LOUD -SPEAKING ON SHORT WAVES - WorldRadioHistory.Com · 2020. 5. 11. · May 5th, 1926. Vol. 8. No. 12.-THE 100% VALVE PAPER LOUD -SPEAKING ON SHORT WAVES A SUPERHETERODYNE ADAPTER

May 5th, 1926.

Vol. 8. No. 12.

-THE 100% VALVE PAPER

LOUD -SPEAKING ONSHORT WAVESA SUPERHETERODYNE

ADAPTERBy L .H. THOMAS

-"' ,

ilmilinnupti011111111

2 WIRELESS WEEKLY ADVERTISEMENTS MAY 5, 1928

4Published

1St ofevery month.

Price

1 '''

Monthly.

MODERN WIRELESS, the original I/. monthly Wire-less magazine; fully maintains its high standard.Every issue contains articles interesting and instructiveto you. Take it regularly and keep pace with your hobby.

A SUPERHETERODYNE FOR THEOPEN Ant By C. P. Kendall, B.Sc.A portable receiver which will appeal to

all who desire a set for use in the open airand which gives a wide choice of pro-grammes on the loud -speaker from Britishand foreign stations.

A MASTER OSCILLATOR TRANS-MITTER. By R. W. H. Bloxam (5 LS).Transmitters will be particularly in-

terested in this efficient 10 -watt trans-mitter for working on 45 metres.

A SINGLE CONTROL FOUR -VALVERECEIVER. By A. Johnson -Randall.This set has been designed with a single

control for the reception of the local stationand Daventry. Music lovers will appreciatethe pure reproduction given.

A COMBINED REACTION THREE -VALVE RECEIVER. By E. H. Berry.The provision made for varying the

inductive reaction and capacitative controlenable the best proportion for smoothworking to 132 secured.

AN INDISPENSABLE TESTING UNITBy H. J. Barton-Chapple, Wh.Sch., B.Sc.(Hons.), A.C.G. I., D.I.C., A.M.1.E.E.This simple unit enables accurate

measurements of resistances and capacitiesto b^ made and will prove useful to allconstructors and experimenters.

A MULTIPLE CIRCUIT SINGLE -VALVE RECEIVER. By E. J. Marriott.Several types of aerial and reactioncoupling arrangements can be tried withthis set.

OTHER INTERESTING FEATURES.CIRCUITS THAT WILL NOT HOWL.

By J. H. Reyner, B.Sc. (Hons.), A.C.G.I., D.I.C., A.M.I.E.E.SINGLE OR MULTI -VALVE? - - - By Percy W. Harris, M.I.R.E.IMPROVISING AERIALS FOR THE COUNTRY OUTING. By A. V. D. Hort, B.A.LOCAL RECEPTION ON FRAME AERIALS. - - By D. J. S. Hartt, B.Sc.

Obtainable from all Newsagents, Booksellers and Bookstalls or direct fromThe Publishers. - (Subscription Rates, 15/- per annum; 7'6, 6 months.)

Radio Press, Ltd., Bush House, Strand, London, W.C.2.

i,

Wireless

MAY 5TH, 1926 ADVERTISEMENTS WIRELESS WEEKLY' I -

ARE YOU A PATIENT MAN ?

[20 0OF YOU ARE

" Let's see- five separate units give five capacities,taken singly. Then I can have the first two inseries or parallel-total seven. Then the firstthree all in series or all in parallel --two more.The first and third and second and third in series,total 9. Ditto, in parallel, 11. First and secondin series, and in parallel with the third 12.... And the total number of different capacitieswi,h the five units is ? " What is it ?

If you get it right,you win £200 !

Whatever your skill in counting capacities, how-ever, the purchase of a Dubilicon will bring youone sure reward. The Dubilicon gives anycapacity up to 0'011 mfd. simply by varying theconnections of the eight unit capacities of whichit is composed ; so that by using the Dubiliconyou will be able to select with unfailing certaintythe best value of fixed capacity for any desiredpart of your circuit.The Dubilicon is a multiple condensereight separate units, the terminals of each unitbeing brought out to sockets on the lid. Byusing Clix plugs (made by Messrs. Autoveyor",Ltd., 84, Victoria Street, S.W.1) of which twoare given with every Dubilicon, the units can beconnected in a variety of series, parallel and com-bined series parallel arrangements giving a verylarge number of different capacities.The uses and advantages of the Dubilicon, whichwe have summarised above, make it more thanworth its low price of 30/-,In addition, the purchase of a Dubilicon entitlesyou to enter for the £200 prize competition. Allyou have to do is to estimate the number ofdifferent capacities you can get by connectingup the first five units in various ways.Ask your dealer about one to-day-and mind youenter for the £200 competition ! He will tellyou all about it !

RE C.1STE RED

81 LIE-

TRAOE MARK

DUBILIERCONDENSER CO (1925) LTD

A nvERT. OF THE DUBILIER CONDENSER CO. (1925) LTD., DUCON WORKS,VICTORIA ROAD, N. ACTON, W.3. TELEPHONE: CHI,WICK 2241.2-3.

F P.S. 193

AN ADVERTISEMENT IN " WIRELESS WEEKLY " IS A GUARANTEE OF SATISFACTION TO BUYERS.

WIRELESSii WEEKLY ADVERTISEMENTS MAY 5, 1926

Reducedfacsimile of

ilectron EarthMat

BETTER RESULTSFROM THIS SIMPLEAND INEXPENSIVEAERIAL and EARTHLOTS MORE FUN !Listening -in is the greatest fun in the world. Thereare programmes of every description which pleaseboth young and old.For perfect reception a good aerial and earth system

is more than half the battle. The most ingenious and expensiveset will not give satisfactory results if the aerial and earth systemis bad.Use ELECTRON WIRE or SUPER IAL and make sure ofperfect reception by completing the circuit with the ELECTRONEARTH MAT, the most amazing earth ever devised.Many crystal users do not know the capabilities of their sets, andare generally satisfied with very ordinary reception. They hearsomething-a tinkle of music, a whispered talk-and that's allthey expect.Tell them to install the SUPER IAL and ELECTRON EARTHMAT and they will he amazed at the increased volume.

t h-EL

k214:Ii4 LI 11° k A A

THE PERFECT EARTHCHEAP, SIMPLE AND PERFECTThe ELECTRON EARTH MAT is supremely efficient.Its very simplicity compels it. The enormous surfaceoffered by the innumerable strands of the fine mesh ofwhich it is composed affordsunusual freedom of releaseto the high frequencycurrents. The ELECTRONEARTH MAT is made of themost expensive phosphorbronze fine-grained gauze,mounted on a strong metalrim, to which is fixed 25 feetof EARTH WIRE, complete.Remember the price alsoincludes 25 feet of EARTHWIRE already fixed.

2/6Postage 6d.

143W easy it is to run the Famous ELECTRONEXTENSION WIRE from the set in one roomto the loud speaker in another, or even outdoors !Furthermore, you actually get improved receptionbecause the EXTENSION WIRE considerablyenhances the musics! tone.

THE KING F AERIALSEXTRA HEAVY INSULATIONFOR LONG-DISTANCE RECEPTIONThe mathematical combination of heavily tinned strandswith a plated copper core in SUPERIAL-the King ofAerials-greatly improves the reception, both of voice andinstrumental music. SUPERIAL, 1,,ing insulated withextra -heavy vulcanised rubber, renders insulators anunnecessary extravagance, besides increasing the long-distance range of your set.

2/6Postage 9d.

IncludingWoodenSpool.

50 feet 100ft. (50ft. double) - 2/-1 (25ft. double) 300ft. (150ft. double) - 5/-

1/- 500ft. (250ft. double) - 8/ -Carriage Paid.

Postage 3d. Any length supplied.

If unobtainable from yo tr Dealer send direct to us, together with HIS NAME ANDADDRESS, and we will deliver promptly by return. Do not be persuaded to buyanything else.

NEW LONDON ELECTRON WORKS, LTD.Dept. No. 65. (Members of the B.B.C.)

EAST HAM, LONDON, E.6.Telephones Grnngewood 1408-1409. Telegrams " Stormont, London."

AN ADVERTISEMENT IN " WIRELESS WEEKLY IS A GUARANTEE OF SATISFACTION TO BUYERS.

MAY sTit, 1926 ADVERTISEMENTS WIRELESS- WEEKLY ii -

r_lllll ini)

..re V V or V nue V she V nue V,.. V %.0Vs1.0 %I V na

Phone: City 9911EDITED Ev-

JOHN SCOTT-TAGGARTgechnicai editor :

J. ILREYIVER ElSeWons, I. A C.G.I,DIC,A.MIEE."A/.n se1a " Â^ A en A." " "Ai% A ^sr

Loud -Speaking on Short Waves. By L. 11Thomas (6QB)

Is Your B.F. Choke a Source of Loss ? ByW. S. Percival, B.Sc. (Hons.), A.R.C.S.

Short-wave Notes and NewsA Model Radio House -

Circuits that will not Neutralise. ByJ. H. Reyner, B.Sc. (Hons.), A.C.G.I., D.I.C.,

Getting the Best from the " NeutrollexTwo." By N. J. Gibson

CONTENTSPage Page

Wireless News in Brief 372

(1111111111111111111111111111,,

<

Non -Radiating Single -Valve Circuits. Bythe Staff of the Radio Press Laboratories

The Week's Diary Circuits for the Experimenter, No. 12 Readers' Comments ...Practical Topics. By G. P. Kendall, B.Sc.New Radio Press Envelopes ..Apparatus we have Tested

371 Is Your Problem Here ?

359

363365366

368

373

375

377379381

382383

385

Nothing contained hereto is to be regarded as permission 1-1.0-0".# or encouragement to infringe any patent rights:l IMP

llllll I llllll UM1111111111111111llllllMIMMI llllllllllll llllllllMI lllll llllll lllllllllllll llllllllllllllllllllllllllllllll llllllll

RADIO PRESS, LIMITED,ammommommi

141=11111111111=1

TEMPRYTES(REGD. TRADE MARK.)

The Perfect Control for allValve Filamentsi 11Manufaclured in values , 2I6 , Holder Mountings for I

. to suit all valve;. From ,

I I'3 to 50 ohms. I Temprytes - 1/6 each. I

i 1 each. i I

Full particulars with valve chart on application.

Grounded

'00 I'0005'0003'00025'0002'0005'0003

The absolute

Square Law.Mfds. 21/- each

17/616/6 With16/- 4' Knob15/6 Dial.

Dual 27/625/-

L 0(pronounced Sil-don)

Rotor Condenserspinnacle of Condenser Perfection,

Straight Line Frequency.'0005 Mids. - - 15/6 each'00035 - - - 15/ -

Large 4' Knob Dial, assupplied with SquareLaw Condensers - - 2/-

ALL POST FREE BY RETURN ON RECEIPT OF REMITTANCE.

ManEur;amctuthreers : SYDNEY S. BIRD & SONS,Cyldon Works, Sarnesfield Road, Enfield Town.

Phone ENFIELD 672.

Bush House, Strand, London, W.C.2

Anyone can build- and operate-the

KeystoneSuper-HetTlIg Super -Het has been regarded in the

past as an instrument which is diffi-cult and costly to build and complicated inoperation. This idea has, however, nowbeen dispelled ; for, by the Keystonemethod, you can build a really trust-worthy Super -Het, quickly and economic-ally. In operation it is the essence ofsimplicity - the whole range of wave-lengths is covered by means of plug-ininterchangeable oscillator. couplers, theprinciple of which will be seen in theillustration alongside. In the Keystone,in fact, all the advantages of a Super -Hetare available for the first time withoutits costliness and complicated working.

You can listen to more than 30Stations on the Loud Speaker

if you build a

KEYSTONESIMPLIFIED SUPER - HET

(BUY THE KEYSTONE BOOK'\Everything you want to know aboutSuper -Het work will be found in thego pages of the Keystone Book. Itsmany simple diagrams and clear photo-graphs will enable anyone .to build areal Super -Het. Price4/6,,post free,

1 or complete with full size Blue '931 /Prints, 3/-, Write for itto-day tial

PETO - SCOTTCo., Ltd.,

77, City Road, E.0 .1Branches at

62, High Holborn, W.C.I,Wahhamslow, Liverpool

and Plymouth.

AN ADVERTISEMENT IN " WIRELESS WEEKLY IS A GUARANTEE OF SATISFACTION TO BUYERS.l'6. 5097

iv WIRELESS WEEKLY ADVERTISEMENTS MAY 5, 1926

BURNDEPTCOMPONENTSwhich ensure perfect filament control.

BurndeptFixedResistors

From .75 ohms 2 ampsto 55 ohms .25 amps.

1/6 to 2/.

Burndept Screw Holdersready for mounting either onwood, ebonite, or behind a panel.

1/6 each.

Burndept Dual Rheostat(5-30 ohms)

6/.

BURNDEPTFIXED

RESISTORSconsist of fibre rods wound with resistance wireand adjusted accurately to definite resistances.They are intended for use either in place of arheostat to control the filament current of valvesor in series with an ordinary low -resistance rheostatwhen it is desired to modify an existing receivingset to operate with various low temperature valves.

On sets- fitted with Shorting Plugs it only occupiesa moment to replace the Shorting Plug with afixed Resistor of a value suited to any valve itmay be desired to use and without otherwise alteringthe set. Suitable screw holders for fixing BurndeptResistors may be obtained. By fitting the BurndeptDual Rheostat (5-3o ohms), a bright or dull emittervalve can be used as desired. This component isnow made in a new form embodying improvementsand suitable for one -hole fixing.

The Burndept range includeseverything for efficient radioreception. Components,GUARANTEED SUPER -VALVESand complete installations.Ask any Burndept Dealer to

demonstrate them.

l_IL3URNDEPIT:j,'/V17,7/.77:,'V,7"OCA

Aldine House, Bedford Street, Strand,London, W.C.2.

Telephone: Telegrams:Gerrard 9072 (4 lines). "Burndept, Wesirand, London."

BRANCHES AND AGENTS EVERYWHERE.

AN ADVERTISEMENT IN " WIRELESS WEEKLY Is A GUARANTEE OF SATISFACTION TO BUYERS.

May 5, 1926

V4

NI

Edited byOHN SCOTT-TAGGART,

EInst.IP.. A.M.I.E.E,Technical Editor

J. H. REYNERB. Sc. (Hons

Wireless WeeKly

Loud -Speaking on Short WavesA SUPERHETERODYNE ADAPTER FOR EXISTING SETS

By L. H. THOMAS (6QB).This simply -constructed superheterodyne unit is designed to operate in conjunctionwith an ordinary short-wave receiver, so that either C.W. or telephony signals may

be heard at full loud -speaker strength.

HE average recep-tion enthusiast'sopinion of super -heterodynes is, ifthe remarks of thewriter's acquaint-

ances are any criterion, that theyare hard to construct, harder stillto operate, and consume

aan enormous mount ofcurrent, in addition totheir initial cost beingvery high. The super-heterodyne " unit " de-scribed in this article wasconstructed with some-what less trouble than isgenerally experiencedwith a " straightreceiver, is reasonablyinexpensive, and con-sumes a total filamentcurrent of .38 ampere.It was, in fact, madefor the purpose of show-ing that a superhetero-dyne need not be beyondthe capabilities or the purse of themajority of users of the popular" detector and note-mag."

Autodyne CircuitIt is by now fairly well known

that when it is desired to use asuperheterodyne on the higherfrequencies there is no need to

use a separate oscillator in con-junction with the first detector, oreven to employ, the well-known

Tropadyne " circuit, since thepercentage detuning necessary toobtain a beat note with the in-coming signal is small enough tobe practically negligible. A

Only the input and output terminalsthe front panel.

straight autodyne circuit is per-fectly efficient for the initial detec-tion and. heterodyning of thesignals. For this reason thewriter thought it advisable toconstruct, for short-wave work, asuperheterodyne " unit " which_may be added to any existingsingle -valve' set just as simply as

are mountedon

if it were a low -frequencyamplifier.

A Separate UnitThe short-wave set might then

be kept .quite separate, and dif-ferent circuits could be employedfor the first detector, the " super -

het " part of the appara-tus remaining quitestandard and untouched.during these experi-ments, which would berendered much moresimple by this arrange-ment. The ends of thewinding of the " filter "transformer are there-fore simply brought outto two " input " ter-

" minals on the left-handside of the front panel,and these are connectedto the- *telephone ter-minals of any single -valve receiver (whichmust, of course, be made

to oscillate) that it is desired totry out.

It should be mentioned herethat, unless a separate oscillatoror a " Tropadyne " circuit isemployed, this arrangement willnot be efficient on the broadcastfrequencies ; it is, however,eminently suitable for the recep-

359

Wireless Weekly

LOUD -SPEAKING ONSHORT WAVES

(Continued)

tion of KDKA, WGY, and, in fact,all stations employing frequencieshigher than about 3,000 he. (i.e.,wavelengths below loo metres).

-

Valve ArrangementAs will be seen from the photo-

graphs and diagrams, the construc-tion of this set is quite a simplematter. Actually, to assemble itand get it into thorough workingorder took much less time than isusually spent on 'a three- or four -valve receiver. Five valves are in-corporated in this unit, three of thesebeing amplifiers at the intemediate

fiLTER

a - C71

should it be desired to listen onheadphones, as it is usually dis-tinctly uncomfortable to do so withthe note -magnifier in circuit. Aloud -speaker is generally left in theanode circuit of the last valve, andit is not often found necessary totune in with the headphones in cir-cuit, so great is the strength 'ofsignals. The writer, however,

0 0 0

Compact layoutis a feature of

the set.

0 0

always prefers telephones whenlistening to C.W., and for this pur-pose the L.F. valve is very rarelyemployed.

The battery terminals are affixed,in the conventional manner, to astrip at the rear of the set. Threehigh-tension positive terminals areprovided, one supplying the voltagenecessary for the intermediate-.frequency amplifier, and the others

I. F.

4

3

6 .001

POT EN T9

May 5, 1926

interaction between these is capableof causing a great deal of trouble inoperation. Fortunately the conven-tional superheterodyne circuit lendsitself to a neat layout and shortwiring. The simplicity of the latterwill be apparent from the back ofpanel photographs.

ControlsThe controls on the front panel,

four in number, are simply a poten-tiometer controlling the grids of thethree intermediate -frequency ampli-fiers, and three rheostats. One ofthese latter is wired in series with ar7 -ohm fixed resistor, and controlsthe filaments of the I.F. valves; thesecond, in series with a similarresistor, the filament of the seconddetector, and the third is wired inthe filament circuit of the note -magnifier, no resistor being used inthis case.

Filament SupplyA six -volt accumulator is used to

supply the filaMent current for allthe valves, and provided that thevariable resistances used Lave aresistance of not less than 30 ohms,valves of the .o6 ampere type maybe employed as the I.F. amplifiers.Actually the writer employs, inaddition to these, ,a valve of theP.M.4 type as second detector, andeither another of this type as thenote -magnifier, or one of theB.T.H. B7 (6 volts, .o6 ampere)type. In any case, if a six -volt:

MAT

Cs

, +1

T2

L.S.

5

5

0+2-4)+3

H.T.

3

C +L.T.

Fig. 1.-The terminals for the telephones place them in circuit in the position shown dotted in the diagram.frequency, one the second detector,and the last an ordinary stage of.note magnification.

Loud -Speaker or TelephonesTerminals are provided for con-

necting the telephones across theprimary of the L.F. transformer,

the potentials for the second detectorand the note magnifier.

Layout of ComponentsProbably the most important

feature of the layout of the com-ponents on the baseboard is thespacing of the I.F. transformers, as

4C. B.

accumulator is used, the fixed re-sistors in the filament circuits of theI.F. valves and the second detectorwill be necessary.

Special ConnectionsThe grid of the second detector,

which employs the grid condenser360

May 5, 1926 Wireless Weeklyand leak method of rectification, istaken through the secondary wind-ing of the last intermediate -fre-quency transformer, not to thecentre point of the potentiometer,but straight to the positive low-tension terminal. It should be notedthat all the rheostats and resistorsare wired in the negative filamentleads of the valves that they control.The capacity of the grid condenserneed not be greater than .0003, butthe grid -leak should have a fairly lowvalue. The writer uses one of .5megohm resistance, and finds thatto be the most satisfactory value.

One of the most important com-ponents in the whole set is the fixed


(Continued)

condenser, of .001 capacity, shuntedacross the primary of the L.F.transformer. Without this thereceiver becomes unstable andvery difficult to operate. The con-denser shunting- the potentiometerwinding should also not be over-looked. This is connected from themoving contact to the end of thewinding which is connected toL.T. +.

Intermediate Frequency Trans.formers

With the particular make of I.F.transformers used in this set,another rather puzzling trouble isliable to occur unless the operatorhas been warned about it, for thefollowing reason : the primarywindings are capable of being tunedby small variable condensers con-nected across them (these, of course,being incorporated in the com-ponents themselves), and the filtertransformer is similarly constructed.This means that no other capacitymust be connected across' theprimary of this transformer, or the

Fig. 2.-The core of the L.F. transformer is connected to L.T. positive.361

Wireless Weekly May 5, 1926


(Continued)

matching of the set of transformerswill be completely upset.

Oscillation ControlFor this reason there must be no

by-pass condenser across the ter: -

smooth control can be obtained inthis way, and one that is quite inde-pendent of the frequency.: That isto say, for C.W. reception thepotentiometer is simply turnedtowards the negative side until theslight " mushy " noise indicatingself -oscillation of the LF. valves isheard, and it may then be left alone.Should a station using telephony bepicked up it is simply necessary to

/3/4

/0(7

34i

0/6"

/4

Ps

144

.PHONES

L.S.4_

Fig. 3.-Interchangeable fixed filament resistors are conveniently mountedon the front panel.

minals on the receiver to which theinput terminals to this set are wired,and it is therefore preferable to useone of the many forms of theReinartz circuit for the first detec-tor. This always works excellentlyon short waves, and has, of course,the additional merit that no tele-phone condenser is required. Thereis no need to provide any form offine reaction control for the firstdetector, as signals seem to be justas strong when it is oscillating hardas when it is just on the oscillationpoint.

It is, of course, advisable, for thebenefit of neighbouring listeners onshort waves, to arrange that the firstdetector is not oscillating too hard !The writer has found, however, thatno reaction control other than thefilament rheostat is necessary. Thusthe whole superheterodyne is, inreality, a single -control receiver.

Telephony

For telephony reception the short-wave detector must be in an oscil-lating condition, but the inter-mediate -frequency stages must not.For C.W. reception, however, theintermediate valves are made tooscillate by adjustment of thepotentiometer, which, by the way, isnot connected direct across theaccumulator, but across the filamentsof the valves that it controls. A

take the potentiometer a shade-towards the positive side, and thespeech will be clearly received.'

C.W. ReceptionActually, there does not appear to

be the slightest necessity to make

The leads to the I.F.

lating. In addition to the thumpsthere is generally quite enough

mush " from Northolt and otherlong -wave stations (being received,of course, on the short-wave re-ceiver) to make the average C.W.station sound rather like a sparksignal when tuned in in this way.

Transformer AdjustmentThe intermediate -frequency to

which the writer's transformers aretuned seems to be approximatelytoo kc. (3,000 metres), and is vari-able over a range of some to kc.,enabling one to clear any interfer-ence from long -wave stations whichmay be received by direct pick-up onthe part of the set. All four trans-formers must be carefully tuned,and this is best done simply bylistening to a short-wave signalwhen in the oscillating condition andadjusting the four small knobs untilthe maximum signal -strength isobtained. This occurs at a fairlysharply defined point on each one,and rotating them does not vary thepitch of the signal appreciably, sothat it will be seen that this initialadjustment is quite an easy matter.

ComponentsFor the benefit of readers who

wish to construct an exact facsimileof. the set appearing in the photo-graphs and diagrams, the manufac-turers' names are given in thefollowing list of components :-

One cabinet, 16 in. by 8 in. by

transformers should be short and symmetrically.arranged.

the intermediate stages oscillate toreceive since this can be readquite clearly by the " key -thumps "heard when the receiver is not oscil-

9 in. deep, with baseboard and twopanel brackets (Carrington Manufac-turing Co:).

(Continued on page 382.)362

May 5, 1926 Wireless Weekly

IS YOUR H.F. CHOKE A SOURCE OF LOSS ?By W. S. PERCIV AL ,

B.Sc. (Hons.), A.R.C.S.

How do dielectric losses affect the effi-ciency of H.F. chokes? Continuing hisinvestigations into this subject, Mr.Percival gives the results of measure-ments on standard coils and draws

some interesting conclusions.

HE function of a high -frequency choke in awireless receiver is toprovide a path of highimpedance to radio -frequency oscillations.

According to the usual electricaldefinition of a choke it should dothis by virtue of its inductance, itsself -capacity being small, or, at anyrate, insufficient, to tune it to theincoming radio frequency. Inpractice chokes frequently. tune toa frequency lower than that atwhich they are required to operate._

An Examplein a previous article (Wireless

Weekly, Vol. 8, No. 8) a choke ofa well-known commercial make wasmentioned which was found to havea natural wavelength of about 1,600metres, although this instrument isemployed quite successfully on thelower broadcast band: If weremember that certain stray capa-

" Lattice" winding for choke coils hasthe advantage thc. no wax or similar

supporting substance is needed.

cities between wiring-, etc., will bein parallel with the choke when inuse in an actual receiver, it is clearthat the effective natural wave-length will be considerably higher.

Such a choke will function in areceiving set like a very large coilwith a capacity in parallel, the

The provision of efficient H.F. chokes is of particular importance inshort-wave receivers.

44.-4,- - 4- ----- 4-* 4- NH 4-4- -.0-6 -4- 4.-+-4-0-4.-4-------4.- 4,--4^-4-4-4-4-+-4.4-4-4.111

latter being more than sufficient fortuning purposes. This capacitywill not, however, possess an airdielectric, unless the choke is airspaced, but the dielectric will becomposed of the insulation betweenthe turns and layers of the choke.We must therefore be prepared toexpect serious dielectric losses, un-less the choke is thoroughly welldesigned.

Dielectric Losses and Self.Capacity- Now if the self -capacity of a

choke is just sufficient to tune it. tothe frequency with which it is re-quired to deal, then the currentthrough the self -capacity will beequal to the current through theinductance. If the -self-capacity isin, excess then the current throughthis self -capacity will be greaterthan that through the inductance.Finally, if the self-Capacity is suffi-ciently small, most of the H.F. cur-rent will pass through the induct-ance. Clearly in each case dielec-tric losses will play a different part,being greatest when most of thecurrent passes through the self -capacity.

Some Experimentsin order to obtain a clear idea of

what happens when a choke is used

it was decided to make a number ofexperiments. For this purpose thecircuit shown in Fig. I was em-ployed, where L is a coil of knowninductance and H.F. resistance, C atuning condenser, .and M the choketo be tested. It was in practicenecessary to place a vernier con-denser in parallel with the maintuning- condenser, in order to enablemore accurate readings to be taken.For the sake of simplicity, however,this is not shown in the diagram,. -

The oscillator coil was looselycoupled to L and was necessary for

OSCILLATOR COIL

Fig. 1.-The circuit used by the authorfor testing H.F. choke coils, M being

the coil under test.

measuring H.F. resistance, the de-tails of this method having beendescribed in a previous, issue of117ife/ess Weekly (Vol. 8, No. 3)..

To avoid the trouble of winding alarge number of chokes, a series ofcommercial coils of a fairly well-known make were employed. All

363


Is Your H.F. Choke a Source of Loss? -continued

measurements were made at the fre-quency of the London, station.

MeasurementsThe results are tabulated belovi.

The third column shows the capaci-tatiVe effect of the choke. Thus inthe first line it is shown that a No.

that of a No. 250 coil somewhatabove. It is curious to note, how-ever, that the No. 25o coil is out oforder, its capacitative effect beinggreater than that of a No. 300 coilof inductance 5,000 p.H, and even ofa still larger coil of inductance9,000 µH.

L. Choke M.

EffectiveAdded

Capacityin p.ktF.

EquivalentSeries

Resistancein ohms.

No. 40 coil of induc-tance Too µH and H.F.Resistance 6.5 ohms

No." 25 Coil of Induc-tance 25 µHNo.

No. 75 coil°No. TooNo. 150No. 175No. 250

1

No. 300I

( 5,000 p.11)(... Coil of 9,000 p.11.

No. Too coil .

250 coilCoil of 9,000 ktil

- 85- 20- To- 2± 62+ T6

+ 25

---

0

466.5

19

9.5

16

Less than 1About TAbout- T

75 coil had the apparent effect ofsubtracting .000085 microfaradsfrom the circuit. This simply meansthat it was necessary to increase thecapacity of C by that amount toretune the circuit after the chokewas placed in parallel.

The fourth column shows theresistance which, placed in serieswith L, would exert the same damp-ing effect as the choke.

Fig. 2. - An inefficient choke in thiscircuit may have a damping effect on

the tuned circuit LC.

A Curious ResultThe results shown in the third

column are of the order to be ex-pected and indicate that the naturalwavelengths of the coils graduallyincrease, that of a No. 175 coil beingslightly below that of 2L0, and

Coup ed with this fact we notethat the equivalent series resistanceof the coil is higher than that of anyother.

A DeductionIf we now examine the other

figures we see that the more posi-tive is the capacitative effect of thechoke the greater is its H.F. resist-ance. It will be admitted that thisaffords strong presumptive evidencein favour of regarding dielectriclosses as of paramount importance.This is further supported by otherevidence.

Thus coils of the particular makeemployed, while quite satisfactorywhen used in the ordinary way, areparticularly inefficient as chokeswhen dielectric losses would be ex-pected to become of greater import-ance.

Construction of CoilsFurther, on examining the interior

of the coil, which was of a commonplug-in type, it was found to consistof a number of layers of impregnatedcotton -covered wire, separated bythin brown paper. One would cer-tainly expect a coil of this type tosuffer from dielectric losses.

Lastly, one or two air -spaced coilsof about Nos. 200 and 250 weretried. These were found to give a

negligible equivalent series resist-ance, as might be expected, owingto the absence of dielectric losses.

Effect of Size of Tuned CoilAlthough this article is designed

primarily to emphasise the import-ance of dielectric losses in chokes,yet it would not be complete withoutreference to the effect of the size ofthe tuned coil L on the equivalent

-series resistance introduced by achoke. Theory indicates that if thecoil L is made smaller, and C corre-spondingly increased, then the damp-ing due to the choke would be lessowing to the relatively smaller cur-rent flowing therein.

Decreased DampingFor the purposes of examining this

a No. 25 coil of inductance 25 jullwas substituted for the No. 40 coilpreviously employed for L. Themarkedly decreased effect of theclamping introduced by even theworst choke coils is shown in thetable. On the other hand it shouldbe remembered that if the size of thecoil I, is increased then the clamping -introduced by the choke becomesmuch more pronounced.

Application to CircuitsIn Fig. 2 is shown a circuit which,

with minor alterations, is frequentlyemployed for intervalve coupling.The iffect of the damping of an in-efficient choke M on the circuit LCwill be immediately apparent fromthe foregoing discussion.

There is wide scope for experiment intesting the merits of different types of

windings.

The choke coil M is, in effect, inparallel with the tuned circuit, sincethe H.T. and L.T. batteries are atthe same potential as far as high -frequency variations are concerned;consequently the full damping effectof the choke will be evident, as hasjust been described.

364

may 5, 1926

Si-IORT-WAVENotes&News

LTHOUGI-I conditionshave been by nomeans good on thereception side, the pastfortnight has seensome excellent low -

power transmitting feats, and theBritish stations still seem to be veryactive. No new countries have ap-peared " on the air," but the sta-tion SS-8LBT, mentioned in the lastissue of these notes, has been foundto be in Straits Settlements.

Low Power DXG-6YD is apparently the star per-

former at present. He uses amaximum power of ro watts and amaster oscillator, and his signalshave been heard in India, Uruguay',to times in Brazil and 22 times inthe United States ! The questionnow arises-" Why does anyoneever use more than 10 watts? "5YG, of Glasgow, has also put upan excellent performance, havingworked Brazilian, 69A with an in-put of 8.62 watts, his signals beingreported a steady R4. This is reallong-distance DX with low power,and to work Brazil with S watts .isnaturally much more creditablethan to cover a distance of, say,200 miles with' .02 watt, althoughthe " miles -per -watt " figure is notnearly so great.

. We have a letter from Denmarkbearing the glad tidings that theDanish Government are at lastgranting licences for amateur trans-mission. We hope to obtain a com-plete list of the addresses of theDanish transmitters very. shortly.

(IRA's in All CountriesWe now have in our possession

what is probably the most completelist of call -signs of amateurs all Overthe world, and feel that this will beuseful to those who wish to sendQSL cards to amateurs that theyhave worked or called. Such a listcannot be published without fullpermission of all the stations in -

eluded in it (many of whom are un-licensed), but we are always willingto communicate, in confidence, withanyone sending in a request for theQRA. of a station. The list will becomplete by the time this appearsin print, and all letters relating tothis service should be addressed" QRA Section," Wireless Weekly.

Irish ActivityThe Irish stations are now bid-

ding fair to outdo the ordinary plainGs " as far as DX is concerned.

Whether this is due to the compara-tive absence of QRM in Ireland orto specially good " local condi-tions " it is not possible to say.The fact remains, however, that

Mr. T. Woodcock -(G600) has done somegood low -power work on the " In-expensive Shirt -Wave Transmitter"recently described in " Wireless

Weekly."

practically every active Irish sta-tion has some particularly good feattor his credit. 6MU has now workedIndian HBK on telephony with aninput of less than 3o watts ! Hewas reported at a fair strength withno distortion. He has now workedall Europe, Africa and Asia on tele-phony, and the other two continentson C. W.

The latest feat has been two-wayworking; with PI-rAU (PhilippineIslands) on C.W. with 18-20 watts.GI-6YW, it will be remembered,worked PR -4S.\ with an input of

Wireless Weekly

2 watts. Belfast looks rather likebeing the " Hams' Paradise " sooften mentioned in " QST " !

Why " Raw A.C." ?The interference problem is be-

coming really serious now, as moreand more stations are using the6,667-kc. band. The French sta-tions, practically all of whom use" raw A.C.," are casting the blameon the Italians, who, it is believed,are attempting to blame the Germanstations. Why .use ",raw A.C."at all, when a rectified A.C. notewith half the power will carry justas far, if not further? Fortunatelythe majority of British stations useD.C. notes, and those who haveA.C. generally take the trouble tctrectify it.

An Aerial ExperimentThe horizontal experiments by

6QB- mentioned in the last issuehave yielded results that are notquite up to his original expectations.They consisted, briefly, of using anaerial divided in the centre by aseries of insulators, with two sepa-rate down -,leads, one half beingused as aerial and the other ascounterpoise. He had several in-teresting reports on his transmis-sions when this system was in use,but apparently the steadiness of thenote, which was not affected byswinging on the part of the aerie,was the main advantage. Signalstrength at a distance appeared tobe the same as when the usualarrangement was in use.

Transmissions from SchenectadyWe continue to receive reports of

reception of the various " WGY "stations, and have ascertained thatthe call -signs used are 2XK, 2XAF,2XAL and 2XAS. A summary ofthe, reports will probably be publishedlater. A letter will be found amongthe " Readers' Comments " in thisissue, asking for further reports onthis s-hort-wave telephony.

365

Wireless Weekly May 5, 1926.

I III 11111 III! I III III 11111111111 III! liii 1111 IIII1 III IIIIIII IIIIIIII'IIII III1IIII lIllIllIllIllIll I III 11111 III II

A MODEL RADIO HOUSEA few days ago a house in New York, completelyequipped with wireless receiving apparatus, wasopened by Captain P. P. Eckersley from RadioHouse, London. This article describes in detail

the equipment of this model Radio House.

ii1111111111111111111111111111111111.111111111'111111111111111111111111111111111111111;11

RADIO HOUSE exemplifiesthe ideal in radio broad-casting service in the home.

It is designed to give the public awholly new and broader conceptionof modern home installations, andrepresents radio engineering's mostrecent achievement in home radioinstallations, introducing suchfactors as remote control receivers,concealed wiring, " "switches, automatic clock operation,and many other features.

Economy and Remote ControlThe Radio House project is an

example of what can be accom-plished economically and effectivelyin greatly increasing the usefulnessof a single receiving set, _by theaddition of a single distributionsystem with radio outlets or" feeders " in different parts of thehouse. Moreover, the principle of

0

A control panel for the second floor setis placed at the head of the bed in the

" Master's" bedroom.

controlling the central receiver fromdistant points in the house, adecidedly necessary considerationwhere convenience is desired, ismade use of to tie fullest extent.Again, the possibilities of multiplereceivers for a plurality of simul-taneous programmes are fullydemonstrated. In brief, the story ofRadio 1 -louse the story of theradio -equipped home of the future.

The receiver takes its place as part of the ordinaryfurniture of the room.

1111111I1111111111111111111111111111111111111111111111111111111111111M11111

Equipment in Radio HouseOn the first floor, the living -room,

dining -room, kitchen and porch areequipped with receiving apparatus.

The master set for this floor, in-cluding the porches but excludingthe kitchen, is an eight -valve super-heterodyne receiver, with a loop

The interesting descriptionof a Model Radio House onthese pages perhaps fore-shadows a developmentwhich may become beforelong a regular and normalfeature of domestic archi-

tecture.

aerial. This set supplies the inputfor a power loud -speaker in theliving -room, opposite the set, andfor another in the dining -room.

A three-way switch, convenientlylocated close to the set, enables theoperator to transfer the set outputto either loud -speaker, and to con-trol the A.C. entering the power -speakers at the distant points. Atwo-way switch in the dining -roomprovides remote control of theliving -room set, and A.C. to thedining -room loud - speaker. . Nobatteries, outside aerial or eartharc used.

11,11111i11111:ii111111111111111i111111111illi: 111111111111111111[111111111111114

The main porch, reached throughdoors in the living -room, is pro-vided with suitable receptacles' toaccommodate the living -room loud-speaker, which may be moved onlyfive feet from its living -room posi-tion to the porch. Control of thespeaker, when in its porch location,can be effected at either of the twopoints in living -room or dining -room.

Time ClockA timepiece of special design

which automatically operates aswitch, all mounted in a smallmahogany case, takes its place onthe cover of the receiver. A cord,connected to a terminal block insidethe case, extends to the master con-trol switch plate by the living -roomset, where connection is made to theA.C. circuit. The clock may be setin advance, and when the hourcorresponding with the settingarrives, the switch automaticallycloses, and the entire first -floorinstallation is set in operation.

The kitchen receiver is battery -operated and uses an aerial. Thisreceiver is smaller than that used inthe living -room, and because of thecomparative size of the kitchen, asmaller loud -speaker is used, thisbeing plugged into the receiver.The aerial and earth connectionsare made by, a duplex cable, theterminal plug of which engageswith a double receptacle mounted inthe baseboard, the leads beingarranged out of sight.

366

MAY .5TH, 1926 ADVERTISEMENTS WIRELESS WEEKLY 11)

NOW that's what I call a goodSet " exclaimed Simpson en-

thusiastically, after he had heardChopin's beautiful Mazurka in AMinor. " And yet "-here a note ofdoubt crept into his voice, " it seemsvery much like the Set you wereusing before Christmas." " It is thesame Set," I conceded, " but withdifferent valves. You'll rememberClarke who was with our crowd inMespot ? " " Yes, rather, good oldNobby ! " " Well, I dropped acrosshim in the City the other day, and ashe mentioned that he now had a jobwith a wireless firm, I asked him tocome over and look at my Set. Hesaid the Set was fine but that I wasusing the wrong valves."" But I thought all valves were verymuch alike," cut in Simpson. " Andso did I until Clarke enlightened me,"I replied. " First of all he gave mean explanation as to how my Setworked. He showed me how thefirst valve had to act as a highfrequency amplifier, the second as adetector, whilst the third valve, heexplained, was responsible for obtain-ing good volume and pure tone from

Another man who hnever known really gooBroadrol sting

the Loud Speaker. And then heproved to me why these threedifferent jobs required three differenttypes of valve. He had broughtwith him three Cossor Wuncell DullEmitters. Taking out the first twovalves from my Set and inserting intheir places a Wuncell W2 and a WI,he asked me to compare the differ-ence. It was startling. But themost amazing thing was still to come.He substituted a Cossor W3 for thethird valve, increased the H.T.voltage, and literally the LoudSpeaker leapt into life. I remembera piece called " In a Monasterygarden " was being broadcast at thetime."" Oh, Yes, I know it," interruptedSimpson, " it has lots of little trillsamong the high notes to imitate thebirds in the garden." " That's thepiece," said I, going on with mystory, " the moment he put in thatthird valve I realised that I had neverreally known how good Broadcastingcould be. All the time I had beenblaming the makers of my Set whenit was the valves which had been atfault."

" There certainly is a tremendousdifference," admitted Simpson," turn the Set round and let's have alook at these remarkable valves." I.

did so. " Why," he cried in amaze-ment, " you can't see any glow fromthem ! " " No," I answered, " thatis another advantage. They constantso little current and work at so lowtemperature that Clarke swears thatthey will last longer than any othetvalve on the market. He says thatthe filament which the Cossor peopleuse is quite different-being made ofwire having a very thick coating ofsome special substance which pro-duces lots of electrons at a very lowtemperature."" That must be an advantage,"suggested Simpson, " for the extracoating must make the filamentstronger and thicker." " Yes," Iagreed," even when one rolled off thetable last night it came to no harm.Quite frankly I'm very much indebtedto Nobby Clarke for the good advicehe gave me." " You can includeme in that," said Simpson with asmile, " for it is a long time since Ispent such an enjoyable evening."

*W.1. For Detector and L.F. use - 14/- 'W.2. (With red top) for H.F. use 14/- W.3. The Loud Speaker Valve - 18/6Consumption : '3 amps. Consumption : '3 amps. Consumption :'5 amps.

'All the above valves operate at 1*8 volts, but those marked are also supplied with speectal base with resistance to suit 2, 4 -or6 -volt Accumulator. 16/-

kfe,71*4tfc.fe.&kk.,,0**-.-.,Z*QM0*,,MM-7M-retkaltmgIssued by A. C. Cossor, Ltd., Hoghbury Grove, London, N.5.

Ad. 5osio.


V1 WIRELESS WEEKLY ADVERTISEMENTS MAY 5, 1926

PERFEC.T. 25.

Filament Volts .. .. 5-6Filament Amps .. .. .25Anode Volts .. .. 30-300Voltage Amplification Factor 9Impedance .. .. 10,000Mutual Conductance .. 800Plate Current Saturation at 50

Volts over 30 milliamps.

15/-

A merica's foremost valvenow made in Britain'snewest factory. ::

ET VALVE

Avg

11

4

YOU CANNOT -5 0 +5 +i0

be using the valve with qualifications for the supreme realities ofwireless generous volume, pure and sonorous tones or longerdistances - unless you use CLEARTRON Valves, which are real .yguaranteed under CLEARTRON'S IRONCLAD GUARANTEE.

12/6 STANDARD PRICES 15/-They are ALL Dull Emitters,with lowest current consumption, and sold at Standard Prices.

For 2, 3, and 5-6 v. Accumulators and Dry Cells, H.F. Detector and L.F.Full technical data jrcm your Dealer, OY :

CLEARTROINI RAD1101 CHARING CROSS, LONDON ; (Works : BIRMINGHAM).

Telephone: Regent 2231;2. 'Grams: Cleartron, Westrand, London.

British

4 65 95

Made.



A Model Radio House-continued

Bedroom EquipmentOn the second floor there are

three bedrooms.The " Master's " bedroom con -

thins a six -valve superheterodynereceiver. This set is located on a

the dining -room, from whence theloud -speaker can be silenced bytouching the dining -room control.The same plan of control applieswhen the loud -speaker is -moved toits porch position.

table at one side of the bed, whileat the other side, at the head, is acontrol panel consisting of a num-ber of " push " switches. Theloud -speaker and H.T. batteryeliminator is located on a smalltable at the foot of the bed, aboutfifteen feet from the set, the L.T.batteries being concealed in a smallcloset, where they may be reachedconveniently.

The equipment in the " Guest "bedroom consists of a push-buttonswitch, easily reached from theguest's bed, an H.T. batteryeliminator and power loud -speaker.The loud -speaker, battery elimina-tor, and power amplifier are com-bined in two units, these unitsresting on a small table at the footof the guest's bed.

Radio service for the Nursery issupplied by the loud -speaker in the" Master's " bedroom. A shortextension cord permits the speakerto be moved slightly from its usualposition, thus permitting the chil-dren to hear " Children's Hour "programmes in their own bedroom.

Operation of the ReceiversThe living -room, dining -room and

porch are served from a master re-ceiver. Having selected the broad-casting station, the button at themaster Control panel is depressedfor the living -room. Pressinganother -button .sends the concert -to

0 0 0

No external wir-ing is visible inthe rooms, all theleads being runinside the walls.

The kitchen battery -operated re-ceiver has no external or remotecontrol connections, this receiver.operating in the usual manner. Itìs independent of all other receivingapparatus in the house, but may beoperated simultaneously with anyand all other receivers withoutcausing any interference.

The master set

on the first flooris a superhetero-dyne with a frameaerial, seen in thefar corner of this

room.

0 0 0

Control UpstairsThe bedrooms are served by one

set. Having selected the .broad-casting station, the button at themaster control panel is depressed,and service:is made available in the" Master's " bedroom and the

Nursery. Another button controlsthe circuit to the " Guest " bed-room, while the loud -speaker there .may be disconnected by touching abutton beside the bed, withoutaffecting reception in other rooms.

By pressing two buttons at thecontrol plate, all of which are suit-ably marked, the receiver is readyfor operation, as the A.C. and D.C.circuits to the eliminator and re-ceiver have been closed. The re-ceiver is then tuned, and radioservice is available in the" Master's " bedroom. By closinganother switch, the signal is alsotransferred to the " Guest " room,and, pressing still another, makesthe radio service available in the"-Guest " room only.

House WiringThe radio wiring for the Model

Radio House is entirely standard,the work having been handled bythe same electrical contractor whodid the electric light wiring, with-out complications or additionaldifficulties. The Model RadioHouse can thus heduplieated anywhere. It is inter-esting to note that the cost of RadioHouse wiring, in the final analysis,is considerably less than that of agood receiver, yet it serves to in-crease immeasurably- the -servicerendered by the radio installation.

THIS WEEK'S INTERVIEW

The above feature is unavoidablyheld over from this week's issue, andwill appear at an early date.

367


Circuits That Will Not NeutraliseBy J. H. REYNER, B.Sc. (Hons.),

A.C.G.I., A.M.I.E.E.Experimenters with neutralisedH.F. circuits will probably havefound that stable neutralisationis difficult or even unattainablewith some arrangements. Thecauses of this trouble are dis-cussed here by Mr. Reyner, andsome of the possible solutions

suggested.

11.41-4-4.4-0--------4-4.4-4.HE problem of theneutralisation of theinter -electrode capa-city of a high-fre-q u e n c y amplifyingvalve is one which has

been receiving a good deal of atten-tion recently. Many circuits havebeen tried and experimented on withthe object of devising an arrange-ment which would remain stableover the whole of the particulartuning band employed.

Bridge CircuitsMany of the devices used employ

a bridge arrangement, which is not,strictly speaking, a neutrodyne,since this word really only appliesto the particular methods adoptedby Professor Hazeltine, who hasregistered the name " Neutro-dyne " to apply to his circuits. It

V

ingness of the part of the circuit tobe stabilised. It may be found thatthe circuit behaves in a correctmanner during the process ofstabilising, but on switching on itis not really stable. For example,one of the methods of neutralisingconsists in tuning the set to thelocal station, turning out each valve

Fig. 1.- With this circuit failure to obtain complete neutralisationfound to be due to coupling between the coils Ll and L.I.

is more correct, therefore, to referto such circuits as neutralisedrather than neutrodyned, becausesuch a term covers any ,of thevarious methods which may beemployed.

Now any experimenter who hascarried out work on these circuitswill have found himself puzzled atone time or another by an unwill-

was

in turn, and adjusting the setting ofthe appropriate neutralising con-denser until no signals are observed.It is quite possible for a set to give.quite sharp and crisp zeros on theneutralising condenser when thismethod is adopted, and yet todevelop instability at different partsof the circuit when it is actually inuse,

Some of the apparatus used by Mr. Reyner at Elstree in his experimentswith neutralising methods.

Parasitic OscillationsI am not referring at all to the

generation of parasitic oscillations,which have already been discussedin these columns, and the possi-bility of which is now fairly wellknown. The oscillations which areproduced in such cases are at a veryhigh frequency, and will not .pro-duce any heterodyning of the local.station. They are chiefly evidencedby a sudden drop in signal strength,the set going completely dead. Ifthe condensers of the set aretouched with the moist finger theusual clicks will be obtained, show-ing that the set is oscillating.

A Circuit Which Gave TroubleIt is assumed, however, that with

the particular neutralising methodsadopted, precautions have beentaken against .the generation ofthese parasitic frequencies, so thatany oscillations produced here areat or near to the frequency which isbeing received, and for that reasonare perhaps even mare puzzling. Aparticular circuit which gave troublein this respect is that shown inFig. r. This circuit was -a tunedhigh -frequency circuit, using a split -anode method of neutralising. Thesecond anode coil was not split, inorder to avoid the tendency towardsthe production of parasitic oscilla-tions.

InstabilityNow this circuit, when first tried,

neutralised perfectly according to368

May 5, 1926

the ordinary methods, a crisp zero'being obtained on the neutralisingcondensers when the -respectivevalves were turned out. On switch-ing on the valve again, however,the circuit was not found to bestable. While at times it wouldgive satisfactory results, at othertimes it would burst into oscillation,

CIRCUITS THAT WILL NOTNEUTRALISE

(Continued)

Unwanted CouplingsThe coils in the particular circuit

had been placed at the critical angle

This receiver, the " Screened -Coil Long -Distance " Set, was the outcomeof successful experiments with coil screens specially designed to eliminate

stray couplings.

and behaved in a generally unsatis-factory manner. A slight variationof the neutralising condensers wouldusually check the oscillations at oneparticular setting, but it was imme-diately found that such an alterationintroduced instability at other partsof the dial, so that it was impossibleto find a setting of the neutralisingcondensers which - would givestability throughout the entirerange. In other words, the circuitpersistently refused to neutralise.

The Cause of the TroubleThis was a matter which occa-

sioned considerable thought. It isimmediately obvious that since asymmetrical arrangement has beenemployed, there is no very clearreason for this lack of neutralisa-tion. Moreover, the fact that thecrisp zeros are obtained on the neu-tralising- condensers when the valvesare turned on indicates that eachindividual valve is being correctlyneutralised. Strictly speaking, thecircuit therefore is neutralised, andthe oscillations are occurring fromsome other cause. This can onlyarise from stray magnetic or capa-city coupling between the variousportions of the circuit, and a littleinvestigation showed that this wasreally the cause of the trouble.

of approximately 57 degrees, inorder to obtain a zero couplingbetween the various coils. Nowexperiments showed that thecoupling between the first andsecond, and the second and thirdcoils was practically zero. Thecoupling- between the first coil andthe third was, however, by no

V0 0 0

Fig. 2. The de-sign of the inter -valve transformeris a vital factor inneutralisation i nthis type or circuit.

N .0

wz>L,

,c>K

1

Wireless Weeklyselectivity of the circuit must in-evitably suffer if such direct transferof energy from beginning to end ofthe set is possible, since the middletuned circuit is completely useless.,Secondly, if this coupling is in the.correct direction, it will produce re-action from the back to front of theset, and the energy so regeneratedwill set up and maintain continuousoscillations throughout the amplifier.

It might be observed in passingthat if the coupling is in the reversedirection, then exactly the oppositeeffect is obtained, and the amplifieris damped. If this is the case, thenthe sensitivity of the receiver as awhole will be very poor, because theamplification of each individualstage is immediately discounted bythis reverse reaction couplingthrough the stray fields. Selec-tivity will be just as bad in such acase because this does not dependupon the direction of the coupling.From all points of view, therefore,it is desirable to reduce this straycoupling as far as possible.

Zero Coupling the CoilsIt is well known that spacing the

coils at the critical angle of approxi-mately 57 degrees is alleged to pro-.duce zero coupling, irrespective ofthe distance of the coils apart. Inthis particular instance this was notfound to he the case, and a littlefurther investigation showed that,whatever position the coil wasplaced in, it was not possible toobtain a zero coupling arrangement.This has led to some definite re-search on the question of coupling

means zero. In fact, when the setwas tuned to the local station, themiddle coil of the receiver could beremoved and the middle valveturned out, and excellent loud-speaker results were still obtained,-the arrangement functioning simplyas a loose -coupled circuit,

Reaction EffectsObviously such an arrangement

as this is totally undesirable. The

t IfC2

between coils, and I hope to publishsome very interesting resultsshortly, showing that beyond acertain distance it is impossible toobtain a zero coupling position withthe normal arrangement of coils asused in receivers.

A RemedyIn the pthictilar case it was

found that the coupling could .bedefinitely reduced to a much smaller

369

Wireless Weekly

CIRCUITS THAT WILL NOTNEUTRALISE

(Continued)

value by reversing, the connectionsto the first coil. When this wasdone the transfer of energy frainthe first to third circuits with thesecond coil removed was very small,and, as was expected, the circuitthen became perfectly stable. Itshould be observed that this was notequivalent to introducing dampinginto the circuit. If the reversal ofthe coil had simply reversed thedirection of the reaction, then therewould still have been a couplingfrom the first to the third circuit.It was found, hoWever, that thiswas not the case, and, in fact, alack of symmetry is introduced, dueto the fact that both capacity andmagnetic coupling are present.This point, however, will be dealtwith at considerably greater lengthduring a future article, the pointbeing that it is particularly im-portant to avoid stray couplings ofany sort between the first and thirdcircuits of a multi -valve amplifier.

Another CircuitAnother type of circuit which will

often give trouble is that shown inFig. 2. Here we have a trans-former coupling after the high -fre-quency valve, the secondary of thetransformer being tuned while theprimary winding is centre -tapped.One half of the winding is includedin the anode circuit of the firstvalVe, and the other half is em-ployed as a neutralising winding.

One would expect that thisarrangement, being perfectly sym-metrical, would give satisfactoryresults, but this is not always the.case. The neutralising action in r,

case like this is not quite the sameas that when the neutralising wind-ing is definitely part of the tunedcircuit. It is obvious that if thetwo sections of the primary wind-ing were not coupled to each otherno neutralising action would beobtained. In other words theaction .depends essentially upon thecoupling existing between the twohalves of the primary winding.

Importance of Tight CouplingAs a matter of fact it can be

shown that, unless this coupling be-tween the primary winding properand the neutralising winding is verytight, then troubles are introduced.The ideal tight coupling is one inwhich all the possible magnetic

field from the one coil is interlinkedwith that from the second coil. Ifany portion of the. flux does notaffect the secondary winding, then it

,produces an effect similar to theintroduction of =a- small inductancein series with the coil.

. Fig."3 shows a circuit in which aleaky .transformer (that is to say,one -in which the coupling is notperfectly tight) has been replacedby an ideal 'transformer and asmall " leakage " inductance, as itis called, in series with the primarywinding. It will immediately beobvious from an inspection of thiscircuit that we are here not obtain -

Fig. 3.- Lo is a "leakage " inductancein series with the transformer primary.

ing a correct balance, but we arebalancing a pure capacity againsta capacity and an inductance inseries, and an adjustment which is__correct in one part of the circuit\\ ill not be correct in another.

Effect of Small PrimaryIt is often found that if the pri-

mary winding of the split trans-former (such, as is shown in Fig. 2)is made small, possibly with theidea of improving the selectivity ofthe circuit, then the coupling be-tween the two halves of the coilis too small, even if they are woundin one continuous length, and nosatisfactory neutralisation can beobtained. The circuit will not evenbehave in a correct manner, it beingimpossible, if one of the valves isturned out, to balance out thesignals by adjustment of the neutro-dyne condenser. The trouble maybe overcome by increasing the sizeof the primary, in which case theselectivity suffers.

A Curious PhenomenonI have also come up against a

peculiar phenomenon here which Ihave not yet explained to my ownsatisfaction. Some experimentswere carried out with a transformerof this type employing two screenedunits for the grid coil of the firstvalve, and for thetransformer be-tween the first and second.

The secondary consisted of goturns on a 2 -in. diameter former,while the primary consisted of 120

May 5, -1926

turns of No. 36 gauge wire, woundon a former inside thesecondary. This primary windingwas centre -tapped, one half beingused in the anode circuit of thevalve and the other half beingemployed for neutraliSing purposes.

Imperfect NeutralisationI found that correct neutralisation

could be obtained with this arrange-ment according to the usual testswith the valve out, and good andstable results could be obtained overpart of the range. There was aportion in the middle, however,where a different oscillation tookplace, at about the same frequencyas that being received, but notquite the same. It was not a para-sitic oscillation, but showed quiteclearly that there was some formof instability in the receiver. Thetrouble was overcome by reducingthe size of the primary winding to70 turns only, instead of the pre-vious I20: This arrangementneutralised perfectly, but the energytransferred across the transformerwas considerably reduced, and itwas necessary to employ reactionon to the last valve, an adjustmentthat had not previously been neces-sary. A still further reduction ofthe primary winding resulted in thecircuit becoming incapable ofneutralisation, as has previouslybeen described.

Further Researchlf, however, as has been sug-

gested, the trouble is really due toinsufficient coupling between the

In some of his experiments Mr. Reynertried enclosing the coils in perforated

zinc screens.two halves of the primary winding,then it would mean that betterresults might be obtained by wind-ing these two halves one over theether. It would be possible to keepthe capacity coupling between thetwo halves of the primary windingand the secondary quite small, andstill retain the tight coupling be-tween the two halves of the pri-mary. Experiments on these linesare proceeding at the present time.

370

May 5, i926 Wireless Weekly

Getting the Best from

the "Neutroflex Two"By N. J. GIBSON.

Neutralising Adjustments-Valves-Tuning-Reception Results.

N last week's issue ofIVireless Weekly, be-sides the theoreticaland constructional de-tails, a few notes onthe operation of the

Neutroflex Two " receiver werepublished. It is thought, however,that a few further details on theoperation of this receiver will bewelcomed.

Neutralising the ReceiverThe method of neutralising the

receiver, by adjusting the neutra-lising condenser with the reactioncondenser at its minimum position,until no oscillation occurred at anysetting of the tuning condensers,was described last week. If, how-ever, it should be found that withthe neutralising condenser at itsminimum no oscillation takes place,and that on increasing it reactionbecomes evident, it does not neces-sarily mean that the set is notneutralising correctly, as, if thevalve in use is of a sufficiently lowcapacity the minimum of the neutra-lising condenser, supplemented bystray capacities in the wiring, etc.,of the set, may be sufficient toneutralise the H.F. valve,

In the same way this capacitymay be sufficient to over -neutralisethe valve in some cases, if very lowcapacity valves are employed, andthus cause oscillation. In this eventit will he necessary to substitute asmaller neutralising condenser. If,however, the valves employed by theauthor are being used this will notbe the case.

A Word of WarningOwing to the design of the

receiver giving great stability, itmay be found that, if valves otherand (smaller than the .25 -amperesmall power type are used, reaction

may be difficult to obtain. In "viewof this, it is strongly advisable thatthe above type of valve should beemployed, the detector valve in anycase having a high impedance suit-able for anode bend rectification.

Method of SearchingWhen the set is properly neutra-

lised it is possible, without causingre -radiation, to search for stations

ELSTREETEST REPORT

The set was found easy to handle,complete stability being readilyobtained. In operation the setbehaved after the manner of a

" straight " set, using H.F. detectorand L.F. Na sign of the howlingcommon in some reflex receiverswas present.

London, Bournemouth, Birming-ham, and Nottingham were receivedon the loud -speaker, and also someContinental stations.

On the telephones all the B.B.C.main stations were picked up andnumerous Continental stations.

with the detector valve oscillating,by obtaining the carrier on thedetector grid tuning condenser, andbringing the high -frequency tuningcondenser into tune until the carrieris heard at its loudest. The reactioncan now be decreased until thedetector valve ceases to oscillate andthe actual signals become audible.

It may now be necessary to re-adjust the two tuning condensers tobring the signals up to their maxi-mum strength. It will be found,

however, that once the set has beenadjusted to a sensitive condition itwill not be necessary to oscillate andheterodyne the carriers to tune in themajority of the stations, as byrevolving the two tuning condenserssimultaneously and at the same timekeeping them in tune, the stationswill come in without further adjust-ment of the reaction over practicallythe whole waveband.

It will probably be found advan-tageous with the above method ofsearching to use whilst searchinglarger coupling coils than are nor-mally used, substituting smallercoils when' the station. is tuned in(and slightly readjusting- the tuningcondensers) if greater selectivity isrequired to cut out interference.

ResultsUsing the receiver on an aerial

twelve miles north of 2L0 it waspossible practically to separateCardiff and Manchester from Lon-don on the headphones, whilstBournemouth, Newcastle, Birming-ham, Aberdeen, and two or threeforeign stations were audible on theloud -speaker. Nearly all the B.B.C.main stations, several of the relays,and numerous Continental stationscould be received at good headphonestrength.

THE " MAGIC FIVE "A New Set of Outstanding

Merit

In the next issue of Wireless1Veekly will be given a Tull descrip-tion of a new 5 -valve set, designedby Mr. J. Reyner. Features ofthis set are that it is compact, -non-radiating, and highly selective ; ithas only three controls and no re-action adjustment, and it is com-paratively inexpensive to construct.


WirelessNews

in Brief

In order that all the patients in St. George'sHospital Hospital, Hyde Park Corner, may take partBroadcasting .in the religious services, a microphone hasbeen installed in the chapel. This installation was usedfor the first time on St. George's Day, the patients inthe wards listening by means of the ordinary receiverand headphones.

*

While staying at the Savoy Hotel, London,Ruxgbriments.the

wifey 'of a distinguished American wasEpe enabled to converse with her children in New

York, via the Rugby station. Conversation was carriedon without any difficulty, perfectly clear speech beingobtained.

*

Pictures byWireless.

* *

Continuing theexperiments inthe transmission

of pictures by wireless, asdescribed in our last issue,Capt. R. H. Ranger re-cently transmitted to NewYork in twenty-five minutesa photograph of the captainof the Mauretania. Thisphotograph, together withan explanation in Capt.Ranger's handwriting, alsotransmitted, was handed tothe Mauretania's com-mander on her arrival inNew York.* * *

Sunday, May 9.From theProgrammes.S

-hLa okenspdeaoren's:

Heroines, by Mrs. PatrickCampbell ; " Lady Mac-beth."

Monday, May Io.--Glasgow : Beethoven's Piano-forte Sonatas.

Tuesday, May II.-London : John Henry from anaeroplane. Birmingham : Musical Operetta, " Mar-riage by Lantern Light " (Offenbach).

Wednesday, May 12.-London : The WirelessFollies Concert Party. Edinburgh : The EmbassyOrchestra. Nottingham : An evening of variety.

Thursday, May r3.-London : Wireless SymphonyOrchestra. Bournemouth : A Sussex Evening. Bel-fast : Ascension Day music.

Saturday, May vs.-London : Brighton CoMpetitiyeMusical Festival, relayed from Brighton. Newcastle :A brass band night. Aberdeen : The Aberdeen RadioPlayers in " Nettles," a rural Scots comedy.

Friday, May 14.-London : " The Valkyrie," re-layed from Covent Garden. Jack Payne's Hotel Cecildance band.

Bra; dc istOpera.

In addition to the operas already announcedfor broadcasting during the coming season,on June 1 Act 2 of " Othello " will be

heard, and on June 4 Act r of " La Boheme."

A modern liner is very completely equipped for thetransmission and reception of ordinary wireless tele-grams, and often for the reception of broadcasting also.

* * *

We hear thatfwernationalBroadcast. on the night

of May 26/27,the broadcasting station(KOA) at Denver, Colo-rado, is to send out pro-grammes intended for re-ception by the world. Thistransmission xvill be in con-nection with the Rotarian.Convention, and we gatherthat the part of the pro-gramme specially arrangedfor this country and forWestern Europe will takeplace between 4 arid 5 a.m.The KOA station works on322 metres with a powenof 5 kw., and its transmis-sions have already beenheard in England.

* *Bourne- Part of the special Sussex programme, whichmouh'sSussex is to be given by the Bournemouth stationEvening. on May 13 will be relayed from Worthing.The Bournemouth Wireless Orchestra, conducted byCapt. W. A. Featherstone, will also perform, and theevening's programme will be relayed to Daventry.

* * * *

jam Henry The broadcast which John Henry will giveto get a from an aeroplane between io and io.3oRise. p.m. on May r r is in connection with thecampaign in the London area for the Ground Defencesand Auxiliary Air Force.

372


Non -Radiating Single -Valve CircuitsBy the Staff of the Radio Press Laboratories.

Is it possible to design a single -valve circuit which will not radiate while retaining the full advantages ofreaction ? Some experiments in this direction carried out at our Laboratories throw light on this question,

which is of universal interest.

HE Radio Press jour-nals have for a con-siderable time beenpublishing details ofmulti -valve receiversin which the carriers

from very weak transmissions canbe heterodyned, thus enabling sta-tions to be more easily picked up,and this without any trace of radia-tion from the aerial. Thesereceivers have invariably involvedthe employment of one or moreproperly neutralised stag -es of highfrequency before the detector valve.It is then possible to cause thedetector or second stage of high -frequency to oscillate, without theoscillations produced being trans-ferred to the aerial circuit.

A One -Way Coupling DeviceThis is owing to the fact that a

properly neutralised valve will actas a one-way coupling device. Inother words, high -frequency poten-tials impressed on the grid willproduce amplified versions of theseoscillations on the plate, whereasoscillations impressed on the platewill cause no corresponding varia-tion of the grid potential. If itwere not for the grid -to -platecapacity of the valve no neutralis-ing would be required. As it is,however, this capacity couples thegrid and plate circuit in the sameway as any other capacity. It istherefore necessary to balance outthe unwanted capacity, the procesSbeing known as neutralising.

This one-way action of the valveis entirely separate from its pro-perty of rectifying, and must not beconfused therewith. A crystal willrectify, but cannot act as a one-

way coupler. In the same way atwo -electrode valve, although itpossesses; the property of rectifying,cannot be used in the same way asa three -electrode valve to enableoscillations to pass in one directionand not in the other.

That non -radiating receivers usingtwo or more valves can be success-fully designed has been amplydemonstrated by several Radio

Press receivers.

The problem of incorporating thisdesirable feature in a single -valveset (with reaction) is more difficult,and this article indicates some

possible lines for experiment.

At Least Two Valves NeededIt will thus be clear that, as far

as present development is con-cerned, it is necessary to have two

Fig. 1.-This typeof neutralisedtwo -valve circuitwill not radiatewhen properly

adjusted.

aerial. One of these valves mustbe properly neutralised, thus actingas a one-way device, while the othermust serve to introduce reaction,and if necessary to oscillate. Asimple circuit of this nature isshown in Fig. 1, so that the actionof the two valves may he clearlyseen. In this circuit the oscillatingcurrent in the aerial coil L, willappear in an amplified form in thecoil L2, whereas if the second valveoscillates the heavy oscillatory cur-rents produced in L, will not betransferred hack to L,.

The Single ValveIf we now transfer our attention

to the single valve, it will be seenhow difficult it is to make this valveoscillate without at the same timetransferring energy to the aerialcoil, which must in some way becoupled to the grid circuit. Weare now called upon to combine thefunctions of the two valves V, and

C37-

E

valves at least if it is to be possibleto heterodyne a carrier withoutradiation being transferred to the

V., in the previous circuit. Clearlythe valve is the only practicablenon -return device to employ, so

373


Non -Radiating Single -Valve Circuits -continued

that we must in some way utilisethis property of the valve.

Tropadyne and Super-autodyneThere are, it is true, circuits in

which a detector valve can be madeto oscillate and yet not radiate,but these are unsuitable for otherreasons. The best known of thesecircuits are the Tropadyne and theSuper-autodyne. In the first case

Fig. 2.-In spite of the fact that thereaction coil is not coupled direct tothe aerial coil, radiation will be pro-

duced with this circuit.

a centre -tapped coil is employed,and if the exact electrical centre isobtained no appreciable energy isradiated when the circuit is oscil-lating. In the Super-autodyne cir-cuit, which is really an improvedform of the Tropadyne, two con-densers are employed, so that thetapping point on the two neutralis-ing condensers can be made tocorrespond with that of the coil.Thus as regards oscillations pro-duced by the valve, these points areat the same potential, and no oscil-lating current gets into the aerialcircuit.

DisadvantagesBoth these circuits, however,

suffer from a very serious disadvan-tage that, if the balance is properlyobtained, no reaction effect can beproduced. Their use is thereforelimited to superheterodyne circuits,for which they were originally de-signed. For a non -radiating- 'single-valver to he of any use, it is im-portant that not only must it be

àlways entirely non -radiating, butalso that reaction must be almostif not quite as effective as in theusual detector.

The difficulty in the. case ofsingle -valve circuits really lies inthe fact that is 'order to obtain re-action it is essential to have some

coupling, either magnetic or electro-static, between the grid and anodecircuits of the valve, and this mustnot be balanced out or neutralisedas in the case of a high -frequencystage.

Use of a Loose -Coupled AerialClearly, however, there is no need

to make the grid circuit identicalNwith the aerial circuit. Although

it is essential to apply reaction tothe grid coil, yet this reactiveeffect might conceivably bebalanced out, so that no oscillatingcurrent produced by the valve couldreach the aerial, and thus beradiated. The idea is thus sug-gested of employing a loose -coupled aerial circuit.

The importance of 'a separately -tuned, or at any rate semi -tuned,aerial circuit will be realised whenit is remembered that in one tunedcircuit of which the aerial formspart it is essential to reduce theresistance of the aerial by reactionin order to increase the signalstrength. On the other hand, ifwe employ two tuned circuits ,be-fore a detector, then it is quitesufficient to reduce the resistanceof the second or grid circuit inorder to obtain almost the fullbenefit from reaction.

Two Tuned CircuitsFig. 2 shows a case in which two

tuned circuits are employed beforethe detector, magnetic reactionbeing applied to the tuned gridcircuit. It is not right, however,to suppose that this circuit does notradiate, fOr the coupling betweenthe reaction and grid coils willcause a heavy oscillating current topass in the grid coil, which willthen be transferred by means ofThe magnetic coupling between thegrid and aerial coil into the aerialcircuit.

If we now introduce an extrareaction coil in series with that pre-viously employed, and couple it 'ina negative sense to the aerial coil,then it is possible to arrange thecoupling so that, although the gridcircuit' oscillates, yet none of thiscurrent should be transferred to theaerial, provided the second reactioncoil is correctly adjuked. In prac-tice it was not found possible tomake this circuit entirely non -radiating, but at the same time a

considerable degree -of success wasobtained 4n this direction.

InteractionA drawback in this circuit, which

completely nullifies its use in prac-tice, however, lies in the fact thatthe setting of the second reactioncoil depends on that of the first,and also to some extent on that ofthe variable condenser.

The solution to the problem ofthe non -radiating single-valver doe'snot therefore seem to lie alongthese lines, owing to the fact thatnot only is the adjustment, whenfound, extremely critical, but alsoit varies considerably as other con-stants of the circuit are changed.

Necessary QualificationsThe only really satisfactory

method of making a single -valvedetector non -radiating would takethe form of a simple attachment,which, while not impairing theefficiency of the set for broadcastreception, would enable the receiverto oscillate violently without any ofthe oscillation reaching the aerial.

Test transmissions from the vesselconveying the Byrd Expedition to Spitz-bergen via Norway may be heard on40 metres. Other wavelengths are also

used, the call -sign being KEGK.

An attachment which would notcompletely bar the passage of allradiation in the aerial circuit wouldbe worse than useless, for it wouldencourage the amateur to oscillateviolently with the expectation thatno interference would be caused.

374

May 5, 1926 Wireless WeeKly

I AM sure warm welcome will begiven to L. G. Mainland for his

talks during what we may call the" Adults' Hour." OrdinarilyNatural History talks of the con-ventional kind do not particularlyinterest me, but I could not helplistening to every word of his talklast week on " Old Bill, theWalrus " and " The Strange Waysof Lobsters and Crabs." 1 do notwonder that the children are so fondof " Uncle Leslie," and he shouldnot be any less popular with thegrown-ups. .

* * *

THE way of the wireless trans-gressor is steadily being made

more and more hard. I see thatproceedings have been taken outagainst 135 persons for installingwireless sets without a licence, andof this number 134 convictions weresecured. These figures were givenin answer fo a question in the Houseof Commons recently. Many of thepeople prosecuted have been verysurprised and have wondered howtheir activities could have been de-tected. The Post Office inspectorsare becoming very clever in suchwork, and the special cars theyhave equipped as a result of over ayear's experimenting have some re-markably ingenious pieces of ap-paratus in them.

THEMarconi Company is having

considerable success with" itslatest equipment known as the" Orchestra Repeater," which canbe fitted to any passenger steamerwithout in any way interfer-ing with the ordinary wirelesstelegraph equipment used for com-municating- with other ships andwith the land. The installation isthe result of long experience withwireless microphones and otherbroadcasting equipment, and thedetail design is largely the result ofCapt.-- Round's experiments. Theobject of the - " Orchestra Re-peater " equipment is to enable a

band in, say, the first-class saloonto be distributed by loud -speakersto other parts of the ship. Whenthe band is not playing, music can,if necessary, be provided by gramo-phone records. The New ZealandSteamship Company's Rentuera isone of the latest vessels to be sofitted, and I am told that the equip-ment has met with an excellent re-ception among the passengers.

ECONOMY IN L.T.CONSUMPTION.

When valves of different fila-ment ratings are employedtogether in a receiver, as forinstance 2 -volt and 6 -voltvalves, it is uneconomical torun the 2 -volt valves inparallel with the 6 -volt, with

separate rheostats.It is more satisfactory toconnect the 2 -volt valves inseries, with a single rheostatto control them, leaving the6 -volt valves in parallel in

the ordinary way.

The apparatus to. which I havejust referred is not, of course, really" wireless " equipment, but issimply the application to anotherpurpose of the technique which hasbeen developed in connection withbroadcast transmission and recep-tion. Similar apparatus was usedlast Saturday week for the DailyMail's broadcast of the Cup Finalteams. Microphones at theStadium picked up the sounds ofthe cheers for. the King and thesinging of the National Anthem, andby means of the land telephonewires, the sounds were reproducedin Manchester to the immense crowdin Platt Field, Manchester, and the

.Wanderers' ground at Bolton. Itis estimated that about 25,000people at Manchester and a similarnumberat Bolton heard the enthusi-

375

astic cheers when Smith, carryingthe cup, led his team out on to thefield.

* *I SPOKE a few weeks ago of the

thrills which would be given usby Transatlantic telephony, when atan early date the Post Office willbe able to connect us by landlines toRugby and thence by wireless to theUnited States. During some re-cent experiments between Riverhead(United States) and Rugby (Eng-land) the wife of a distinguishedAmerican staying at the SavoyHotel, London, was permitted tospeak by wireless telephony to herchildren in Park Avenue, New York.She had only to pick up the receiverof her telephone in_the Savoy Hoteland chat to. her children just as ifthey were speaking on the telephonefrom some other part of London.Even her small son., aged 7, wasable to talk to her, and his firstwords were, " Hullo, Mummy ; it isII o'clock here. What time is itwith you? "

I am told by all who have beenprivileged to speak.- across theAtlantic in this way that the repro-duction is exceedingly good ; in fact,quite different from the results ob-tained when an American broadcast-ing station is reproduced throughthe B.B.C. stations here. It wouldbe a good idea if the B.B.C. wereto take an early opportunity ofarranging with the Post Office tobroadcast some interesting publicfunction in the United States bymeans of the new system. At thepresent time experiments are beingconducted every Sunday afternoon.Why could we not have a Sundaymorning Church Service in Americabroadcast here during Sunday after-noon? The five hours' differencebetween the two countries wouldmake this possible.

* * *

just found that my oldjack Binns, of CQDnow Director of the,Department of the

IHAVEfriend,

fame, isService

Wireless Weekly

THE WEEK'S DIARY(Continued)

Hazeltine Corporation, the ownersof the Neutrodyne patents. Binns has had a varied career sincethe famous wreck of the " Re-public," including a spell as warcorrespondent in South America andas a newspaper reporter in NewYork.

T.HE news comes that 2ZY hasA been heard in California. This does

not surprise me, as the Editor' ofRadio Broadcast has just written totell me that not only California butColorado, North and South Dakotaseem to be excellent receiving spotsfor English signals. This -un-doubtedly has some bearing on thetheory put forward by Capt. Roundand others that so long as thestations are far enough away, theyWill be heard quite well ! I knowthis is not quite the theory, but it isa remarkable fact that sometimeswhen stations a few hundred. milesaway are inaudible, stations ..at

For example, I have heardlistener express the opinion that'soprano songs " always come outbadly." On many occasions it hasbeen possible to prove that it wasthe apparatus and not the pro-grammes that caused bad reproducetion. Probably the only defect inthe B.B.C. reproduction now notice-able on good apparatus is that ofthe drum and other percussioninstruments. Incidentally, I amtold that many hours of experimenthave been devoted to finding somemeans of satisfactorily broadcastingthe sound set up by the slammingof a door !

* *

SPEAKING of -sound effects, I doreally wish the announcers

would manage to avoid that irritat-ing rustle of papers when they areleading their announcements andnews bulletins. It is quite easy todo so if they will only try. Oneartist who manages'to get a remark-ably natural effect in h.; delivery,and who actually reads his contri-bution (although everyone imagineshe delivers it without notes), hasgone to a great deal of pains to

double theexcellently.

HAVE you noticed how manypeople blame the loud -speaker

for faults which are really those ofthe set itself?

distance come in

The leading - inpoint of the aerialand counterpoiseat the new high -power Rosenhugelbroadcastingstation, near

Vienna.

avoid broadcastingbroadcasting unnecessarysounds. His " story," instead ofbeing typed on sheets of thin paper,is prepared on thick pieces of card,which are easy to handle and canbe laid down silently page by pageas they are finished with.

May 5, 1926

AFRIEND in New York has justsent me full particulars of the

newly -opened Radio House, in NewYork, on which I commented inmy last week's diary. The Editortells me that he is publishing inanother part of. the Journal this week

The broadcasting station at Stockholm,in Sweden, utilises a cage -type aerial.This station operates on a wavelength of428 metres, usually between 7.30 and

11 p.m. or midnight.

a description of the House, so thatI need not give you any descriptivedetails here. The Radio Corpora-tion of America -was responsible forthe scheme, and my friend tells methat the Ptiblishing 'Department hadto work overtime and to spend noend of energy in getting the detailsperfected. Americans enter withextraordinary enthusiasm into stuntsof this kind.

Dr. Alfred N. Goldsmith, ChiefBroadcast Engineer of the RadioCorporation of America, welcomedthe visitors to Radio House, andgave a most poetical talk to theassembly, bringing in references toMark Twain's stories, The ArabianNights, and so forth. Not knowingquite what to make of everything,the awestruck visitors were led intothe kitchen, where a battery -operated receiver with aerial andearth connection connected to plugsin the wall provided entertainmentin ample variety and volume for 'theworkers in the kitchen. As theintroductory speech was in such apoetical strain, I am surprised thatnobody thought of suggesting thatKing Alfred's experiences with thecakes might be repeated by the cookin a slightly -varied form.

376

MAY 5TH, 1926 ADVERTISEMENTS WIRELESS WEEKLY vii

MN MN MS MO WM ME Wit f. IN 3IE UNE II

Why use Accumulators and

o

parts of a wireless receiver cause so much trouble1 V and expense as do the accumulator and high tensiondry battery.

Apart from the actual cost of recharging and constantrenewals, who has not experienced the annoyance of findingthat the batteries are exhausted, just when some speciallyinteresting programme is due.

E AERO BATTERY ELIMINATOR is connected to theTA iearest electric light (direct current), when it supplies thereceiver with BOTH High and Low tension current and needsNO ATTENTION WHATEVER.

It is cheaper to run than other sources of supply ; thecost being LESS than ONE PENNY for 3 hours.

Batteries ?

Brown roAllied Companies -

THOMSON AND BROWN BROTHERS LTDBROWN Ei R OTHER 1.144N LT°

WHOLESALE ONLY GREAT EASTERN STREET, LONDON E.C.2 126, George St., EDINBURGH, and Branches.N s Ns m !EN Il

The "Hero"Battery Eliminator

DIRECT CURRENT MODEL100-240 Volts.

No. A.B. 75/5 - £7 - 10 - 0

MO

Please : :orderfromyourlocal :Wireless :Dealer :

ASTOUNDING REDUCTIONS IN(a0M,DgM.°03 alla"

AMLATUNING COILS AND FIXED CONDENSERSThe Herne of "Atlas" beg to announce that owing to the enormoussales of Coils and Condensers and cons( quent reduction in Productioncosts, they are now able to offer these articles at the following prices :

RetailNos. Price ea.25-50 2,6

75-150 3,S175-300 . 4/6

ATLASCOILSPatent

No. 215,053

Nos.Retail

Price ea.FIXED CONDENSERS

500 7/6 Capacity. Retail Price600 .. 9,6 .0001-.0005 Mfd. .. 1/6 each750 ... 10/6

1000 12/61250 .. 14/-1500 15/6 '01

We are maintaining our Quality in every way, thus enabling us toill adopt our now World-wide Slogan :

" We make them good-good judgesmake them famous."

SOLE MANUF.4CTURERS -

H. CLARKE & CO. (MCR.) LTD.Atlas Works, Old Trafford, Manchester.

JOnly the perfectCondenser passes thestrenuous T.C.C. testsyOUR fixed condenser

is one cf the most vitalcomponents in your set;

yet you buy it on faith.For without an elaboratetest you cannot tell whetherit is functioning correctly.Experts saythat the ma-jority of faultsin home -builtreceivers aretraceable tothe use of in-ferior and bad-ly insulatedcondensers. Itis false economy to buy anunknown condenser, foralthough you save perhapsa few pence in the firstplace, it even-tually becomesmuch morecostly whenbreakdownoccurs. Onlyby producingCondenserswhich give ab-solute satisfac-tion can T.C.C.hold their goodname. When'you buy a T.C.C. Con-denser you know that you

PRICES AND

Mansbridge, 2 mfds. - 4/8Mansbridge, 1 mfd. - 3/10Mansbridge, '5 mfd. - 3/4Mansbridge, '4 mfd. - 3/2Mansbridge, '25 mfd. - 3/ -

have chosen a componentthat because of the strenu-ous and elaborate teststhrough which it haspassed, can be indefinitelyrelied upon to be not onlybreakdown - proof but to

have an almostnegligiblepercentage oferror. Lookthrough t h efiles of any ofthe techni-cal Wirelesspapers a n dyou'll find re-

peated testimony to thequality of the T.C.C.-itsspecification in circuitafter circuit by experts

who know.Can you affordto overlookthis Condenser-renownedfor its accur-acy and de-pendability -for one ofdoubtfulorigin andstill more

doubtful qualities? Do as theexperts do-specify T.C.C.

CAPACITIES

Mansbridge, mfd. - 2/6Mansbridge, '09 to 'o 1 - 2/4Mansbridge, 'oo9 to 'oo5 2/ -Mica, oo4 to oor - - 2/4Mica, '0009 to '000t - 2/4

T. C. CCondensers

(Mica and Mansbridge)Manufactured only by:

Telegraph Condenser Co., Ltd.,Wales Farm Road, N. Acton, W.1

G.A. 5104.

AN ADVERTISEMENT IN " WIRELESS WEEKLY IS A GUARANTEE OF SATISFACTION TO BUYERS.

Vitr WIRELESS WEEKIN ADVERTISEMENTS MAv 5r 1926

IGRANic - PAC ENTJACKSET

*GRAMM -PACENTAUTOPLIJG

IGRANIC -PACENTUNIVERSAL PLUG

Take the speakerinto the garden-leave the setindoors

With the use of Igranic-PacentJacks and Plugs it is perfectlysimple to have your loud -speakerand head -phones wherever you wishin the garden. No need to movethe set about-thus securing maxi-mum enjoyment with a minimumof trouble.

No need to worry about loss ofsignal strength through faultyconnections-gOod c ontac t iscertain when Igranic-Pacent Jacksand Plugs are used.

Here we illustrate four of the range-write for the Booklet Y84, whichdescribes them all, and see howeasily they will solve your ownparticular problem.

All reputable dealers stock Igranic-Pacent Jacks and Plugs.

IG PANIC -PACENTOPEN CIRCUIT JACK

coMPANti

Exclusive Manufacturing Licenseesof Pa cent Radio Essentials.

149, QUEEN VICTORIA ST.,LONDON.

Works : BEDFORD.

Branches:

BIRMINGHAM BRISTOL CARDIFF GLASGOW

LEEDS MANCHESTEP NEWCASTLE

(kikAlkikAAAAAtkAA AA

Better Resultsat less cost!

using7minum"MELLOWTONE"/COUPLERS

The " MELLOWTONE " Couplerreplaces coils and holders at half

the cost and gives far better results.It eliminates distortion, gives excel-

lent selectivity and perfectly smoothreaction control. Is neat, finelyfinished, and takes up small

PRICES panel space.FROM Obtainable from all re -

/6 putable dealers. Writefor Catalogue.

LONDONDEPOT:Triumph House,

BRETTELL LANE WORKS

TOUR BRAD°Radia-Ads.

BUILTTO

LAST.

189, Regent St., WA

..........

t Oct ii

Ota&-' s;beav9viatic +,

51, ,

t 10'1'1E.

TWO TYPES:For outside panel

mounting:Two-way . 7/.Threo.way .. 10/6For inside baseboardmounting, with 6 in.

handle:Two-way .. 8/ -Three -way .. 12/6

Tuning is. - - accurate because the

moving block cannot fall.Holds the heaviest coil securely in posi-tion and prevents the fading away ofvolume. The vernier movement con-sists of three sets of enclosed precisionmachine cut gears and reduces the speedof the moving coil block by eight times.

From all Radio Dealers.

emusVERNIER

COIL HOLDERSGarnett, Whiteley & Co,, Ltd.,Lotus Works, Broadgreen Road,

LIVERPOOL.Makers of the new Lotus Buoyancy

Valve Holder.

AN ADVERTISEMENT IN " WIRELESS WEEKLY " Is A GUARANTEE OF SATISFACTION TO BUYERS.


rCI-RCUIT-SFOR THE EXPERIMENTERNo. 12-A FRAME AERIAL CIRCUIT FOR THE LOCAL STATION

torr+3

911T+2

1

R-F.C.

11.1:

H.T. -

L.1:+

Li -8.4 -I

-2BY quite a number of experi-

menters the frame aerial isprobably- regarded as an in-

strument to be used only with sensi-tive circuits, such as superhetero-dynes or receivers with severalstages of high -frequency amplifica-tion. It is quite true that this stateof affairs is for long-distance workgenerally true, if we leave out ofconsideration special circuits, as,for instance, the " Armstrong "types or similar circuits, whichmake use of special reactionarrangements. As a matter of fact,it is quite possible to get goodresults on a frame aerial with a" straight " circuit, as long as thetransmitting station to be receivedis within a reasonable short distanceof the receiver. Experiments inthis direction under various localconditions should prove of particularinterest.

Advantages of a FrameThe frame aerial has certain un-

doubted advantages over theordinary outdoor aerial, especiallyin crowded areas, where the erectionof an outdoor aerial is difficult, ifnot impossible. Under such cir-cumstances the frame may even bethe only possible solution to theaerial problem. Again, the direc-tional properties of a frame are toowell known to need recapitulationhere, but a further point which mayappeal to a good _many people isthat such things as earthing

switches for the aerial can be dis-pensed with altogether. The fearof damage from lightning is anatural instinct with many people,and even with proper switchingarrangements they often do pot feelaltogether happy when thunder -

CIRCUIT No. 12SPECIAL FEATURES1. No tuning coils required.

2. Reaction provided on theframe aerial.

3.. Smooth reaction control.

4. Quality of reproduction.

storms are about. The frame doesaway with all this.

A Simple CircuitThe circuit of the type shown

above should meet the needs ofanyone residing within about tenmiles of a main station, who re-quires loud -Speaker results. Withonly two of the valves in use itshould be possible at this range toobtain moderate loud -speaker sig-nals, the addition . of the secondstage of amplification being avail-able if required for, greater volume.It should be understood, of course,that loud -speaker strength will notnecessarily be attained with this eir-

cult, even quite close to the trans-mitting station, if the immediatesurroundings of the receiver offerbad screening. It is well knownthat in, for instance, buildings witha framework of steel girders it isnot infrequently found that signalsof only weak telephone strength canhe picked up even on sensitive re-ceivers at a distance of a mile ortwo from a main station. This is amatter which must be determined byexperiment.

ReactionComing now to the details of the

circuit given, it will be seen that the" Reinartz " type of reaction is pro-vided. The use of the grid con-denser and leak method of rectifica-tion by the detector valve Vi intro-duces a certain amount of dampinginto its grid circuit, and in order tocompensate for this it is advisableto provide reaction. The cus-tomary method of providing re-action with a frame aerial, of usingcoils separate from the frame itselfin order to secure the necessarycoupling, has the disadvantage thata certain number of additional com-ponents are required. In this cir-cuit the only coil needed, apart fromthe frame, is the radio -frequencychoke coil in the anode circuit ofthe valve Vi.

A Tapped Frame AerialIn order to secure this advantage

the frame aerial itself is tapped asindicated in the diagram, the larger

377


CIRCUITS FOR THEEXPERIMENTER

(Continued)

portion of the winding serving asthe grid -tuning inductance and theremainder for reaction. The con-denser C, tunes the grid circuit,while C2 gives the necessary smoothcontrol of reaction needed with areceiver in which the main tuningwill be sharp.

Size of FrameFor the lower broadcast range of

wavelengths the frame, which mayhave 2 -ft. sides, should be woundwith about twelve turns of wire,with half -inch spacing between theturns. The solenoid form of wind-ing is indicated here, rather moreturns being required if a flat spiralwinding is employed. These twelveturns are included in the grid circuitof the detector valve, a further twoturns being added for the reactionwinding.

Variable CondensersThe two variable condensers, C,

and C2, may be of .0003 capacity.Larger values than this are not to.be recommended, since the reactioncontrol will he rendered easier by

the use of a reasonably low -capacityvalue for C2, while the tuning ofC, may be expected to be quitesharp. A vernier or slow-motiondevice may be of assistance in con-junction with this latter condenser.The aim should be to keep theparallel tuning capacity as small aspossible, the number of turns on theframe being adjusted to suit thelocal station.

Hand -CapacityOne trouble that may be ex-

perienced with the circuit as shownis the presence of hand -capacityeffects. If this offers a seriousdifficulty in operation, the followingmodification of the circuit willoften set matters right.

The reaction winding of theframe aerial should be disconnectedat the tapping point, the reactioncondenser C2 being placed in circuitbetween the tapping point on theframe and the inner end of thereaction winding. The tappingpoint, which is connected to L.T.negative, should then he earthed,

the remaining connections beingleft as before. This will have theeffect of placing the batteries atearth potential, and it will usuallybe found that hand -capacity

are much reduced, if not altogethereliminated. Some effect may benoticed when the hand approachesthe frame itself, but this can beremedied by fitting an extension armfor the purpose of rotating theframe.

Low -Frequency AmplificationThe two stages of low frequency

amplification call for no particularcomment, these as shown consistingof the conventional methods oftransformer and resistance -capacitycoupling.

The inclusion of the by-pass con-denser C4 may be found to effectan improvement, this being a!

matter for experiment.Valves

The detector valve V, shouldpreferAbly be of the high -imped-ance type with a high -amplificationratio, such' as the D.E.8 H.F.,D.F..4 or D.E.5b. For V2 avalve of the D.E.5b or D.F.A.4type should be found suitable, whileV3 may be of the D.E.r, B4 orD.E.A. r class.

Suitable values for the compo-nents in the last stage of amplifica-tion are roo,000 ohms for R5, o.rmicrofarad for C5, and .25 megohmfor R6.

, forlexacar.-.-zatoWeFAff ///,'ZeZZZZ:N=550,,,,k,

b;;;;.45"12,:tri"MJ0:53,( se Oz.,

gCALIBRATION with certainty to the

1.000th part of the variable capacity.This Is the tuning efficiency obtained withthe Colvern Selector. The complete circleof the dial is divided to provide a value of100 degrees for everyrotation of the Index.Pre -supposing your condenser and induc-tance to cover 300 metres, the degreeinterval represents .3 metres - obviouslyevery station can be calibrated definitely.

THE COLV ERN SELECTOR.LOW LOSS

Reading to 113,600th capacityCapacity-

'0005 mfd. 21 1 0'0003 mid. 51 0 0

TYPE F., without gearattachment.

Capacity-'0005 mf.l. . 15 0'0003 mid. - 14 0

One hole fixing,Other capacities if required.

Descriptive Folder uponrequest.

COLVERN INDEPENDENTVERNIER Price 216Ask your dealer also for theColvern Low Loss Coil Former

Price 6/ -

enables calibration

and relocation to

a high degree ofaccuracy

The Colvern Is logically the only consdenser worthy of the attention of seriousexperimenters. An insulated spindle re-duces the effect of hand capacity to aminimum, a point of paramount itmportance inthe reception of distant signals.

See the Colvern at your dealer's ITHE COLVERN LOW LOSS SELECTOR

(Geared 20-1.)

COLLINSON PRECISION SCREW CO., LTD.,Provost Works, Macdonald Road, Walthamstow, London, E.17

Tetephope: Walthamstom 532

AN OLD OFFENDERThe Dry H.T. Battery is incorrigible.It is forever making itself a nuisance.That is why it must be sentenced tolife banishment and its post given tothe Westam H.T. Accumulator. Thepeace will then be kept: your concertswill not be disturbed by'so much as awhisper of noise.

The Westam H.T. Accumulator is sold at the extraordinarily low price of 6d. a -

volt. It gives perfect reproduction with an absolutely silent background, can berecharged at any charging station and is so constructed that self discharge andcreeping is impossible. The container (made of imitation crocodile leather) isacid proof and rot proof. Plates are interchangeable. Spare parts at pro-portionate prices. Obtainable in any voltage from Radio Stores or, in case ofdifficulty, direct from makers.2 amperes model as illustrated 6o volts 30/-, also oo volts £2 5s.

120 volts £3. Carriage 2/- extra.

WESTAM ACCUMULATOR COMPANY,335, Katherine Road, London, E.7.

Telephone: Orangewood 1745.

WESTAM UMW U 'ATOP,

378


READERS' COMMENTS )

Reception of WGYSIR,-In the issue of Wireless

Weekly for March to, on page 136,there is a reference to reception ofshort-wave transmissions from WGY.It happens that last February I got theGenerkl Electric Company to carryout some tests on the short waveswith a view to putting across a specialprogramme intended for Germany. itwas in the course of these tests thatthe wavelength was shifted from the40 -metre region to 35 metres. Also,transmissions were carried out in this

send in more extended form the infor-mation which you have at hand as tothe signals from Schenectady. I amparticularly anxious to have the exactdates and times of reception, withindications as to quality, fading, and" intelligibility." What is of particu-lar value is to learn at what times the" intelligibility " was best, and aboutwhat percentage of words could be cer-tainly understood. Quite a bit ofGerman speech was put out in thecourse of the tests last February. Wasany of this heard?

0 0 0

Six Telefunkenrectifying valvesare used at thenew Rosenhugelbroadcastingstation, nearVienna. Thisstation is trans-mitting at presenton a wavelengthof 882.5 metres,with an input of

about 28 kw.

0 0

connection between 2 and 3 p.m.(Eastern standard time), which wasquite out of the ordinary. I take itthat some of these transmissions wereheard by your staff or your readers.We had a number of reports fromGermany, all of which were Most un-favourable.

Now, it would be greatly appreciatedif you would be so very kind as to

Any general information as to thequality of American short-wave sig-nals during the past season would bemuch appreciated. All such informa-tion is of much value, and any whichyou can send will be passed on toother interested parties. I am in con-tact with KDKA and with Bellevue,Washingtop.

With many thanks in advance for

any reports which you may be ableto communicate, I am,-Yours faith-fully, S. MCCLATCIIIE.

Cleveland, Ohio, U.S.A.

SIR,-I do not suppose very many:of your readers realise how amazinglysimple it is to receive WGY at goodloud -speaker strength at this time ofthe year. Of his many simultaneoustransmissions, that on 9,375 Kc. (32metres) is rrobably the strongest, andhas the additional merit of being al-most entirely free of interference. Iam surprised that the B.B.C. do notgive us more of WGY, for the qualityof his transmission is excellent, andon three valves he sounds very muchlike 2L0 (eight miles distant) does ontwol

I am also experimenting on WGYwith a superheterodyne, and wouldlike to compare my experiences withthose of your readers.-Yours faith-fully,

Sydenham.

LF. Transformer DesignSIR,-We have observed on the back

pages of one of your journals a state-ment by a transformer manufacturerwhich we believe to be incorrect. Itcertainly is incorrect when it says that" all radio experts agree," etc.

In our opinion the impedance of anyparticular valve is an almost constantfactor, and since the impedance of thetransformer necessarily varies o\'er anenormous range as the notes vary overthe musical scale, it is almost anabsurdity to talk of transformer impe-dance suiting or matching the valveimpedance.

We venture to suggest to you thatstatements of that character made inadvertisements should be submitted toan independent expert before you allowthe publication of them in a mannerwhich we, for example, think is cal-culated to mislead your readers.-Yours faithfully,

FERRANTI, LTD.Hollinwood, Lancs.[Messrs. Ferranti raise an interest-

ing point in their letter. The amplifi-cation of a transformer -coupled stagedepends upon two factors. There is,first, the amplification of the valveitself, which is dependent to a largeextent upon the impedance of the ex-ternal anode circuit, in this case, theprimary winding of the transformer.

J. R. HALLIWELL.

379


SUPREMEVALUE WIRELESS OFFER.A highly efficient 1 -Valve Set, built up entirelyof components of undoubted quality and un-challengeable merit, offered at a Keen cutPrice, on Easy and straightforward Terms.

SPECIFICATION:Solid Oak Cabinet Polished Jacobean Finish.Utility' Low Loss Condenser (Square Law).

Two-way Aermonle' Coil -holder, Low Loss.Igranic Rheostat and 2 Igranic Cells.'Cosmos' Valve (Metro -Vic) S.P.18 D.E. 2 -volt.General Radio Headphones80 volt. N.V. Battery.Exide 2-vett Accumulator.Ebonite Panel, Post Office Grade LSolid Ebonite valve -holder. £6:0:0

With complete

Accessories.itAerial Outfit.

Each instrument incorporates the MarconiPatents in respect of which we pay a full

Royalty fee of of proved1 216 on everyset that isnroduced8'

NOW

TERMS : 8/ -now & balancein 14 mon-thly pay-ments of

i fYOU areentirely satisfied.Money refundedif disappointed.

CATALOGUEof Valve & Cry-stal Sets, &c.,Post Free. Keen-

est Prices.C. Graves Ltd,

Sheffield.

Ail Post Free ^ Al- Callers PricesS.O.S. BATTERYTESTER

3 -Bead Type Onlytells immediately /6If full or emntV.

Square Law Var.Condenser.

With Knob and Dial.001 Panel type 6/6.0005 .. 5/-.0003 .. 4/8

Vernier Blade extra 1/4angler, McMicheels,

Edison -Bell, Lissen,Mallard (usual prices.)New Mansbridge,Smfd. 316. 1 mid. 2/6

Coil Holders.Reliability Vernier 3/8

Lotus " 2 -way 7/-Newey " 2 -way 6/-L. it P." 2 -way 8/0

" Polar " 2 -wayCam vernier.. 6/-

N]oldtone"Vernler 7/- Back Of Panel 6/

Aerial Wire 7/22'sEnam., Bright 4 strd100ft., 8/8. 2/8.. 1/1do. Electron . 1/8Shell Insulators, 3d.Lead-in Tube 9in. 1/ -

RELIABILITYWIRELESS

GUIDE, No. 2.Fele on 7800,4.

OIL FORMER.

TheReliability 46 Spoke Type

Mark. with instructionsBritish Wires. Ebonite Panels.

swg. des. dec. Matt. 5" 3/16'18 1/11 3/5 9" x 6' 2/2 1/1020 2/2 4/2 12" x 9" 4/6 8/922 2/6 4/7 12" x 12' 5/9 5/-24 2/11 5/- 12"x 9' 5/8 4/926 3/4 510 15" 012' 7/6 5/820 3/9 6/6 4" x 8d. 6d.10 4/10 7/8 7'x5' 1/6 1/212 5/6 8)9 6" x x 1' 10d.36 8/- 12/- Any 8178 cut.40 17/- 20/- Sq. in. id., I', ldTransformers L.F.

RadioInst.25/-,27/8Igraine 21/- and20/-Eureka, No. 2 21/-C'neert Grand 25/- Baby Grand 15/ -email A.1".4 17/6

Only

1/3

Special Values.WatesMierostate 2/9R. I. Detector.. 6/-LlbertyDetector 8/6Lissenola Uait 18/6Antipong Valve -

holder 1/6A.F(EMPlm) 7/8 With Wander Plugs'Formo'Shr'ded 10/- 11/-, 60v., 7/6

McMichael II.P.10/ 36v., 4/6, 15v., 1/10'Y'lmic' Coil 10/-

Valve Holders. 60,., Ey'r-r'dy 12/6Type A 7d. Polar 1/8 36v 7/-, 16v., 8/8Sorewed 8 nuts Slemen. ermine price.Ebonite ..led. Unfelt 67v 11/6Antiphonic 1/8Security Type 1/-Sullivan's 120 -ohmPhones. er-Govt. 4/6

5 RADIO HOUSE.MAC Au LAY So HUDDER501110

341 Gram,. 'T.OROUCH HUDDE,5FIILO

Orders 6/6 value,carriage paid.

Under5/0,2d.per 11.for packing.

Secondly, there is the step-up ratio orthe transformer.

Now, if the impedance of theprimary winding is made equal to thatof the valve, then the amplificationobtained is 0.7 times the theoreticalvoltage amplification factor of the par-ticular valve. As the impedance of theprimary winding is increased, so theamplification of the valve graduallybecomes nearer and nearer to thetheoretical value. If the transformerimpedance is made three times that ofthe valve, then the actual amplificationis nearly 0.95 times the theoreticalamplification factor. Obviously, there-fore, very little is gained by makingthe primary impedance any more thanabout three times that of the valve.

Turning now to the consideration ofthe second factor, the step-up ratio,the secondary winding on a trans-former is limited, not by considerationsof ratio, but by the self -capacity of thewindings. There is a limit wherefurther increase in the number of turnsceases to increase the step-up ratio toany appreciable extent, owing to thecounteraction of the self -capacity.Improved methods of winding enablethe number of turns on the secondaryto be increased, but, nevertheless, thelimit is present.

Obviously, therefore, if the secondaryturns are fixed and the primary turnsare varied, the step-up ratio must vary.A transformer having a high primaryimpedance will of necessity have a lowstep-up ratio, while conversely a cor-rectly designed transformer with a lowprimary -impedance would have a highstep-up ratid.

The application of these principlesto a valve is as follows :-Following ahigh impedance valve, the transformerprimary must be of high impedance,and consequently the step-up ratio islow. Following the next valve, how-ever, which is usually made of lowimpedance the primary impedance ofthe transformer need only be aboutthree times that of the valve. Thesecondary, however, remains the same,so that the step-up ratio of the trans-former is considerably increased. If ahigh impedance primary was used inthe second stage, then the step-upratio of the transformer would have tosuffer.

While, therefore, Messrs. Ferrantiare quite correct in stating that it isunnecessary to match the primaryimpedance with that of the valve, it isdesirable to use different ratios fordifferent stages, a low ratio for thefirst stage and higher ratios for suc-ceeding stages. Messrs. Ferranti raisean important point in drawing atten-tion to the fact that impedance dependsessentially upon frequency, and forperfect quality the impedance of thetransformer should be high at verylow frequencies. With such anarrangement, however, there is gravedanger of producing resonance pointsin the transformer, occurring actuallyin the audible range, so that the designof a transformer is very' largely amatter of compromise.- n.9

. . . we might be in thestudio-will be no uncommon remark now the Watmel Auto -Chokehas come into being. Never before has there been such an ampli-fying instrument. Though building up whispers into volu-minous sound, never does it sacrifice tone for volume. Thesecret Iles in the patent core and specially balanced windings.Ask your Dealer for a demonstration and send to 118 for descrip-tive booklet-" Straight as a dle."

18/6Lance. Bright parts heavily nickelled. PriceComplete with Condenser and fixed resis-

THE WATMEL WIRELESS CO., LTD.332a, Caswell Road - - London, E.C.1

Telephone: 7990 CLERKENWELL.Lancashire R Cheshire Representative:Mr. I. B. LEVEE, 28, Hartley St., Levenshulme, Manchester

Telephone : 475 Keaton Moor

Subscription RatesMODERN WIRELESS

15/- per annum United Kingdom.13/6 per annum Canada and

Newfoundland.15/- per annum Other Countries.

THE WIRELESSCONSTRUCTOR

8/6 per annum United Kingdom.7/6 per annum Canada and

Newfoundland.8/6 per annum Other Countries.

WIRELESS WEEKLY1714 per annum United Kingdom.17/4 per annum Canada and

Newfoundland.19/6 per annum Other Countries.

WIRELESS13/- per annum United Kingdom.13/. per annum Canada and

Newfoundland.13/- per annum Other Countries.'

Lesser periods than 12 months pro rata.

RADIO PRESS LIMITED,Bush House,Strand,London,W.C.2

380

1ity 5, 1926

****************************************

****************************************

PRACTICAL TOPICSBy G. P. KENDALL, B.Sc.

H.T. Accumulator Troubles-Sludge Deposit- Stiff or Free -running Condenser Bearings ?

WEEK or so ago I meta man who proceededto grumble bitterlyabout his accumulator,.saying what a rottenbad battery it was --

wouldn't hold its charge a fortnight,and always ran down before itshould.

An Unusual TypeNow, the battery in question was

a somewhat unusual one, the con-tainers being glass boxes sealedacross the top with pitch, while theplates also were out of the ordinary.As it happened, I had used one ofthese batteries myself with everysatisfaction for over two years, andI knew that whatever its drawbacksfailure to hold its charge was notone of them. As a matter of fact, itwas particularly good in thatrespect, so that I told him I thoughtthere must be something wrong inhis treatment of it.

Not InsideI was eventually shown the bat-

tery, and certainly the plates lookedin perfect health, there was little orno sludge, the acid was up to thecorrect level and gave a satisfactoryhydrometer reading. All the same,the cause of the trouble was quiteobvious, because the same thing hadhappened to me and I knew what tolook for.

Where it WasThe pitch tops of the cells were

slightly sunk so that any moistureand dirt which might collect thereonremained in a layer which constantlythickened. Each time the accumu-lator was charged a trace of acidwas emitted from the vents in theform of spray, so kr eping the depositmoist, and the net result -was aleakage path of comparatively lowresistance between the terminals.

A Good RuleThe trouble is one which it is well

to be on one's guard against, and'it is a very safe rule to keep theinside of an accumulator well

charged and the outside thoroughlyclean, especially round the terminals.

An H.T. GrumbleTroubles with accumulators

remind me of a very sore point ofmine : why on earth do some manu-facturers of H.T. accumulators pro-vide only a most microscopic spaceat the bottom of each cell to allowfor the deposition of sludge?

It may be argued that an accumu-lator does not throw down a depositwhen properly looked after, but it

* oa

While well -designed bearingsare important in variablecondensers, skill in manipu-lation counts for a great deal.

must be admitted that it usually doesunder . everyday, as distinct fromideal, conditions. And just imaginewhat a job it will be when it becomesnecessary to wash the sludge out ofsixty separate cells !

A Point in Condenser DesignDo you like your variable con-

densers to run freely or stiffly? Amatter of taste, no doubt, but ithas always seemed to me that theideal is a condenser running freelyand smoothly as though fitted withball -bearings ; of course, withoutsloppiness or backlash.

A Personal ViewI expect the condenser makers

would like us to prefer the stiffly -moving type, which is probablyeasier and cheaper to produce, butmy personal feeling about it is that

Wireless Weeklythe extra few shillings would not begrudged if I knew that by payingthem I could be sure of the motionwanted.

A Free -Running PointApart from the necessity of a high

standard of workmanship in thehearings, a very free -running con-denser presents. special problems ofits own. The obvious one concernsits method and position of mounting,involved herein being another of thefactors which put up its cost.

If the condenser is mounted on avertical panel the moving vanes willobviously tend to fall from certainsettings, and a eounte.r-weight-musttherefore be fitted. Now, a counter-weight involves an arm to carry it,and space for that arm to turn, andso up goes the bulk of the condenser.

Is it Worth It ?Almost inevitably, then, a very

free -running condenser is one ofgreater cost, weight and bulk, and

some of my readers may doubtwhether it is worth while to incur allthis ; much depends, I think, on thedegree of manual dexterity possessedby the operator.

If he is capable of the delicatemanipulation of fine controls (andmost people can become so withpractice) he will appreciate and reapthe benefit of such a condenser asI have described.

When it is FeltGiven such capabilities on the part

of the operator, a condenser re-sponding to a light touch may makeall the difference when it comes totuning -in a really weak station. Ifthe operator is heavy -banded, how-ever, he will probably be actuallyworse off with a free condenser thanwith a stiff one.

381

Wireless Weekly May g, 1926

New Radio Press Envelopes

WE have much pleasure in announcing the issueof two new Radio Press Envelopes, each deal-ing with the construction and operation of a

set of outstanding merit.

The "Super Seven"Superheterodyne receivers are becoming increasingly

popular, so that the home constructor will welcome theappearance iof. the " Super Seven," which is fullydescribed in Envelope No, 12. This receiver has beendesigned and the comprehensive instructions for build-ing it are written by Mr. Percy W. Harris, M.I.R.E.

The " Super Seven " is highly selective,, works on aframe aerial, and it possesses the great advantage ofextreme simplicity of tuning. Included in theEnvelope, the price of which is 5s., are full-size blue-prints of the layout of the wiring and of the panel,while eleven photographs, reproduced on special artpaper, give a clear impression of the appearance ofthe finished receiver, as well as being of considerableassistance in the constructional work.

The "Three -Valve Dual"The " Three -Valve Dual " Receiver, which is

described in Envelope No. 13, was designed by Mr.John Scott -Taggart, F.Inst.P., A.M. I. E. E. Theeconomy in valves effected by the use of the reflexsystem makes an appeal to a large number of con-structors. The " Three -Valve Dual " is an econo-

mical receiver, which employs a reflex Circuit of Provenutility, and the home constructor can embark on theconstruction of this receiver with complete confidencein his ultimate success.

Results ObtainableLoud -speaker reception is possible with this receiver

from the B.B.C. stations and from many Continentalstations. Every possible constructional detail is fullyexplained, and the Envelope, of which the price is2S. 6d., includes two full-size blue -prints and foursheets of clearly reproduced photographs. The instruc-tions and 511ustrations combine to render perfectlystraightforward the building of a receiver which shouldgive the constructor every satisfaction.

Rtaders are asked to note that the prices of theseEnvelopes post free are 5s. 44d. for Envelope No. 12,mld 2s. 9d. for Envelope No. 13.

Amateur Transmitting Notes

QRA's WantedG-2BOW, PI-CD8, GI-5GH, R-DE2, D-7WA,

I.A X X, DCN, EAC9, E4, 2JD, KWS, LFG, PE-6XC,WBR, K-4ZM.

QSL Cards HeldWe have cards for the following :-From India to : G-2CC, G-6CM, G-2QM, G-6EP,

D-7PK, U-xAI, SMUV, F-8FU, F-SRST.From Austria to : B-08, PCLL, N-oRP, OCNG,

GBM.


(Continued from page 362)

One mahoganite panel, 16 in. by8 in. by 3/16 in. (American HardRubber Co.).

One supersonic filter transformer

and three supersonic intermediatetransformers (L. McMichael, Ltd.).

One Soo -ohm potentiometer (L.McMichael, Ltd.).

Two fixed resistors, type " DE,"with sockets (A. J. Stevens, Ltd.).

One .00i fixed condenser (A. J.Stevens, Ltd.).

One 3 : i L.F. transformer (U.S.Radio Co.).

Five Lotus non-microphonic valve -holders (Garnett, Whiteley & Co.).

One 7 -terminal strip (Burne-Jones& Co:).

The arrangementof the wiring willbe clear from this

photograph.

Three 3o -ohm rheostats (C.A.V.).One .0003 fixed condenser,_ with

clips for grid -leak (H. Bowyer &Co.).

One .00i fixed condenser (WatmelWireless Co.).

One .5 megohm grid -leak (Dubi-lier Condenser Co.).

Six lacquered brass terminals.Bolts, woodscrews, etc., and a

quantity of square tinned copperwire or " Glazite " for wiring up.

Radio Press panel transfers.

ConstructionVery little need be said regarding

the actual construction of the set,since the lay -out of the componentsis very clearly visible in the photo-graphs, and the wiring is perfectlystraightforward. It should be men-tioned, however,, that the first com-ponents to be wired should be thegrid -leak and condenser, the valeholder connections coming next;

Further notes on the best H.t.:values, etc., and the method` oPoperating the set will appear in nextweek's issue of Wireless Weekly.

"MODERNWIRELESS"

MAY ISSUE.

NOW ON SALE. PRICE 1/-

382

May 5, 1926 Wireless WeeKly

APPARATUSWE HAVE

TESTED

Conducted by the Radio Press

Plug -In CoilsMessrs. The Penton Engineering Co.

have sent us a number of their plug-incoils for test and report.

The coils; which are fitted with plugand socket mounting, employ a specialform of winding which is built up onan insulated former. The whole coilis covered by a strip of celluloid, andis fixed to the socket by a strongthread binding.

The three coils were numbered 35,5o and 75, and their values are approxi-mately the' same as those of othermakes of coils with the same num-bers, although the value of the No. 35coil appears to be somewhat on thelow side. Their high -frequency re-sistances were found to be satisfac-torily low and the coils gave a satis-factory performance in a set, both foraerial and H.F. purposes. They werenot, however, found to be a particu-

larly good fit in various sockets inwhich they were tried, being somewhaton the, tight side.

A number of diamond weave coilswithout mountings were also submittedfor test, and these were found to havesatisfactory high -frequency resistances,while their inductances were of suit-able values to enable them to be usedon the broadcast wavelengths.

Laboratories, Elstree.

A GridleakMessrs. Metro -Vick Supplies, Ltd.,

have sent us one of their 2-megohmgridleaks for test and report.

This is of the conventional patternwith a metal cap at each end to enablethe component to be mounted betweenspring clips. Its resistance is clearlymarked, the rated value being 2

megohms. When placed on test theactual resistance was found to be 1.8megohms, which is near enough to therated value for all practical purposes.

When used in a set it was foundto be satisfactorily silent in operation,and we can recommend this gridleakfor use.

A Multi -Ratio L.F. TransformerWe have received from Messrs.

Radio instruments, Ltd., one of theirmulti -ratio L.F. transformers for testand report.

0 0 6

The coils sub-mitted for test byMessrs. ThePenton Engineer-ing Co. are of thestandard plug-intype.

This instrument is of the shroudedtype, and is finished in an attractiveblue colour. A strip of insulatingmaterial carries six terminals at thetop of the instrument, each of whichis plainly marked. Instructions aregiven for the connections to be followedin order to obtain given ratios, ofwhich there are seven. The lowestratio obtainable is i to 1 and highest

i I I 111111111111111111111111111111111111111111111111111111

Build your ownloud 'speaker for

the summer.Summer Time ! To bespent in the gardenbasking in the sun yourdiverion the invisibleentertainer, radio. It isa thing to look forwardto, this restfulnessand to the full rowerand mel ow music ofthe "Lissenola " And thecost ? - negligible ; for yourfinished loud sp aker worksout at less than 15/- (tt e"Lissenola" is 1316, and withit we give you full-size dia-grams and clear instructionshow to build a proved hornfor a few pence'. You couldnot have a better loud speakerwhatever pr ce you paid.If you prefer it you can easilyconvert the " Lissenola' tocarry a cone or any otherdiaphragm work ng on thereed principle by attachingthe Lissen Reed (1,'- extra).In addition, if you possess agramophone you have onlyto substitute the Lissenola forthe sound -box to convert itat once into a radio loudspeaker.

Ask your dealer to showyou the

LISSENOLALISSEN LIMITED,30.32, Friars Lane,Richmond, Surrey.

Managing Director: Thomas N. Cole 4

L47

111111111111111111111I1111111111111111111111111111111111111111

383

Wireless Weekly

CtetrAeconentettdr

TrellebOrg$GUARANTEED

GENUINEEBONITE" 120,000 Volts per m.m.

No surface leakage."-N.P.L. Test Report.

ciadad bre r&'All Trade Enquiries to t-

TRELLEBORGS EBONITE WORKS,LIMITED,

AUDREY HOUSE, ELY PLACE,E.C.1.

NNZNNNNNNNNNWANNNNESlW,INW.01%.;.l

"The Allwoodorn"

Hours : 9 till 6.30. Sot.2 o'clock.

No metal stripsor dust collectingribs. Improvementin tone, detailand volume guar-anteed.Send for list of othermodels.

Manufacturer andPatentee --

H. MADDISON2a, RONALD'S RD.,Holloway Road Nearilighbory Station, N.5 4.

NNNNNNNNNFANNNNNNNNNNNNNNN

The POLYTECHNIC309, REGENT STREET, W.1.

ELECTRICAL ENGINEERINGDEPARTMENT.

(Wireless and High Frequency Section.)A special course of Six Lectures on

The Thermionic Valveand its

Uses in Wireless Circuitsby

W. H. DATE, B.Sc., A.M.I.E.E.on Wednesdays, commencing

May 12th, 1926, from 6.30 to 8.30 p.m.The lectures will be fully illustrated bydemonstrations (including transmission)

and lantern slides.FEE FOR THE COURSE 7/6

Particulars and syllabus from theDirector of Education.

EASY PAYMENTS.Waysupply by Any make of accessories

easy Any make of setspayments Any make of components

10% down. Balance spread over one year.Carriage Free. No References.

Send hat of requiremma,

London Radio Supply. Co., 11, Oat Lane,London, E:C.2. 'Phone : City 1.911.

APPARATUS WE HAVETESTED(Continued)

9 to 1. The transformer is guaran-teed for one year by the makers. Thistransformer was placed on our stan-dard test panel and was tried out as afirst stage inter -valve transformer.The ratios recommended for first stagewere tried out, and with a D.E.5bvalve as the detector. The best resultswere obtained with the connectionswhich are recommended for first stageonly. The actual ratio is 3 to 1, andthe amplification obtained was in everyway up to standard, while the qualityof both speech and music was verygood indeed. With a ratio of 41 to I

the amplification obtained was some-what above normal, but the quality,although very good, was somewhathigher in pitch.

The Multi -Ratio R.I. Transformer isfitted with six terminals on an insu-

lating mount.

When tested in the second stage witha D.E.5 type of valve the best resultswere obtained with the 4,1 to I ratio,and not only did this give an increasedamplification as compared with thestandard, but the quality was in everyway highly satisfactory, giving naturaltones of both music and voice. Withthe 6 to i ratio the amplification wassomewhat less, whilst the tone ofmusic was inclined to be somewhatthin ; the 9 to f ratio was found to besomewhat better as regards quality,although a slight drop in amplificationwas still observed.

The insulation between primary andsecondary windings was found to beInfinity, and although slight variationsin quality of reproduction wereobserved with the different connections,it was in all cases of a very satisfac-tory order. The instrument is wellfinished and robustly constructed, andcan be thoroughly recommended for allpurposes, since the most suitable ratiocan be chosen for use in the particularcircuit being employed.

384

May 5, 1926

Wireless Weekly Small Advertisements.

BARGAIN-Fada latest model long -short fivevalve neutrodyne receiver-complete with

valves-conditions as new-perfect reproduc-tion-gets almost anything -230, no offers.Edwards, 111, Leeside Crescent, GoldersGreen. Speedwell 3395.

PATENTS, Trade Marks, Inventions,Advice, Handbook and Consultations

free. B. T. King, Regd., Patent Agent,146a, Queen Victoria St., London, E.C.4.

TELEPHONE RECEIVERS and LoudSpeakers Rewound, 2,000 ohms, 3/6.-A. Roberts & Co., 42, Bedford Hill,

Balham, S.W.12.

Ir).06,DE'S 10/6Our Valves are admitted to be the bestBritish made valves on the market. 3 Volt

kW_ '06 L F. or H.F. only 10/6 2 Volt '34 onlywist I 10/6. Power Valves from 12/6. Write at once for

our FR HE HOOK and get full particulars. Ifyour dealer is "tied" we seer'?direct. RA DIONS LTD. RadionWorks, BOLLINGTON,Macclesfield. England.

TRIOTRON VALVES. EmWhy

terpay 1

V4/-for Dullitalyes when

you can obtain the famous Triotron Dull EmitterValve, 2 volt, 2 amp., 5/6., 3-4 volt. '06 amp., 6/6.Power Valve, 10/6 post free.

WHAT OUR CUSTOMERS THINK.-R. S. E., East-bourne, writes: " The best Dull Emitter I havetried. I enclose P.O. for another."

SATISFACTION guaranteed or money refunded. By postfrom H. E. NICHOLLS, 29-30, Trinity Sq., Tower Hill,E.C.3.

ECONOMY VALVES FOR PORTABLE SETS.2v. '06 H.F.L.F.. and 234 P.V.

LOUD SPEAKER RESULTS FOR 46 AMPS.THE BETTER BRITISH VALVE

Obtainable from Lewis's Ltd., Liverpool andManchester, and

Lustrolux Ltd., West Bollington.Nr. Macclesfield.

p`.703931=CEP I

M 'PA as S t 13 irmin Olarn

c .0 D AAny Wireless

Goods advertised

. the " WirelessWeekly " can

beobtained by return of post

on C.O.D.frora.---

Y WING'S(GI,A.SGOW),

LTD

40, STOCKWELLST., GLASGOW.

11

All communications regardingadvertising in " Wireless Weekly,"should be addressed to :-

Advertisement Manager," WIRELESS WEEKLY,"

Bush House,Strand, London, W.C.2.


r ft

Is Your . . .

Problem Here

Neutralising with an H.F.Transformer

" I am contemplating constructingan H.F. and detector set, the H.F.stage being neutralised by the Cow-per method. I have a number ofH.F. transformers to hand andshould esteem your opinion as towhether these would be suitablefor the set ? "Certain types of H.F. transformers

function satisfactorily as neutralisingunits in Cowper -type circuits, whilstothers prove practically useless.Barrel -type H.F. transformers are tobe preferred in which the couplingbetween primary and secondary wind-ings is somewhat looser than is usualin mushroom types. It is generallyfound best to employ the larger wind-ing, that is, the secondary winding, asthe anode coil, whilst the primary

forms the neutralising winding. Thecorrect connections for this latter mayeasily be determined by experiment,since if the set fails to neutralise pro-perly with one set of connections, theleads to the " primary " orneutralising coil can be reversed.

Trouble with a Reinartz Receiver" I have a 3 -valve loose -coupled

Reinartz type receiver, somewhaton the lines of that described byMr. Underdown in the April, 1926,issue of MODERN WIRELESS,the only difference being that Ihave not arranged to lead the gridand plate coils with ordinary plug-in coils, but merely to use thehome-made coil described. Theset worked excellently until re-turned from a friend's house,where it was tried. Now, how-ever, I can hear no signals, but

only a humming noise, which,when the reaction condenser isadjusted to a setting which wouldnormally make the receiveroscillate, results in a howl. If Itouch either of the grid condenserclips; when the set is thus adjusted,shrieks are obtained. Can youtell me where the fault is likely tobe located ? "From the symptoms given it is

.11most certain that the trouble is dueto a break in the aerial coil whichshould therefore be tested with tele-phones and a dry cell for continuity.A humming noise such as you men-tion usually denotes that there is abreak in the aerial or a grid coil, andthe search for the faults should alwaysbe directed to these quarters. The faultcan often be found by inspection, themost likely point for it being wherea tapping is brought out from thecoil. Therefore, examine these pointscarefully, moving each tapping witha pair of tweezers, when any breakshould be easily detected.

Long Loud -Speaker Leads" I have a Transatlantic 5 -valve

receiver and wish to wire myhouse so that the set will runthree loud -speakers simultaneouslyin different rooms, if required.The house is large and rambling,and this will mean that leads upto 70 feet in length will be required.I should like your opinion as tothe best method of wiring to adopt,and whether twin flex or separateleads should be employed. There

CM CP1C IC OF GR RA la I 0 EXPERTS

AMERRCA'S BESTSUPERHETERODYNE KRT.

331

nmmmo

li'GENERAL RADIOCOCAMBRIDGEMASS

pRI

271

Complete Kit of 4 Trans-formers -ONE Tuned,Type 331 ; THREEinterstage, Type 271.

Price £4 10s.Original - Shielded -Noiseless GuaranteedLaboratory matched, insealed carton. Sold sep-arately at 22/6d. each.

Recommended BluePrint 1/6d.

All CR Parts are guar-anteed and may be seenat our London Stockists.

HAMLEYS LTD.200, Regent St., W.1.Remit direct if ,your dealercannot supply, and ask forComplete Catalogue, free andpest free : obtainable from :---

Sole Concessionaires for Great Britain :-

Radio Specialist. CLAUDE LYONS76, Old Hall St., LIVERPOOL

Phone: Central 4E41. 'Crams: Minmetkem, L'pool."

Est. 1918.

GENERAL Rik1210 CO.AMERICA

" Money saved is Money earned-So when your ' VALVES' get old or burnedSend them to us-and we, to you,Will send them back ' MADE GOOD AS NEW.'"

tffillRestored to functionwith original charac-

teristics.EFFICIENCY MAINTAINED.RESULTS GUARANTEED!B.E. 46, D.E. 2V. '376,

D.E. '06 9,/6.Price Lest for Power Valves

applwatIon.We return the actual Valve yousend us, post tree, within 7 days.

THE NORTH LONDON VALVE CO., LTD.,221, CAZENOVE ROAD - - STOKE NEWINGTON, N.I6.

Liberal Discount to Wireless Agents.

Two in One !The new Dual Rheostat-a" Peerless" product in everyway. Specially designed tomeet the demand for a resis-tance equally applicable tobright or dull emitters. It hastwo windings-one offering a

resistance of 6 ohms, whilst acontinuation of this is of 3oohms resistance. The resis-tance element is wound on ahard fibre strip under greattension. One hole fixing isprovided and the terminals areplaced in convenient positions.The contact arm has a smooth,silky action, and all metalparts are nickel -plated.

Ask your Dealer or send direct

3/9 PEERLESS 3/9DUAL RHEOSTATTHE BEDFORD ELECTRICAL

& RADIO CO., LTD.,22, Campbell Road, Bedford.

385


3 to 10 fold AMPLIFICATION WITHOUT VALVES, DIRECTFROM THE 'PHONE TERMINALS OF ANY CRYSTAL ORVALVE SET

BY THE NEW NON -VALVEMAGNETIC MICROPHONE

BAR AMPLIFIER(Patent No. 248581/25).

REALLY GOOD LOUD -SPEAKER RESULTS fromCRYSTAL RECEPTION of average strength.

WEAK CRYSTAL or VALVE RECEPTION madeSTRONG AND CLEAR.

Enables even very deaf persons to hear from crystal sets.Not a Microphone Button. Entirely free from dis-tortion and microphonic noises. No valves, accu-mulators or H.T. batteries. No fragile parts. Nothingto get out of order. A child can adjust it. Operateson one or two Dry Cells lasting over 3 months.

EQUALLY EFFICIENT ON VALVE SETS.MICROPHONE BAR and other PARTS of Amplifier also supplied separately. Fully illustrated

Lists Free.Order from your dealer or from Sole Manufarturers and Patentees:

NEW WILSON ELECTRICAL MANUFACTURING CO., LTD.,Phone : Museum 2703. 18, Fitzroy Street, Euston Road, London, W.I

13 Your ProblemHere ?-continued

is A.C. lighting and power supplyin the house. The three loud-speakers will not always be in useat any one time ? "The problem of employing three

loud -speakers, in separate rooms,separated by appreciable distances, isnot such an easy one as appears atfirst sight, and special precautionshave to. be taken if satisfactory resultsare to be obtained. The use of longleads sometimes tends to make the setunstable, giving rise to howling,whilst reproduction may be slightlymuffled. It is advisable that somesystem be adopted so that the platecurrent for the last valve of the setdoes not have to traverse the longleads to the loud -speakers, and herewe have the alternative choice of em-ploying either a filter circuit arrange-ment or an output transformer. Inyour case we think a Miter circuit,such as that indicated in Fig. 1, is tobe preferred. The choke coil Z maybe of the types such as are normallyemployed for choke -coupled note mag-nifiers, whilst the two condensers Cmay be of 2 microfarads each. Byusing two condensers instead of theusual one, the likelihood of H.T.leakage is minimised.

Where very long, leads have to beemployed, as in your case, it is usuallypreferable to use separate leads andnot twin flex to the loud -speakers,since the capacity between leads maybe sufficiently large to introduce slightmufffing. The presence, however, inyour house of alternating current light-ing and power mains precludesseparate leads to the loud -speakers,since there is a tendency for such leadsto pick up, by induction, the hum fromthe alternating current, which maycompletely drown signals, or at thebest make the background far frompleasant. This difficulty can be over-come by employing- twin lead -covered

Fig. 1.-This filter circuit is speciallyuseful when long leads to loud -speakers

are needed.cable, of which the outer metallicsheathing should be earthed at con-venient points. Care should be takenin choosing the " runs " for thevarious leads, and, some experimentmay be necessary before the best wayof taking them is found. If, throughthe employment of the wire mentionedabove, muffling is introduced, this maybe corrected by eNverimenting with

the values of one or both of the con-densers C, these being decreased incapacity, as found necessary. Forconvenience we would suggest thatopen circuit jacks be employed, soThat any loud -speaker can be insertedor withdrawn from circuit as desired.

Single -Valve SelectivityWhat is the simplest and cheapestway of increasing the selectivityof my single -valve reaction re-ceiver ? I use series tuning atpresent ? "The cheapest method, yet one which

is thoroughly effective, of increasingthe selectivity of your single -valve re-ceiver is to adopt the so-called " semi-aperiodic " aerial coupling arrange-ment. You should wind, to thediameter of your present aerial coil, acoil of No. 24 gauge or similar sizewire, of 15 to 20 turns. This coilshould be tied to the present aerial coiland the aerial should be taken to oneof its ends, whilst the other end shouldbe joined to the earth terminal of theset and to earth. The connections tbyour aerial tuning condenser will haveto be altered so that this is connectedin, parallel instead of in series withyour original aerial coil. No alteraition in coil size will have to be madehere, since series tuning was originallyused.

The coil indicated is suitable onlyfor the higher broadcasting frequencies,and for Daventry and Radio -Paris acoil of 6o to 70 turns should be wound.

GOOD NEWS FOR CRYSTAL min VALVE USERS!

CompleteAmplifier

Price

38/ -Post free.

1Rabio 1rcei3 information 3Dept.

2/6 QUERY COUPON 2/6

WIRELESS WEEKLY. Vol. 8. No, 12. May 5, 1926.

This coupon must be accompanied by a postal order of 2/6 for eachquestion, and a stamped addressed envelope.

AND MANUFACTURER.Cdited by John Scott-qoggart. FInefP.AnNEE

THE ohMIC COIL

LMMICHAEL'

Fehnisr, isth, 1916

Spacial featuresThe N a R.M.W.T end eue

Should the 55C InterfereT,ade Matters/

Do We Need Urge Coils)

et17-14r.re

The a::::: Wiggins

The Slew Seiewias ...wen

WNW Trude in Swain

"."

The Wireless Industry's DirectorySubscription Rates - - 7/6 per annum (10/- Abroad)

Available to the Trade only.Business Card or Letter Heading must accompany remittance.

THE WIRELESS DEALER, Bush House, Strand, London, W.C.2

386

M A Y 5T1L 1926 ADVERTISEMENTS WIRELESS WEEKLY 3

Now huild or Power

"The Super SevenBy

PERCY W. HARRIS, MITIX.

This set has to its credit the receptionof 28 British and Continental Stationsat full Loud -speaker Strength in oneevening. With it you are able tocompletely eliminate the local stationeven at close range.

Having only two tuning dials, oncepreliminary adjustments have beenmade, manipulation of these two knobsand the occasional rotation of the frameaerial is all that is necessary to tune instation after station.

Price 5/- Nett

Complete constructional details andfull instructions for operation areincluded in this envelope, together withfull-size Blue Prints of wiring andpanel layout, etc.

Many thousands ofhome constructorstake their initial stepinto wireless withthe aid of an R.P.Envelope. T h einformation given isfound by them tobe precise, completeand concise. Littlewonder that theynow define RadioPress Envelopes theeasiest method ofbuilding a morecomprehensive re-ceiver.

The two new R.P.Envelopes illustratedhere contain every detailand every piece of help-ful advice which maybe necessary for thesuccessful constructionof the powerful re-ceivers described.

*4:474I4:0:4:0`.0'. 0:4 070:****0. 4-0:04:0:0.4.0"0:**.00.0:4:0:0:00,00-4k.

11

II!

III

Its

!I

11,

II

II

.16-41-41..4.30:4>-*-4:owco:0-0-.0:e:cowc.Kownlowo:otowof coNeceArowo:

The Three -ValveDual Receiver

Designed byJOHN SCOTT-TAGGART, F.Inst.P.,

This handsome and economical Three -Valve Receiver will give Loud -speakerresults from B.B.C. and ContinentalStations, and is sufficiently sensitive toreceive American Broadcasting whenconditions are favourable. It employswhat is known as the reflex: principle,in which one of the valves performstwo functions, and in this way threevalves are made to do the work of four.

Easily constructed, the only toolsrequired are a hand -drill, a few twistdrills, a screwdriver, a scriber, a 12 in.rule, a soldering iron, a steel centrepunch and a pair of pliers.

Price 2/6 Nett

Complete constructional details andfull instructions for operation areincluded in this envelope, together withtwo full-sized Blue Prints and foursheets of photographs.

RADIO PRESS LTD., Bush House, Strand, London, W.C.2

.4:4:4:0Woxiowole 4:4 '414 4' 00 *WOW* WO 0V 4 4'4'0 4.4:AVO'neCtWOWSIette0:4>W4Ir

4 \VIRELESS WEEKLY ADVERTISEMENTS MAY 5, 1926

For a 2 voltaccumulatorask for the

P.M.2.Price -18/6

HE wonderful "N" filament valvesare so economical that no sign ofglow can be discerned. Theyrequire only ONE -TENTH

AMPERE from a 4 -volt accumulator (or3 dry cells). This means SEVEN TIMESTHE LIFE of each accumulator charge ;a distinct saving of your time and money.

ASK FOR THE P.M.3 - 16/6The general purpose Valve, suitable for everycircuit. Gives clear strong signals free frommicrophonic disturbance.

A power valve for majestic Loud Speakervolume. The finest Loud Speaker Valveever produced.

GET THEM FROM YOUR RADIO DEALER

ADVT., THE MULLARD WIR'I.LESS SERVICE CO., LTD., BALHAM, LONDON, S.W.12Published by RADIO PRESS, LTD., Bush House, Strand, London, W.C.2, on Wednesday of each week, and printed for them by THE AVENUE PRESS(L. Lpcott Gill A Son, Ltd.), 55.57, Drury Lane, W.C.2. Address for Subscriptions and Editorial Communications:-Bush House, Strand, London,W.C.2. Address for Advertisements :-ADVERTISEMENT MANAGER, " Wireless Weekly," Bush House, Strand, London, W.C.2. Registered as a newspaperand for transmission by Canadian Magazine Post. Subscription rates:-U.K., Canada and Newfoundland, 17/4 per annum; other countries, 19/6 perannum. Sole Agents for Australasia :-GORDON A GOTCEI (Australasia), LTD. For Canada :-IMPERIAL NEWS, LTD. For South Africa :-CENTRAL NEWS

AGENCY, LTD.

Documents

LOUD -SPEAKING ON SHORT WAVES - WorldRadioHistory.Com · 2020. 5. 11. · May 5th, 1926. Vol. 8. No. 12.-THE 100% VALVE PAPER LOUD -SPEAKING ON SHORT WAVES A SUPERHETERODYNE ADAPTER