No Slide Titlearchive.nsarc.ca/hf/ancient_radio_rev2.pdf10 March 2015 NSARC 2 Preface This is a Story about a very old radio Remarkable Discoveries An Interesting Letter Technology

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NSARC 1 10 March 2015

ANCIENT RADIO

A Story

by

John White

VA7JW [email protected]

Revision 2

http://www.nsarc.ca/tech_archive/Articles/Browning_Drake/

http://www.nsarc.ca/tech_archive/Articles/Browning_Drake/

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Preface

This is a Story about a very old radio

Remarkable Discoveries

An Interesting Letter

Technology of the Past Re-Discovered

Challenges

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It Starts Here

This is the Horse Barn store, Kamloops BC

Horse tack, ranching supplies, feed, western clothing …

http://www.panoramio.com/photo_explorer

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This is about Radio ?

My wife owns and boards a horse

Great store for horse supplies

We ski once a year at Sun Peaks and Horse Barn is right on the way, so we have to stop in

VA7JW does not have much to do with the horses and so he looks around the store – lots of interesting farm stuff …

There is even an out-of-the way dusty “antique” section of old farm equipment and furnishings

Guess what I found …

https://www.google.ca/url?q=http://www.search-best-cartoon.com/cartoon-horse-page-5.html&sa=U&ei=JJQnU_u8OouCogTnroHQBA&ved=0CD4Q9QEwCQ&usg=AFQjCNH73AnZwBuvjECoHyWXHxfgSaWQ9A

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An Old Radio

An old radio of sorts … looked rather beat up

No idea what it really was, but had to be looked at!

Proprietor pulled it down off the top shelf

Very old in a wooden cabinet with a hinged lid

Looked inside - besides dirty radio apparatus

discovered a letter inside

Immediately studied the contents of this 7 page

letter.

https://www.google.ca/url?q=http://forums.qrz.com/showthread.php%3F256235-Old-ham-radio-cartoonists&sa=U&ei=cJQnU5jFBtDtoATD24KYAw&ved=0CGwQ9QEwIA&usg=AFQjCNEk6Hr2R7l_lkV_7pdK6_xuua4_Gw

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The Letterhead

A service letter to the radio owner, a Mr. F. H. Hoadley

From: C-W Radio Service Co Ltd, 719 Fort Street, Victoria, BC

Proprietor: Mr. G.M Warnock, 1086 St Louis St. Oak Bay, in Victoria

What a Connection - I grew up in that neighborhood ! (Appendix III)

Dated: 26 August 1926. Now know the vintage

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Front Panel Instructions

By inspection, and reading the letter ..

D1 and D2 are

LC Tuned circuits

R1, R2, R3 are

rheostats, i.e.

wire-wound pot’s

#1 and #2 are audio

output phone jacks

Tickler is a variable inductor, part of D2’s tuning inductor

Bat. Switch is the On / Off control

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Power Supply – Batteries

Eight 1.5VDC dry cells in

series - parallel

Three 45 Volt dry cell

battery packs in series

with +45V, +90V and +135VDC

tap-off voltages

Two dry cell battery packs

providing -3V and -6VDC

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Farm Radio?

In rural 1920’s, there was no electrification for farms

Think what that means in terms of isolation

For farm folks to have a radio was miraculous

The radio will have to run on batteries

Fancy cabinet work is not a requirement

Simplicity of operation is required

Appendix II - always trouble with new technology – then and now

Low Cost

https://www.google.ca/url?q=http://www.mprnews.org/story/2010/08/05/1975-mn-memories-pt1&sa=U&ei=cZUnU_yTB86CogSg9IGoAQ&ved=0CEwQ9QEwDw&usg=AFQjCNGfwYCJ5NSyuHhlv7JcwYcrDJm-hA

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Inspection

The design appears to be a TRF (Tuned Radio Frequency)

Pre-Superheterodyne

Typical of the 20’s era

External batteries

Very Plain cabinetry

Low component count

This TRF probably a “Farm Radio”

Lets have a look >


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Front Panel

Complete

Finish destroyed

Controls, by

inspection

On-Off Switch

RF Tuning Dials – 2 Stages

Audio jacks (no speaker)

Three Rheostats

Wire Wound pot’s

Probably filament circuit Tickler control linked to RF tuning

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Chassis – Top View

3 rheostats

4 tubes

2 cylindrical things

2 transformers – appear to be audio devices

2 RF tuning stages with paired variable “condensers” and coils

String of binding posts on rear apron for battery connections

(Condenser is old (period) nomenclature for a Capacitor)

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Chassis, Underneath

Buss-bar style of wiring

Very few components: 3 condensers, 1 switch, 2 jacks

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Cabinet

Very plain

Front / top view

Radio slides in

Found out later this style is often referred to as a “coffin”

Open top, hinged

Back is closed off with drilled

holes for passing battery wires

through

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The Clincher to Buy

While dirty, nothing appeared broken, parts appeared to be

original, and complete

Front panel was horribly scrubbed with no identification of

brand, model, manufacturer or control functions

The cabinet was very plain; finish gone, banged up ….

But - the Letter was a bonus and provided a badly needed

Instruction Manual. What to do ..

Would you pay $125? Guess.

https://www.google.ca/url?q=http://mikerowse.com/%3Fpaged%3D3&sa=U&ei=nTUmU4fbM5LyoATU5YDoAw&ved=0CCwQ9QEwAA&usg=AFQjCNGBIz0it-KWkkonUQolZPAvVJMQaQ

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The Challenge

No idea of the manufacturer

No Schematic

No Parts List

No supplier of replacement parts

Don’t even know how it worked, let alone, could it work

And what about batteries, today ?

https://www.google.ca/url?q=http://imgarcade.com/1/confused-person-cartoon/&sa=U&ei=ax0mU4_WI9LcoAS0moGYAw&ved=0CDIQ9QEwAw&usg=AFQjCNFfjlXFbM2HoXuMpk00f4wX86TVPw

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Web Search

Look for photos and images of antique radios of similar

appearance to determine manufacturer

There are many, long gone, antique radios

Similar radio product identified as made by Browning-Drake

Found: Browning-Drake Corp. Brighton MA

Developed and manufactured radios 1925 through 1930

This radio closest to a Model DB-6 Kit offered in 1925 ~ $25

Was it a kit? Don’t think so, but don’t know

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Browning–Drake Web Site

Browning-Drake Corporation website

http://www.browninglabsinc.com/browning_drake_corporation.htm

“Both Browning and Drake were closely involved with the National Company * for many years, but Glenn Browning terminated his relationship with National in July 1927 to devote his energies to the newly formed Browning-Drake Corporation…. “

“Various models put out by the Browning-Drake Corporation were sold using a 4 or 5-tube circuit with two tuning dials, one at each end of the front panel, or with both dials at the left hand of the panel… “

* This was the National of the famous National Radio Company

Drake is NOT related to Drake Amateur Radio radios of the 60’s – 70’s

B-D continued as Browning CB, until closed 1979

http://www.browninglabsinc.com/browning_drake_corporation.htm

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Chassis Layout

Feb 1926 Article on line

Near same component placement as Farm Radio

Near same chassis size 8”x 24-1/2”

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Front Panel Controls

Tuning – RF amplifier 1st Stage

Tuning – RF Amplifier, Detector & Audio 2nd stage

R1 Gain control for Stage 2

R2 Gain control for Audio Pre-Amplifier 3rd Stage

R3 Gain control for Speaker Amplifier 4th Stage

Refer to Appendix X for tuning & Operating

Tuning

RF

Amplifier

R1 R2 R3

HEADPHONE SPEAKER

Tuning

RF Amplifier

&

Regenerative

Detector

POWER

Detector

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Earliest Dated Schematic

15 Oct 1924, described by Glenn Browning, Nov 1924

Circuit Symbols are

typical of early

schematics

Tube symbols particularly

“odd”

Electrically, looks like

a Farm Radio, simple.

(Appendix V for 1926 schematic)

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Dismantle Radio

Take radio totally apart

Every lead circuit traced

Every connection verified

Every pin-out connectivity determined

Every part is examined and identified

Cleaned and tested every component

After all, they are ~ 90 years old

https://www.google.ca/url?q=http://www.superstock.com/stock-photos-images/1802R-1504&sa=U&ei=u80oU42eLs3qoATAooCoDw&ved=0CLQBEPUBMEQ&usg=AFQjCNHYOAL8EAmgdW2H_mCmhQf-uCZqpg

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Strange Parts Identified

Condenser

0.001 MFD

Measures 0.9 nF

Resistor, Grid Leak

Should be ~ 2 Meg

Resistor, Ballast

Should be ~ 25 ohms

Tubes (4) UX 199 two, UX-112, UX201-A

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Duds & Parts

Resistor Duds – Ballast & Grid Leak, intermittent rheostats

Tube duds – one UX -199 dead

No speaker or headphones or plugs for audio jacks

OK for static display – but what if functionality is desired…

Where to get working replacement parts ?

https://www.google.ca/url?q=http://www.clker.com/clipart-confused-man.html&sa=U&ei=rSAmU-HyL9LtoASxxYGgAw&ved=0CEAQ9QEwCg&usg=AFQjCNG6VElefi4Ya3OWvU43WpDFoBQpQw

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Play Things of Past

Why didn’t I think of that!

http://www.oldradioparts.com/

Thousands of radio parts, 1920’s onwards

Was able to purchase, on line,

used, tested UX-199 tubes $20 ea

grid Leak resistor, New Old Stock (NOS) $1.40

ballast resistor, NOS in original packing $2

the “Very Best” earphones with 2000 ohm coil $20

plug ¼” for tip jack connection $1

http://www.oldradioparts.com/

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Faceplate Labeling

Web Picture, Knobs are identical

Logo font is a custom script

Uncertain that the Farm Radio

ever had any labeling due to

faceplate damage

Do it for restoration purposes

Want to use “rub-on” transferable decals (Letraset style)

Fonts unknown. Full custom requirement

but how and who ?

https://www.google.ca/url?q=http://leadershipfreak.wordpress.com/2009/12/28/frustration-or-inspiration/&sa=U&ei=BSgmU5SPCtCgogSZq4GoBg&ved=0CDIQ9QEwAw&usg=AFQjCNEjAFKtIzuUitpnquPAlkzMLrUlDA

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North Vancouver

Desperately scoured the web with no success

Nick Massey VA7NRM advises of a LOCAL graphic artist

Custom Rubdown Transfers

Manfred and Jocelyn Schleger 1195 Esquimalt Avenue West Vancouver, BC CANADA V7T 1K2 604 922 2392 http://www.allout-graphics.com/index.htm

Send web photo, list of required labels. Had a transfer sheet within 3 days. $150 to create custom script incl. rework – Terrific talent and service.

http://www.allout-graphics.com/index.htm



https://www.google.ca/url?q=http://chantrynotes.wordpress.com/&sa=U&ei=HikmU6DfCsi7oQThwIC4Aw&ved=0CDYQ9QEwBQ&usg=AFQjCNER3KCubRq8oEqcvN6LuMnvIk_VTA

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Reassemble Radio

New parts ordered and received

Schematic was generated part by part as put back together

Faceplate restored to gloss black using lacquer spray paint

Cabinet sanded, filled, stained and using a semi-luster polyurethane clear coat

Still more stuff to get, but first ….

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The Schematic

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Functional Diagram

Tuning Dial 1

ANTENNA

EARTH

TUBE

UX-199

Tuning Dial 2

RF

Coupled

Coils

Tuned RF Amp &

Regenerative

Feedback Coil

Head

phone

Jack

+45 V

AF

Amplifier

Rheostat 1

Gain

Control Rheostat 2

Gain

Control

Speaker

Jack

+135 V

Speaker

Amplifier

Rheostat 3

Gain

Control

Audio

Transformer

Audio

TransformerTUBE

UX-199

Tuned RF

Amplifier

TUBE

UX-112

TUBE

UX-201-A

Regen

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Get Headphones

Modern head phones (8 ohm / no DC) will not work on old

sets

The headphone plugs directly in to the high voltage plate

circuit of the detector tube (+45V)

C. Brandes Inc. Superior, no less

Coil resistance is about 2000 ohms

No isolating capacitors / HV appears

on exposed screw terminals

Not comfortable & not very effective

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Get Speakers

Period speakers, 1920’s, not easy to find

Voice coils have to be high Z ~ 2000 ohms

eBay

Horn “Trumpet” style

SAAL, 1925 cost $25 Paid $190 (good deal)

Complete & it actually worked

Friend

donated a mantle style speaker

RCA – 100A, 1925 cost $22

early 8“ speaker cone design

needed work – cabinet buffing

and new grill cloth (eBay)

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Get Batteries – No

Were Carbon-Zinc chemistry

Use of original style dry cell primary,

non-rechargeable batteries not feasible

Can’t buy these anymore

Do I need them ?

Are we going to get this thing working ?

YES

1.5 V Dry Cell

6 required

45 V Dry Cell

pack

3 required.

$45 on eBay

for dead,

display bat!

https://www.google.ca/url?q=http://www.santeelynchescog.org/aging_info.html&sa=U&ei=rSAmU-HyL9LtoASxxYGgAw&ved=0CMQBEPUBMEw&usg=AFQjCNG9kS7JwBuSmLAsmYoedmMoY1Yuew

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Build a Power Supply

Supply the various DC voltages from an AC source

Requirements:

+135 VDC @ 10 ma for the Speaker Amplifier tube (UX-201)

+90 VDC @10 ma for the first Audio & first RF tubes (UX-199’s)

+45 VDC @ 10 mA for the second RF / Detector tube (UX-112)

+ 6VDC @ 800 mA for the tube filaments

-3VDC at 0 mA for the grid of the first audio tube

-6 VDC at 0 mA for the grid of the speaker amp tube

Can’t buy such a supply, have to make one

(Appendix VIII & IX about batteries and tubes)

https://www.google.ca/url?q=http://www.theguardian.com/money/work-blog/2012/dec/03/fed-up-frustrated-want-more-working-life&sa=U&ei=SSYmU5r2Mo_roASCz4KoAw&ved=0CFQQ9QEwFA&usg=AFQjCNFIkw4onazcAxN5wk6YN1obcZam2Q

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Power Supply Diagram

RegulatorRectifierTransformer

115 / 12 V

+ 6VDC

at 0.8A

Voltage

Inverter

Reguator

- 6VDC

Zener

Regulator- 3VDC

Filament “A” Supply & “C” Supply

Plate “B” Supply

FILAMENTS

GRIDS

RegulatorRectifierTransformer

115 / 120V+135 VDC

Zener

Regulator

Zener

Regulator

+90 VDC

+45 VDC

PLATES

115VAC

Regulated = well filtered DC

required as no AC / hum filtering

in radio

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Restoration Status

Radio been rebuilt

All components have tested good

Power supply works & speakers are on hand

Is there any chance radio will actually work?

Moment of truth arrives

Guessed at knob settings & powered up

No smoke, Good

No sound, Not so good ….

https://www.google.ca/url?q=https://mgleeson.edublogs.org/category/ipad/ipads-in-literacy/&sa=U&ei=97UoU-2FCYuwoQTWxYHYAQ&ved=0CDQQ9QEwAw&usg=AFQjCNE8pVufY8b9SZb4jWq7AkhGg-iIUQ

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Problem Solved

Detector tube UX-112 filament not glowing. Bad sign

Earlier noted a 30 ohm resistor in the detector filament

circuit in addition to the 35 ohm rheostat. This seemed odd

as such a high amount of resistance would starve the

filament and lower tube gain, so..

Removed the 30 ohm resistor that was installed (presumably)

to prolong filament life of the UX-112

Radio burst into life. Miracles happen …

DONE. Finished Product >

Whoopie Whoopie

https://www.google.ca/url?q=http://classicbookreader.wordpress.com/2013/07/12/jumping-for-joy/&sa=U&ei=b-YoU4sVhvygBKGFgugP&ved=0CJgBEPUBMDY&usg=AFQjCNG60TR4UQs3zz-XslSbQSLcu3hMHA

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Radio with Speakers

RCA-100A

SAAL Jr Horn

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Performance

Tunes lower portion of the AM Band ~ 540 to 1350 kHz

Primitive Radio - performance greatly depends on

Antenna and ground situation are critical

Combined RF environment today unlike the 1920’s

Susceptible to overload and noise

AF bandwidth is narrow & fidelity is poor

Only takes 4+ controls to “tune’r up”

Notable Distortion most likely due to regenerative detector

Audio output levels are low

Horn Speaker has no low end response & sounds “tinny” with resonances

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Summary

LOT of work – three years, on and off

Total “investment” about $700

LOT of satisfaction

A much greater appreciation for technology at the dawn of

consumer wireless

Quick Look at a couple of the Appendices

Now, we will TURN IT ON and hope for the best ..

https://www.google.ca/url?q=http://www.dreamstime.com/royalty-free-stock-photography-happy-music-headphones-note-smiley-face-image8008677&sa=U&ei=ETUmU8mKEY_ooASOgYKwAw&ved=0CEIQ9QEwCw&usg=AFQjCNFYnR-qLV9iI1ut9AMDyEBDJnXOUA

https://www.google.ca/url?q=http://jennifers25.wordpress.com/&sa=U&ei=YpEnU5KMKpK7oQT1oIGYAw&ved=0CHIQ9QEwIw&usg=AFQjCNHe_qqPJamUlrsbpzdt-PNUNoloMA

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Appendix

I Browning Drake with Earphones

II Mr Hoadley’s Problem

III Mr. Warnoch’s Residence – Historical Register

IV Chassis and Faceplate Materials

V Schematic Published 1926

VI Audio Quality

VII The Superhetrodyne

VIII Short Course on Tubes

IX Operating Instructions - 3 pages

X A, B, & C Batteries Explained

XI VII Parts List, partial

XII Regeneration and Detection

XIII XIII Measured Audio Bandwidth

XIV Measured Sensitivity

XV Measured Tuning Calibration

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Appendix I

Browning-Drake

C. Brandes Superior headphones Browning- Drake Radio

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Appendix II

Mr. Hoadleys Problems

Mr Hoadley finds out that operating the radio is not easy

Letter of 31 Jan 1927 from Mr Warnoch to Hoadley. “Sorry to

hear you are in trouble, it’s a bad business when things go

wrong up where you are .. trouble is most likely to be in your

batteries.. “ Don’t know where “..you are ..” is.

Two independent RF dials to tune stations with no indication of

station frequencies. (New meaning to “Search and Pounce”)

Tickler coil to adjust to keep radio from oscillating

Three rheostats to adjust for gain – only 1 seems effective

Ensuring conservative settings to prolong battery and tube life

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Appendix III

Mr Warnoch’s Residence

Mr. Warnoch’s residence, per his letters, at 1086 St Louis St. Oak Bay, a suburb of Victoria, BC

VA7JW, being VE7AAL grew up

less than 3 km from this address and

frequented this area on his bike

Listed in Canada’s Historic places

as the James Stewart Clarke house

Visited residence March 2014. No Warnoch relatives live there now

Built 1912. Architect: David Cowper Frame. For history visit,

http://www.historicplaces.ca/en/rep-reg/place-lieu.aspx?id=6688

C:/Ham/Presentations/Tunes lower portion of the AM Band ~ 540 to 1350 kHz





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Appendix IV

Chassis & Faceplate Material

Glossy, black, sheet material used

for the chassis and faceplate

Pyralin, early plastic, by Du Pont, 1915 researchers discovered that nitrocellulose, when

combined with certain solvents, yielded a solid solution

that could be molded and hardened for commercial use

Browning–Drake and others advertised it

as Pyradiolin – note the RADIO modification

Ideally suited for early radio construction

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Appendix V

1926 Schematic

Browning-Drake Receiver published Feb 1926

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Appendix VI

Audio Quality

SAAL horn speaker lack bass, sound tinny

RCA -100 Cone speaker, no treble, muffled, too bass-y

Modern speaker somewhat better

Audio bandwidth of radio is really poor

Center of pass band ~ 820 Hz

-3 db ~ 330 Hz BW

-6 dB ~ 565 Hz BW

-12 dB ~ 1,000 Hz BW

Distortion products, detector & audio. Tune to minimize.

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Appendix VII

The Superheterodyne

Next Generation radio

Designed in 1918 by Armstrong

Entered the market in 1924.

The beginning of the end for the

TRF era was in sight as performance

of the superhet was much superior,

although cost was much higher

Wikipedia

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Appendix VIII

“A” “B” and “C” Batteries

This radio requires 6 differing operating voltages

Designations (of the day) for differing voltage functions

“A” = filament batteries heat tube filaments, 4 x 1.5V = +6 V

plus a second bank in parallel sustains the current

“B” = plate batteries provides high voltages for the tubes,

+45 +90, and +135V from stack of three 45V battery packs

“C” = grid batteries provide negative volts of -3V & -6V from

series of 2 x 1.5V = 3 V, plus another series of -3V = -6V

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Appendix IX

Short Course on Tubes

Filament F+ and F- heater, glows red hot

boils off electrons into vacuum

low voltage, high current

“A” battery provides ~ 6 VDC

Grid Signal input; Controls electrons

flowing from filament to Plate

low voltage, but no current

“C” battery provides -3V and -6 VDC bias

Plate Signal Output

Collects electrons from filament

“B” battery, high voltage, low current

F+F-

B-

A-

A+

C-

C+

B+

GRID

PLATE

FILAMENT

Signal Out - Amplified

Signal In

Different tubes require

different Plate Voltages hence

+45, +90 and +135 VDC

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Appendix X

Operating - Page 1 of 3

Push IN Radio On-Off Switch to Off Position

Connect external Antenna / Ground as required

Plug radio power cord in to external power supply

Plug in speaker to Speaker Jack, #2

Turn on power supply All green lamps should be ON

Pull On-Off switch Out to power up radio

Signal will not be heard if radio has not previously been

tuned to a radio station

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Appendix X


Resonance Dial 1 – First RF Amplifier

Adjust D1 according to radio station freq. per Appendix XIII

Adjust dial to peak signal

Wavelength Dial 2 – second RF Amplifier & Detector

Adjust D2 to approximately same dial setting as D1

Adjust for best signal strength and clarity

Re-adjust both dials to peak signal strength

Detector Knob

Adjusts RF gain of Detector stage

Do not operate past the 2 o’clock position.

Normal 12 to 1 o’clock. Higher settings will reduce tube life.

This control is dominant in setting audio volume

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Appendix X


Regeneration Knob (Tickler Coil)

Adjust the regenerative feedback necessary to recover the audio from

the RF carrier.

Adjustment may induce oscillation. Tune “past” to avoid squeals

1st Amplifier Knob – Audio Amplifier

Set to 12 o’clock position

Does not make much difference to speaker volume

2nd Amplifier Knob - Speaker Amplifier

Set to 12 o’clock position

Does not make much difference to speaker volume

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Appendix XI

Parts List (partial)

1 - 3-plate vernier condenser for balancing (B.C.) 4 - standard tube sockets or four UV199 tube sockets. 1 - audio transformer (AFT No. 1). 1 - 3-1 audio transformer (AFT No. 2). 2 - Rheostats (one of ten ohms and one of thirty ohms resistance). 1 - .0001 mf fixed condenser (c). 1 - .001 mf. or .002 mf. fixed condenser (cb). 1 - .00025 mf. flxed grid condenser (cg). 1 - grid leak (Rg). 1 - double open-circuit filament control jack (32). 1 - filament switch (SW). 1 - 1mf. by-pass condenser (This is optional) 9 - binding posts. 4 - tubes. 1 - .0005mf condenser. 1 - .00035mf condenser. 1 - antenna coil as described above. 1 - regenaformer as described

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Appendix XII

Regenerative Detector

Positive feed back circuit

Designed in 1914 by Armstrong

Single tube provides very high

amplification by routing the output

back to the input for increased

amplification

Unstable - can easily oscillate

Grid leak circuit acts as a rectifier

thereby recovering AM (audio)

Tickler coil (feedback adjust) is the Regeneration control on radio

More at: http://www.zen22142.zen.co.uk/Circuits/rf/marr.pdf

Wikipedia

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Appendix XIII

Audio Bandwidth

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Appendix XIV

Sensitivity

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Appendix XV

Tuning Calibration

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Epilog - Live Demo at NSARC

As surmised in Performance slide, reception was expected to be difficult due to building shielding at AM radio wavelengths. That was demonstrated with a portable AM radio – no signal could be heard within the room.

Stringing a long wire antenna within building did not produce results.

Connecting to the Amateur wire antennas on the roof produced mixed results but this was accompanied by broadband, very high noise levels, masking any AM signal that could be heard.

There was the possibility that the radio had failed, but when returned home the same night, it worked perfectly well, and next morning, I am listening to it as this epilog is being written. Much later discovered an intermittent solder joint in first RF stage coil.

Conclusion – the radio, being primitive, was underwhelmed by lack of a long wire antenna and overwhelmed by the ambient electrical noise at the location, known to be severe.

Documents

No Slide Titlearchive.nsarc.ca/hf/ancient_radio_rev2.pdf10 March 2015 NSARC 2 Preface This is a Story about a very old radio Remarkable Discoveries An Interesting Letter Technology