method of finding sus-ceptances and reactances and is just asaccurate.

What Is an Underground Antenna?

EACH radio season sees the adventof a crop of devices commonly ad-vertised under the name of "under-

ground antennas." To read the claimsfor such devices, as set forth in theirpublished advertising and mail circulars,creates an expectation that they willgive absolute freedom from static,power line interference, and other an-noying noises usually present when aconventional type of antenna is used, andat the same time with no sacrifice ofdistance, selectivity or other impairmentof operation of the receiving set.

As this seemed too good to be true,an investigation of the various devicesof this type w as made, with a view to de-terminin.:, their merits, if any, and alsoto obtain an accurate definition of anunderground antenna as conceived byits inventors.

The principal patents covering under-ground antennas were granted to JamesHarris Rogers of Hyattsville, Md., in1919 and 1920, and we understand thatthese patents have been sold by Mr.Rogers to other interests. A study ofthe patent papers discloses some veryinteresting data, and in Fig. 1, a re -

PUT OR TUBIN6-,, \IMUIRTION-N

By G. M. BEST

grounded. Many variations of thismethod are covered by the patents, in-cluding such an arrangement as is shownin Fig. 2, in which equal lengths ofburied, shielded wire are placed on eachside of the coupling inductance, and noground connection whatsoever is used.

his opinion they are not comparable in ef-ficiency with the elevated antenna or the under-ground antenna when buried substantiallyparallel with the surface of the earth.

Again thanking you for your esteemedletter, I beg to remain,

Very truly yours,(Signed) JAS. C. ROGERS.

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Fig. 2. Underground d ntenna of Equal Sections

Other variations place the shielded cableon top of the ground but in contacttherewith ; place the cable on supportsso that it is elevated a few inches abovethe earth ; and several of the arrange-ments include grounding of the far endof the buried cable instead of insulatingit as is done in Figs. 1 and 2.

Dr. Rogers developed his variousunderground systems before and duringthe World War, his first applicationfor patents being made on May 2, 1917,and to him should go the credit for the

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Fig. 1. Roger: Underground .intenna

production of one of the many types ofantenna systems covered by Mr. Roger'spatents is shown, as a typical example.

The principal claim covering this typeof antenna defines the antenna as "Aradio signaling system comprising anantenna extending horizontally sub-stantially parallel to the surface of theearth and insulated therefrom, a metalliccovering inclosing said antenna but in-sulated therefrom and in intimate con-tact with the earth substantially through-out its length, signal instruments asso-ciated with said antenna, and a balanc-ing connection on the opposite side ofsaid instruments."

Referring to Fig. 1 it is obvious thatthe underground antenna consists of anindeterminate length of insulated wireenclosed in a metal sheath such as alead cable, buried sufficiently so thatthe sheath is in good electrical contactwith the earth, and parallel to its sur-face, the lead-in being brought to oneside of the coupling inductance of thereceiver, the opposite end of which is

remarkable work which he did at a timewhen radio was in its infancy and theapparatus with which he had to workwas necessarily of crude form. Beinginterested in knowing just what Mr.Rogers thought of the various so-calledunderground antennas being sold to thegeneral public, a letter was addressedhim on the subject, and the reply theretois reproduced below:

ROGERS RADIO RESEARCH LABORATORYHyattsville, Maryland

August 22, 1928.Editor, RADIO

Sir: My brother Dr. J. Harris Rogers,who is unwell, begs me to acknowledge re-ceipt of your kind letter of August 10, andto thank you for the credit you propose togive him for his pioneer work in under-ground and underwater radio, in your val-uable publication.

His attention has been called to variouspublications and advertisements of devicesutilizing the underground principle and mak-ing exaggerated claims, for which he is inno way responsible, and which are mislead-ing and unwarranted, and likewise unjust tohimself and to the public.

Referring to the class of devices referredto in your letter, he is frank to say that in

RADIO FOR NOVEMBER, 1928

Having thus received confirmation ofour opinion from the man best informedon the subject, a further investigationwas made as to the nature of the variousdevices being sold, and the results ob-tained with them when used with anaverage broadcast receiver.

Practically all of them consist of ametal container, usually sealed andmade of brass or copper, to which isconnected a length of lead-in wire. Inone or two specimens, the container wasfilled with a mixture of charcoal andcommon salt, the assumption apparentlybeing that after the device had beenburied for some time, the moisture inthe soil would penetrate the containerand make a better contact between thelead-in and ground. Some of the patentgrounds which do not claim to be under-ground antennas have various combina-tions of chemicals, chiefly copper sul-phate, which when combined with moistsoil is supposed to provide an exception-ally good ground. This phase of groundconnections is covered in detail in anarticle by Heckert Parker in August,1928 RADIO.

All of these devices have ordinary rub-ber and cotton covered lead-in wire,and the accompanying instructions di-rect the buyer to install it directly out-side the wall of the house, under thewindow through which the lead-in wireis to be brought. From our own exper-ience, when used with a broadcast re-,ceiver having an average degree of sen-sitivity, the results were so poor as tomake the set useless except for localstations.

Experiments with a real Rogers an-tenna, similar to Fig. 1, using a sensitivesuperheterodyne, showed that a rangeof 500 miles at night, in the winter,might be expected, with loud speakervolume, from stations having a powerof at least 1030 watts. The static levelwas very much lower than when usingan elevated antenna, 40 ft. above the ,ground, and 80 ft. long. Although the

21

volume on distant stations was much lesswith the underground antenna, a well-defined reduction of static to signal ratiowas noted, and except for stations at dis-tances of over 500 miles, the Rogers an-tenna was preferable.

However, when using the under-ground antenna with a 7 -tube tuned r.f.set of well-known make, the results weremuch poorer than those obtained withthe superheterodyne, due of course, tothe lower degree of sensitivity in thetuned r.f. set. Stations 500 miles awaywhich came in with good volume withthe elevated antenna, could not be heardwith the underground antenna, and thisperformance was made with the under-ground antenna arranged in such a man-ner as to receive the signals of thedistant station to the best advantage. Onlocal stations, however, the performanceof the set was very satisfactory, andwhile the static level on the elevatedantenna was so far down as to be barelynoticeable, a difference could be de-tected when the underground antennawas used.

So much for the conventional buriedwire in metal conduit. Several of theburied container antennas were then con-nected to the superheterodyne, and theresults compared with those obtainedwith the Rogers system. Distant sta-tions could not be heard, and only thoselocals which were within 6 or 7 milesof the receiver could be picked up withsufficient volume to give a satisfactoryperformance. In fact, with the super-heterodyne, better results were ob-tained when a good water -pipe groundconnection was used, with no antenna,than with the buried antenna. Hence,the conclusion was reached that if thelead-in from the buried antenna wascut off close to the ground, and only thelead-in used, better results would behad, and this proved to be the case. Howmuch better it would be, then, for oneto dig a small trench, say six inchesdeep, out through the back yard for adistance of fifty feet or more, and burytherein a length of lead covered wire,rather than to spend more money, andinstall what actually is nothing but ahigh resistance ground, with a small ef-fective capacity thrown in.

It is necessary to give the devil hisdue, however, for one device proved tobe quite satisfactory with sets such asthe superheterodyne, and was the nearestto being an underground antenna of anyof them. This device consisted of asealed metal container, in which wascoiled a roll of lead covered wire per-haps 60 ft. long. The wire passedthrough a hole in the container, and a15 ft. piece was provided for the lead-in.Directions for installation called forburying the device in a vertical position,directly under the window throughwhich the lead-in would pass, and didnot call for any section of buried wirelike the Rogers system.

The station log obtained with thisantenna, using a superheterodyne, provedthat a considerable amount of energywas being collected by the antenna, andthat as compared with an elevated an-tenna, it was preferable except for thereception of extreme distance, in whichcase the elevated antenna was by far thebest of the two. But the strangest partof the whole thing was that when thecoil of wire was removed from the can,and laid out flat on the ground, theresults were much better than whenthe coil was wound up and sealed withinthe buried container. "Why not elim-inate the metal container then, dig atrench for the cable the same as for theRogers system, and do a real job of it?"you might ask, but this would never do,for who would dare ask ten bucks for75 ft. of lead covered wire? A copper -plated can filled with mystery looksever so much more worth while to theaverage uninformed radio fan. Ofcourse, digging the trench is a lot ofbother, and conditions may be such thatthere is no room for a real Rogers an-tenna, which is the best argument thepatent ground makers can bring forth.

A fair idea of how much money mustbe made on such devices can be gainedby the writer's experience in answeringa number of advertisements concerningthem, for where the first quotation waslist price, as advertised, subsequent fol-low-up letters gradually brought theprice down until in one case the reduc-tion amounted to nearly 70 per cent. Itwould be foolish to assume that theywere not making a profit even at 70per cent discount, so the reader candraw his own conclusions.

The moral of all this is that if youare satisfied with local reception, a shortelevated antenna will give you the re-sults you want with practically nostatic, except in the summer months, andunless the elevated antenna is impracticaldue to the location, the expense of afactory made underground antenna isnot warranted. If you expect to receivedistant stations, however, do not bedisappointed if you meet with failure,for while you may find the static levelvery much lower than before, you willprobably find the signal level has gonedown in much the same proportion. Soif you buy one, patronize the firm withthe money -back guarantee and here'shoping you get your money back.

NEW SYSTEM FOR DETERMIN-ING SHIP'S POSITION

A radio acoustic system for determiningthe position of a survey ship when it isbeyond the visibility of shore objects hasbeen developed by the U. S. Coast and Geo-detic Survey. As described in the Survey'sspecial publication No. 146, it consists essen-tially of a radio transmitter at each of twowidely separated shore stations and a radioreceiver on the ship.

Each transmitter automatically radiates acharacteristic signal whenever a submergedmicrophone is disturbed by the explosion ofa bomb close to the ship. This disturbanceor noise is also instantaneously transmittedby a submerged microphone at the ship. Atvarying periods of time, depending upon thedistance from the two shore stations, theirradio signals are also received. As thespeed of sound in water is definitely known,as are also the station locations, the ship'sposition may be quickly plotted on the sur-vey map.

When the position of the ship is wanted,a small bomb is fired in the water alongside.The instant of the explosion is automaticallyrecorded on a chronograph aboard the ship.The sound of the explosion disturbs thesubmerged microphones at the shore stationsand their resulting characteristic radio sig-nals are received and recorded on the ship'schronograph. The ship thus obtains the timeof travel of sound in sea -water from herposition to each of the known positions ofthe shore station microphones, and therefromis figured the distances. This method hassuccessfully been used with a ship 75 milesaway from the shore stations.

RADIO SIGNAL TRANSMISSIONSOF STANDARD FREQUENCY,

OCTOBER TO MARCH

The Bureau of Standards announces a newschedule of radio signals of standard frequen-cies, for use by the public in calibrating fre-quency standards and transmitting and receiv-ing apparatus. This schedule includes manyof the border frequencies between services asset forth in the allocation of the Interna-tional Radio Convention of Washington whichgoes into effect January 1, 1929. The signalsare transmitted from the Bureau's stationWWV, Washington, D. C. They can beheard and utilized by stations equipped forcontinuous -wave reception at distances up toabout 500 to 1000 miles from the transmittingstation.

The transmissions are by continuous -waveradiotelegraphy. The signals have a slightmodulation of high pitch which aids in theiridentification.

Information on how to receive and utilizethe signals is given in Bureau of StandardsLetter Circular No. 171, which may be ob-tained by applying to the Bureau of Stand-ards, Washington, D. C. Even though onlya few frequency points are received, personscan obtain as complete a frequency metercalibration as desired by the method of gen-erator harmonics, information on which isgiven in the letter circular. The scheduleof standard frequency signals is as follows:

RADIO SIGNAL TRANSMISSIONS OF STANDARD FREQUENCYSchedule of Frequencies in Kilocycle:

Eastern Standard Time10:00-10:08 P. M.10 :12-10 :2010:24-10:3210 :36-10 :4410:48-10:5611:00-11:0811 :12-11 :2011:24-11:32

Oct. 22 Nov. 20 Dec. 20 Jan. 21 Feb. 20 Mar. 20550 1500 4000 125 550 1500600 1700 4200 150 600 1700650 2250 4400 200 650 2250800 2750 4700 250 800 2750

1000 2850 5000 300 1000 28501200 3200 5500 375 1200 32001400 3500 5700 450 1400 35001500 4000 6000 550 1500 4000

22 RADIO FOR NOVEMBER, 1928

Electric Phonograph Pick-up UnitsA Description of Their Methods of Operation and Suggestions for Improvement

of Tone Quality

By FRANCIS CHURCHILL

WHILE many different phonographpick-up units are available, butlittle information is given as to

their proper use. An electric pick-upunit usually consists of a permanentmagnet, a field coil and a moving arma-ture. The armature is actuated eitherdirectly or through a link coupling, bythe phonograph needle. The magnetictype is the most popular and seems tohave the best frequency characteristic.

The frequency at which the needlemoves across the groove of the recorddetermines the pitch of the sound pro-duced. The needle moves an armature,which in turn generates a voltage inthe field coil, since it is cutting lines offorce produced by the permanent mag-net. This voltage is then applied to anaudio frequency amplifier and loudspeaker and is reproduced as sound.

As the design of the pick-up unitcannot be easily changed by the experi-menter, the output frequency character-istics are not variable for a particularunit. That unit may not be very goodon the low frequencies, or perhaps on thehigh frequencies, but by proper use itmay be made to give satisfaction.

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(b)Fig.l. Usual Methods of Connecting

Pick-up Unit

Fig. 1 (a) and (b) show the usualmethods of connecting a unit into theaudio amplifier of a radio set. Theordinary pick-up unit has an impedanceof about 1000 ohms at the low fre-quencies and may rise as high as 20,000ohms at 5000 cycles, as shown in Fig. 2,whose curves were made with a standardimpedance bridge and are typical.

When such a unit is connected asshown in Fig. 1 (a), the high frequenciesmay be lost if the volume control is oftoo low a value, since the load wouldthen be equal to the pick-up or gener-ator impedance at the lower frequencies.If the resistance is made high enough

so that the pick-up unit works into, ineffect, an infinite impedance, then a moreuniform voltage output would be ob-tained for all frequencies. However, insuch a case the primary of the first audiotransformer would be across a variableimpedance, depending upon the volumecontrol setting, and so would notamplify uniformly.

Considering only the first transformerin the usual two -stage audio amplifier,the impedance across its primary shouldnot be over 10,000 to 20,000 ohms.With impedances higher than this thelow frequencies are lost, as also aregenerally the high frequencies. Thismeans a peaked amplifier and poor tonequality. This is likely to happen at cer-tain volume control settings if the re-sistance happens to be greater than50,000 ohms. With this same arrange-ment at very low volume settings or atthe highest settings, the primary of theaudio transformer will be connectedacross a low impedance, which will im-prove the low frequency response andalso the high end. This is undesirable,since changing the volume causes achange in quality.

A good way to get around this troubleis to connect the volume control as anordinary variable resistance in shunt tothe pick-up unit. With such a connec-

tion, the maximum impedance across thetransformer will be somewhat less thanthat of the pick-up unit, which meansa fairly low impedance at any volumecontrol setting. This is desirable becausethe characteristic of the first audio trans-former stays the same, as does the com-plete amplifier.

Let's see what happens when such alow impedance is connected across theamplifier. Curve A in Fig. 3 is that of apopular type of audio transformer whenconnected across a detector tube havingabout 20,000 ohms plate impedance.Curve B shows the same transformerwith a pick-up unit across it. Due to thelower impedance, the low frequencyresponse is much better and the trans-former is nearly perfect on the lowerend. However, the upper end has anenormous peak. Tests on a number ofmakes of transformers showed the sameeffect with the peak ranging from 4,000to 7,000 cycles. Such a peak wouldcause over -amplification of the higherfrequencies and needle scratch.

All audio transformers have a certainamount of leakage reactance and thesecondaries have distributed capacity andcapacity to ground, as well as the inputcapacity of the vacuum tube across it.All of these capacities resonate with theleakage reactance in such a way as to

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RADIO FOR NOVEMBER, 1928 23

cause a peak in the high frequency range.This leakage reactance can be increasedby adding an external inductance in theprimary circuit, which is exactly whatwe have done when connecting thepick-up unit across the primary. Natur-ally the lower the resistance in serieswith this resonant circuit effect, thehigher will be the resultant peak. Thepick-up unit has a fairly low resistanceand so the curve B of Fig. 3 is obtained.There are two ways of overcoming thispeak but first let us see whether it isdesirable to eliminate it.

If the rest of the audio amplifier isnot peaked on the high frequencies, sucha peak in the first transformer can beput to good use. When the volume con-trol resistance has a maximum value ofsay 10,000 ohms, the pick-up unit willnot give a good high frequency responseand the lower this value of resistancethe poorer the response. Then the peakin the amplifier practically offsets thedroop in output of the pick-up unit andso an excellent sound output is obtainedover the whole range of frequencies.

Suppose that the amplifier has toohigh a peak or that the pick-up unit hasnaturally a greater output at high fre-quencies, then it would be desirable toeliminate this peak. This can be easilydone in two ways ; by inserting a 10,-000 or 20,000 ohm resistance directlyin series with the transformer primary,or by inserting a higher resistance ii. thegrid return of the secondary.

The first scheme has the objection ofcausing a drop in the low frequencies aswell as the highs, since the curve A willgenerally be obtained, but it has the ad-

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vantage of being very simple to install,since it can be external to the radio re-ceiver. The middle frequencies are notdiminished, since even 20,000 ohms isonly a very small portion of the trans-former primary impedance at these mid-dle frequencies.

The second scheme has the advantageof not affecting the low frequencies butdoes drop the higher ones. It has thedisadvantage of having to be inserted inthe audio amplifier and should not beused with a detector tube input, sincethe high frequencies would be practicallylost.

Fig. 4 (a) and 4 (b) show the connec-tions for these two schemes. In the latter,

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Fig. 3. Effect of Different Impedances on Audio Frequencies

the resistance R will vary between 50,-000 ohms and 250,000 for differenttypes of pick-up units and audio trans-formers. Its action is as follows: Thereis a capacity between the two windingsof the transformer which is charged bythe secondary induced voltage. Thecharging current flows to ground throughthis resistance R, causing an emf oppo-site to that of the secondary induced emfin its effect on the grid of the tube. Thusone voltage counteracts the other and sothe hump on the high frequencies is re-duced. At lower frequencies the charg-ing current is less, due to the higher re-actance and so the very low frequenciesare unaffected.

Often the pick-up unit does not de-liver enough voltage to properly operatethe audio amplifier and loud speaker.When this occurs an intermediate imped-ance matching transformer may be usedas shown in Fig. 4 (c) or the unit may beconnected across the grid of the detectortube.

Curve C, Fig. 3 was obtained whensuch a transformer was used in conjunc-tion with the first audio transformer.The rising low frequency response wasobtained evidently from the effect of im-pedance matching at the very low fre-quencies, with a corresponding drop forall higher frequencies. Curve C does notshow the voltage gain when using thisstep-up transformer but merely showsthe frequency response with 1000 cyclesper second as a reference.

Fig. lb shows the method of connect-ing the pick-up unit and volume con-trol into the grid of a detector tube. Thiscan be most conveniently done by meansof a flat adapter which will slip overthe grid and negative filament prongs orcathode of an a.c. tube, after which thedetector tube can be inserted in its socket.The volume control should be connectedto ground and should be at least 50,000ohms. A 590,000 ohm potentiometerwould be more suitable and a more uni-form frequency response would be ob-tained.

As stated before, the low frequencyresponse with this last arrangement willnot be as good as when the unit is con-nected directly across the audio trans-former, but more gain will be obtainedsince the detector tube is used as an am-plifier. There will be no high frequencypeak, at least no more than when usedfor radio reception, but the pick-up unitwill give more output at the high fre-quencies. Scratch filters may be used ifthe needle scratch is objectionable,though if the pick-up unit is used prop-erly, such a filter is unnecessary.

Phonograph records are cut laterally.To prevent the cuts from cutting throughto the next groove, the very low notesare undercut or in effect, attenuated.With a good dynamic speaker mountedin a large cabinet or baffleboard, theaudio amplifier may be made to havr a

(Continued on Page 47)

24 RADIO FOR NOVEMBER, 1928

Radio Picture Transmission and ReceptionPhotoelectric Equipment and Methods for Visual Communication

By JOHN P. ARNOLD, Departmental Editor

SOME of the future possibilities of theelectrical transmission of photographswere strikingly demonstrated when

signals, emanating from radiophone appar-atus installed in the cabin of an airplane,flying a mile above the city of Phila-delphia on the afternoon of August 14,were picked up by Station WFI in thatcity and rebroadcast for radio listenerswho were equipped with picture receiv-ing apparatus.

. Due to the vibration of a wind -drivengenerator which supplied the power forthe radio transmitter, the results werenot highly satisfactory as far as thequality of the received pictures wasconcerned. But the demonstration itself,probably the first in the history of photo -telegraphy, marked an epoch in the ap-plication of still picture transmission tomodern problems such as the dissemina-tion of military information to numerouspoints along a battle front, the locationof forest fires by aerial patrols, and thetransmission of photographs of impor-

Picture Transmitting Equipment in Plane

tant events while an airplane is inflight.

The experiment was undertakenjointly by the Philadelphia airport, Lud-ington Philadelphia Flying Service, Inc.,Station WFI of the Strawbride & Cloth-ier Store and the Radiovision Corp. ofNew York. A Cooley "rayfoto" trans-mitter was installed in the cabin of aFairchild monoplane. The short-waveradiotelephone equipment, having a maxi-

mum input of 75 watts, was mounted inthe cockpit. A 65 -ft. "fish line" antennawas used.

The flight over the central section ofthe city required more than an hour.

Reproduction of Received RadioColonel Lindbergh

Picture of

Half an hour was needed for the planeto gain the high altitude necessary tothrottle down the engine so that it wouldnot interfere with radio transmission.Photographs of Col. Lindbergh andGraham MacNamee, which had pre-viously been converted to a "sound rec-ord" on a phonograph disc in accord-ance with the usual method employed inthe Cooley system, were transmitted.Although this demonstration did not in-clude the actual photographic operationsof taking, developing and preparing thepictures for transmission aboard the plane,there would he no difficulties in carry-ing out these steps on an airplane espe-cially equipped for this work.

The airplane was piloted by RobertP. Hewitt, assisted by John Busher,and the broadcasting apparatus wasoperated by John J. Leitch, FederalRadio Inspector of the Third District.

The picture signals were received ona short-wave receiving set on the roofof Station WFI and rebroadcast on thatstation's regular wavelength.

Essentially the system of transmissionconsists in converting the light and shadeof a photograph into audio -frequency im-pulses which are received on a conven-tional radio receiver and converted tolight impulses by a three -tube amplifier -oscillator circuit. This apparatus con -

RADIO FOR NOVEMBER, 1928

verts the audio -frequencies, which wouldordinarily be fed into a loudspeaker inspeech reception, into ultra -violet lightvariations radiated from a needle -pointstylus. The light impressions are re-corded on sensitive photographic paper,producing a positive reproduction of thetransmitted pictures. It requires butthree minutes to make a 4 x 5 pictureconsisting of 100,000 image impressions.

A REVOLUTIONARY LIGHT-SENSITIVE CELL

READERS of these columns have al-ready been introduced to the well-

known types of photoelectric cells; thatis, those which employ the alkali metalsor selenium as the light-sensitive ma-terial. Still another type is the photo-voltaic cell which is an important de-velopment in photoelectric cell construc-tion. It is quite likely that the recentperfection of this cell will solve somevery troublesome problems in the fieldof visual communication and in the im-provement of various sound recordingand reproducing devices light-sensitive cells are commonly employed.

To go back a bit to the early period ofphotoelectric history. In 1873 Wil-loughby Smith observed a phenomenonwhich is now designated as the photo -

resistive effect. In this case the substancechanges (usually lowers) its electricalresistance when light falls upon its sur-face. The effect is observable in se-lenium, molybdenite, the metallic sul-phides, oxides and various other crystal-line forms. Selenium cells were the firstto be used for practical engineeringwork ; but their response is very slow.

The so-called true photoelectric effect,first noted by Hertz in 1887 and latermore fully investigated by Hallwachs,refers to the emission of electrons froma metal or compound when illuminated.Stated in other words, a photoelectricbody loses a negative charge due to theaction of light. Potassium or the otheralkali metals are usually employed forthe construction of such cells.

The photovoltaic effect is a case wherean electromotive force is generated be-tween two metals in an electrolyte asthe result of the action of light on oneof the metals. The discovery of thiseffect extends back many years, probablybefore either the photo -resistive or photo-electric phenomena were observed. Inany event, in 1878, Sabine designed thefirst practical photovoltaic cell, employ-ing selenium deposited on an aluminum

25

plate for this purpose. Cells of this typeconsist of two electrodes immersed in aliquid or electrolyte and, in operation,do not require the use of an externalbattery as is necessary in using seleniumor potassium cells.

Although this particular effect wasdiscovered many years ago and althoughvarious combinations of electrodes and

Photovoltaic Cell. (Radiovision Corp.)

electrolytes have been tried, satisfactoryresults were rarely achieved. It wouldbe tedious to describe the reasons why thedevelopment of this type of cell wasneglected all of these years; it will sufficeto mention that the general belief is thatfatigue precludes any successful resultswith them. As we learn more about thematter of fatigue, in regard to the photo-electric cell, it is conceded that the emis-sion of electrons is an intrinsic propertyof the light-sensitive material, and thatstrong fatigue characteristics are oftendue to secondary causes which improveddesign is constantly eliminating.

Although it is too early to say thatthis is also true in the case of photo-voltaic cells, nevertheless, careful labora-tory tests, which would detect a delay inresponse of the order of hundredths of a

26

second, have failed to reveal any fatigue.Moreover, there are additional reasonsfor believing that these cells may be usedfor practically all applications which re-quire a high frequency of response. Thecredit for the perfection of the photo-voltaic cell is due to Samuel Wein, ofthe Radiovision Corporation, New York,who has also made other valuable con-tributions to the science of photoelec-tricity.

The construction of this cell may bestudied by referring to the accompanyingpicture. Two metallic plates, rigidlysupported and separated about % in.from each other, are immersed in anelectrolyte contained in a cylindricalglass bulb, 1% in. in diameter and about4% in. long. The cell is fitted with aradio base and the electrodes are con-nected by wires to the prongs which cor-respond to the plate and grid of a radiotube.

By connecting a very sensitive meterin series with the electrodes, a largedeflection will be noticed when one ofthe plates is illuminated. In direct sun-light, the writer has obtained deflectionsof % milliampere when the cell is ex-posed. When an opaque screen is inter-posed between the cell and light, thepointer of the meter immediately fallsto zero. While such relatively smalldeflections may seem insignificant to thelay reader, it is enough to make the in-formed experimenter sit up and take no-tice, since such results are unusual inthis type of cell.

This cell may be temporarily sensi-tized in the following manner. Whenthe terminals of the cell are connectedto a 45 -volt battery for about 10 sec-onds, the battery then removed and ameter substituted, deflections of severalmilliamperes-in fact, three or fourtimes the value before sensitizing-havebeen observed. The effect of this charg-ing gradually diminishes and disappearsin about an hour, but the charge can be'renewed as often as desired. The makersof the cell are planning to insert anauxiliary electrode between the twometal plates, serving a purpose similarto that of the grid in a radio tube, bymeans of which a constant charge maybe maintained indefinitely. However,it is not necessary for the cell to becharged, since its output is sufficient tooperate sensitive relays directly.

Further characteristics of these cellsmay be gathered from the curves illus-trating this article, and from the follow-ing facts which were taken from lab-oratory tests:

Current Output: In very feeble lightthe cells furnish a current of the orderof 10-6 amperes.

Internal Resistance: The internal re-sistance of five cells measured at 1000cycles in the conventional manner rangedfrom 15 to 52 ohms, with an averageof 32 ohms.

RADIO FOR NOVEMBER, 1928

Photovoltaic Potential: The voltageillumination curves (Fig. 1) indicatethat the potentials are proportional tothe incident illumination; the apparentdeviations from this generalization aredoubtless due mainly to the difficultyof measuring closely the distance of theilluminated plate from the source at

to

8

MV4

a

0

...MOMEMMEMMOOMMMOMM

Wel11111111111111111MINEMMIll

OM.EV201111.M.:r0=ZNOOOMM MMMMMM

OSOM MO MOM MMMMMM MI

looIRTOIITITY Di 1,00T CARDIAS`

Fig. 1. Voltage -Illumination Curves forPhotovoltaic Cell Whose Plates Are

Designated as "Pin" and "Back"

high light values. At low intensities,between 10 and 20 -foot candles, there isapparently a critical phenomenon, fornearly every plate exhibits a peculiarreaction as evidenced by change of curva-ture in the characteristic curve.

Spectral Sensitivity: A measure of thesensitivity of this type of cell to differentspectral colors (Fig. 2) was obtained bymeans of Wratten light filters. The lightsource was a tungsten filament lampwith a concentrated filament supplied

4

o

INIMI1110 MMMMM MINNOMINIONNO111M111111111111111MM1111111110110 MMMMM I Mit

MIIMMEMMININIMIIMMEM111111111111101111111111110111111111.111M11111111111M11111MMIMMIMMII IMMIM111111100111

IMMEN MMMMM 111111111111MMIMINMENEMI 1111111M1111 MMMMM111111111111111110111111MI MIIIII11111111111111111

MMMMMMMMMOHNE MMMMMIrarna VON MMMMMMMMMMMM111111111I/WINNLimmulIMMOIMIIMA11111111111PN11111101.11111M10111101111111111111111116,7-aMIESSAMMEMICArnh 1111111&AMEML-1.--11U.,1,1'.*AM -Ln111111r.' 4.* IOW *1111M11111111111111MIIMIIIMIIIIMII

11111MMEMION1111111111111111111111111111,1111111111111,0111111111111111111

MMMM

1111111111111111111111MIIIIIIENIIM11111111111111111111111MMIIIIIMONIN111111IBIONIIMIIMINIMMIONO11111111111111

VA3P41,,VIIGT14. I MICRO

Fig.2. Wavelength Sensitivity Curve

by a storage battery. The curve shownis purely qualitative as is any obtainedby filters which pass a relatively wideband of frequencies. The cell shows arather marked selective effect in theyellow. This rapidly decreases in thegreen and changes sign (positive to neg-ative) in the blue. In the blue -violetthe potential has reached an appreciablevalue of the opposite sign. The variousspectral colors, red, orange, yellow,green, blue and violet are denoted byR, 0, etc., in Fig. 2.

As has been previously noted the newphotovoltaic cell may be employed forall the ordinary applications for whichthe other types of light-sensitive cells areused, with the additional advantage ofnot requiring external batteries.

A PHOTOELECTRIC AMPLIFIER

HE practical employment of photo-electric cells involves as a rule the

amplification of the extremely minutephotoelectric current. To accomplishthis purpose the cell is connected to theinput of a vacuum tube amplifier.

For delicate measuring work or foramplifiers designed for "still" picturetransmission or television, steady sourcesof potential are required; the usual 4,B, and C batteries and, in addition, afourth or D battery, as it is sometimescalled, may be used to charge the photo-electric cell. The use of a power tubein conjunction with the cell requiresbatteries of several hundred volts, de-pending on the types of cell and tube.

Where photoelectric cells are used tocontrol power circuits through a relayor for other similar purposes, variationsin the supply source are not particularlyharmful and it is possible therefore todesign amplifiers which have the advan-tages of greater convenience and lowercost. Circuits have been devised to oper-ate directly from a.c. or d.c. power cir-cuits, although these are not as satis-factory as the "eliminator" describedhere.

The circuits differ merely in the plac-ing of the photoelectric cell and weredescribed in a paper by Fox, Rood andMarburger in the Journal of the Opti-cal Society of America for December,1927. The specific purpose for whichthis apparatus was designed was to con-trol a laboratory clock by photoelectricsignals; but the amplifier itself is suit-able for many other useful applicationsof photoelectric cells.

The circuit diagrams require no par-ticular explanation since they are notunusual in any way. It is necessary,however, to mention that the photo-electric cell should be inclosed in a light -tight box, preferably fitted with an irisdiaphram to control the beam of light

The parts which are suggested for theconstruction of this power amplifier are thefollowing.

1 Photoelectric cell, gas or vacuum type.1 U X-210 Power Tube.1 Type 365 General Radio transformer.1 Raytheon B11 tube.1 Mershon 30 MF electrolytic condenser.

1250 ohm Ghegan relay.2 Daven grid leaks, 7 meg and 0.1 meg.1 Bradleystat.

which falls within. The source of lightmay be an ordinary incandescent fila-ment lamp. The photoelectric cell usedby the authors of the above -mentionedpaper was a potassium hydride, gas -filled cell.

In operation, when light falls uponthe sensitive cathode of the cell, the"light signal" charges the grid of thevacuum tube and actuates the relay inits plate circuit. The relay can be madeto operate any apparatus that is de-signed.

A NEW TYPE OF SELENIUMCELL

N extremely simple process of mak-ing selenium cells was recently de-

scribed by R. E. Martin in the April,1928 Journal of the Optical Society ofAmerica. This simplicity of construc-tion should appeal to experimenters whoare interested in making light-sensitivecells and those who must workwith limited resources.

Powdered vitreous selenium is placedin a pyrex test tube and heated to

slightly above its melting point (217

deg. C.) in an electric furnace or overa Bunsen flame. The selenium is thenallowed to cool slowly and, as the tem-perature decreases, it becomes more plas-tic. By turning the tube nearly upsidedown, the viscous selenium can bepoured from the edge of the tube in longcylindrical threads, the diameters of

RgY7NfON Pi CID ITX 210-

R,4'YTHLON UX-2.10- R11070 E.ECTRLC 07L

Circuit Diagrams for a Photoelectric Power Amplifier

which depend upon the temperature. Thesize of the threads which were found tohe most suitable for making up intocell form were about 2 cm. long and0.1 cm. (79 x .039 in.) in diameter.

The annealing or rendering the selen-ium light-sensitive is the next step tohe undertaken. A thread of seleniumis placed on a piece of glass or micawhich rests on a copper plate. This isheated from below by an open flame or,preferably, by an electric heater, thelatter permitting better temperatureregulation. As the temperature is

gradually raised to about 130 deg. C.(266 deg. F.), the selenium changesfrom a shiny black material to the fa-miliar dull grey of the light-sensitivecrystalline variety. After the thread isentirely crystallized, the temperature isslowly raised toward the melting pointand the thread is observed through asmall magnifying glass. When the firstsigns of melting are noticed (that is, assoon as the crystalline structure showssigns of disappearing), the temperatureis immediately lowered 6 or 7 degreesand held constant for about 30 minutes.Again the temperature is gradually low-ered to about 180 deg. C. (357 deg. F.),held there for several hours, and finallyreduced slowly to room temperature.

ffIE 7ERNINALIC

Sflf1Y11141 W U MICA

T//RfAD/ORG.LAM

Fig.l. Construction of Selenium Cell

The electrodes or terminals of thecell are now attached. These may befine wires of platinum, nickel or copperwhich are passed through the holes pre-viously drilled in the glass or mica in-sulating base and bind the seleniumtightly to it. The advantage of thisform of construction is that the elec-trodes may be attached after the cellhas been annealed, since the metal of theelectrodes combines with the selenium toproduce metallic selenides, a combina-tion which is thought to be detrimentalto the action of the cell.

When this cell is connected in serieswith a battery and a current measuringinstrument (0 to 15 scale milliammeter),a current flows through the cell evenin the dark. Exposure to light lowersthe electrical resistance of the seleniumand the pointer of the milliammeter willindicate this by moving to a higher valueaccording to the intensity of the light.These cells have a resistance of aboutY2 megohm.

Selenium fumes are poisonous, espe-cially affecting the delicate membranesof the throat. Therefore, the experi-menter should work either in the openair or carry out the heating under ahood as used in chemical laboratories.

RADIO FOR NOVEMBER, 1928 27

SYNCHRONOUS MOTORS FORVISUAL COMMUNICATION

IN a recent paper T. Thorne Bakerobserves that the attainment of ab-

solute synchronism between transmittingand receiving equipment is one of thechief reasons for the success of modernphototelegraphic systems, as the greatestfailures in the early days of this meansof communication were largely due tothe lack of perfect timing between theapparatus of the two stations.

The earlier methods of obtaining syn-chronism included the use of electricallycontrolled clocks, pendulums, etc. Theso-called "stop -start" system was also invogue. By this method the receivingcylinder was turned over at a rateslightly in excess of that of the trans-mitting cylinder and was stopped at thecompletion of each revolution by somemechanical means until a signal fromthe sending station released it as thetransmitting cylinder began the nextrevolution. This system, while simpleand economical, is not very effective inthe transmission of photographs in whicha high grade of reproduction is de-manded.

Synchronism for television is only an-othe} name for trouble raised to thenth power. When it is seen that thesending of a single picture in about fourminutes involves difficulties, the syn-chronizing of apparatus which must dealwith about sixteen pictures per second,might seem to come under the head ofimpossibilities, although someone has saidthat the word should be banished fromthe dictionary.

At any rate, modern television experi-menters, with very few exceptions, em-ploy synchronous motors. Motors ofthis type are controlled by the applica-tion of a pulsating current. They areused, of course, to rotate the conven-tional Nipkow disc or some similar de-vice which scans the scene or object be-fore the transmitter, and recomposes theimage at the receiving station.

Alternating current motors for thiswork must built in accordance withrigid specifications to obtain satisfactoryresults. The motor should be of the in-duction type, which does not rely upona commutator either for starting or run-ning. Since this motor must be placedrather close to the amplifying apparatus,a sparking commutator would createelectrical disturbances which seriouslydistort the pictures. The ideal motorshould be silent in operation and freefrom hum. Moreover, the motor atthe receiving station must be so designedthat, by inserting a suitable controlmechanism in the form of a switch, anda variable resistance, reactance, or a com-bination of the two, its speed may bechanged to and kept constant with thespeed of the motor at the transmittingend of the system.

28

As some of the problems of photo-electricity and electrical image trans-mission are highly technical, and con-sequently not of general interest to theaverage reader, such problems areoften not fully treated in these col-umns. But in order that we may beof service to the more advanced ex-perimenter, we will gladly answer spe-cific questions of this nature by mail.There is no other obligation than thatthe correspondent accompany such re-quests for information with a self-ad-dressed, stamped envelope. Address thecommunication to John P. Arnold,541 S. Yewdell Street, Philadelphia,Penn.

A recent engineering test of the re-quirements of motors employed for driv-ing television scanning discs has revealedsome interesting facts. The scanning discas used for television reception is usuallyanywhere from 9 to 24 in. in diameter,1/16 to A in. thick, and is often madeof aluminum, although other metals andsome materials like bakelite are used.Such discs can be driven by 1/15 h. p.,110 -volt, 60 -cycle, single-phase motors.With a perfectly true 15 -in. disc, sucha motor runs within 50 or 75 revolu-tions of the synchronous speed.

In order to reduce the speed to thatrequired for the particular television sys-tem, it is only necessary to place a seriesresistance in the circuit with a means ofshort-circuiting about 15 per cent of theresistance. For example, a 15 -in. disc,%-in. thick, with a required speed of1080 revolutions, needs a fixed resistanceof 160 ohms, with a switch shuntedacross 25 or 30 ohms for the purpose ofcontrol.

Although this method has provedfairly successful, there is another way ofobtaining more stable operation. As aflat disc is practically a frictionless loadupon a motor, it is an advantage to loadit in some way. For instance, if sixsmall blades, 1 by 2 in. are placedaround the circumference of the scan-ning disc, a slight load is placed on themotor, enabling the receiving operator tohold the speed of the disc more constantbecause the motor then responds tochanges in speed much more readily. Themotor will require only 30 ohms fixed

H. P. Baldor Condenser Type Motor(Interstate Elec. Co.)

RADIO FOR NOVEMBER, 1928

resistance, with approximately 5 ohms tobe short-circuited for adjustment, as-suming the use of a 15 -in. disc turningat a speed of 1080 r.p.m.

With a load of this kind, it is pos-sible to produce any speed from about1700 r.p.m. down to 300 and maintainit very easily by the selection of theproper amount of resistance placed inthe supply lead. A mechanical resist-ance, such as fins or blades attached tothe scanning disc, helps to stabilize andenables the operation to more rapidlysynchronize the receiving motor with thetransmitter.

Although the 1/15 h. p. motor is quite

OUTPUT Of(IIMPLIFIER

AO Y0171

Rio

SCIINNING DISC si

MOTOR CONTROL

WORT ....C,',QC1/17116

5-1177611-

118 a MN 110 P-A CI

Fig. 1. Circuit Diagram of TelevisionReceiving Equipment

satisfactory in the case of scanning discsof from 9 to 15 inches, when larger sizesare used or heavier loads are involvedthe 58 h. p. Baldor condenser typewill be more suitable for the work. Amotor of this type is shown in the ac-companying illustration and is em-ployed in both transmitting and receiv-ing stations. Such motors can also beused for synchronizing in "still" picturesystems.

The circuit diagram (Fig. 1) showsthe use of such a motor with the usualtelevision receiving equipment. Theoperator views the illuminated plate ofthe neon tube, the brightness of whichvaries in accordance with the televisionsignals, through the scanning disc. Whenthe motor gets slightly out of step withthe transmitter, which will be notedwhen the image appears to be "out offrame," the short-circuiting switch maybe closed, speeding up the disc slightlyor, when open, the speed is somewhat de-creased. In this way, synchronism ismaintained between the transmitting andreceiving discs.

The Unholy WritWE MAKE no bones about defyingthe lexicographer when it suits

our fancy to torment the language ofour fathers; yet the recent verbal atroc-ity, "to televise," causes a rill of shud-ders to course our spine. We look for-ward with horror to the possibility ofthe report that some operatic tenor was"highly enthused to have been televisedand broadcasted to an admiring world."

PICTURES TRANSMITTED INONE MINUTE AT RADIO

SHOW

ARADIOPHOTO apparatus capable ofpicking electrical impulses out of

the air and converting them in less thanone minute into a complete 5x7 photo-graph was demonstrated at the NewYork Radio World's Fair. This appa-ratus, developed in the research labora-tories of the Westinghouse Electric andManufacturing Company, has been usedin experimental transmissions over shortwaves from Station KDKA at EastPittsburgh, Pa.

Because of the difficulty in securingradio wave channel assignment, the dem-onstrations at Madison Square Gardenused wires, rather than air channels,for the transmission of the pictures.Westinghouse engineers state, however,that the equipment functions equally aswell by radio as by wire within thelimits of fading and static.

The Westinghouse apparatus employsstandard photographic processes formaking pictures. Its pictures are madeby the exposure of sensitized paper tolight, in exactly the same way picturesare customarily made in photographicstudios.

Dr. Vladimir K. Zworykin, WestinghouseResearch Engineer, Inserting One of His

Photoelectric Cells Into the Radio-photo Transmitter

In addition to ordinary short wavetransmitting apparatus, the system usesthree principal pieces of equipment: asending set, a receiving set, and a "syn-chronizer."

In the sending set, an ordinary photo-graph or manuscript is placed on a cyl-inder which rotates slowly and at thesame time moves forward longitudinally.In this way, every point on the picturecomes within the range of a tiny beamof light. By a system of mirrors, the

beam of light is reflected at an anglefrom the photograph to a photoelectriccell, which gives out an electrical im-pulse corresponding in intensity to thedegree of light or shadow of the par-ticular pin -head of space on the photo-graph covered by the beam of light at

Westinghouse Radiophoto Receiving Set

that particular moment. This proce-dure, in other equipments, generally re-quires that a transparency be prepared.

For radio transmission, the feeble cur-rents given out by the photoelectriccell pass through three stages of ampli-fication and then go by wire to the radiobroadcasting station, which may be lo-cated a short or long distance from theradiophoto sending set. There the lightwaves, already converted into electricity,go out into the ether in the form ofradio waves. At KDKA, the short-wave63 -meter channel was used.

At the receiving end, which could besituated anywhere within the effectiverange of short waves, a standard shortwave receiving set is used to pick theimpulses out of the air. The impulsesare carried to a special lamp, whichflickers according to the fluctuations inintensity of the current. The lightfrom this lamp is focussed into a tinybeam which plays on a cylinder movingin the same ways and at the same speedas the cylinder at the sending end. Thiscylinder is covered with sensitized paper,and as the light falls on it with varyingbrightness, a series of impressions ofvarying degree are made on the paper,which, when "developed," present a

facsimile of the picture placed on thesending cylinder.

An essential feature of this system isthat the cylinders at the sending set andat the receiving set rotate and move for-ward at exactly the same speed. To ac-complish this very difficult feat is theduty of the "synchronizer." Synchroni-zation is accomplished by the transmis-sion, over the same wavelength used forthe radiophoto transmission, of a con-

stant frequency note which regulates thespeed of identical synchronous motorsdriving the two cylinders.

The finished photographs, after pass-ing through the "dark -room" processesof developing and drying, correspond inpractically every detail with the origi-nals. If the pictures are held two feetaway, it is impossible to tell the originalfrom the copy which has been sentthrough the air.

SCANNING FOIBLES

Aristarchus, a Greek and astronomerof classical times, noted that the moonhas always providentially avoided col-lisions with our earthly planet. Feelingcalled upon to exploit away this per-verse circumstance, he did so by re-course to the principle which Huygens,later, denominated vis centrif uga, a

phrase which seems to denote, beingtranslated, the centrifugal force of thephysics textbooks. To bring this para-graph up to the very minute, we maypoint out that the conventional scanningdisc for television is an excellent exampleof the tendency of parts of rotating sys-tems to move away from their center ofcircumvolution. We mention this be-cause it has been brought to our atten-tion by experimenters who have beentreated to impromptu demonstrations ofthe phenomenon that a disc, insecurelyattached to a motor shaft, may departfrom thence on a tangential and destruc-tive journey and end up abruptly andpartially buried in a wall or ceiling or,mayhap, in some other semi -inert bodywhich stands in its path. Thus, by theoperation of the very principle whichAristarchus believed governed the move-ments of the heavenly orb, a scanningdisc will perform certain parabolic pere-grinations which may reduce a parlourlaboratory to debris and an ardent ex-perimenter to sampling the contents ofthe arnica bottle. Such happenings areto be deplored; yet to suggest the remedypartakes of the obvious.

Satisfactory radio reception for alltenants in an apartment house may besecured from an untuned antenna and acentrally located r.f. amplifier having aflat characteristic for all broadcast wave-lengths. The amplified r.f. current cor-responding to each channel may then beseparated by a system of filters or fixedtuners. The amplified detector outputfrom each channel can be conducted toa terminal board in each apartment.This board may be equipped with a num-ber of jacks into any one of which thelisteners can plug a loudspeaker cord.By providing each jack circuit with a re-sistance unit having the same impedanceas the speaker, a listener may changefrom one channel to another withoutaffecting the volume of reception in otherapartments.

RADIO FOR NOVEMBER, 1928 29

Radio Aids Air Races

OF

the 350,000 people who watchedthe 1928 National Air Races fromthe grandstands at Mines Field,

Los Angeles, from September 8 to 16,not to mention other thousands whofailed to get closer than the gates, it isprobable that only a few hundred wereaware of the important part played byamateur radio in contributing to the suc-cess of this great event. The contribu-tion was not "spectacular" in thecommon meaning of the word in com-parison to the hair-raising aerobatics ofthe contestants, but in the minds of theofficials it exceeded all expectations forits utility. The Amateur Radio ResearchClub of Los Angeles, affiliated with theAmerican Radio Relay League, sawtheir opportunity to render a service.With the assistance of radio friends,they rendered this service to their credit.

In addition to the transcontinentaland international races which finishedat the field, several races were scheduleddaily over distances of 25 to 120 milesaround courses of five and ten mileseach. The courses were marked by"pylons"-steel towers flying the "windsock" at the top and having black andred checkered sides for greater visibility.As the planes circled the pylons, ob-servers checked them according to theirlap numbers and closely watched forfouling or cutting pylons, forced land-ings, plane trouble of any kind, crashes,etc., which made it necessary to havespeedy and reliable communication frompylon to pylon and with the judges'stand at the field. Many minor needsfor fast communication developed as theraces progressed.

Signals by flags or semaphore betweenpylons were obviously impractical be-cause of distances. Telegraph and tele-phone were too expensive and the timewas too short for such installations. Asa last resort, radio seemed to be the onlypractical solution to the problem, but theexpense likely to be incurred mightamount to more than the cost of eithertelephone or telegraph. The air meetwas not intended to be a financial profi-teering stunt, but rather as a means ofcontributing to the "air -mindedness" ofsouthern California, in which endeavorit certainly succeeded.

M. E. McCreery, 6LJ, was a memberof the committee on communications assponsored by the Los Angeles JuniorChamber of Commerce. He saw theneed of the race officials and put up theproposition to Robert Parrish, 6QF,president of the A. R. R. C. Parrishtook the proposition to the members ofthe club who gave their hearty approvalof the stunt and conferred upon their

By WALLACE S. WIGGI

Bert Fox at 6EMI, Transmitter Construe edby Don Champion, 6FA

president full authority to supervise thejob-and a generous share of the work.

Licenses were obtained from the Com-mission for five stations: one for each ofthree pylons, one for the judges' stand,and one for an aeronautical exhibitbooth in the exposition. "Bob" Parrish,manager of the Pacific Engineering Lab-oratory Co., supplied the main transmit-ters and a few receivers. Other trans-mitters and receivers were supplied bymembers of the club.

The pylons were not supplied withpower, so portable power was necessary.The final decision was for batteries, buthow could they pay for them ? Theaverage radio club never gets endow-ments. At least 350 volts were necessaryat each pylon to supply plate current tothe 7% -watt transmitting tubes intuned -plate tuned -grid circuits. Storagebatteries were needed for all filamentsupply, but there was no means for re-charging them. What to do? Theanswers to these questions came in theform of friendly cooperation of theFrench Battery Co., the Durkee ThomasCorp., and the Western Auto Supplywho furnished all the batteries and tubeswithout charge.

From an inclosed box at the top ofthe crowded grandstand, a splendid viewof the field was had by the operator at"6EMF." Directly in front of thestand was Pylon Number 1. Off to theright and to the west could be seen PylonNumber 2, at a distance of a mile. Herewas located station 6EMH. On a linesouth of the grandstand and about twomiles away was Pylon Number 3, withstation 6EMI. Pylon Number 4, twoand a half miles farther on and in linewith Pylons 2 and 3, was designated asstation 6EME. It was five miles aroundPylons 1, 2 and 3, and ten miles aroundall four pylons.

Let's watch a race! Here are sixplanes at the starting line ready for the720 cu. in. event. The planes are "atrest," waiting for the starter's flag, withmotors turning over slowly. Dots anddashes from 6 EMF in the grandstandare flashed to all pylons and they form

the following words: "QST QST DE6EMF RACE ABOUT TO STARTQRX (Stand by) FOR QST TON(Take -off numbers)."

The operators at the pylons informthe observers and everyone is in read-iness. The starter walks out to the firstplane and suddenly dips his flag. Themotor roars, the plane moves, rapidlygains speed, and soars into the air towardPylon Number 2. 6EMF flashes:"THEY'RE OFF!" The remainingplanes are started at thirty second inter-vals and are flown against time. To startall the planes at once would invite need-less dangers. Take -off numbers arebroadcast to the pylons, and as the lastplane leaves the field, the first one maybe seen on the home stretch of the firstlap. When the "QST TON" has beencompleted, all pylons answer: "QSTOK 6EMH," etc.

Watch these three planes in a bunchas they go around Pylon Number 1!Look at that little monoplane. See howit flits past the others like a little spar-row! Zoom! Zoom! Zoom! The threeplanes dart off toward Pylon Number2 again on their second lap as the ob-servers call off the numbers and check.The operator at 6EMF is constantlymoving the dial on his receiver betweentwo points. Operating on the 80 -meterband, he finds the pylon stations onlya few kilocycles apart. 6EMH is at 54,6EMI at 49.5, and 6EME at 45.5.Not so bad.

Several laps have been completed now.Here comes a plane that seems to behaving trouble. The motor sputters, in-dicating a broken pipe or valve, perhaps.Awful strain, these races on planes andpilots. The plane makes a graceful land-ing and taxis out of the way. The num-ber is immediately flashed to all pylons.Why? Inside of three minutes wouldcome as many inquiries about the planeand its failure to appear.

Now let's go out to 6EMI, at PylonNumber 3. We are out of sight of thegrandstand, but we could reach it byauto in ten minutes through traffic. Byairplane, we could get there in oneminute! The surrounding country ispractically level, but between us andPylon Number 2 is a small ravine andsome trees. We can see the planes com-ing straight toward us, flying danger-ously low, barely clearing the tree tops,and now skimming along the ground tothe pylon. They bank sharply, usuallygaining a little altitude, circle themarker, and fly off toward the field.This is a five mile race, so they are notusing Pylon Number 4.

(Continued on Page 46)

30 RADIO FOR NOVEMBER, 1928

Battery Charging with a Synchronous RectifierComplete Details Regarding the Construction and Operation of a

Synchronous RectifierBy G. F. LAMPKIN

ASYNCHRONOUS rectifier is an ex -cellent source of high potentiald.c. for transmitting, as testified

by the many "syncs" owned by amateuroperators. Such a rectifier, as may beknown, utilizes a synchronous motor, acommutator disc, and a brush rigging.The commutator is rotated in step withthe alternating current, and functionsas a switch, reversing at the correct in-stant so as to bring the output voltageright side up. In its use for high -volt-age, full -wave rectified supply it is emi-nently satisfactory. With a smallamount of care it will function just assatisfactorily to deliver several amperesat comparatively low voltages.

The chief advantage of a sync lies inthe range of currents and voltages overwhich it can be used. In the role ofbattery charging 20 amperes is by nomeans the limit of current obtainable;while for a transmitter the output volt-age can be run upwards of 3000 volts.The metal to metal contact assures ahigh rectification efficiency. A disad-vantage is that the rectifier works bestinto a resistance load. If an attempt ismade to work into a condenser or in-ductance, as in a filter system, troubleimmediately develops through sparkingat the brushes. Only by special meanscan a filter be used on a sync.

A description of a synchronous recti-fier will serve the dual purpose of illus-trating the processes involved in itsoperation, and of affording a basis forconstructional work. The heart of therectifier is of course the synchronousmotor. The usual nameplate data for async -rectifier motor are IA h.p., 1800r.p.m., single-phase, 60 -cycle, 110 -volt.An 1800 r.p.m. motor allows thesimplest sort of commutator constructionwith only two segments.

The brush rigging uses two brushesinto which a.c. is fed, and two fromwhich full -wave d.c. emerges-a total offour brushes equi-spaced around thecommutator periphery. Fig. 1 showsthe commutator position and current

Fig.l. Commutator Position,

Complete Charging Outfit

flow at the beginning of a positive halfcycle, and at the start of the succeedingnegative half cycle. The disc, turning1800 r.p.m., advances one -quarter of arevolution in a half cycle, 1-120 of asecond. Thus the conditions of thesketches hold true-though the directionof current in the a.c. source reverses,the commutator maintaining unidirec-tional flow in the output.

A I/4 h.p., single-phase induction mo-tor can be made into a synchronousmotor of only slightly less capacity byfacing off four flats on the rotor, ap-proximately 1/16 -in. deep, as indicatedin Fig. 2. It is a simple machiningoperation, which, with the turning of thecommutator disc, is the total of machinework necessary. The flats on the rotor ofan induction motor form air gaps acrosswhich the flux is reluctant to slip, andthe rotor holds in step with the impressed

frequency. The induction motor mustof course have four poles, so that itsname -plate speed would be around 1740or 1760 r.p.m.

Fig. 2. Conversion of Induction toSynchronous Motor

The commutator disc in Fig. 3 wasdesigned as small as was consistent foroperation at 3000 volts. The larger thewheel, the greater is the space available

Fig. 3. Commutator Disc

RADIO FOR NOVEMBER, 1928 31

for insulation. But also greater is thepower necessary to turn the disc, for thefriction and windage losses are increased.The disc proper, shown in the sketch,was cut from %-in. micarta. The bush-ing for the shaft was turned from 272 -in. round brass bar; and the commutatorwas made from 3/32 -in. brass. The lat-ter was fastened to the disc by screwsinside the brush path. Both this, and thefilling of the slots between segmentswith drive -fit formica plugs, afforded asmooth brush path. Such a path not onlyreduces brush friction, but aids mate-rially in keeping sparking at a minimum.In turning the disc a final smoothingcut should be taken over both segmentsand insulating sectors.

lamp to the other two. Determine andfix the position 9f the brushes for maxi-mum brilliancy of the lamp. The rec-tifier is then ready to feed 20 amperes toa battery, or 3000 volts to a transmitter.

For ordinary battery -charging, a 50 or75 -watt toy transformer is ideal. It ischeap, convenient, and usually with ad-justable secondary voltage so that thecharging rate can be varied. For eachcharging rate it is necessary to adjustthe position of the brushes slightly. Bothangular position and pressure on the discshould be changed till sparking is at aminimum.

The design data for a transformerwhich has been in this use by the authorfor over a year are as follows:

Fig. 4. Brush Details

Two bakelite dials were made to thefoundation of the brush rigging. Coppergauze brushes and brass fittings com-pleted the assembly, of which Fig. 4gives details. The set -screw in one dialwas removed and replaced by a threadedinsert in an insulating rod. The latterwas to afford a means of brush adjust-ment. Four thicknesses of medium cop-per gauze were used in each brush.

In the adjustment of the brushes liesthe secret of sparkless commutation.When motor, commutator disc, andbrush rigging have been assembled, thebrushes should be carefully adjusted tobear equally on the commutator ; theends of the brushes should be parallelto a radius of the disc; the brushesshould be exactly 90° apart; and twodiametrically opposite brushes shouldmake and break contact with the seg-ments at the same instant. It is essentialthat severe sparking be eliminated, other-wise the brush and commutator life willbe short. Elimination of sparking on atransmitter sync spells the difference be-tween hash, and the distinctive, musicalsync note.

Before using the sync under load thedisc should be thoroughly cleaned, espe-cially around the insulating sectors, ofall metallic dust. Then place 110 a.c. ontwo brushes, 180° apart, and connect a

Core cross sectionCore windowPrimary winding 330

long leg.Secondary winding 45

primary.Voltage primary 110, secondary 16.3, 60 cycles.

The layout was used to charge an8 -cell, 20 -ampere -hour Edison battery ataround 20 amperes. Such a charge filledthe battery up in short order. More con-servative rates should be used, of course,when charging lead cells. The secondaryvoltage of the transformer may be cutas desired by reducing the secondaryturns proportionally. That is, for a sec-ondary voltage of E, the new numberof secondary turns is E.-16.3 x 45. Thecharging rate may be varied by usingvariable resistors of appropriate ratingin the transformer primary or secondary.The best method is to use a tapped trans-former.

A battery may be charged at around5 amperes by connecting it to the rec-tifier output, and placing an electric ironin series with the 110 -volt lines on theinput-though such is hardly economical,because the iron gets most of the watthours. The service man, however, mayhave enough batteries to connect in seriesand charge directly from the 110 supply.

The polarity of the output must bechecked each time the rectifier is started

PA" x 11/2"PA" x 4"

turns No. 20 SCE on

turns No. 12 PE over

32 RADIO FOR NOVEMBER, 1928

up. The reason is that the rotor of themotor does not always pull into stepwith the a.c. in the same relative posi-tion. A reversing switch should be putin some portion of the circuit, for in-

Fig. 5. Circuit Diagram with ReversingSwitch

stance as drawn in Fig. 5. With a d.c.voltmeter the polarity of the rectifiercan easily be determined, and correctionmade if necessary, before closing thecharging switch. An a.c. voltmeter canbe used by closing one side only of thecharging switch. The voltage of bothbattery and rectifier in series is then readacross the other open side of the switch,and that polarity of the rectifier whichgives the smaller reading is correct forcharging.

It is a simple matter to make a shuntfor a milliammeter so that it will readthe d.c. charging current, and by doingso it will aid materially in the operationof the sync. The meter in the picturewas a Jewell, pattern 54, 0-100 d.c.milliammeter. A shunt of 17A" of No.14 tinned bus wire converted it into a 20 -ampere meter. If a standard ammeter istemporarily available it is only a mat-ter of minutes to find the size and lengthof wire necessary to give any desiredammeter scale on a milliammeter.

The overall efficiency of any a.c. tod.c. unit is something that is seldommentioned. Figures for such range from50 to 5 per cent. With this outfit theinput to the motor on the sync was 220watts. If no resistances are used forcharging -rate regulation, that figure maybe taken as representative of practicallythe total power loss of the system. Themore power put through the rectifierinto the output circuit, the less is thecost per unit of output.

As stated before, the rectifier may beused for a 3000 -volt transmitter sup-ply. Actually it has been used to rectify3300 r.m.s. or 4650 peak volts, whensupplying 150 milliamperes to a c.w.transmitter.

Any a.c. hum from a filter circuit maybest be reduced by increasing the ca-pacities of the second and third conden-ser so as to by-pass the a.c. component ofthe rectified current. Humless operationrequires that this component be less than0.1 per cent. With a load of 75 milli-amperes, 4 mfd. each in the second andthird condensers give 0.07 per cent ofhum, whereas 2 mfd. condensers give 0.3per cent. When an eliminator is in-tended to supply more than 85 milli-amperes a condenser block of 2-6-6 mfd.is desirable as such a great current drainincreases the tendency to hum.

A Complete Tube Testing Set

WHILE a number of tube testershave been described in past issuesof RADIO, there have been none

so complete in the number of possibletests which can be made, as the one de-scribed herewith. This tester was madeup from suggestions contained in a tubedata book recently published by E. T.Cunningham, Inc., and with it, the serv-ice man, experimenter or tube salesmancan tell practically everything necessaryabout the condition of any of the stand-ard tubes.

The tester is shown in the picture,and the circuit is shown in Fig. 1. Theset has been designed to test all types oftubes, both a.c. and d.c. with the ex-ception of the 374 glow tube, the 376resistance lamp and the 300-A detector.It will give an accurate indication ofthe condition of the elements and, if thetube is operative, will also indicate theefficiency of the filament. Above all, itis inexpensive to construct.

The necessary materials for construc-tion are given in the list of parts. Thework is simple inasmuch as there are nocomplicated circuit arrangements; themeters, sockets, rheostats, etc., may beconveniently mounted on a bakelite orwooden panel, with a cabinet to concealthe wiring, or can be laid out on abaseboard. The actual layout and con-structional details are left to the judg-ment of the builder, as it is thought that

0- 32 7.

C1-.322CX.C7X- 220.

5 2

By CLINTON OSBORNE

the circuit diagram and picture will fur-nish sufficient data for all practical pur-poses.

In building the test set, the variablerheostat should be of the 10 -ohm size,capable of carrying PA amperes undercontinuous load. The fixed resistance Rshould be exactly 6 ohms, and is placedin the negative A lead from the No. 2and 3 sockets to the 4 -volt line of thebattery. The switchboard key must beconnected so that in its normal positionit will indicate short circuits. If thisconnection is reversed so that the emis-

6 0/MV

.101YATT HoYaIMISSION.

1 2 C-377PROYCT/Y1

P .90.YOITS/9MP

1111I 1111 r2 791,11

MA

040 M " MpDf1 SO, 7.3 DIEPao KfY .16M7Pir

SHORTS

sion reading is taken first, the meters orthe tube may be damaged, it the tubeelements are shorted together.

To place the set in operation. turn therheostat on slightly and set the switchto the point indicating the correspondingsocket number or numbers, these figuresindicating which tubes may be tested inthe correspondingly numbered socket.For example if switch is on contact 2-3,type '99s, 220s, or 322s in socket No. 2may be tested, and '99s in socket No. 3may be tested. If switch is on contact4, C -11s, 12s and 326s may be tested

Panel New, showing .4rrangement of Sockets and Meters

CX 300 kCX-30.1A

.C.112 .671- 540.a.326 :CE- 37 CI-.1.122t

CE -57 - CI -371A4

4Se

- 4-5 rags

Fig. 1. Circuit Diagram of Complete Tube Tester

RADIO FOR NOVEMBER, 1928

in socket No. 4 and so on: the tubeto be tested is then inserted into itsproper socket.

Note very carefully whether the diallamps Nos. 1 and 2 are lighted, or evenvery faintly glowing. If they are, it isan indication that two or more elementswithin the tube are shorted, or that thefilament is open and resting against thegrid. To determine if the latter is thecase, turn the rheostat up and if no reg-ulation of voltage is possible, an openfilament is indicated. If lamp No. 1

lights, a short between filament and gridis indicated ; if No. 2 lights, it indicatesa short between filament and plate; ifNos. 1 and 2 light, it indicates a shortbetween grid and plate.

If neither lamp lights, then the ele-ments are free from short circuits andthe rheostat should be turned up untilthe voltmeter shows that exactly theproper voltage, as given in the accom-panying chart on voltage and emissionlimits, is being applied to the filament.If the rheostat has no effect on the fila-ment voltage it indicates an open fila-ment, either broken or burned out.When the voltage is correct, momentar-ily press the switch indicating the emis-sion current.

(Continued on Page 50)

33

The Marshall Short -Wave ReceiverA New Short -Wave Circuit Developed for the Navy and Using Screen -Grid Tubes

By S. R. WINTERS

NEW high -frequency receiving setdesigned and built at the BellevueNaval Research Laboratory incor-

porates the screened -grid or four -ele-ment electron tube. This receiver, in-tended for use on battleships and otherfloating units as well as at shore stationsof the United States Navy, marks theintroduction of a push-pull, screened -grid type of receiving set in the Govern-ment service-a type of amplifier alreadypopularized by broadcast listeners andradio amateurs. However, this novelcircuit is said to be the most sensitiveyet developed by the Navy for high fre-quencies.

This high -frequency receiver is de-scribed as a single -stage tuned radio -frequency amplifier, preceding an auto -dyne detector and two stages of audio -frequency amplification. It is a six -tubeunit, including two four -element tubes,connected for push-pull operation, aswell as two detector tubes. A frequencyrange from 4,000 to 25,000 kilocyclesis embraced-this extensive wavelengthrange requiring the use of five inductancecoils of varying sizes. Thomas A. Mar-

a student and researchworker in electron tubes at the BellevueNaval Research Laboratory-designedthis receiver.

The so-called "Marshall Receiver"employs two tubes of the '22 type in theradio -frequency circuit-each of thesetubes having two grid elements and beingwired for push-pull operation. Thesetwo four -element tubes operate on 3.3volts for the filaments, 120 volts for theplates, and 60 volts for the platescreens.

The two detector and two audio -fre-quency tubes are the '01A type and re-quire 5 volts on the filaments. Forty-five volts are impressed on the platesof the detector tubes but this potentialmay be varied by use of a potentiometer.The two audio -frequency tubes use only60 volts on their plates as the sole nega-tive bias available for the grid elementsis a one -volt drop in the filament rheo-stat. The batteries necessary for theentire power supply are a 6 -volt, 100 -am-pere -hour storage battery for the A sup-ply, and a 120 -volt B battery with 45 -and 60 -volt taps.

The antenna circuit of this novelshort-wave Naval receiver consists of asmall antenna coupling condenser, con-nected through a series inductance to theground. This series inductance coil iscoupled to the tuned input -inductanceof the amplifier. These two inductanceunits are wound on a plug-in coil system.

When the latter is plugged into the re-ceiver, the tuned -input inductance is con-nected across the tuning condenser orseries inductance. A compensating con-denser is employed across the tuning con-denser to compensate the extra residualcapacity which is present in the tuneddetector circuit. This effects a dial align-ment of the two circuits, thus insuringa similarity of dial readings for both theradio -frequency and detector variablecondensers. The tuned circuit of theradio -frequency amplifier tuning con -

that of the internal tube output impe-dance. This could, in a receiver of lim-ited tuning range, be accomplished byadding a plate -circuit tuning control.But as simplicity of control, and a mini-mum of parts and space, is a general andimportant requirement in Naval servicereceivers, attempt has been made to em-ploy fixed chokes for this purpose."

Therefore, in the "Marshall Re-ceiver," two high -inductance, low -ca-pacity chokes are employed throughoutthe frequency range of 4,000 to 25,000

Marshall Short -Wave Receiver, as Used by Navy

denser and the radio -frequency amplifiergrid -circuit inductance feeds to the gridsof the two push-pull tubes through twogrid -coupling condensers.

The tuning condenser comprises twoseries halves with a rotor member com-mon to both. The rotor is connectedto the filaments and virtually is atground potential. This is intended toeliminate hand or body capacity effect.Likewise, this series connection affordsa relatively low capacity value-a mini-mum of approximately 8 mmfd. anda maximum of 57 mmfd. This givesa ratio of about 7.1 to 1, and yet themaximum capacity is quite small-result-ing in a relatively high ratio of induc-tance to capacity. This is essential toeffective amplification. The radio -fre-quency amplifier grids obtain theirdirect -current bias through 1-megohmgrid leaks, which are connected to thejunction between two filament -controlresistances, thus affording a negativebias of 1.7 volts. The plate screens aremaintained at plus 60 volts with respectto the filaments.

"In all amplifier work," emphasizesthe Bellevue Naval Research Labora-tory, "it is essential for greatest ampli-fication that the external plate circuitimpedance be kept relatively higher than

34 RADIO FOR NOVEMBER, 1928

kilocycles. A third and similar chokehas been positioned at the junction of thetwo plate chokes and in series with theB battery lead -wire. The latter chokecoil serves the function of barring radio -frequency currents from the B -batterycircuit. This additional or third chokelikewise serves the purpose of isolatingthe junction of the two plate chokes fromthe ground potential. This permits ofthe chokes finding their own electricalcenter, which may be different from thatof the apparent center, due to electricalirregularities in the two tube and chokecircuits. This arrangement is an aid inthe preservation of symmetry, which isessential to efficient and stable operationof the receiver at the ultra -high fre-quencies.

The detector circuit and the radio -frequency amplifier are in individualshielded compartments. The two arecoupled by two fixed condensers, smallenough to prevent reaction of the am-plifying circuit on the oscillating detec-tor circuit. The capacity values of thesetwo condensers, however, are not detri-mentally low-that is, they do not causea loss of signal in so far as ear testscan determine.

The tuned detector circuit employs a"plug-in" inductance system similar to

that used in the antenna circuit. This,labelled "Detector Coil," includes thegrid inductance and the tickler feed -backinductance. The tuning condenser inthe detector circuit is similar to that em-ployed in the amplifier circuit. Thepush-pull performance of the two de-tector tubes again gives practical appli-cation to the sound engineering principleof a large inductance in relation to ca-pacity. This insures a greater amount ofinductance with which to couple the in-ductive tickler feed -back than any single -

ANT.

GND

C3 C4 C4 Cs

tube circuit. Furthermore, we are as-sured by the Navy Department, thiscombination gives a circuit that oscil-lates with ease throughout the entire fre-quency range from 4,000 to 25,000kilocycles.

The tickler feed -back inductance coilis tapped in the center-the two endsbeing associated with their respectiveplates and the center to the plus -B bat-tery through a radio -frequency chokeand the primary winding of the firstaudio -frequency transformer to the re -

V4

420

0

1C71L

C5

(15

Cio

V,-Radio-frequency amplifier tubes, typeUX-222.

V, V.-Detector tubes, type UX-201-A.V, V.-Audio Amplifier tubes, type UX-

201-AL,-Antenna Coupling Inductance.L.2-Radio-frequency amplifier grid circuit

inductance (Both L, and L, wound on r.f.amplifier coil form).

L,-Tickler feed -back inductance. (Woundon "DET" coil form).

L.-Detector grid circuit inductance. (Woundon "DET" coil form).

L, L.-Low distributed capacity 250 m.b.plate chokes in r.f. plate circuits.

L, L.-Low distributed capacity 250 m.h.plate chokes in battery leads.

74

generative -control potentiometer slider.This, in turn, is connected across 45volts. Regeneration or oscillation con-trol is effected by varying the direct -cur-rent voltage on the plate elements of thetwo detector tubes, using the potenti-ometer for varying the potential. Thepotentiometer slides, operated by manip-ulation of a knob on front of the radio--receiver panel labelled "RegenerationControl," is by-passed to shield orground through a 2-microfarad con-denser.

Cpl

47

-6 +6 -B +45 +60 PHONES

Circuit Diagram of Marshall Short -Wave Set

C,-R.F. amplifier tuning condenser.C,-Detector circuit tuning condenser.C,-Antenna coupling condenser.C.-Compensating condenser to assist in dial

alignment of r.f. and "DET" tuning con-denser.

C, C.-Grid coupling condensers from tunedr.f. circuit.

C, C.-Balancing condensers to balance outreaction of amplifier on autodyne circuit.

C. C,.-Coupling condenser from r.f. stage toautodyne circuit.

C,, C,,-Detector grid condensers.CH, --Bypass condenser on plate screen volt-

age lead.CH-Bypass condenser on oscillation control

resistance.

RADIO FOR NOVEMBER, 1928

C,, C,. CH-Bypass condenser on batteryleads.

C,,-Tuning condensers on second audiotransformer to cut out audio oscillation.

R, R,-Grid closure resistances to establishproper bias on amplifier tubes.

R. R.-Grid leak resistances for detectortubes.

R.-Fixed resistance in series with R. giving3.3 volts on amplifier tube filaments.

R.-Variable filament control resistance.R,-Potentiometer 100,000 ohms on 45 -volt

detector plate battery for oscillation con-trol.

S,-Filament switch that also disconnects R,from circuit.

T, T2-Audio-frequency transformer typeCAY 4342.

35

The first audio -frequency tube is fedfrom the secondary winding of a trans-former - type CAY4342 - while thistube's plate circuit feeds into the primarywinding of another transformer, of thesame type as the first. The primarywinding of the second transformer isslightly tuned with a .0001-microfaradby-pass condenser on the oscillation -con-trol resistance. This, in effect, cuts down'the amplification of the higher audio -frequencies, above 1,500 cycles, and cor-respondingly reinforces the lower fre-quencies. The secondary winding of thistransformer feeds the second audio -fre-quency tube, while the plate circuit ofthe latter extends to the telephone con-nection and through the head telephonesto the 60 -volt B -battery terminal.

The controls on the front of the re-ceiver panel, reading from left to right,are the radio -frequency tuning condenserfor bringing into resonance the radio -frequency amplifying stage, the auto -dyne -detector -circuit tuning condenser,and the regeneration control. An "on"and "off" filament switch is located cen-trally and near the bottom of the frontpanel. This switch opens both sides ofthe filament battery and at the sametime opens the potentiometer across the45 -volt supply, thus preventing the B -battery from discharging when the re-ceiving set is not in operation.

A voltmeter gives indication of thefilament voltage on the '01A type tubes.When the voltmeter -push-button switchis pressed the maximum B voltage as ap-plied to the two screened -grid tubes isindicated. These four -element tubes re-quire a filament voltage of 3.3 volts andthis current is supplied when the volt-meter reads 5 for the 'A tubes. A singlefilament rheostat is supplied for the Abattery control. The screened -grid tubesare fed with energy through the latterresistance unit and through an addi-tional series resistance. The latter shouldafford a drop of 1.7 volts as requiredfor the efficient operation of the receiver.

The receiver is 22% in. long, 10.34in. high, and 9r/4 in. deep. The parts,including diaphragm shielding and wir-ing, are made secure to the front panel.Withdrawal of the latter displaces com-pletely the receiving set from the boxand at the same time automatically dis-connects battery, telephone, antenna,and ground leads. These leads, enteringthe box or receiver container, are per-manently fixed to the box fittings. Theexternal connections are made to the re-ceiver circuits through sliding contacts,which close when the panel is securedin place.

The outstanding feature of this newshort-wave circuit-its extreme sensi-tivity-is also its serious limitation."This receiver has much greater sensi-tivity at the higher frequencies than anypreviously supplied to the service," isthe unqualified statement of the NavyDepartment. For this same reason, the

set must be mounted on a shock -absorb-ing pad and the detector tubes insertedin jackets of sponge rubber; otherwise,microphonic noises are so disturbing asto practically defeat the otherwise su-perior merit of this receiver, namely, ul-tra -sensitivity.

"The high -frequency receivers as de-veloped in the past," points out the Bel-levue Naval Research Laboratory in dis-cussing the theory and operation of thisnew circuit, "using the customary three -element tubes, have been incapable ofgiving much amplification over thehigher -frequency end of their range andin some cases give a loss above 8,000 kilo-cycles. With the development of thenew four -element tube, which may becalled the shielded -plate tube, togetherwith a new circuit arrangement, it ispossible to get an appreciable amount ofamplification over the entire high -f re-quency band as now employed.

"The two factors which have pre-viously prevented radio -frequency am-plification at the higher frequencies havebeen the relatively low input impedanceof the tube and the low ratio of induc-tance to capacity, which has existed whenusing the three -element tube. The lowinput impedance has resulted from therelatively high grid filament capacitywhich has under operating conditionsbeen in effect several times the geometri-cal capacity-being controlled principallyby the grid -plate capacity.

"The new circuit employs a push-pulltype of radio -frequency amplification,where each of the tube -grid -filament cir-cuits are across but half of the tunedcircuit input voltage. This decreases thegrid -filament conductance to half foreach tube and as the two reactances arein series the total conductance acrossthe tuned circuit is one quarter what itwould be for a single -tube -amplifierstage. When the effect of the grid -platecapacity of the three -element tube is con-sidered it is apparent that the push-pullcombination with four -element tubeswill increase the tube input impedancemany times. This improved conditionmakes it possible to maintain a muchhigher potential across the tuning -con-denser terminals, or the two input grids,than by previous methods. The use ofthe symmetrical push-pull circuit, whichpermits a larger ratio of inductance tocapacity to prevail, together with theadoption of the four -element tube, hasbeen highly responsible for the improvedresults at the higher frequencies."

The two screen -grid tubes areequipped with balancing condensers toavoid interplay or disturbing reactionbetween the stages of radio -frequencyamplification and detector. These con-densers are located beneath the two holesin the cover which have been blanketedwith a butterfly -spring arrangement.Reaction between the different stages inthe circuit may be overcome by shiftingthe vacuum tubes in different sockets.

36 RADIO FOR NOVEMBER, 1928

If, however, the trouble persists, theNavy Department indicates that the bal-ancing condensers will accomplish thedesired result if this procedure is fol-lowed:

The receiver-which may be operatedon an antenna only a few feet in lengthor one several wave -lengths long-isconnected to the pickup system andNo. 1 inductance coil brought into use.The cover over the adjusting holes inthe main cover is removed or loosenedand turned 90 degrees, in order to renderaccessible the condensers with the maincover closed. The lock -screws on theseunits are loosened.

The receiver circuits are brought inresonance with the detector oscillating.An unbalanced condition is evidencedwhen the tuning of the radio -frequencycircuit through resonance with the de-tector circuit, when it is barely oscillat-ing, produces a squeal in the headtelephones or stops oscillation. This con-dition is well-nigh ever present, but it ispossible to obtain an adjustment wherethe reaction is not evident when theoscillation control is set one-half of asmall division beyond the point whereoscillation starts.

The oscillating circuit should be setto this point and the radio -frequencycontrol operated back and forth past theresonance point until the balancing con-densers are adjusted. If the receivingset is apparently balanced at the top,middle and bottom of the frequencyrange of inductance coil No. 1 then it isto be assumed that a satisfactory balancehas been assured for the four other in-ductance coils. For the balancing con-denser adjustments a bakelite, fiber orhardwood screwdriver is used, since thepresence of metal would defeat any at-tempts to adjust these balancing con-densers.

While the Radio Division of the Bu-reau of Engineering is prone to classifythis new short-wave receiver as still inan experimental stage ---clue to its ten-dency to set up microphonic noiseswhen not situated in a shock -absorbing,steadfast position-twelve or fifteenunits have been manufactured. Severalof these have been introduced to Navalservice-both on surface and subseacraft-and when subjected to compara-tive tests with a standard short-wave setof Navy design the results have beengratifying, in some particulars at least.

For example, while in service on theEagle, a patrol boat for conductingsound and radio experiments, thestrength of the signals received by the"Marshall receiver" were stronger thanthose tuned by the standard Navy short-wave set-though the signals of thelatter were more readily tuned and thedistant stations more easily located. Theselectivity of the "Marshall receiver"was marked and once the stations werelogged the dial could be consulted time

(Continued on Page 49)

TECHNICAL BRIEFS

TRANSATLANTIC radiotelephone serv-ice between the United States and

Great Britain as well as various citiesof Continental Europe, Canada, andCuba is normally available from 5:30a. m. to 8:00 p. m., eastern stand-ard time. The British receiving stationis at Cupar, Scotland, as far north asconveniently possible so as to reduceinterference caused by atmospheric dis-turbances.

THE R. C. A. projector system usedin long distance radio communica-

tion includes both directive transmissionand directive reception on short waves.Several receiving antennas, directive inthemselves, are spaced so as to eliminatethe momentary fading which originallylimited the use of short waves.

RILWAY radiotelephone equipmenthas been developed for front -to

rear communication on long freighttrains. A four -months test of the equip-ment by the Chesapeake & Ohio Railroadshowed that telephonic communicationcould be maintained between the loco-motive and caboose whether the trainwas standing or in motion and evenwhen the train was broken if the separa-tion did not exceed five miles. A signalsystem of lower power has been de-veloped for service between the frontand rear of long freight trains. One-way telephonic communication with lowpower equipment may also be maintainedbetween the yardmaster's office and anylocomotive in the yards.

THE demand for quartz crystals forcontrolling the frequency of radio

transmitters is supplied mostly fromBrazil. The present price is about $3.00per lb. To be acceptable to the NavalResearch Laboratory at Anacostia, D. C.they must be single crystals weighingat least two pounds and must showgrowth lines on at least two faces.They must be free from imperfectionssuch as internal fractures and inclusionsof foreign matter. They must be ab-solutely clear when viewed by trans-mitted light.

THE radio experimenter may findmuch interest in utilizing the ra-

diated output of a short-wave oscillatorto produce luminous discharges throughrarefied gases in tubes such as the neontubes which are now used in electricsigns. Whereas a high voltage is necessary to produce a glow when low fre-quency alternating current is used,relatively low voltages are needed athigh frequency.

Thus James and Wilfred Taylor, ina recent issue of The Wireless Engineer,London, describe some experiments witha 35,000 k.c. (8.57 meters) oscillatorwhereby beautiful discharges were pro-duced at 15 volts. In the circuit diagramof Fig. 1 the plate B and the grid D areconnected to two parallel copper wiresabout 50 in. long and 3 in. apart. A

DISCHAROETUBE

Fig. 1. Circuit Diagram for High FrequencyGenerator and Discharge Tube

.001 mfd. variable condenser is shuntedacross the ends of these wires at A C,being connected to the positive terminalof a 220 -volt d.c. source and C to thenegative terminal. E, F, G, H is a tunedsystem coupled to A B D C by theLecher wire method. Two annular ringsof copper foil are wrapped around theoutside of the glass tube to serve aselectrodes.

Different colors and forms of dis-charge occur as the gas pressure or gascomposition is varied. The experimentswere made with air, neon, helium andmercury vapor. The discharges arecaused by the motion of the electronsbetween the electrodes; light is emittedas an electron jumps from an outer toan inner orbit as it collides with a gasmolecule.

THE economically -minded personsometimes objects to the thought of

using an apparently wasteful voltagedivider to supply 45 and 90 volts to

RADIO FOR NOVEMBER, 1928

a radio set from a rectifier -filter systemwhich also supplies 180 volts or morefor a power tube. But when it is re-alized that the waste current throughthe divider not only may improve thevoltage regulation or stability of voltageoutput, but also reduce the strain on thefilter condensers, its use is well justified.

A rectifier -filter system is a constantwattage device. The voltage drops asthe load or current drain increases, in-creasing the load resistance decreases theload current. When the current drainis increased from any tap, the voltageoutput and current supplied from theother taps is correspondingly decreased.Part of the increased load current comesfrom the rectifier -filter system and partfrom the voltage divider system, bothat the expense of decreased voltages.

These facts are used by the AerovoxWireless Corporation the ad-vantage of a low resistance voltage di-vider over a high resistance device, i. e.the advantage of a voltage divider hav-ing a relatively high waste current. Testswere made with eliminators having awide range of regulation curves andwith voltage dividers having waste cur-rents of 5, 10, 20 and 30 milliamperes.In all cases the calculated load was as-sumed to be 20 m.a. at 180 volts, 12m.a. at 90 volts, and 2 m.a. at 45 volts.The results are tabulated herewith toshow the voltage change produced atany tap by increasing or decreasing theload by 1 m.a.

I. 5 MIL VOLTAGE DIVIDERTap 45V. 90V. 180V.45V. 4.25 1.85 negligible90V. 2.20 3.98 1.88

180V. 0.53 1.40 1.25II. 10 MIL VOLTAGE DIVIDER

Tap 45V. 90V. 180V.4-5V. 3.02 1.37 negligible90V. 1.53 2.95 1.30

180V. .38 1.05 .87III. 20 MIL VOLTAGE DIVIDER

Tap 45V. 90V. 180V.45V. 2.05 .96 negligible90V. 1.12 2.03 .93

180V. .25 .73 .63IV. 30 MIL VOLTAGE DIVIDER

Tap 45V. 90V. 180V.45V. 1.75 0.56 negligible90V. .92 1.17 0.77

180V. .21 .50 .50

Thus it is shown that an increase inthe load resistance at the 45 -volt tap ofa 5 m.a. divider so as to produce a de-crease of 1 m.a. at that tap, will cause

37

increases of 4.25 volts at the 45 -volttap, 2.2 volts at the 90 -volt tap, and 0.53volts at the 180 -volt tap, as comparedto 1.75, .92 and .21 volts respectivelywhen using a 30 m.a. divider. A de-crease in the load resistance to producea 1 m.a. increase in current causes volt-age drops of corresponding values. The90 -volt tap is evidently the most easilyand greatly disturbed, and the 180 -volttap, which feeds without passing throughthe divider, the least disturbed by anychange in the load. As the 45 -volt tapis very sensitive to changes of load at45 volts, many eliminators do not worksatisfactorily when feeding a set whichhas a large 45 -volt load, like a super-heterodyne.

It is evident that voltage variationsdue to variable loads may be minimizedby using as heavy a waste current aspossible. Furthermore the rise in voltagedue to removing the load is thusminimized.

THE general theory of sound picturereproduction which was recently

explained in these columns, was basedupon the Vitaphone and Movietone sys-tems, which record the sound waves onphonograph records, or film respectively,in the form of parallel lines. A thirdsystem was inadvertently omitted, thisbeing known to the trade as the Photo -phone system. The latter is similar tothe Movietone in that the sound wavesare recorded photographically on thesame film with the picture, but thesewaves are in the form of a single, jaggedheavy line that looks like a cross-sectionof a mountain range. Its width variesin accordance with the frequencies re-corded. A photoelectric cell and aperturesomewhat like the Movietone systemconverts this solid black strip into sound,to be amplified and projected into thetheatre by means of loud speakers.

Many of the latest types of motionpicture projectors are equipped with spe-cial fittings so that any of the three sys-tems of sound reproduction can be usedby changing the aperture plates, projec-tion lenses, and making minor adjust-ments requiring only a few minutes. Thesize of the picture on the Photophonefilm is somewhat smaller than for ordi-nary silent pictures, so as to allow agreater width for sound recording, butthe picture is rectangular in shape in-stead of square as for the Movietone sys-tem shown in the September issue. Thisrequires a different set of lenses, and asmaller aperture for the picture, but thechange is quickly made, and hence noinconvenience is caused by the differentsystems. Probably the first radio movieswhich will eventually be made availableto the general public will use this system.

AN exhaustive series of measurementsof the amplification and selectivity

of sixteen different types of r.f. coils,by Alfred J. Daniels of Aero Products,

Inc., shows that in the conventionalr.f. circuit the most efficient prac-tical type of those coils tested has itsprimary wound to occupy in. insideand opposite the low potential end ofthe secondary. But by means of a spe-cial circuit, herein described as the"Chronophase," still better results withscreen -grid tubes were secured from anautotransformer whose primary is a por-tion of the secondary, the low potentialends being common.

All of the coils were of the typeshown in Fig. 1, being air -spaced woundto approximately the ideal shape -factor

Fig. I. Type of Coils Tested

and supported by a skeleton bakeliteframe to minimize insulation losses.Each type had various numbers of prim-ary turns and, where possible, was testedwith variable coupling. The secondaries,measured independent of the primaries,

7

6

5

CC

2z0

sit!

had an inductance of 167.4 microhenriesand an r.f. resistance of from 3.85 ohmsat 550 meters to 9.6 ohms at 200 meters.These figures are changed by the pres-ence of a primary.

490 +RV

Fig. 3. a. R. F. Circuit Connections forScreen -Grid Tube with Conventional

Transformers

The coils under test were suppliedwith a constant input signal at variousfrequencies in the broadcast spectrum,and the output was measured with a

1.90 4-180

Fig. 3. b. R. F. Circuit Connections forScreen -Grid Tube with Autoformer

vacuum tube voltmeter. The test condi-tions were nearly identical with thosesurrounding a coil in an actual receiver.

Fig. 2 shows the amplification curvesobtained with the autotransformer and

(Continued on Page 56)

.... .....18... ........... ....

36.....-

......36 ....

36...... ....

s` .II,'Z'

i''//...../

../

........ ...

0.''''

/...../

.-........................9 ..... .............

...... 4............5.... .......

...--

-.-

AUTOFORNIER

iPRIMARY

1.2 PRIMARY

ric..2

_200 250 300 350 400 450 530

WAVELENGTH IN METERS

Fig. 2. Amplification Curves for Three Types of Coils with Varied Number of Turns

38 RADIO FOR NOVEMBER, 1928

hC COM MERC I A LBRASSP OU N DE

Sk Departmentfor the Operatorat Sea ad Ashore

A LEITER from Fred M. Winckel commentsupon L. W. Gillis' article in June RADIO.

Mr. Gillis, you remember, pointed out sev-eral reasons why radio operating conditionsseem to be going from bad to worse, andmade a few suggestions which might helpremedy the situation.

Mr. Winckel believes that the only wayto improve matters is to go right down tothe bottom of things and attack the existingradio laws. No doubt he is right; but, ashe goes on to say, the radio operator aloneis not in a position to approach the radiocommission or the senate committee on sucha subject. He feels that the idea of an asso-ciation of sea -going operators is still good,even if it has failed on several attempts.That is a subject that is always open fordebate.

Even if we had an association of radiooperators; even if we were solidly organized;where would it get us? Our strength wouldserve as a threat, but would the threat scareanyone into improving conditions for us? Itwould certainly antagonize the steamshipcompanies, the radio companies and even theill-informed public. "Radio operators imperilmany lives." We can see the newspaper head-lines-and the general public thinks we arehaving a lovely time of it.

No, radio operating is a profession, andstrikes always belittle a profession. The worldas a whole is drifting away from such meth-ods of improving conditions; conditions areimproving themselves. Employers are ac-quiring educations; they are learning,through the advancement of psychology, thatit is to their advantage to show a little con-sideration to their employees.

We'll agree with you that our theorizingsounds very nice, but that it does not applyto our situation. Why? Are we so differentfrom all other professions?

Well, here's our theory; and this is opento argument. We may be on the wrongtrack entirely. Anyway, it is our humbleopinion that the great majority of operatorstake life too easily. It is difficult for a manto go onto a job, boss of his own time andunwatched by any authority, without fallinginto easy going habits. It is extremely diffi-cult when the operator knows full well thathe can do all that is required of him in threeor four hours a day. If he can handle hisjob in four hours of concentrated effort, whyshouldn't he do so? That's reasonable logic.But here's the reason why he shouldn't; thereason why he should find enough work tokeep him busy for at least eight hours a dayas regularly as any man on the crew.

The general impression is abroad that thewireless operator has an easy time of it. Thisstarts with the other officers immediately as-sociated with the op. It spreads to the crew,to the marine offices, to the higher officials.Not one man in a thousand gives the radiooperator credit for doing a good day's workin all his existence. And here we have it.The officials require very little from an

-,4111

Edited by P. S. LUCAS

R. 0. CooK, Assistant

operator; and pay him what the fulfillmentof those requirements are worth to them. Theoperator works about as hard as he is paidfor; the report gets out that the operatorhas an easy life; the officials-etc., etc. Itgoes around in circles.

Now what can we suggest as a remedyfor this peculiar condition? In the first placethe operator, every operator, must make uphis mind to putting in a good, full eight -hour day. He should make out a schedulefor himself and, figuratively speaking, "punchthe clock." He should win the captain andthe mates to his side by voluntarily givingthem every available aid to navigation. Heshould insist that that is a part of his workand he is paid for doing it. (Fingers crossed).If the engineers ask for any aid on theirgenerators he should jump at this oppor-tunity of winning their friendship. Whilelistening in for "roll -calls" and other signalshe should not only keep his log up to date,

And one parting shot to the man who in-tends to take one trip or spend one year,then quit. You will get a whole lot moreout of your trip or your year, you will havemore to look back upon, and you will equipyourself for a more successful future if youwill play the game as if it were to be yourlife's work. While you are in it feel yourselfa part of our development program. Men,it's up to you.

A PRACTICAL "B" ELIMINATORFOR SHIP USE

By R. M. HUGHES

Many sea captains, as well as mates, engi-neers and radio operators, have their ownbroadcast receivers aboard ship. Yet fewof them use a B eliminator, although thereis no place where local conditions are bettersuited for its use. The ship dynamo supplies

"B" Eliminator for D.C. Supply

but file away in his head, every bit of infor-mation possible so that if anyone asks himany questions he might be able to give theimpression that he is well informed. In brief,he must consider his job more important thanhis officials consider it, and organize it ac-cordingly. How long, under such conditions,would it take for a vastly different sort of"underground telegraph" message to be buzz-ing in the ears of the officials?

This should be the one great object of anorganization: to so enthuse the mass of oper-ators with the possibilities of improving con-ditions ashore and afloat that they will carryout the suggestions just made. Let the or-ganization be formed to promote the mem-ber's interest in his work. Every operatormust feel his responsibility in this matter orthe situation will be worse twenty yearsfrom now than it is today.

RADIO FOR NOVEMBER, 1928

direct current at about 110 volts. This con-tains a commutator ripple which must befiltered out before it is suitable for use asthe plate supply for a radio set.

All that is needed to make the satisfactorybattery eliminator shown in the picture andcircuit diagram herewith, can be bought ata chain store for less than four dollars, orfor slightly more if purchased from a reg-ular dealer in radio parts. This equipmentcan be quickly and easily assembled on abaseboard and will furnish hum -free currentat 45 and 90 volts.

An ordinary snap -switch is used to turnthe current on and off. The choke coil hasan inductance of about 20 henries. Each ofthe three condensers has a capacity of 1 mfd.and should withstand 200 volts. The voltagedividing circuit consists of two 2 c.p. lampsconnected in series, one being connected di -

39

rectly to the negative side of the ship'sgenerator and other through the choke coilto the positive side of the line. The centertap gives 45 volts.

As a ship's power system is not grounded,a necessary precaution requires a 2 mfd. con-denser in the ground -lead of the receiver.This does not interfere with the receiver'sr.f. ground, but does prevent shorting theship generator.

70 tth

6fiYfREOR

Circuit Diagram

All of the parts can be assembled on abaseboard 6 by 10 by in. The condenserscan be stacked on top of one another andheld in place by a small strip of brass. Thisdevice has proven to be satisfactory withmany different receivers in many locations.

TRANSLATION OF ESSENTIALWORDS USED IN XDA

WEATHER

By PAUL 0110Several operators have asked me where I

got the impression that XDA weather is easyto translate l Here is a list of twenty wordsthat chiefly constitute the construction of theseweather reports. Of the twenty, there are onlyeight whose meaning in English is not self-evident. Judge them for

From experience I have found that theweather contained in the number groups, fromcoast towns, is the most desired.

In the first group the first three figures arethe barometer in centimeters. The fourth isthe wind direction, and the fifth the windforce. In the second group the first figure isthe state of the weather, and the third is thesky report. These figures can be very easilydecoded by referring to a copy of "RadioAids to Navigation," which can be purchasedfor seventy-five cents at any store that car-ries hydrographic publications.

Here are the words:

ENGLISH

SomewhatLowerCapeCoastOfLightOf theTheEastStrongGulfAs far as, or toModerateVeryNorthWestEastShifting, or changingSouthWindsNortheastNorthwestSoutheastSouthwest

SPANISH

AlgoBajaCaboCostaDeDebilDelEl, or LaEsteFuerteGolfoHastaModeradoMuyNorteOccidental,OcsteRolandoSurVientosNoresteNoroesteSuresteSuroeste

or Occ.

CCA, ANTOFAGASTA, CHILI

By CHARLES F. STEWART

Having read pleas for South Americanmaterial in the Commercial Brasspounder,I decided to take advantage of a stop -overin Antofagasta last May to check up onStation CCA.

CCA is a naval station and handles Gov-

# .90- V017(

0 CI.' PIM?

# 4S Y 017if

CPPIMP

for Eliminator

ernment business only, on 1800 and 2800meters. It is intended, however, to install a600 -meter spark, with which to handle com-mercial ship to shore traffic. Perhaps thisservice has already been inaugurated.

I was cordially met by the chief operatorof CCA, Mr. Stienbacher, who kindly showedme the installation and later introduced meabout the town, even throwing a party forme. He told me that I was the first Amer-ican operator he had met and asked that Iextend the invitation to any other operatorswho might come to Antofagasta, which Ihereby do. Take him up if you ever dropyour hook in Antofagasta; you will not besorry.

Now for the station: CCA is housed in athree-story building. Mr. Stienbacher andfamily live on the first floor where the powersupply is also located. On the second floorare the living quarters of the three assist-ant operators, while on the third floor arethe receiving apparatus, control room andland line.

There are two receivers, one Marconi, theother made by Telefunken. The transmitteris on the ground floor near the generators,and is a 10 kw Marconi outfit, with 10 1 kwtubes. The transmitter occupies a room toitself and is surrounded by a brass rail, onlythe tubes and rheostats being mounted on apanel.

Although the soil is extremely dry aground is used for transmission and recep-tion. I asked Mr. Stienbacher about the pos-sibilities of a counterpoise, but he had neverheard of one and was quite interested whenI explained it to him. A Marconi engineermade the installation and I cannot under-stand why he didn't install a counterpoise.

The Chilean Navy was experimentingwith short waves at that time, and was send-ing its operators small booklets on that sub-ject. It might be well to mention that allstations in Chili are under the control ofeither the Chilean Army or Navy. TheNavy maintains a school in Valparaiso,where its operators are trained. Englishequipment predominates, although a fewTelefunken tubes and receivers are used.

To listen to a Chilean coast station han-dling commercial traffic you would think theoperators and equipment very poor, but thestations handling government traffic havefirst-class equipment and operators. Onlymen with a high rating are used for thistype of service. It is easier to understandthis when it is known that the Chileans be-lieve the Army and Navy to be the mostimportant elements of their country's organ-ization.

Mr. Stienbacher speaks excellent Englishand is very anxious to get acquainted withAmerican operators. As we said before, ifyou want to be well received, drop in onCCA.

40 RADIO FOR NOVEMBER, 1928

AN EASILY CONSTRUCTEDBREAK-IN

By J. A. BENDER, S. S. West CactusA LOT of fine machine work can be put in

on a break-in, but when the all-im-portant consideration is cash there is just oneitem, outside of efficiency, to be discussed,and that is simplicity. Therefore, if you areinterested, read about the one you can makeout of parts retrieved from your junk -box.

Delve into the aforementioned curio shopand bring out the following trinkets:

I piece of bakelite panel 5"x3".1 piece of bakelite strip 3"x1/2".1 piece of heavy brass strip 3"x1/2".1 piece of heavy brass strip 11/2"x1/2".1 piece of spring brass strip 2"x1/2".2 binding posts.1 8/32 screw about 2" long with nut.1 brass bushing about 1/2" long, tapped on

one end to an 8/32 thread and on the otherend to same thread as on the key contactsnamed below.

1 piece of brass bushing about 1/2" longtapped 8/32 thread for key stop.

2 key contacts.

IND Of/KEY RN

ORFAKEY KEY., TO INT "OF

NISZ STOP Of RECEIVER, et,

View of the After End of the Key Bate

First, mount the key on the piece of panelso that about 3 in. of the base extends outin back of the key proper.

Second, drill three holes in the panel about1/2 in. from the end; the two outer holesbeing about 1/2 in. from the edges of thepanel and the center hole in line with theadjusting screw of the key proper. All theholes must be in line.

Third, take the brass 1/2 in. bushing andscrew it into the center hole.

Fourth, take the piece of strip bakelite anddrill a hole in each end, tapping one holewith the same thread as the adjusting screwon the key. Remove the back adjusting screwfrom the key arm and bolt the bakelite stripto the arm, using the hole from which thescrew was taken. Now screw the adjustmentscrew into the tapped hole of the bakelitestrip.

Fifth, drill and tap one hole on the longstrip of brass and bend the strip to right -angles about yt in. from the end, using an8/32 tap to tap the hole.

Sixth, drill a hole in the other end andbend in the opposite way about 1/2 in. fromthe end. Screw the long 8/32 in. screw intothe tapped hole, leaving the nut on the screw,and screw the key contact to it, using the1/2 in. bushing. Nov take the finished pieceand bolt to one side of the panel, using abinding post.

Seventh, take the brass spring, drill a holein each end and screw the other key contactto it. Take the short brass strip and drill ahole in each end, then bend it at right -angles about IA in. back from each end, re-versing directions. Bolt the spring to thestrip and bolt the whole thing to the panel.

Eighth, replace the arm of the key and youhave the break-in completed. Not much tolook at, but it surely does the work.

In hooking up the break-in, disconnect thetransmitter from the r.f. ammeter, at A. Runa lead from the ammeter to the binding postC on the break-in. Run a lead from thebinding post D to the antenna binding poston the receiver, also to the transmitter at A.

(Continued on Page 48)

With the Amateur OperatorsAN ALL -SHORT-WAVE RECEIVER

By A. BINNEWEC, JR.

UNLESS particular attention is given tostation design for 1929 conditions, ama-teurs may have difficulty in working

at the higher frequencies. The experimenterwill use the 10 -meter and 5 -meter bandswith reflectors. Those who will use the 20and 40 -meter bands must use special careand apparatus.

The usual 40 and 20 -meter receiver willnot also operate at 5 and 10 meters, as theparts are too large. To satisfy 1929 require-ments, the set must tune sharply over a nar-row band, which means that midget con-densers will be used. Many amateurs willleave the narrow bands and experiment withthe much wider 10 -meter one which has ex-ceptional possibilities. The writer has de-veloped a receiver which covers efficientlythe 5 and 10 -meter bands and meets the 1929requirements for the 20 and 40 -meter ones.

The receiver is constructed in two sections:a two -stage screen grid amplifier in one anda regenerative detector and two -stage audioamplifier in the other. The r.f. amplifiersection is especially useful for the higherfrequencies as the amplification falls off. Itmay be added to any short-wave receiver.By proper circuit design and parts placement,it is possible to operate the amplifier withoutany great amount of skidding, a groundedcopper sheet between the two tubes usuallybeing sufficient to prevent oscillation at 5

and 10 meters. Fig. 1 shows the completecircuit diagram.

The r.f. amplifier coils must be of smalldiameter to limit the field and minimize in-ductive feed -back. For 40 meters, 2 -in. coilswith 12 turns are about right, and at 20meters 4 turns will do, the exact size de-pending upon the range of the tuning con-densers. The antenna coil and its associatedsecondary are mounted on a 3 by 4 -in. pieceof bakelite placed directly below the con-denser so that the wiring is short and direct.The plate coil of the first stage is mountedin a similar manner. A 10 by 11 -in. base-board provides ample space between the parts.

Separate batteries can be used for eachstage. Separate binding posts are providedfor each .4 and B battery supply and twoposts are left free for the leads of the out-put coupling coil.

Filament current for each r.f. amplifierstage is supplied through two rheostats con-nected in series. One is variable for filamentregulation. The other is fixed as regards

Short -Wave R.F. .4mplifier with Screen -Grid Tubes

filament voltage, but is adjustable so as togive the best grid -bias. This bias adjust-ment is secured through a lead from themovable arm to a separate post. The fourrheostats and binding posts are mounted ona 4 by 11 -in. piece of bakelite, which is sep-arated above the baseboard by two woodenuprights.

The second r.f. stage requires a .0002 mfd.grid condenser and 1 or 2 meg. leak. Thisamplifier will operate well at 40 meters with-out by-pass condensers. For shorter wavework .002 or .003 mfd. will serve.

The clips for the control grids consist oftrimmed fahnestock clips to which the leadsare soldered.

The main panel measures 7 by 12 in. andshows two 100 -degree dials and a filamentswitch between. The ground post is mountedon the small panel, with the antenna coil,which is fitted with a strip of bakelite and

a G. R. plug; this rotates in a jack which canchange the coupling. A flexible lead to theantenna coil connects to the antenna post atthe rear of the set. The small panels support-ing the plug-in coils are fastened to woodensupports and clear the baseboard about Y2 in.

The tuning of the amplifier is not sharp atany frequency so that one can tune some-where near the band, and the receiver is thenthe usual two -control affair. The inputtuned -circuit to the amplifier has the mosteffect on the overall amplification.

The construction of the regenerative de-tector and audio section is almost self-evidentfrom the circuit diagram and picture.

For reception at 5 meters, both 100 pfd.midget shunt condensers are set at minimum,the 2 -turn secondary is used, and tuning isas easy as usual. The shunt condensers areadjusted for a certain minimum capacitywhich is desirable in the secondary circuit,

Fig. 1. Circuit Diagram for All -Short -Wave Receiver with Screen -Grid R.F. Amplifie

RADIO FOR NOVEMBER, 1928 41

for the throttle -control has a large detuningeffect when the total secondary capacity isnear that of the tube capacities.

To operate at 10 meters, simply plug inthe next coil and listen anywhere between 5and 10 meters. The secondary shunt con-denser is used to shift to a new band.

To operate at 20 or 40 meters, a large in-ductance can be used, or else the shunt con-denser can be set somewhere near maxi-mum and a smaller coil employed.

It is interesting to compare receiving con-ditions with the different LC ratios possible.Any size of inductance, within reason, is allright, as adjustment is made with the shuntcondenser. When the proper position is oncelocated, the knob -setting is noted, and rapidwave -changing is then possible. It certainlyis a relief to have a receiver which will oper-ate efficiently at the lower wavelengths also.

For 5 and 10 meters, the plug-in coils areself-supporting and are mounted in '99 bases;for 20 and 40 meters, the larger bases may beused with the coils wound directly on them.

If desired, celluloid -supported coils maybe mounted horizontally on these bases. Agood tube socket should be used for the plug-in coils; by a simple test, at even 10 meters,the capacity between the socket terminals(and what little wiring there is) alone, issufficient so that the operation of one con-denser has some effect on the other. Thesocket is mounted on a block between thecondensers and the leads are thus short.

The throttle -control is a 100 pfd. midgetwhich is sufficient for the shorter wave -bands.For the higher wave -bands, the other 100pfd. midget, shunt condenser, is utilized andthe receiver can thus cover a very largerange without changing coils. It is impor-tant to adjust the tickler so that good regen-eration -control is secured with the condensernear a maximum setting, so that detuning ofthe secondary circuit will be negligible.

The midgets are mounted on small brassangles; some midgets already have these.Extension handles are used, which allowsefficient reception at the highest frequencieswithout any body effects. A half -inch woodenpanel, screwed to two uprights, to which thesub -panel is screwed, makes a sturdy set.To properly center the extension handles, thecondensers are first mounted in place andthe handles extended to the panel, which isthen marked and drilled. Large holes aredrilled half way through the panel for thevernier -dial screws, and smaller ones the restof the way. Often the advantage of a goodvernier dial is lost by motion at the bottom;if two brass wood screws fitted with washersare used to hold it here, no trouble will behad. A small dial or knob is used on theregeneration control.

A good choke, which will cover the 5 and10 -meter bands also, consists of several smallwindings in series on a V. -in. dowel; thesewindings consist of 20, 40, 60, 80 and 100turns, bunch -wound, and are spaced about'A -in. apart. Basket -weave coils may be usedif desired.

LIST OF PARTS FOR ALL SHORT-WAVE RECEIVER

4 100-mmfd. Midget variable condensers1 15-mmfd. Midget variable condenserTube bases for coils2 sockets for amplifier tubes.5-meg. grid leak1 filament switch1 detector rheostat112 detector tube2 amplifying tubes2 peaked audio amplifying transformers2 fixed filament resistors2 extension handlesWire for coils (No. 12 and No. 20); wire

for chokes (No. 36), bakelite (7 by 12and 7 by 7 suggested); baseboard anduprights, screws for same, etc.

The capacity of the grid condenser has con-siderable effect on the operation of a re-ceiver of this type. If too large, considerableeffect of one control on the other occursthrough the tube capacities. For "all -wave"use, it is preferable to use a variable con-denser so that best values may be selectedin different bands. A midget having a maxi-mum of 100 pfd. gives good results. At 5and 10 meters, this condenser is turned down

(Continued on Page 52)

All -Short -Wave Receiver

A SELECTIVE SHORT-WAVERECEIVER

By R. WM. TANNERThe selectivity of the usual regenerative

short-wave receiver can be greatly improvedby adding a Hartley oscillator and removingthe tickler coil as shown in the accompany-ing circuit diagram. The oscillator controlhas no tuning effect on the detector. Thepitch of the signal is not changed when thesecondary condenser is varied after a sig-nal is tuned in. This is in marked contrastto the detuning of the grid or secondary cir-cuit which occurs when the tickler is variedin the usual form of regenerative receiver.If the tickler coil is retained when the oscil-lator is added, greater sensitivity is possible,but another control is added thereby.

While complete shielding is desirable, itis not necessary if the oscillator harmonicsare used to produce beats. A slight rushingnoise is heard when one of the harmonicscrosses the wave of the detector. Althoughthis set is a little harder to tune than astraight regenerative receiver, the resultsare more than worth it. R, is a 1 megohmclarostat used in place of a pick-up coil.

The antenna coupling coil L has S turns

A* A- B.#a2v- .134.9owCircuit Diagram for Selective Short -Wave Receiver with Oscillator

42 RADIO FOR NOVEMBER, 1928

of No. 18 enamel wire and may well bevariable so that close coupling can be usedon weak signals and loose coupling on strongsignals. The secondary plug-in coils Li, arespace -wound with No. 18 enamel wire on a3 -in. form. They have 19, 8 and 3 turnsrespectively for the 80, 40 and 20 -meterbands, being tuned by a .00014 mfd. con-denser C. The detector grid condenser C,is .00015 mfd. and the grid leak R 6 meg-ohms.

The oscillator coil L, has a wavelengthrange of about 180 to 400 meters when tunedwith a .00025 mfd. condenser C.. A highratio vernier dial must be used on this con-denser. The coil consists of 50 turns of No.26 d.c.c. wire on a FA -in. bakelite form, witha filament connection tap at the 25th turn.

(Continued on Page 54)

Inside Stories of Factory Built Receivers

THIS is the first factory -built a.c. receiverto use a screen -grid tube as an r.f. am-

plifier. The other tubes in this four -tube setare a '27 tube as a detector, a '26 tube as afirst audio amplifier, and a '71 tube in thesecond audio stage. Filament current at 3.1,2.25, 1.4, and 4.8 volts, respectively, is sup-plied through a stepdown multiple -tappedtransformer from a 110 -volt a.c. source. Platevoltages are supplied through a full -wave

III. Freshman Model Q-15and sensitivity, a volume control, wherein arheostat varies the antenna current, and an"on -and -off" switch. It uses an outside an-tenna and ground.

The tuning condenser and power plant arein separately shielded compartments. Thescreen -grid tube is also shielded.

The r.f. amplification from the screen -gridtube and its associated transformer is claimedto be from 25 to 40, despite the limitations

TYPE NUMBERSOF TUBES

Freshman Model Q-15 Chassis

rectifier -filter system using an '80 tube. Theentire receiver, including the power supplyequipment, is compactly assembled on a steelchassis.

The set has four controls: a 190 to 570meter tuning dial which operates a two -gang.00036 mfd. condenser, a vernier .00004 mfd.condenser which adjusts for fine selectivity

0ANT. GND

.25 MFD. Soo V.25 MFD. boo V.

MFD -1000V.I MFD.-1000V.

I MFD.- 1000 V.4 MFD- 1000 V.

111F0 2000Y.

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imposed by operating the filament on raw a.c.Such amplification is as good or better thanis secured with the usual two stages of r.f.amplification. One of the secrets of its per-formance is the use of a high grid bias toprevent a.c. modulation.

A small amount of regeneration is in-geniously introduced into the detector circuit

5

aor

SO

C4

N

N N8

BLUE

ORANGE

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to more than compensate for the slight re-duction in shield -grid tube gain. This isautomatically maintained well below the os-cillating point so as to avoid distortion.

Most of the circuit constants for the re-ceiver and power plant are shown in theaccompanying circuit diagram. The generalconstruction and arrangement of the chassismay be seen in the picture thereof.

NEW RADIO CATALOGS

Radio Insulators of all types are kilus-trated and described in a pamphlet fromKnox Porcelain Corp., Knoxville, Tenn.,which also shows such antenna accessoriesas wire, lead-ins, and lightning arresters.

A new bulletin on socket power condensersfrom the Dubilier Condenser Corporation ofNew York City shows a complete line ofpaper dielectric condenser blocks as designedfor use with various standard transformers.Dry "A" 2000 mfd. condensers are also listedand described.

Publication No. 84 from the U. S. Bureauof Standards is a Standard Time Conver-sion Chart which gives a direct reading forthe standard time at any desired longitudecorresponding to the time at a given place.The chart is printed on heavy Bristol boardand consists of two concentric circles, oneof which can be revolved. This can besecured from the U. S. Government PrintingOffice for ten cents.

Scientific Paper No. 568 from the U. S.Bureau of Standards contains "Methods,Formulas and Tables for the Calculation ofAntenna Capacity," by Frederick W. Grover.This information is of value to an amateurtransmitter who is designing an antenna sys-tem whose fundamental wavelength he de-sires to know.

N

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ti 2 10000,

12500o.,HEAVY CREEK

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ti=100-125 V. 60

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SWITCH /YELLOW

Circuit Diagram of Freshman Model Q-15 Receiver

RED

120 V.

FUSE .5 AMP.

0

SPEAKER

RADIO FOR NOVEMBER, 1928 43

Radio Kit ReviewsHFL MODEL 10 ISOTONE

°T1 HE HFL Model 10 Isotone is a standardI screen -grid superheterodyne, utilizing

nine d.c. tubes as a radio receiver, with atenth tube available as an extra stage ofaudio amplification for phonograph reproduc-tion. It incorporates several new features,including a radiophone control switch onthe panel. When this switch is turned to thephonograph side the oscillator, detectors andi.f. amplifiers are completely disconnectedfrom the circuit, leaving three stages of a.f.amplification with '12A tubes for the firsttwo stages and two '71As in push-pull forthe third. This a.f. amplifier may be used inconnection with any external detector, shortwave or broadcast, by plugging the latterinto the tip jacks designed for the phono-

is shunted across each of the larger .0001secondary condensers, allowing each i.f. cir-cuit to be separately tuned. This compen-sates for variations in the internal capacitiesof the tubes, making it possible to maintainthe utmost selectivity of the amplifier at alltimes. The sensitivity of the i.f. amplifier iscontrolled by variation of the voltage appliedto the screen grid. Each stage is said to havea radio -frequency gain of 65.

In the tuning unit a small trimmer con-denser, shunted across the oscillator coils,makes it possible to adjust the oscillator andantenna tuning dials so that they read alike.In balancing the instrument for best resultsit is necessary to leave all the shield canscovered with the exception of the one to bebalanced. Once the intermediate amplifier isbalanced it should be left that way until such

HFL Model 10 Isotone

graph pickup. When the switch is turned to"radio" one stage of audio is disconnected,and the other tubes thrown back into thecircuit.

Either a loop or an outside antenna maybe used. In the case of the latter, the phonetips hanging from the antenna coupler areplugged into the tip jacks marked for theloop. The oscillator and first detector use'01A tubes, the three i.f. stages use '22 type,the second detector and first two stages ofa.f. use '12A type, and the last stage ofpush-pull audio '71A tubes.

The i.f. transformers are peaked at 450 k.c.so as to give one -spot tuning. It will benoticed that a 25 mmf variable condenser

T1 1T I TT

L

I

time as any of the screen grid tubes have tobe replaced. The only remaining variablecontrol is the small trimmer condenser in theantenna tuning stage. This is non -critical inadjustment and does not usually have to betouched. It is possible, however, to make thereceiver oscillate by tightening this con-denser. All units are thoroughly shielded.

The kit comes in four parts; namely thebase pan, the front control unit, the i.f. am-plifier unit and the a.f. unit. All are fastened

1466/000 60665 01

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to a metal sub -base drilled for speedy mount-ing. Six bakelite strips protrude through thebottom of the base pan and the terminalsthereon are easily booked up with nickel -plated connecting strips. The whole job ofassembly can be done in less than an hour;each unit fitted into place and made fast,bottom connecting strips screwed on, paneland knobs mounted on front, tubes put intotheir sockets and covered with the indi-vidual shield cans. The panel is 7 x 26 in.in size, of walnut grained Micarta.

The manufacturers of the HFL Isotonehave also designed a power pack which fur-nishes all of the required voltages to the re-ceiver. This is sold completely assembledand wired and provides the following cur-rents and voltages: A current, VA amperesat 6 volts; C voltages variable 0-15 and fixed45 volts; B voltages 45 (variable 0-90), 135and 180 volts. There is a variable resistor inthe 21 supply circuit which allows the fila-ment voltage to be increased or decreased.Oversize condenser sections and heavychokes eliminate all tendency toward motorboating and voltage fluctuation. The instru-ment uses dry rectifiers and condensersthroughout and the plate current is furnishedby means of a 280 rectifier tube.

When using the power pack on the a.f.amplifier alone, i.e., on phonograph reproduc-tion, with the filaments of the six unusedtubes turned off, it was found necessary touse a compensating resistance. This is incor-porated in the set.

The parts in the kit are:1 HFL Isotone assembled and wired

tuning unit, 1 HFL Isotone assembled andwired screened grid amplifier, 1 HFL Iso-tone assembled and wired audio amplifier,8 HFL Isotone shield cans with tops, 1 baseassembly plate, 1 drilled and engraved frontpanel, 1 seven -wire cable and plug, 2 goldescutcheons with knobs (attached), 2 diallights (inside of drums), 2 large walnut con-trol knobs, 1 small walnut switch knob,2 steel panel supporting brackets, 12 plateconnecting strips, 55 6/32 hexagon brassnuts, 14 44 in. hexagon spacer studs, 1434 in. by 6/32 R.H. machine screws, 61/4 in. by 6/32 F.H. black machine screws,4 A in by 6/32 R.H. machine screws, 11tinned copper lugs, 6 ft. push -back wire.

(Continued on Page 58)

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Circuit Diagram of IIFL Model 10 Isotone

44 RADIO FOR NOVEMBER, 1928

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Thirteen years of experience andtireless research combined with aguarantee against mechanical andelectrical defect stand behind thissimple monogram.

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46

RADIO AIDS AIR RACES

(Continued from Page 30)

Here they come! There they go!Zoom! Zoom! That was a close one.He didn't miss the pylon very far thattime! And we're inside, too. Herecomes one that whines like a siren. Afterit passes, an observer calls:

"Operator! Plane number 159 fouledpylon! Sixth lap."

The operator grabs the key."6EMF 6EMF 6-"He doesn't complete the third set of

call letters before headquarters station,6EMF, answers, using the "break-in"system.

"6EMI DE 6EMF GA (Goahead)," says 6EMF.

6EMI: "QFP (Foul pylon) NR 159SIXTH LAP K."

6EMF answers: "OK QRX."(0. K., stand by.)

In a few seconds come the signalsfrom 6EMF again: "6EMI DE 6EMFNR 159 DISQUALIFIED AND SIG-NALLED QSU (Will call you later.)"

The whole operation hardly took overthirty seconds! Before the plane couldreach the field, flying well over 100miles an hour, the judges knew what hadhappened at Pylon Number 3. PlaneNumber 159 is flagged out and is savedfrom going around several useless laps.

Even more important than "QFP"was QRR. This signal in amateur radiocorresponds to the "SOS" of commercialradio. At the air races it was used asthe signal for a crash, and we are gladto say that its use was seldom required.

One day, a plane failed to appear atPylon Number 3 after three laps.6EMI advised 6EMF, and the lattermade an immediate investigation. Itwas found that the plane had completedthree laps at Pylons 1 and 3, and hadpassed Pylon Number 2 on its fourthlap. The plane was therefore between2 and 3. A search was made by a scoutplane and it was found only a few min-utes after it had made a forced landingbecause of minor trouble.

On another occasion one of the pylonsreported a grass fire in the vicinity. Ascouting plane was dispatched to thescene and an accurate report of the blazewas made to firemen within a very shorttime, thus aiding them materially inhandling the situation.

It was one thing to tap out a feworders and acknowledgements at the keyfrom time to time, but it was anotherthing to continue this work from hourto hour and from day to day. It wasalso quite a job to make five completeinstallations and then remove them afterthe races. Sometimes during the daythere was considerable time betweenraces. The most you had and tne leastyou wanted was dust and heat! Icecream sodas at a dollar each would be

Tell them you saw it in RADIO

tSERVICE6If you are interested in commer-cial servicing of radio receivers,you should investigate the un-usual merits of the followingWeston instruments - each onea testing authority in its specificfield.

Model528

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Volt-

meter

This compact little instrumentshown above has three ranges -150/8/4 volts. It is designed forline supply and filament voltagetests of A.C. Receivers. A handykit instrument, exceptionally ac-curate, light and durable. Con-tained in mottled red and blackBakelite case.

MODEL 537 A. C. - D. C.SET TESTER

A complete servicing outfit that willquickly diagnose the trouble in any typeof radio receiver set made-without needfor any additional equipment. The metersprovided are equivalent to ten instru-ments: A 3 -range A.C. Voltmeter -150/8/4 volts; a D.C. Volt Milliam-meter with five voltage ranges -600/300/120/60/9 volts, (all 1,000 ohms pervolt); and two current ranges -150/30milliamperes.With this Weston Set Tester filament,grid, plate and cathode voltages aredetermined under actual operating con-ditions. It determines filament currentrequirements and plate current drain. Itlocates "shorts" between grid and plateas well as distortion in the audio systemdue to tube overloading. It provides forfilament circuit and general continuityteats, and also serves u a rapid tube tester.

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cheap! But the boys stuck it out to thelast day with perfect scores.

As a reward for their services theyreceived the sincere thanks and apprecia-tion of the race officials and the satisfac-tion that they had contributed, in nosmall way, to a good cause. They hadsaved the management some thousandsof dollars. They had eliminated a largeamount of worry for the officials. Theyreceived not a cent of money, as this isagainst the amateur's code of ethics andthe rules of his license.

The boys operating the stations dur-ing the races were: Bert Fox (6DY),Charles A. H i 1 l (6BRO-6DRO),Charles Lundblad (6CYX), WilliamBreuer (6BZR), Charles A. Nichols(6ASM), Donald Champion (6FA),and Bob Parrish (6QF-6PS-6XC).

PHONOGRAPH PICK-UP UNITS

(Continued from Page 24)

rise on the low frequencies to compen-sate for the drop in the phonograph rec-ords. This may be accomplished by usingan audio transformer in the first stagewhich has the primary circuit resonatedat a low frequency, somewhere between40 and 80 cycles per second. There areavailable on the market at least threevarieties of transformers which have aresonant primary, generally with thecondenser and B battery feed resistance,mounted inside of the transformer case.Such a transformer will give a decidedpeak on the very low notes when theunit is connected across it and the vol-ume control is simply a variable resist-ance in shunt. With this arrangementmuch better music is available fromphonographs than is available from mostbroadcast stations.

BOOK REVIEW"Practical Radio," by James A. Moyer and

John F. Wostrel, third edition, 378 pages,5 by 71/2 in. Published by McGraw-HillBook Co., New York City. Price, $2.50.

This text provides a simple answer to thequestion of what is radio and how is ittransmitted and received. In an elementarymanner it describes the circuits and partsordinarily used in radio telephony and tele-graphy. Its discussion of vacuum tubes isespecially helpful to the novice. As part ofa section devoted to the testing of sets isprinted a trouble chart which shows at aglance the probable cause and remedy for thecommon troubles to which a set is liable. Italso includes a somewhat sketchy treatmentof a.c. filament tubes, rectifiers and loud-speakers. As a whole, it provides a good in-troduction to the serious study of the subjectof radio stripped from its mathematical tech-nicalities.

A low voltage filament is used in the'26 type of a.c. tube because thereby thea.c. hum is reduced. The lower voltageallows the use of a heavier filament andgreater current with consequent smallerchange in filament temperature and emis-sion. The lower voltage also causes asmaller electro-static field and consequenttendency to hum. L

Editor

M. L. MUHLEMAN

Managing EditorG. C. B. ROWE

Associate EditorsJOHN F. RIDERAUSTIN C. LESCARBOURA

PDo You Read The

TECHNICALJOURNAL

of the

RADIO INDUSTRY

Radio Engineering has beenpublished for eight years for theengineers, technicians, manufac-turers and dealers of the radiofield.

It covers, in some forty text pages each month, thelatest developments in manufacturing and engineering,design, production, etc. It includes valuable material onconstruction, testing and servicing.

In the "Commercial Developments" section, RadioEngineering deals with television, moving picture trans-mission, aeroplane and train communication, speechamplifying systems, etc.

Contributors and authors include the leading engineersin the electrical and radio field.

The Table of Contents of the Latest Issue includes:Isolation and Resonance in Audio -

Frequency CircuitsBy KENDALL CLOUGH

The Mathematics of RadioBy JOHN F. RIDER

The Engineering History of RadioBy DONALD McNICOLPass President A. I. E. E.

Detection with the Screen -Grid TubeBy J. R. NELSON

An A.C. Audio Amplifier for Tele-vision

By J. R. FRANCISNew Developments of the MonthCommercial DevelopmentsNews of the Industry

(and other material)

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CONSTRUCTED BREAK-IN

(Continued from Page 40)

When the key is up you are receivingthrough the secondary of the transmitter'soscillation transformer. When the key ispressed the receiver is grounded out and theground circuit of the transmitter is closed.

Be sure to adjust the contacts of thebreak-in so that they close just a fraction ofa second before the main power contacts ofthe key close. In other words, the receivermust be grounded before the power goes intothe transmitter for full protection. It is ad-visable to put a safety gap across the antennaand ground posts of the receiver as an addedprecaution; that is, if the receiver is notalready so equipped.

AMATEUR RADIO RESEARCHCLUB BANQUET

By WALLACE S. WIGGINS

The largest amateur radio banquet in twoyears for Southern California took place inthe Chamber of Commerce Building, Septem-ber 12, 1928, sponsored by the Amateur RadioResearch Club of Los Angeles. Over 115enthusiasts of "brass pounding" were presentin the banquet hall, which echoed and re-echoed with shrill whistles in true "ham"style.

A. H. Babcock, A. R. R. L. director, de-scribed the situation at Washington withregard to the status of the amateur, andstressed the importance of keeping up withthe times in the design of transmitters andreceivers for efficient operation in the newkilocycle bands. He also spoke of operation

other than the amateur bands,explaining the "American Eagle Channel,"for the Army and Naval Reserve Units.

"Bob" Parrish, 6QF, president of the A.R. R. C., and chairman of the banquet com-mittee, introduced the speakers. "Jimmie"Warner of KHAB, the "Southern Cross,"first plane to fly from Oakland to Australia,modestly described part of the flight in ashort speech, saying that the trip was "un-eventful," but that he appreciated the co-operation of the amateur operators. BobHutchings, 6AKF, related a most interest-ing story of a trip to Siberia and China onwhich they took portable receiving and trans-mitting equipment. The big "kick" of theevening came when Hutchings said that al-though reception was none too good, thestrongest signals from the United States camefrom 6CUT. As the owner and operator ofthat station was present, he was called uponto describe his supposedly super -high pow-ered transmitter for the benefit of those un-fortunates who lacked the cash to purchasehigh-powered stuff. He was introduced asHomer F. Beal, Jr., of Riverside, Calif. Thesurprise and wonder of the assembly canwell be imagined when Beal said he wasusing a 71/2 -watt tube with 1000 volts onthe plate through a 30 -henry choke. He ex-plained further, however, that a zeppelinantenna, constructed with the greatest care,was being used. This probably accounted fora large share of the success of his strongsignals in Siberia.

"Wally" Wiggins, 6CHZ, explained theoperations at the National Air Races in con-nection with the club's activities in provid-ing communication. Bert Fox, 6DY, supple-mented this with an explanation of the de-tails of installation and operation. It wasannounced that over 2400 messages had beenhandled, free of charge, for patrons of therecent radio show in Los Angeles.

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MARSHALL SHORT-WAVERECEIVER

(Continued from Page 36)after time without any variation in thedial readings or numbers. Reception on8000, 12,000 and 16,000 kilocycles waseffected without interference. A tem-porary removal of one of the shielded -grid tubes, however, cut down the signalstrength appreciably.

Using this receiver, the Eagle pickedup signals in the daytime with regularityfrom Washington, D. C.; Key West,Fla.; New Orleans, La.; and Guantan-amo, Cuba, while cruising in the Pan-ama Canal Zone. However, the signalsfrom stations northward from Louisianato the Great Lakes were intercepted withthe greatest clarity while the Eagle waslocated in the Panama Canal waters.Amateur stations on the Atlantic sea-board were also heard satisfactorily. Thecomparative tests between this receiverand a standard navy outfit were con-ducted with both receivers connected tothe same antenna-using the so-called"coupled tube" arrangement of theBellevue Naval Research Laboratory.

Tests on a submarine were restrictedby the usual limiting factor of submerg-ing radio in salt water, namely, at adepth of 20 feet there is a sudden andcomplete extinction of the received radiosignal. However, this receiving setoscillated and was as easily controlledwhile submerged as when on the surfaceof the water. Furthermore, when usinga loop or coil of wire as pick-up systemon this submarine the distant signals-from Rocky Point and other transmit-ting stations-were nearly as loud aswhen employing the conventional high -frequency antenna on the Eagle. Theuse of one-half of the loop antenna onthe submarine caused a material sacri-fice in signal strength. When the sub-marine was resting on the surface of thewater, this new receiver appeared tofunction most advantageously when re-ceiving signals from distant stations ona frequency of 18,000 kilocycles.

IMPROVEMENTS IN CRYSTALCONTROL

NATEURS should take particular noteof the improvements which are

being incorporated into many of thebroadcasting stations, in the form of crys-tal control. Several of the stations havetwo crystals, either of which may beused as the main control, and thesecrystals are cut so accurately as to bewithin 100 cycles of each other. To main-tain accurateness of frequency, eachcrystal is heated electrically to a certainfixed temperature, at which it is cali-brated.

With the coming limitations of theamateur bands, there will undoubtedlybe an increased use of crystal control onthe short waves. By the installationof a simple heating system and ther-

(Continued on Page 51)

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Tell them you saw it in RADIO 49

LONGERLIFE

pmowovwczoSEE -CO

RadioTubesWHEN you install a set

of CeCo Tubes inyourradio, you immediately no-tice the greater clarity ofreproduction-the increasedsensitivity and the bettervolume.But your greatest satisfac-tion will come with theirlonger operating life, mak-ing CeCo the most eco-nomical tubes to buy, andworthy of their slogan"they cost no more, but lastlonger." This is made pos-sible partly by the exclusivemethod of evacuation.

To avoid disappointing re-sults, make sure each socketis equipped with CeCotubes. Whether for batteryor A. C. operation-there'sa CeCo for every radioneed - including "specialpurpose" tubes that are notobtainable elsewhere. Theyare sold by leading dealerseverywhere.

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TUBE TESTING SET

(Continued from Page 33)

The reading should then be comparedwith the nominal limits as indicated onthe accompanying table. If the emission

POWER AND RECTIFIER TUBETESTS

Indication for Good TubeCX 310 No. 1 Dull red

No. 2 Dull orangeCX 313 No. 1

No. 2 Dull orange

CX 316B No. 1 DarkNo. 2 Dull orange

CX 350 No. 1 Dull redNo. 2 Dull orange

CX 380 No. 1} Dull orangeNo. 2)

CX 381 No. 1 DarkNo. 2 Dull orange

reading is below these figures it indi-cates, as a rule, that the tube has beenoverloaded due to excessive filament orplate voltage, or both, or that there hasnot been sufficient C battery voltageprovided.

To take an emission reading on a

322, the screened grid amplifier, it is

necessary to connect the two grids to-gether; this may be easily done by ar-ranging an X base socket on an X tubebase, connecting a flexible wire with aclip on it to the grid terminal of thesocket, inserting the 322 into thisadapter, placing the whole assembly intothe proper socket in the test set. If noshort circuits are shown on the lamps,connect the clip to the top contact onthe 322 and then press the emission keymomentarily. To test the C-11 it willbe necessary to use an adapter to ac-commodate the special arrangement ofcontact pins to the C-12 socket.

Type 300-A gas filled detector tubesrequire a special test for sensitivity, andcan only be tested for short circuits andfilament emission in this test set.

The testing of 310, 313, 316-B, 350and 381 tubes is extremely simple, itbeing only necessary to place the tube inthe socket with the switch in positionNo. 1, the condition of the tube beingindicated by the glowing of the lamps.Make certain before placing the tube inthe socket that there is no short circuitbetween the elements. A low emissiontube usually indicates abuse resultingfrom too high filament voltage, too highplate voltage, or insufficient grid volt-age. A gassy tube may cause the lampsto glow as if 0. K., but of course, is de -

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C 11 C-CX' CX CX CXCX12' 299 220 301A 300A

FilamentVoltage 1.1 3.3 3.3 5.0 5.0(Min. MA)'Emission 6.0 5.5 13.0' 20.0' 14.0'

CX CX CX CX CX CX C340 112 112A 371 371A 326 327'

5.0 5.0 5.0 5.0 5.0 1.5 2.5

14.0' 45.0' 45.0' 40.0' 40.0' 35.0' 35.0

50 Tell them you saw it in RADIO

fective. Make certain that there is nodecided blue glow surrounding the fila-ment. A faint glow on the 380s, 381sand 350s is the normal condition anddoes not indicate a defect.

LIST OF PARTS FOR TEST SET

1 Panel 12 x 20 in.4 X base sockets1 Navy type socket2 Dial lamp sockets (Edison Mitt. base)2 110 -volt lamp sockets, Standard type1 Socket for 327 a.c. tubes1 Socket for old style 99 tubes1 Socket for 377 protective lamp, Bayonet

type2 10 -watt, 110 -volt Mazda lamps1 6 -ohm, 1/4 -amp. fixed resistor1 7 -wire cable, 5 ft. long

Kellogg Model 301 Key1 10 -ohm rheostat, PA amps. load1 0-6 V. voltmeterI 0-50 M. A. milliammeter1 4 -contact switch1 ,A -ohm 2 -amp. resistor (6 in. No. 22

Nichrome wire)2 Dial lamps, 6 volts

The thoriated tungsten filament tubesmay be reactivated if the overload hasnot been too severe. The coated type offilament cannot be reactivated due to itsdesign, and any attempt will result in itsimmediate burnout. The tubes whichmay be reactivated are as follows: 99,220, 322, 300-A, 301-A, 340, 371, 310,313 and 316-B.

In reading the tables accompanyingthis description, it is well to keep inmind the following notes:

If the dial lamps light, it indicates ashort circuit; do not then attempt totake an emission reading or you willdamage the meters.

Lighting of lamp No. 1 indicates agrid to filament short; lamp No. 2 in-dicates a plate to filament short; bothlamps indicate grid to plate short.

An open or burned out filament mayfall against the grid or plate, causingthe lamps to light. This may be deter-mined by turning the rheostat up andif voltage regulation is impossible, thefilament is open ; such tubes are calledopen filaments, either broken or burnedout, according to the results of the in-spection at the service station.

IMPROVEMENTS IN CRYSTALCONTROL

(Continued from Page 49)mometer as an indicator, the amateurcan maintain an absolutely dependableconstant frequency of transmission. Byplacing the crystal with its associatedtube, inductance and condenser in aclosed box or compartment, togetherwith a 25 or 40 -watt mazda lamp con-trolled by a rheostat, a control of thetemperature can easily be had, at littleor no additional expense.

The broadcast stations are commenc-ing to use an enclosed automatic heatingunit and crystal which is supplied bythe Western Electric Co. But an ama-teur does not need the automatic fea-ture if he watches the thermometer.

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The new Knapp "A" Power has all of the features of the old model-magic silence-absolutely dry-KB" Eliminator receptacle-voltageregulator-complete, tooled part kit, etc., etc., and also eight newimprovements which make it the finest 'A" Power ever put out.Compare the appearance, read the improvements-and rememberthat the price has been reduced !

The Only"A" Power AdaptabletoShort Wave,Super-Heterodyneand Television ReceptionThe Knapp "A" because of its supe-rior filter system and the special Elkonrectifier is so silent and so steady thatit functions perfectly.

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Tell them you saw it in RADIO SI

ALL -SHORT-WAVE RECEIVER

'UNGARO 40025 MFD.MOULDED CONDENSER

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POWER TRANSFORMERSfor the UX 250 Power Tube

TYPE 565-A TRANSFORMER(200 watts)

The General Radio Type 565 PowerTransformers consist of two modelsfor both half and full -wave rectificationutilizing the 281 type of rectifier tube.The Type 565-A Half -Wave Trans-former illustrated consists of one 600-

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52 Tell them you saw it in RADIO

(Continued from Page 42)

to a low value and the setting noted. A pairof grid -leak clips are mounted on it and avariable grid leak is best, although 5 meg-ohms is the usual value.

A 112 used as detector oscillates easily atthe highest frequencies. No tube -socket isused, since different tubes change things somuch. The set ought to be built around theparticular type of tube employed. Holesare drilled through the bakelite and the leadsare soldered in place. Should another tubebe necessary, the 112 is easily removed as itis at the rear of the set.

No short-wave receiver should be withouta filament switch, as best oscillation is alwayssecured at some particular filament -setting.These tubes usually work best with very lowfilament and about 67'/2 volts on the plate;other tubes will sometimes require compara-tively large values of tickler turns and oftenhigher plate voltages. The correct adjust-ment of the set, for the higher frequencies, isimportant and will require some experimen-tation for values giving best results.

The arrangement of apparatus is conve-nient for the experimenter as the filamentrheostat and switch, phone jack and audioamplifier are mounted on a separate panel.All parts are arranged so that they can beused separately.

The whole set is mounted on a heavy base-board and is supported above it. The 41/2 -volt C battery is mounted underneath. Drycell tubes can be used and the set made semi -portable; it is a simple matter to mount thelayout on the seat of the car and study the5 or 10 -meter signals at a distance from thestation.

The audio transformers peak at 1000 cyclesand the set therefore gives best response atthis audio frequency. There are still ACsignals on the air so that a very selectiveaudio amplifier would hardly be desirableyet, especially for all -wave use. In thisamplifier, the better signals are received withexcellent results and extraneous noises aregreatly reduced. Often one can "tune" anaudio transformer to about the correct valueby using condensers across the windings;some transformers are designed for peaks inthe audio range.

The selection of proper midget condensersis important, as many types are not so good.If these are of the one -bearing type, thisbearing should be well -constructed and aboutthis the amateur knows. These condenserswill eventually replace the larger sizes formost short-wave uses. Almost a whole setof these may be obtained for the price of theusual large instrument. They are as goodelectrically, if not better, than the largersizes, especially at the higher frequencies asshown by repeated tests at 5 and 10 meters.

The coils can be celluloid -supported andNo. 20 wire is about right for the well -spacedturns. The 5 -meter coil consists of about 2heavy turns on a 1 -in. diameter, and the10 -meter one is about double that; at 40meters, 18 or 20 spaced turns is about right,but the values are not critical because theshunt condenser will compensate. Large coildiameters for 5 and 10 meters should beavoided as movement of the body then hasconsiderable effect on regeneration.

Fixed filament resistors are used in theaudio amplifier. To use the set without r.f.amplifier, the antenna is connected directlyto a lug on the secondary condenser througha small midget. The output of the r.f. am-plifier may be similarly connected; it is per-haps better to use separate batteries for ther.f. amplifier but one will work all right withthe same batteries for the whole layout. Oftenthe tube will oscillate much better if thefilament leads to the detector are reversed.

The actual wave -change caused by sup-posedly small effects is too large. In the usual

amateur wavemeter employing a flashlampindicator, the wave may be changed asmuch as /2 meter at 40 meters by simplychanging lamps or shorting a given lamp inor out. Such changes are too large for 1929conditions. There are perhaps only two ar-rangements which are practical for averageamateur use.

One of these consists of the tuned circuitdescribed above to which is coupled a 2 -turnloop (at 40 meters) including a flashlamp inseries. Some flashlamps give very broadtuning, but tests show that the 1.25 -volt type("S" filament) is about the best to use, asthe filament cools rapidly and gives a sensi-tive indication. If the main inductance con-sists of about 18 turns on a 2 -in. tube, this2 -turn loop should be set at about 34 in.from it. Indications will be quite sharp, andwith loose coupling, the effect of the lampcircuit causes very little tuning effect. Thelamp when turned into, or out of, the socketwill have a small effect on the wave, but ifleft in place, will give good results andtuning will be sharp.

Wavemeter with Neon Tube Indicator

An accurate wavemeter is necessary forcalibrating picture and circuitdiagram in Fig. 2 show one using a neonlamp as a resonance indicator. It uses a15 mmfd. midget tuning condenser cut downto three plates and a 20 -turn coil, which iswound on a threaded length of 2 in. bake-lite tubing. A 50 mmfd. midget condenseris shunted across the tuned circuit.

51107.f MIDGITWONG CONDINSfk...

fIXED- WHINONCE 011/SKATED

Fig. 2. Wavemeter Circuit Diagram

The condensers are mounted on a hardrubber strip which, together with the panelsupporting the vernier dial, is securely fas-tened to heavy baseboard blocks. A smallextension handle eliminates the necessity ofshielding. The threaded tubing is securedto the baseboard by small metal angles at thebase. Heavy copper wire is used for con-nections.

The neon lamp should be of 5 -watt size orlarger. It is somewhat more sensitive if oneterminal is left open and a length of copperwire, wound around the middle, is used asthe other. The lamp is securely fastenedto a bakelite piece and is held by a pieceof wire passed around the lamp and throughholes.

For accuracy, it is best to have a separateinstrument for the 40 -meter band. The smallcondensers are economical and at small ex-pense accurate instruments can be con-structed for 20 and 40 meters. The 10 -meterband is wide and accuracy is not as impor-tant.

To calibrate the wavemeter accurately, thetransmitter can be operated without an

NEON-IRMP

ESONPNCEINDICATOR

Positive Line Voltage Control SafePROTECT your A.C. tubes

from excessive filament volt-age and insure maximum efficiencyfrom your newA.C. receiver,which is designedto operate at acertain specifiedline voltage. Tobe safe, you musthave some meansof controllingthe voltage fromthe light socket,which varies in different localitiesand during certain times of the day.

26 KeefeAvenue

CENTRAL RADIO

The Centralab Radio Control Boxis the most advanced form of volt-age regulator. It is so designed

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TELEVISIONalthough still in an experimentalstage, has now advanced suffi-ciently to enable amateurs to buildoutfits that will give edifyingresults.

Write today for our price listof television apparatus.

Photo Electric Devices, Inc.594 Fifth Ave. Brooklyn, N. Y.

Gerald Best'sSUPER BLUE PRINTS

The complete working plans in full size forbuilding the new incomparable Gerald Best115 Kilocycle superheterodyne with full in-structions for building.

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FreeA Continental Control Switch will be givenfree with a one year subscription to RADIO($2.50) if you act immediately. Only afew on hand.

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MarvelousReceptionFull en-tire receiving range byequipping your PowerAmplifier with a Pot-ter Condenser Block.No.

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The Choice of LeadingRadio Engineers

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LAST MINUTE SPECIALS!E210 BRADLEYSTATS, list $4.00_ Our Price $1.60 ea.MESCO Wireless Keys, list $2.00 95c ea.U. S. ARMY Aeroplane Spark Transmitters, Gov. cost $47 each SO 4.75 ea.G. E. Kenotron Rectifying Tubes (type T.B.1) 1.25 ea.Eby A.C. Adapter Harness with Volume Control. For 6 tube Sets, list $10.00 " 5.00 ea.Gould Kathanode Unipower, Automatic Radio "A" Power (6 volt), list $39.50 " 13.75 ea.

AMERICAN SALES CO., 19-21 WARREN ST., NEW YORK CITY

Tell them you saw it in RADIO 53

A NOW PF-250Power Transformer

forUX 250 Power TubesA husky transformer built for doing thejob, not for looks. The PF-250 is rated at1200-600 volts plate, Pi volts power tube,7% volts rectifier tube filament. Centertaps are provided on each of the filamentwindings. Continuous rated capacity ofplate windings, 160 MA., continuous rated

capacity of each 73i volt winding,3 Amperes. DC plate output with

two UX 281's full wave, up to450 volts with sufficient ex-

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Price, each -430.00Sightly higber West of Rick, Motostamt

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CUSTOM SET BUILDERSBrowning -Drake has an interesting and

unusual proposition. Take advantage of thefact that more Browning -Drakes are builtthan any other. Write today.

BROWNING -DRAKE CORP.CAMBRIDGE, MASS.

CARDWELL CONDENSERSThe Taper Type

Type "E"Cardwell

Unexcelledfor Short Wave

Receivers

STABILITY Is Vitalin the short wave receiving circuit.

The effect of a rising and falling note so oftentroublesome in CW code reception, due to instabilityin the circuit, will obviously play havoc with Broad-cast Reception on the short waves, if at all pro-nounced.

CARDWELL TAPER PLATE CONDENSERS arerigid and vibrationless and will absolutely hold theircalibration, thus eliminating one of the importantcauses of circuit instability in short wave receivers.

The tuning curve is ideal, midway between SLWand SFL, attained without eccentrically shapedplates, thus concentrating the weight of the rotorclose to the shaft. It will pay you to investigate.

Transmitting Condensers for powersup to SOKW and more. ReceivingCondensers in all standard capacities.Send for literature.

The Allen D. Cardwell Mfg. Corp.81 Prospect Street

BROOKLYN, N. Y.

"The Standard of Comparison"

antenna with a very small input, and so aharmonic falls exactly on the wave of abroadcast station which has been carefullytuned in with any ordinary nearby regenera-tive, broadcast receiver. By using differentstations, various points on the wavemetercalibration -curve are easily obtained. Thewavemeter in each case is checked with thewave of the transmitter, the wavelength ofwhich is calculated from the broadcast fre-quency by dividing by the proper wholenumber.

Operation is simplified by using a sensi-tive grid d.c. milliammeter in the transmitterin series with the grid leak. For a 210 tube,this meter ought to be about a 0/25 size.Resonance is denoted by the dip of the gridmeter. Several check points should be usedand the average curve taken.

The transmitter must also receive specialattention for 1929 conditions. It should besharply tuned and not "modulated" by apoor plate supply, giving the usual broadwave. Good d.c. plate supply will helpconsiderably. Many amateurs may desire tooperate with small "99" transmitters. Theseare quite cheaply constructed and give ex-ceptional results in these days of sensitive,screen -grid r.f. receiving systems, like theone described.

The average amateur transmitter is tooclosely coupled to the antenna. A broadinterfering wave is caused and operation intwo frequencies, close together. With loosecoupling, the wave is sharpened, transmis-sion is on only one frequency, the note is im-proved, and the antenna system has lesseffect on the oscillating circuit, reducingconsiderably, any "wobbling" effects. Oneshould use a large capacity in the oscillat-ing circuit, which usually eliminates "creep-ing." If the tubes are run cool, this effectis greatly reduced. Any circuit, when prop-erly adjusted, gives a good constant oscillat-ing frequency.

Since bringing up a tuned antenna circuitto the primary changes the plate current andtherefore the tube temperature, the value ofcoupling will have some effect on the fre-quency of the transmitter. The couplingdepends on so many factors that a generalrule cannot be given; if one adjusts thecoupling so that 85 or 90 per cent of theantenna current is obtained with close coup-ling, good results will be secured. Thenote should be studied near the set and is af-fected to some extent by antenna tuning. Ingeneral, any change in the transmitter whichchanges the plate current value will have aneffect on the frequency and any such willhave less chance, if a low L C ratio is used.

If all amateurs in the 40 -meter bandwould use direct current plate supply,operation would be improved because of thesharp waves. The high-pitched notes wouldencourage the use of peaked audio amplifiersystems, thus reducing other interference andamplifying, to a maximum degree, the propersignal. A surprising number of such stationscould operate without interference if boththe transmitting and receiving systems weresharply tuned. The all -short-wave receiverhere described is a step in that direction.

SELECTIVE SHORT-WAVERECEIVER

(Continued from Page 42)

The r.f. choke consists of 300 turns of No.36 wire, scramble -wound on a 1 -in. core. A.00025 mfd. oscillator grid condenser Ca and1 megohm grid leak R, lowers the plate cur-rent somewhat. The condenser Cr is of .002mfd. capacity, C, .0005 mfd., C, 1 mfd. andC,, .0005 mfd.

The filaments are all controlled by one6 ohm rheostat R5. Sockets are mounted onsponge rubber cushions to prevent micro -phonic noises. All parts are mounted on a7 by 18 -in. panel.

54 Tell them you saw it in RADIO

"DRESNER" SHORTWAVE CONVERTER

Complete$22.50Special

WaveLengthRange

15 to 550Meters

SIMPLE TO ATTACH-EASY TO OPERATE

Some of the best entertainment ofthe air is broadcast on the shortwaves by many powerful stations.There Is no longer any reason whyall should not receive these excel-lent programs from all over theworld. The Dresner Short WaveConverter Unit is completely as-sembled. It efficiently covers a waveband of 15 to 550 meters, and makesreception easily obtainable for all.Offered at the special price of $22.50-complete ready to plug into yourreceiver in a few seconds.If your dealer cannot supply you, sendmoney order direct and we will ship P. P.Prepaid. Guaranteed.

(When ordering unit, be sure tospecify whether it is to be used onAC or DC set.)

Dresner Radio Mfg. Corp.642 Southern Blvd. New York City

Dept. F

ENJOY44THIRILL.YELECTRIFIEDRADIO at SMALL COSTonly

85 Banish forever all the annoyanceand expense of buying new "B"Batteries with a TOWNSEND "B"POWER UNIT. Hooked up in afew moments-and you have per-manent power from your light soc-ket from that time on. Use same

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way Townsend, improveyour reception and add todistance getting. Morethan 50.000 now In use.Send Coupon today for fullinformationpo and free trialoffer.

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Chicago Illinois-COUPON

TOWNSEND LABORATORIES 11/28Dept. 18, 713 Townsend St., Chicago, m.Please send me full information on the Townsend 'B"Power and Free Trial Offer.

Name

Address

Send for New Radio Book-It's Free!New hook-ups. This book shows how tomake short-wave receivers and short-waveadapters. How to use the new screen gridtube in D. C. and A. C. circuits. How tobuild power amplifiers, ABC eliminators.Up-to-the-minute information on all newradio developments. Its free. Send for copytoday.

KARAS ELECTRIC COMPANY4031L2 North Rockwell St., Chicago, Ill.

Portland. Oregon. 53 4th St.San Francisco, 585 Mission St.Los Angeles, 324 N. San Pedro

NameSt. and NoCity and State

4031L2

I

You Can BuildBetter Than You Can Buy

Aero"CHRONOPHASE"

The Aero "CHRONOPHASE" principlein Radio Frequency Amplification is thefirst outstanding development in broadcastreception since the introduction of theneutrodyne. Now selectivity takes on newmeaning, for sets employing this principlecan be made so selective that even the sidebands of local broadcasting stations canbe cut off. Greater distance range, too,is achieved with remarkable smoothnessof control. No factory -built set has the newand revolutionary "CHRONOPHASE"principle. It may be had, however

In Three WonderfulReceivers

The 1929 six -tube "Aerodyne," the AeroSeven -Twenty -Nine and the five -tube Aero"CHRONOPHASE" all incorporate the"CHRONOPHASE" circuit. Completekits for these receivers may be had fromyour dealer. No expense has been sparedto make these kits the finest you can buy.A beautiful two-tone metal cabinet is apart of each kit. Every part needed forthe construction of the receiver is included-even wire, soldering lugs and woodscrews-so that nothing more need bepurchased. Anyone can assemble an Aeroreceiver in a few hours. Panels aredrilled, which insures proper placement ofparts and full-size pictorial wiring dia-grams eliminate mistakes in wiring. Aerosets can be built for A.C., D.C., or Shield -Grid tubes.

A postcard request brings twovaluable booklets introducingthe new 1929 line of Aero kitsand describing the 64 page AeroGreen Book for 1929. Send to

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Size 26"x40"z16" deep.

Your Own LabelOn This Radio

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Material and manufacture - notadvertising! --determine the qualityand salability of a receiver. PremierPrivate -Label Radio is equal to anyon the market in performance, looks,quality and salability. Table, consoleand combination models,-furnishedstandard in 6 -tube and 7 -tube Push -Pull.

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PREMIER ELECTRIV rOMPANYEstablished 1905-Manufacturers Ever Since

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Helps You PassGovernment Radio

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Tell them you saw it in RADIO

3MI

00 InsuresYourA.Clither

The Vitrohm 507-109 Unit costs$2.00. Installed on your radio set,it lengthens a. c. tube life by auto-matically lowering filament volt-age.Attached in a moment-Nothingcombustible - Nothing to wearout-Does not get excessively hot.It consists of a Vitrohm Resistormounted within a perforatedmetal cage, a plug, and a recep-tacle.Write for free information on thisand other Ward Leonard RadioProducts.

WARD LEONARD VERNONELECTRIC CO. NEW YORK

pscrtitieovEyEkiti4i

c)

With the same creative enthusiasmthat produced the first radiovacuum tube (1906) Dr. DeForesthas now developed the perfectedAudion.

When you replace your tubeswith DeForest Audions you willexperience a new enjoyment inclarified reception.

Send today for your free copyof the interesting booklet by the"Father of Radio."

De Forest Radio Co.JERSEY CITY ^. N.J.

55

X44.11

'N.LessenStatic

Tune More SharplyBring your set up to maximumsharpness with X -L Vario Densers

Practically all of the popular high gradecircuits now use X -L Products. Perfectreception is always assured because of theaccurate values and dependable service thesewell known products give. Endorsed byleading radio engineers, designers andbuilders and standard in most quality sets.Broad and positive capacity range that as-sures exact oscillation control easily obtainedwith both Model "N" and Model "G" VarioDensers.

Model "G" Vario DenserGenuine Bakelite casing, dust and moistureproof. All metal parts phosphor bronze nickelplated. Only the best imported India micaused. Extreme micrometer capacity advance,exceptional accessibility in close quarters.Model "N" has variable capacity adjustablefrom 1.8 to 20 micro -micro farads. Priceeach, $1.00.Model "G" with grid clips made in threevariable capacity ranges. viz: Model G-1..00002 to .0001 MEd.; Model G-5, .0001 to.0005 Mid.; Model G-10..0003 to .001 Mfd.Price each $1.50.

NewBAKELITEINSULATED

X -L PUSH POSTThe most perfect binding postmade. Push down with thumb,insert wire, remove pressure,wire is held firmly. Vibrationwill not loosen but releasesinstantly when you wish. Nochance to forget to tighten.Positive, permanent. Plain orall standard markings. Also X -Lmade in all -metal design. Price Push Posteach 15c.Strip of 7 on black panel with white mark-ings, price $1.50.

Write for interesting and valuablefree copy of our new up-to-date bookof wiring diagrams showing use ofX -L units in all leading circuits.

.a.Radio LaboratoriesDept. 3,1224 Belmont Ave., Chicago, Ill.

TECHNICAL BRIEFS

(Continued from Page 38)

with transformers having p2 -in. and 1Y2 -

in. primaries, for 9, 18 and 36 turnseach. The screen -grid tube circuit con-nections for each type are shown in Fig.3, a showing the transformers and bthe autoformer.

The 1% -in. primary type is that gen-erally advocated for use with a shield-

grid tube when a tuned impedance is notemployed. It will be noticed that thereis little gain in amplification when more

and a consequently greater overall ampli-fication. As the number of turns is in-creased in the portion of the secondarywhich acts as a primary, the amplifica-tion on the higher frequencies is re-duced because the two currents in thisportion of the coil are in quadrature,and the voltage in the grid of the nexttube is consequently lower. This canalso be used in a multi -stage amplifier tosecure uniform amplification over theentire spectrum without so greatly im-pairing the selectivity.

The selectivity curves for these three

60

50

I''Actifel

40

14.

'1,..

30

...-

20

10

fIG. I

PRIMARY TURNS

Fig.4. Selectivity Curves for Three Types of Transformers

than 18 turns are used, thus impairing itspossibilities for selectivity.

With the /-in. primary a variationin the number of turns changes the pointwhere maximum amplification is secured.Hence with a multi -stage cascade ampli-fier uniform amplification can be securedover the whole band by adjusting thenumber of turns in the primary of eachtransformer, although this may result insacrificing the selectivity of one or twostages.

As the inductive coupling is muchgreater with an autotransformer, a fewturns will give a high primary impedance

types of transformers, are shown in Fig.4. The figure of merit considers theinverse ratio of amplification obtainedat the mean of frequencies 50 k.c. distantfrom the oscillator frequency, plottedagainst a percentage cutoff at seven -tenths of the maximum. A selectivityfactor of 50 is fair, 55 is good, and 60gives an extremely desirable point. Itwill be noticed that at 350 meters, forexample, this selectivity figure can beobtained with the autoformer circuitwith an amplification figure of 5.7,whereas the corresponding 72 -in. pri-mary is secured with an amplification

Ca /VT3 TI VT4 T2 VT5

Fig. 6. Chronophase Circuit with Two Screen -Grid R. F. Stages

56 Tell them you saw it in RADIO

0-Mac/drill/aWiffOioice.Shouldfle

The

1101[FILMAJIESTICBROAD Si AND GIRARD AVE.

400 LARGE ROOMSOnly Hotel in Philadelphia with asubway entrance from main lobby.

MOST MODERATE RATES!Single room, running water $2.00

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Wire at our expense for ReservationsJNO. C. GOSSLER, Mgr. Dir.

SPINTITEWRENCHES FREEWith a one year subscription to

"RADIO"3 Stevens Spintite wrenches for round nutsgiven free this month with a subscription to"RADIO." Send $2.50, get "RADIO" forone year, and the wrenches also. We paythe postage. Only few sets of thesewrenches still on hand. Hurry.

Publishers of "RADIO"Pacific Bldg. San Francisco

Your TubesSTEADY AS THE STARSIT hen AMPERITE-ControlledDon't let "A" battery current fluctuations spoilyour radio reception or ruin your tubes. InstallAmperites and automatically keep the filamenttemperature constant according to tube rating.Entirely unlike fixed resistors. With AMPEHITEcontrol tubes last longer and your set soundsbetter. Panel arrangement improved and wiringsimplified. Tuning is easier and volume is in-creased. A type for every tube-battery or A. C.

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of only 3.6, or about 65 %. In this par-ticuler instance the superiority of theautoformer type is outstanding.

Oscillation was frequently encount-ered, even in connection with the sup-posedly non -oscillating shield -grid tube,unless some means were taken to preventit. The best results were obtained byshifting the phase angle of the currentsin various stages by the method illus-trated in Fig. 5.

4.110 MO

Fig. 5. Chronophate Circuit

An inductance L2 of comparativelylow d.c. resistance was shunted aroundthe resistance Ri, maintaining a maxi-mum static value of plate voltage at thetube, while offering a very high imped-ance to r.f. currents. The resistance R1can be varied without affecting the staticvalue of the plate voltage and will befound to serve as an oscillation control.If provision is made so that it can bereduced to a low value, so as to effec-tively short-circuit C2, it can also be em-ployed as a volume control.

In a circuit containing two stages ofradio -frequency amplification, it willrarely be found necessary to employ morethan one such resistance, as sufficient ad-justment of the time relation can beobtained to avoid oscillation while stillmaintaining the satisfactory value ofoverall amplification. Maximum results,regardless of the type of tube used, canbe obtained by varying the proportionof L, which is used in the plate circuitof the preceding tube. Little trouble wasexperienced from inductive coupling be-tween coils.

Shielding always introduces certainlosses in the coil, due to linking a por-tion of the coil's field, and also compli-cates the mechanical construction of thereceiver. It will be seen from the curvethat the necessity of shielding is miti-gated as far as interstage coupling effectsgo, while the diameter of the coil is sosmall that direct pick-up from local sta-tions is reduced to a minimum, as hasbeen demonstrated in practice.

One such receiver using two stages oftuned radio -frequency amplification withshield -grid tubes, employing the "Chron-ophase" system, has been given an ex-ceedingly thorough tryout. On a 25 -ft.aerial located on the shore of LakeMichigan, in the heart of the most con-gested mass of broadcasting stations inthe world, it has been possible to cutthrough locals and secure good loudspeaker reception of stations a thousandmiles distant.

YEARS Ahead!

TheHAMMARLUNI)"Midline" CondenserCondensers come and condensers go, but theHammarlund "Midline" keeps ahead.

Built with watch -like precision and embody-ing every feature demanded of modemtuning instrument, the Hammarlund "Mid -line" Condenser continues to make radiohistory.

If you know radio, you know Hammarlund.If you are a beginner, ask any radio engineerhis estimate of Hammarlund Products. Followhis advice.

Write for Folder

Hammarlund Manufacturing Co.424-438 W. 33rd St., New York

acrt. 1-12-ttiot rinci10-

ammarlundPHCC'S/ON

PRODUCTS$61.00 issBringsues u, ,t Rh nDeIxot

11' BATTERYELIMINATOR

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No more worry with "B" Batteries! Hook up anR. B. "B" Battery Eliminator and forget bat-tery troubles forever. This wonderful new in-vention means better reception, sharper tuning.Gives you more real pleasure from your set.

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Order your Eliminator NOW. Write name and addresson a piece of paper, pin a dollar bill to it, andmail it TODAY. Pay postman balance ($4.95 plus afew cents postage) when he delivers your Eliminator.Use it ten days. If not more than satisfied, returnIt and get your money back.

135 -Volt Eliminator Only $7.95New style Eliminator that gives amazingperformances. Send $1.00 and pay balance of $6.95(plus postage) on delivery. Guaranteed to please-

or money back. Be sure to ask for 135 -Volt Eliminator.

THE R. B. SPECIALTY CO.Dept. D-304. 318 Sycamore St., Cincinnati, 0.

SendI i00

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FREE 3AYTRIAL WITH

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NA ALD

NEW

ELECTRIC

PICKUPWith a NA-ALDElectric Pickup anda good radio set orpower amplifier youcan electrically am-plify the music from

phonograph records and get the results of talkingmachines costing several hundreds of dollars. Thenew NA-ALD Pickup fits A.C. or battery sets. Itis equipped with twin magnets giving a full, richtone quality on both high and bass notes. Every setowner should have one. You may try a NA-ALDPickup for three days and if not satisfied return itand get your money refunded.

ALDEN MANUFACTURING CO.Brockton, Mass. Dept. R1

END RADIO BOTHERSTN() YOU KNOW what's wrong when

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He tells in plain words and illustrations how aset is made, what the parts are called, what are thefew usual troubles and how to fix them. Then helists 103 troubles that sometimes happen and tellshow to detect and fix each one.

The book is a regular cyclopedia of radio infor-mation-only it's in a language anyone can under-stand. Read it five minutes and you'll know moreabout radio than you ever dreamed of.

It will save you many a repair man. It will saveyou hours of guessing and fussing and fuming. Itwill help you to keep the tone of your set alwayssweet and strong. It will keep you from losingmany programs. And, best of all-

IT WILL MAKE YOU STOP SWEARING-MUCH TO THE SURPRISE OF YOUR FAMILY-because radio repairs are expensive. Why hire themdone when you can easily learn how to keep your setfrom needing them?

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58

RADIO KIT REVIEWS(Continued from Page 44)

THORDARSON PHONOGRAPHAMPLIFIER

This two -stage all -electric amplifier usinga 210 power tube, converts an old style me-chanical phonograph into a modern highquality electrical reproducing machine. Inaddition to the revolving turntable and elec-trically recorded records, it requires only agood pick-up unit and the easily assembledequipment listed in this kit to get faithfulreproduction of audio frequencies from anygood radio speaker.

The amplifier is operated completely fromalternating current and is so constructedthat it is readily portable. It is exceedingly

05PfEEIR 0 FIELD INPUT (-.

Pictorial Wiring Diagram of ThordarsonPhonograph Amplifier

compact, being 10x10 -in. and may be placedin one of the compartments or in the tonechamber of the phonograph so that no un-sightly or difficult connections to the radioreceiver are necessary.

The power transformers and filter chokesare completely housed in the ThordarsonR-210 Power Compact. This unit furnishespower for the high voltage supply to the plateof the 281 rectifier tube, power for the fila-ment of the same tube, as well as power forthe filament of the 210 power tube. The rec-tifier and filter circuits are conventional, and

furnish to the voltage divider, direct currentfree from hum.

Filament current for the first audio -fre-quency tube is supplied by the current flowingthrough the voltage divider. When the 100 -volt field of the dynamic speaker is connectedto the terminals marked "Field," about 60milliamperes will flow through the field wind-ings of the dynamic speaker and will beavailable for heating the filament of the 199tube.

The plate voltage applied to the plate ofthe 210 power tube is 385 volts, securedthrough the voltage drop of the 5000 -ohmresistor and the field of the dynamic speaker.

LIST OF PARTS

I Thordarson R-210 Power Compact2 Thordarson R-300 Audio Transformers.1 210 Condenser Block (Dubilier, Tobe,

Potter, Acme, Aerovox, Fast, Splitdorf).1 Electrad Fixed Resistor, 5000 ohms, Type

B.1 Yaxley 400 -ohm Potentiometer.3 Benjamin Sockets (Sub -panel).6 Binding Posts, 2 Input, 2 Speaker, 1 Pos.,

1 Neg.3 Benjamin Sub -panel Brackets.1 Pc. Bakelite 10" x 10" x 1/4".1 Pc. Bakelite 10" x 2" x 3/16".

TUBESI UX-281 Rectifier.1 UX-210 Power Amplifier.1 UX-199 Amplifier.

The grid bias of 25 volts is secured throughthe voltage drop through the filament of the199 tube and the 400 -ohm potentiometer. Theplate potential for the 199 tube is taken fromthe high voltage side of the power field of thedynamic speaker, about 125 volts. The gridbias for the 199 tube is obtained from thevoltage drop between the filament side ofthe 400 -ohm potentiometer and the movablearm. The arm should be adjusted for bestresults. The undistorted output of the 210power tube operating under the above con-ditions is about 1200 milliwatts.

In view of the fact that dynamic speakershave incorporated in their assembly an out-put transformer, none is needed in the am-plifier itself. It is to he noted at this point

Circuit Diagram of Thordarson Phonograph AmplifierTell them you saw it in RADIO

that the type of dynamic speaker used mustbe of the high -voltage field type.

If for any reason it is desired to use thisamplifier with other than the dynamic typeof speaker it will be necessary to use anoutput transformer, for the current output ofthe 210 tube is apt to burn out the fine wirewindings of the speaker. The primary ofthis transformer should be connected to thetwo terminals marked "Speaker" and theloud speaker should be connected directlyto the secondary of this transformer. It willalso be necessary to compensate for the fieldcurrent of the dynamic speaker. This maybe done easily by inserting a 2500 -ohm re-sistor in place of the field, that is, connectthe resistor to the two terminals marked"Field."

The Television Clarostat comprises a spe-cial power type clarostat, together with ashort-circuiting push-button, contained in asturdy, ventilated, metal housing with mount-ing feet. The device has a resistance rangeof from 25 to 500 ohms, or sufficient for the

required range of speed. It dissipates up towatts, and is capable of controlling either

a universal or a condenser type motor, on a.c.or d.c., up to /8th horsepower.

The new REL variable condensers foruse in short-wave receivers and wavemeters,as well as low -power transmitters, are rug-gedly constructed with heavy brass plates andhave a rigid three-point mounting whicheliminates vibrations. They can be mountedon a metal panel without necessarily ground-ing either the stator or rotor plates. Therotor shaft is immersed in a pool of mercuryinside the one-piece bearing, thus givingpositive contact. The stator plates are shapedso as to prevent an increase in capacity whenthe rotor plates pass the point at which thestators are joined together. These condensersare made in various capacities, dependingupon the number of plates. The three -plate

model illustrated has a maximum capacity of54 mmfd. The capacity of the two -platemodel may be regulated by moving the statorplate, thus giving a widespread tuning range.

Arcturus hasit-a "heatertype" Power Am-plifier No. 071H!

The whole radio world has beenwaiting for an "Indirectly HeatedCathode" type '71 tube to elimin-ate troubles inherent in the "fila-ment type."

Now-you can experience thenewest in radio-a revelation inradio reception. Put an Arcturus"heater type" tube in every socket.Note the clear, undistorted vol-ume, the better tone qualities, thequicker reception, the extremely

(( An unbiased )\(view of FACTS)'

long life, the im-munity to currentsurge-all the re-quisites for a

perfect A -C tube.Nowhere else can you get these

advantages except in "heater type"tubes. Leading set manufacturers,recognizing this, are using "heater"tubes throughout their receivers.

You can adapt this greater ef-ficiency to your receiver by us-ing a complete set of Arcturus"all heater type" tubes in everysocket. Get a set from your dealertoday.

ergWest Coast Distributors

Universal Agencies, 905 Mission St.San Francisco, California

ARCTURUSA -C LONG LIFE TUBESNewest Radio Hook -Ups --FREE

Send now for the newest radio hook-up book.Shows how easy it is to build remarkablenew A. C. and D. C. receivers of longestrange, greatest volume, purest, clearest toneand super -selective. Also shows how tomake short-wave receivers and adapters, howto use new screen grid tube in A. C. andD. C. circuits, how to build power amplifiersand ABC eliminators. Latest informationon all new radio wrinkles. Send for freecopy now.

KARAS ELECTRIC COMPANY4031L1 North Rockwell St., Chicago, Ill.

Portland, Oregon, 53 4th St.San Francisco, 585 Mission St.Los Arif&iti 324 N. San Pedro

NameSt. and NoCity and State

4031L1

Tell them you saw it in RADIO

SET BUILDERSGettRisBook

Barawlk, the first and oldest rndiospecialty house, offers you uno-11 Iservice this year. Bigger stocks,Quicker shipments, lower prices.Deal with an old established, reliablehouse. Get honest goods, honest service,honest prices. Ilisrawlk service makes youmore money. Send now for big new Catalog show-ing lowest wholesale prices.

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106 Seventh Avenue

POWER AMPLIFIERS--a The possibilities of making

money from power amplificationare unlimited. There is a demandin every city. Manufacturers,jobbers and dealers everywhereare converting their radios and

C radio phonographs into poweramplified, A. C. Electrics, withthis famous Powerizer PowerAmplifier. Power Amplifiers usedfor demonstrating speakers-forauditorium volume.

THE PX-2 POWER AMPLIFIERis a two. stage power amplifier which can be energized from the detectortube of radio set, providing sufficient volume for homes or small halls-frequently used for demonstrating records or speakers by dealers.

$75.00Uses the No. 226 in the first stage, the No. 210 in the second and theNo. 281 as rectifier-is provided with volume control.

POWERIZER P-4This is a Powerizer which substitutes and contains 210 for the laststage and is easily and quickly connected to any radio set; speciallyadapted for use with dynamic speakers; uses a UX-210, UX-281.Furnishes its own A, B and C.Price, less tubes

List price (tubes extra)

$49.50

POWERIZER PXP-250is a very powerful three -stage push-pull amplifier. It is unique in thatthe amount of emerging amplification is unlimited, using our ownsystem of sectional units. Push-pull 250 units may be added at will.Two units are sufficient to fill house with at least 2,500 people;con of one -stage UY-227, one -stage push-pull No. 171, and one -stage push-pull No. 250; has tapped input and output. For tonalquality and power, this is the last word in power amplification.(Tubes necessary-one (1) UY-227, one (1) UX-280, two (21UX-171, two (2) UX-281, and two (2) UX-250--tubes extra.)List Price $250.00All of our units use alloy steel transformers, insuring maximum volumeover the entire audible range. We would be very glad to handle wryspecial problem that you may have on amplification.

THE PIONEERS IN POWER AMPLIFICATION HAVE IMPORTANT NEWS FOR YOULicensed by Radio Corporation of America and Associated Companies. Write for Bulletin PR -4

RADIO RECEPTOR COMPANYMakers of the Famous

pOWERIZER

STRENGTH -INBUILT!BENEATH the attractive exteriors of Aero-

vox Filter Condensers and Filter Blockslies a sturdy framework built to withstand theonslaughts of voltage surges and unusual ser-vice conditions. A true example of StructuralStrength-INBUILT!

EROVlinWrite for the Aerovox Research Worker,a free monthly publication containingmany articles of paramount interest to you!

68-A Washington Street"Built Better"

Brooklyn, N. Y.

REG.

New York City

Two radiomagazines forthe price of

ONE!Hundreds and hundreds of

readers of "RADIO" haveavailed themselves of ourspecial money saving offerwhereby you subscribe to tworadio magazines for the priceof one. "CITIZENS' RADIOCALL BOOK" and "RADIO"-both magazines sent to youraddress for a full year for the

price of a one year subscrip-tion to "RADIO"-$2.50. Thenext issue of the "CALLBOOK" will be out on No-vember first. Better subscribenow to avoid missing it."RADIO" will be sent to youfor 12 months, starting withour December issue, out onNovember 25th. Save $2.50by subscribing today.

MAIL COUPON NOW!COUPON

"RADIO,"433 Pacific Building,San Francisco, Calif.

Here is $2.50. Send me "RADIO" and "CITIZENS' RADIOCALL BOOK" for one full year starting with the DECEMBERissue of both magazines.Name

Street and No

City and State

60 Tell them you saw it in RADIO

DEPENDABLE! EVERLASTING!

100 Volt Edison Element,Non -Destructive Rechargeable"B" Battery with Charger $12140 Volt with Chemical Charger__ $17180 Volt with Dry Trickle Charger $24

Complete knockdown batteries, allsizes at reduced prices. Detector andIntermediate voltages plainly marked.Greater volume and el than any

other eliminator.

Use this couponto receive our interesting booklet.

SEE JAY BATTERY COMPANY913 Brook Ave., New York, N. Y.Please mail me at once your FREE illus-trated booklet describing your batteries andpower units, without any obligation to me.

Name

Street &

Town State_

DescribedIn OuNew 1929 Catalog

I SENT ON REQUEST 1

WHOLESALE PRICES

Professional Set Builders

1

and Dealers!The latest developments of the 1929 season arefully described in our NEW FREE Catalog.Lowest prices on all nationally advertised kits,sets, accessories, cabinets, etc. Get the BESTin RADIO-at the BIGGEST SAVING. Com-plete stock carried. No shipping delays. Writefor Catalog TODAY.TELEVISION-We have complete informationwhich will prove interesting to SET BUILDERS.

WALTER ROWAN CO.833 Washington Blvd., Dept. 101

CHICAGO, ILL.

Set Builders -Dealers! Save Money!Send for the moot complete book of nationally knownParts. K Its, Cabi nets. Consoles. Speaker., Power Units.Sets, etc_ All at lowest wholesale prices. Quick serviceon all your needs. Write now. It Is FItEE-

SETBUILDERS SUPPLY CO.Sept 14-3 Ramberg Bldg. Mathes wad Market Sic CHICAGO. !IL

FERRANTIAudio Frequency TransformersSend 15c in coin for copy of the

1929 Year Book.FERRANTI, INC.

130 West 42nd St., New York, N. Y.

THE MIRACLE OFTHE RADIO WORLD!Newest Guaranteed 7 -Tube1 -Dial Console Set-Worth $200BUY 1929DIRECT MODEL

A BIGVALUE

ALL EL

COMESCOMPLETE

CTRIC RADIO30 DAYS' FREE TRIAL!

A WonderBargain!

Buy directfrom factory.

S200VALUEOutperformssets selling at2 and 3 timesour low price.Includes con-sole shown,made of com-bination wal-nut; A. e.electric set,all tubes.built-in mac-netio speak.. rand aerialequipment,

COMPLETENothing Else to BuyPowerful Reception-Amazing Tone!

Remember -30 days free trial. You be the judge? W.eth8200 and looks It! Only one dial to tune-illuminated!Marvelous mellow tone. Selective and gets distanceeasily. The radio sensation for quality, price and per-formance. Mall coupon today for our big, money -savingFree Catalog, before you buy any radio or accessories[

Battery SetsOur low factory prices onthe complete line of Dia-mond Electric and batteryoperated radical shown Incatalog will amaze you!

Our New FREECatalog-Just

Published-ShowsYou How To

SAVE HALF!Diamond Radio Company

Dept 226 820 S. Clinton St., Chicago, 111.

MAIL THIS COUPON TODAY!

tate

Diamond Radio Company, Dept. 226820 S. Clinton St., Chicago, III.

Please send me your Free Catalog of Diamondradios and details of your 30 Day FREE Trial offer

Name

Address"Its.

.1

Back Copies of"RADIO" Wanted !!I will pay 35 cents each for the

following back -numbers of"RADIO"-

1924-May, Nov., Dec.1925-Jan., March, Dec.1926-Feb., March, May1927-February issue

Only one copy of each issue is wanted

L. G. SCHNELLER504 Forrest Ave., River Forest, Ill.

Tell them von saw it in RAD10

A Vitrohm 507-109 Unitinstalled on your radioset lengthens the life ofthe a.c. tubes by auto-matically lowering thefilament voltage.

This unit costs only $2.00-a small investment ifone set of a. c. tubes issaved.

Write for free informa-tion on the complete lineof Ward Leonard RadioProducts.

WARD LEONARD VeRuNgELECTRIC CO. NEW YORK

INTERESTED IN DX?It's by no means a lost art. Greater distances thaa

ever before can be covered today-if you know how.Try some of the ingenious stunts described In "TheGateway to Better Radio"-that big, unselfish, under-standable manual of 20,000 words and 88 illustra-tions, which is yours for 25 cents a copy. Get yourstoday from your dealer or direct fromClarostat Mfg. Co., 285 N.6th St., Brooklyn, N. Y.

C LA 5TAT.PAT.REG.REG. U. S.

Send ForWESTERN RADIO

1929CatalogDealers and Set Builders

THE NEW 1929 CatalogIs crammed full of the

FINEST, NEWEST, Nation-ally known A.C. sets, con-soles, cabinets, dynamicopeakers, kits, eliminatorsand accessories at LOWESTPRICES. Largest stock ofradio parts. Prompt delivery.Write for our FREE catalog.Western Radio MEg. Co.128 W. Lake St., Dept. R-11

CHICAGO

a

Clhe BfMend yRadio House'

FRSr

Don'tBurn Out TubesOne of the chief troubles in the

new A. C. sets using either A. C.tubes or D. C. tubes in series isparalysis or damage to the tubesdue to incorrect filament voltage.This invariably can be traced to linevoltage, which in some localitiesvaries considerably throughout atwenty-four hour period. In the setsusing the new A. C. four and fiveprong tubes it is very importantthat the filament voltage is right, asit is sometimes found that a par-ticular filament setting is necessary to eliminate hum.

All of the above troubles call for some definite method of adjustment andthis can be best accomplished by a suitable A. C. voltmeter having rangeswhich cover the trouble expected.

Such an instrument and one used by many service men in their work is the JewellPattern 77 triple range portable A. C. voltmeter. It is a very desirable instrument for the setowner as it enables him to operate his set at safe filament voltages at all times. The com-bination range is 0.3-15-150 volts. The scale is silver etched with black characters, and themovement is mounted in a metal case on a bakelite base.

Every owner of an A. C. operated set should have one. Write for descriptive circularNo. 1145.

Pattern No. 77

Jewell Electrical Instrument Company1650 WALNUT STREET, CHICAGO

"28 Years Making Good Instruments"

FREE RADIO IBOOK

AND NEW SUPPLEMENT C44 pages chock-full of vital information for setbuilders and all radio enthusiasts. 16 new easy -to -build circuits-receivers, transmitters, radiophones,short wave. Complete construction data, schem-atics, photos, etc. Also full information about Aeroair -dielectric coils. Write for FREE copy TODAY.Address AERO PRODUCTS, Inc., Dept. 764,4611 Ravenswood Ave., Chicago, Ill.

w. SHERMANSQUARE

HOTEL70y ST.

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FOP TWO 1400 (.9

NEW SHIELDEDSUPER -10

5 Screen Grid R. F. Amplifiers

4 Stage Power A. F. Amplifier

A new and Superior Receiver,representing highest type of effi-ciency obtainable, in point ofextreme range, selectivity and

quality of reproduction

Illustrated literature gratis

Complete Constructional Blue Prints$2.00, postpaid

NORDEN-HAUCK, INC.Builders of Highest Class Radio

A ptaratus in the World

Marine Bldg., Philadelphia, Pa.

Cable Address "NOMA UCK"

62 Tell them you saw it in RADIO

RADIOADSA CLASSIFIED ADVERTISING

SECTION READ BY BETTERBUYERS

The rate per word is eight cents net.Remittance must accompany all adver-tisements. Include name and addresswhen counting words.Ads for the December Issue Must

Reach Us by November Fifth

MAKE MONEY WITH PATENTS! We offepatents with money -making possibilities; circularfree. Floyd Clymer, Denver, Colo. (3T)

IMAGINE AN ORGANIZATION of radio"nuts" with over 3000 clients scattered throughoutthe world, hundreds of them hams. all of themradiowise-dealers, builders, experimenters. Over$40,000 stock of high-grade receiving and transmit-ting parts only, no sets. Spend over $5,000 yearlyon our own experimenting, carry nothing until itpasses our tests. 25c will bring prepaid over fourpounds, catalog. circuits, data, etc. Weekly datasheets for experimenters and builders (more reliabledata than all radio magazines together) -20 weeks,$1.00, 52 weeks, $2.50. Full dealer's discounts tolicensed hams, and radiowise builders. We carryapproved items advertised in "RADIO." KladagRadio Laboratories. Established 1920, Kent, Ohio.

(6T)

WANTED-Men to work with National RadioService organization. No selling scheme. RadicDoctors, Inc., Dept. R, Essex St., Salem, Mass.

DEFECTIVE AUDIO TRANSFORMERS Re-claimed Using Factory Windings, Original Guar-antee-$0.90. Reclaimed transformers for sale.most makes, $10.00. Inquiries invited. TRANS-FORMER RECLAIMING SERVICE, 9 SouthReed Ave.. Mobile, Alabama.

CHILLICOTHE WALNUT CABINETS. 7x26inches and II inches deep. Genuine walnut withfull length piano hinge. Several of these are instock. Never used. Originally purchased for edi-torial photographing. Retail price $30.00. We willsell these while they last for $12.50, express charges -collect. Eight on hand. Publishers of "RADIO,"Pacific Building, San Francisco, Calif.

ELECTRICAL BARGAINS. - New 1/4 -HPWestinghouse 110 volt, 60 cycle, 1750 speed alter-nating motors with pulleys, $8.75. Variable speed.motors for television 110 volt alternating current,$7.00. Also other sizes motors and generators. Elec-trical Surplus Co., Dept. 1, 1911 Chicago Ave.,Chicago.

FOR SALE.-Latest model Best's Shielded GridSuper without cabinet. Perfect condition. $100.Address Owner, 1129 Mandana Blvd., Oakland, Cal.

NAVY SURPLUS offered at fraction of originalcost. General Electric 24/1500, 24/750, 12/350volt. Holtzer-Cabot 12/500, Westinghouse 10/350.Battery driven also adapted for external drive. 50C.and 900 cycle generators. All ball bearing. Litera-ture. Henry Kienzle, 501 East 84th Street, NewYork. (2T)

KENNEDY TUNER, 200-3600 meters; Magna-vox 2 -stage amplifier, tubes; Magnavox dynamichorn. Lot $25.00. Roy Strong, Manteca, Calif.

FOR SALE!-Gerald Best's "Modernized" 45 -KC super exactly as described in the editorialcolumns of October "RADIO." This receiver was -built by G. M. Best for use in gathering editorialmaterial for the story, and the publishers of"RADIO" will sell the receiver, as illustrated, for$75.00. A fine genuine walnut cabinet with pianohinge is included in the price. In perfect conditionand accurately matched and balanced. First moneyorder for $75.00 takes it. Set will be shipped toyou express charges collect. PUBLISHERS OF'"RADIO," 433 Pacific Bldg.. San Francisco, Calif.

BIG PAY.-South American work. Americanfirms pay fare, expenses. South American ServiceBureau, 14,600 Alma, Detroit, Mich.

RADIO STATION stamps bought, sold and ex-changed. Chas. A. Phildius, 510 East 120th St.,New York, N. Y. (4T)

USE THE CLASSIFIED ADSIN "RADIO"

They Bring Results

Mail Your "Ad" Now

AIR-RINq

PATENTS PENDING

12.50

Per Set asIllustrated

THE ULTIMATEin Precision Short Wave Plug-in Coils

THE Air -King Precision short wave coils have been built scientific -ally to meet all the exacting requirements of high frequency work,

such as extremely low losses, rugged construction and permanencyof calibration.(1) The low loss feature has been obtained by winding the turns "onair," and by using the least possible amount of solid dielectric. Thedielectric is all air except at the few places where the wire touches thelateral ribs upon which it is wound. The turns are spaced so that thedistributed capacity is very low. This decreases the losses and increasesthe tuning range of the coils.(2) Ruggedness in an unusual degree has been secured by riveting thelateral ribs firmly to the sturdy bakelite end pieces. The ribs aremounted edgewise so that they offer the greatest resistance to bendingunder the stresses set up by the tightly wound wire and so that theleast amount of solid material comes in contact with it. The strengthis so great that a coil may be dropped on the floor from a distance ofseveral feet without the slightest damage or change in the shape of thecoil or in the alignment of the wires. You cannot disturb the coil con-struction by twisting with your hands, although you exert all yourstrength. A coil can also be inserted into and taken out of the coilreceptacle times without number, and remain unimpaired. This is animportant feature in plug-in coils which must be inserted in andremoved from the base many times.

Price

(3) Permanency of calibration is also an important feature secured bythe rugged construction. The wires cannot shift, for they are firmlyheld in the slots in the ribs. Hence both the inductance and thedistributed capacity of a coil remain fixed. It is thus possible to log areceiver built with these coils with the assurance that the log orcalibration chart is valid every time the same coil is inserted and thesame tube used.(4) The coils are designed to tune with a condenser having a maximumcapacity of .00014 mfd. When a condenser of this value is used the setof coils will cover the entire short wave band from about 15 meters to133 meters with suitable overlapping of ranges for the separate coilsto prevent any dead spots.(5) The tickler winding on each coil has been designed so that whena regeneration condenser of .00025 mfd. is used, oscillation control atall settings of the tuning condenser is complete.(6) The same antenna coil is used for all the tuning coils, therefore, itis mounted on the coil receptacle. So that the required degree of coup-ling may be obtained for any of the tuning coils, at any setting of thetuning condenser, for any range of frequency, and for any antenna, theantenna or primary coil is mounted on hinges. The primary may beturned as required to given maximum signal strength in any case and isheld securely in place by friction.

$12.50 per Set of 3WAVELENGTH RANGES OF THESE COILS

The tuning ranges of the three coils of the Air -King kit, when used with a .00014 mfd. tuning condenser, are as follows:No. 1-Small coil -15 to 331/2 metersNo. 2-Intermediate coil -311/2 to 68 metersNo. 3-Large coil -57 to 133 meters

These wavelength ranges are engraved on each coil frame. Other coils available in ranges up to the broadcast bandand down to 8 meters.

MFD. by AIR-1(1NQ PRODUCTS CO.216 WALLABOUT ST. BROOKLYN,N.Y., U.S.A.

rOrder from Offenbach if you live in the West. > > > Order from Factory if you live in the East.r

OFFENBACH ELECTRIC CO.1452 Market Street,San Francisco, Calif.Here is $5.00. Send me by parcel post at once a set ofAir -King Short Wave Plug-in Coils as advertised inNOVEMBER "RADIO." The small balance is to be paid byme C.O.D. upon receipt of shipment. Dealer discounts areallowed if your order is attached to your letterhead.

I

I

I

I

City and State

RADIO DEALER'S SUPPLY SERVICEWholesale Division of

Name

Street and No.

I

I

I

I

IIIIII

Street and No.

AIR-KING PRODUCTS CO.216 Wallabout Street,Brooklyn, N. Y.Send me immediately one set of AIR -KING SHORT WAVEPLUG-IN COILS as advertised in "RADIO." I enclose$5.00 in part payment. Balance C.O.D. It is understood thatthe usual discount is to be allowed to me if I am a dealer orjobber.

Name

and Stateass

Tell them you saw it in RADIO 63

I Will TrainYoua at Home to Filla Big PaRadioJob

Here.i thePROOF

Made $185 inThree WeeksSpare Time

"1 have met withcontinued success.For Instance, re-cently I realizeda profit of $185in three weeks,

$1.50 an hour. I have beenmaking good money almostfrom the time I enrolled. TheN. R. I. has put me on thesolid road to success."-PeterJ. Dunn, 901 N. Monroe St.,Baltimore, Md.Made $588 in One Month

training Ireceived fromyou has done mea world of good.Some time agoduring one of ourbusy months Imade $588. Iam servicing allmakes of Radio receiving sets.My boss is highly pleasedwith my work since I havebeen able to handle our entireoutput of sets here alone."-Herbert Reese, 2215 So. E St.,Elwood, Indiana.

Earns Price of Course inOne Week Spare Time

"I have been so busy withRadio work that I have nothad time to study. The otherweek, in spare time, I earnedenough to pay for my course.I have more work than I cando. Recently I made enoughmoney in one month sparetime to pay for a $375beautiful console all -electricRadio. When I enrolled Idid not know the differencebetween a rheostat and a coil.Now I am making all kindsof money."-Earle Cummings,18 Webster St., Haverhill,Mass.

If you are earning a penny less than $50 a week, sendfor my book of information on the opportunities in Ra-dio. It's FREE. Clip the coupon NOW. A flood of goldis pouring into this new business, creating hundreds ofbig pay jobs. Why go along at $25, $30 or $45 a weekwhen the good jobs in Radio pay $50, $75 and up to$250 a week? My book "Rich Rewards in Radio" givesfull information on these big jobs and explains how youcan quickly become a Radio Expert through my easy,practical home -study training.

Salaries of $50 to $250 a week not unusualGet into this live -wire profession of quick success.

Radio needs trained men. The amazing growth of theRadio business has astounded the world. In a few shortyears three hundred thousand jobs have been created.And the biggest growth of Radio is still to come. That'swhy salaries of $50 to $250 a week are not unusual.Radio simply hasn't got nearly the number of thoroughlytrained men it needs. Study Radio and after only a shorttime land yourself a REAL job with a REAL future.

You Can Learn Quickly and Easily in Spare TimeHundreds of N.R.I. trained men are today making big money

-holding down big jobs-in the Radio field. Men just like you-their only advantage is training. You, too, can become aRadio Expert just as they did by our new practical methods.Our tested, clear training makes it easy for you to learn. Youcan stay home, hold your job, and learn quickly in your sparetime. Lack of education or experience is no drawback. You canread and write. That's enough.

Many Earn $15, $20, $30 Weeklyon the Side While Learning

My Radio course is the famous course "that pays for itself."I teach you to begin making money almost the day you enroll.

My new practical method makes this possible. I give you SIXBIG OUTFITS of Radio parts with my course. You are taughtto build practically every type of receiving set known. M. E.Sullivan, 412 73rd Street, Brooklyn, N. Y., writes: "I made$720 while studying." Earle Cummings, 18 Webster Street,Haverhill, Mass., "I made $375 in one month." G. W. Page,1807 21st Ave., Nashville, Tenn., "I picked up $935 in myspare time while studying."

Your Money Back if Not SatisfiedI'll give you just the training you need to get into the Radiobusiness. My course fits you for all lines-manufacturing, sell-ing, servicing sets, in business for yourself, operating on boardship or in a broadcasting station-and many others. I back upmy training with a signed agreement to refund every penny ofyour money if, after completion, you are not satisfied with the

course I give you.

ACT NOW -64 -pageBook is FREE

Send for this big book of Radioinformation. It won't cost you apenny. It has put hundreds offellows on the road to bigger payand success. Get it. Investigate.See what Radio has to offer you,and how my Employment Depart-ment helps you get into Radioafter you graduate. Clip or tearout the coupon and mail itRIGHT NOW.

J. E. SMITH, President,Dept. 33-R,

National Radio InstituteWashington, D. C.

- A.-_1-...JP-

RAIONEEDS

TRAINEDMEN!

Lm loyment Salim to all 6IOrifinators of Radio Home SktbfTraininkj

uates

t4 Tell them you saw it in RADIO

You can buildloo circuits withthe six big outfitsof Radio parts

I give you

3 of the 100youcan build

Find out quickabout Thispractical;tayto big pay

J. E. SMITH, President,Dept. 33-R, National Radio Institute,Washington, D. C.

Dear Mr. Smith: Kindly send me your big book"Rich Rewards in Radio," giving information onthe big -money opportunities in Radio and yourpractical method of teaching with six big outfits.I understand this book is free, and that this placesme under no obligation whatever.

Name AgeAddress

City State._...._.........Occupation

Tobe Type 250 B -Block

B BLOCKS-Model 760

VACUUM MECO LEAKS

TOBE 1300 Line Hi -Voltage

SURGPROOF Condensers

TOBE 'A -Condenser

TIINYTOBE Condenser*

A manufacturer can haveno greater faith in hisproducts than to guaran-tee their faithful operal.tion and with such gua-rantee TOBE productsare sold.

The test of the manufacturer's faith inhis products is how long will he guaranteethem. Tobe apparatus is unconditionally

guaranteed for one year.

tElp FILTER CONDENSERS

TOBE A -Filter

Radio Interference Filter No. I.

S WATT VERITASFITS ALL STANDASO. MUMS

1000 Volt & 2000 VOie

Transmitting Condenser

TOBE By -Pass FilterCondenser New Model

THE MECHANICAL MASTERPIECE

NEW 1929

Eight tubes in line-aluminum constructionthroughout-all powerequipment an integralpart of chassis-thisyear's masterpiece ofmechanical precision.

ake

EIGHT IN LINE

Special Browning -

Drake circuit, famousfor tone quality anddistance-cabinet ofselected walnut withhand -rubbed Duco fin-ish. List $135.00.

In radio sets, as in most everything else, you get about what you pay for. Thecheapest is never the best.

Your customers are willing to pay a little more and get a Browning -Drake.Refinements, which make for beauty, power, and tone quality, are obtained

through precision assembly, rather than mass production. Among those whoappreciate and require the best, Browning -Drake is the outstanding choice.

Quality never fails to satisfy.

BR NGTRADE MARK

Preis ofTHE JAMES H. BARRY COMPANY

SAN FRANCISCO, U. S. A.