30FXC for 5, 10 and 20 Meter

The 30FX smitter can be supplied with the new | 0x t to amateurs who are par- ticularly int n the higher frequencies. The 10X R-F quires the same panel space as the 10M rdinarily supplied but it em- ploys a spe e and circuit arrangement adapted to r frequencies. The tubes are:

I—CI0 ator

I—6L6 quency Multiplier I—6L6 1] Frequency Multiplier 2—6L6 T Frequency Multiplier 2—C80 -C10! Power Amplifiers

The frequ nge of the type 10X R-F Unit is 10 to 60 m es. The nominal plate input to the C800 final amplifier is 150 watts, giving an out f 100 watts at the lower radio frequencies to 75 watts at the highest radio frequ The output circuit of the 10X R-F Unit is to that of the 10M and may be used wit eactive high frequency lines, or it may b ed with a matching network. Frequency can be accomplished by means of p assemblies. Both the grid circuit and ¢ te circuit of the final amplifier are tuned b panel controls. All dials, in-

cluding th tor and frequency multiplier stages are fi th locks for fixing the position of the tunin lensers.

Kennet AR.R.I Business Associat Technic. mer, A Clark ( Editor; | culation Beek les Charles Sertisine

The standard 30FXC with 10M R-F Ur’ frequencies between 1.5 me. and 0 Power output on phone or CW is I75+4 The 10X special high frequency illustrated in inset.

Collins Radio Company =

a —_—— ee Title , CEDAR RAPIDS IOWA. U.S. A. patent © New York Mexico City : li West 42nd St. Edificio “La Nacional”

OS!

PUBLISHED, MONTHLY, AS ITS OFFICIAL ORGAN, BY THE AMERICAN RADIO RELAY LEAGUE, INC., WEST HARTFORD, CONN., U. S. A.; OFFICIAL ORGAN OF

devoted entirely to

AMATEUR RADIO

AT THE INTERNATIONAL AMATEUR RADIO UNION

DECEMBER 1936

Volume XX Number 12 *

Kenneth B. Warner (Secretary, AR.R.L.), Editor-in-Chief and Business Manager; Ross A. Hull, Associate Editor; James J. Lamb, Technical Editor; George Gram mer, Assistant Technical Editor; Clark ( Rodimon, Managing Editor; David H. Houghton, Cir- culation Manager; F. Cheyney Beekley, Advertising Manager; Charles Brunelle, Assistant Ad- vertising Manager.

Editorial and idvertising Office 38 La Salle Road West Hartford, Connecticut

Subserij)t rate in |! ted St and |’ s and Canada, $2.50 per yea mstpa 4 tie in tries, $4.0) r ar.1 tpa ngle Copies t Foremgn remitt should ternat al post r xpr ift Uni golia t { ; ( 3 t r 1 att 175 che Ac \ i ' y ° rat " ed t 110 vet » r 191 authorize Septem 1 Ad , ord H., a r ! ar. » § ) Act Februar) 1 ud ntr t al editions author i », 1935. Copyright 1936 by

in Radio Relay Leagiu« tered at United State

The (ontents

Editorials Columbia Announces Annual Award

An Inexpensive Five-Band Low-Power Transmitter George Grammer, W1DF

A Versatile Crystal-Controlled U.H.F. Transmitter Walter H. Grosselfinger, W2ATQ and Thomas Prosser What the League Is Doing Operating Notes on the Transmitting-Type Beam Power Tube A Moving Coil Tuning System for the High-Frequency

James Millen, WI1HRNX

An All-Band 'Phone Transmitter Using Beam Power Tubes . . . .G. Mathis, W3BES and J. B. Carter

Receiver

Rebuilding a Commercial-Type Condenser Microphone for Practical Ham Use Robert S. Coe, W1ICBG

Miniature Cathode-Ray Tube Announced A.R.R.L. Copying Bee December 11th

Circuit Design of a Modern Amateur U.H.F. Superhet- Guee « ik ite itive xn te + + ee

WIHRN

Amateur Radio Stations .

Hints and Kinks

Cathode Ray Oscilloscope Switching Circuit A Voltage Quadrupling Circuit A Different Keying Monitor Arrangement Negative Bias from the

Plate Power Pack Dixie Jones’ Owl Juice The 1936 VK ZL DX Contest First Scores Calls Heard I.A.R.U. News Operating News Correspondence Department Silent Keys . a New Amateur Tubes Types 154, 807, RK-39, 808. A.R.R.L. QSL Bureaus Circulation Statement Standard Frequency Transmissions Delta Division Convention . Hamads .

OST’s Index of Advertisers .

35 37

38

Bowdoin-Kent's Island Expedition Reports: |

“Aid Secured..Under Most Trying Conditions

—a Tribute to Burgess Portable Power” ee

“Expedition boatlost most trying conditions— power source— in dense fog—unable Burgess Batteries—this incident consti-

toreachbaseonKent’s _ tutes a real tribute to your product.”

Buree for communica- Island” —so runs radi- A P - aa , a Scores ane wr Safety in time of danger—a friend in Bow nd Expedition. Ogram received from : .

oi time of need—Burgess Portable Power

0. Gross (left), director of the . —— . meets all emergencies. Choice of ex-

loin-Kent’s Island Expedition. But . cal perienced scientists and amateurs— bes

ontinued . for your own radio and experimental

\id was secured by communicating work. five-meter transceiver which was BURGESS BATTERY COMPANY ted for a very long time under Freeport, Illinois

rir

* BurGess =

t Say You Saw It in QST It Identifies You and Helps QST

V

191 Re! blu Our in t lay mea Ded subt Our nan priv late and atta that cour in tl O inte! ama was a col work done finan had | grow mucl tains ensec an is the | woul job Vi Maxi mail drive day, long days ers ey Th be pre shelf, amate our e! texth« amate

Dec

2

ao

.

QST comes of age. Twents this month, in December of f the American Radio

_ this issu

1915, the early members «

Relay League received their first copy, a little blue-covered magazine twenty-two pages Our League itself is older, having been formed in the spring of 1914. The rapid growth of the re- lay idea soon made it imperative to have som« means of regular contact between the members Dedicated to this need, the first issue of QST was subtitled the December Radio Relay Bulletin Our League of those days having almost no fi-

if its own, the n igazine appe ired as the private venture of Clarence D late Hiram Perey Maxim, our and president of that time. Announcing now the uttainment of our n that GST is the oldest radio country and, iS tar as we ire in the whole

Our earhest vears were ng Phe

amateur radio

nances ¢ Tuska and the secretary-editor ajority, we are proud to say magazine in this iware the oldest world

immensely American

received & magazine of its own

hectic but

interes ividity with which was inspiring. The office of our youthful editor, a college student, was in the attic of his home, the work done afte The printing was lone by the father of another local The finances were elementary: the month’s receipts mbe rship list had now

hours

class

amateul

had been so much, the me

grown to so many, how many pages would this uch money print? Thus QS7’ straightway at- iined respectable proportions and was firmly ns ed as the amateur’s own magazine. When n issue came off the press, the early officers of the League and the members of their family vould devote an evening to wrapping the issue, a

Job a table in Mr. Maxim’s library. The copies were then put in a mail tossed into Mr. Maxim’s ear, and What a far ery from to-

as regularly done on

iriven to the post offies

Lay, when a considerabl stall works the month ng on the job and when machinery spins fo! lays to grind out tons and tons of copy for read-

rs everywhere!

The owner of a complete set of QST’s may well e proud of them. Filling nearly five feet of book- five-foot shelf of are a history ol

shelf the y constitute the They movement, a record of its traditions, a k of its technical practices. So great is the

amateur appreciation of OST that the early files

truly imateur radio knowle dge our entire textboc

THE EDITORS

Le

MIL L

\ SS

\ SS

ittained a considerable money value. Ou Circulation Department has long had no copies prior to 1925 and we do not deal in the older ric but we notice a brisk trade in them in

a collector's

Ham-Ads.”’

ind seems to command a price of about

ur first issue is now

$15.00, the whole of Volume I at least $30.00, the pre-war issues £¢ nerally several dollars piece, the earlier post-war issues at least a dollar piece, while a complete file is easily worth

round $200.00. Of course this is just a sidelight it one that we think our readers may find inter- Since the war, QST has been owned by the itself, that is to say, by the members of the League. A place where they may foregather the discussion of triumphs and problems

ke, it has been built largely by their own con- Certainly it may be said that it has altogether by that splendid spirit Since 1925 it has also been the official organ of he International Amateur Radio Union. Today it is read by nearly amateur in America, by innumerable for- gn hams, and copies find their way to almost very civilized spot on the globe. It will be found n every laboratory worthy of the name, includ-

League

putions

1 built

hich is amateur radio’s.

ery TY

ng many a one of a foreign government. When amateurs first began to work interna-

tionally, there were many persons who believed that this relationship would lend great impetus » the movement for an international auxiliary o1

nthetic language which could be readily mas- tered by peoples of every tongue. We ourselves thought so in those « arly days and devoted much tudy to the question. The project railed com- pletely, for rather astounding reason, and we don’t know but that it then and there sounded the death knell of the auxiliary language move-

ent The

nateurs sprang into existence In other countries,

explanation now sounds simple: As

following the early transatlantic successes, they it imperative to read QST' as a guide to successful As a result of this need to read and understand QST, countless thousands of foreign amateurs have acquired a satisfactory working knowledge of English. It is indeed called ‘OST English.”” Thus English has become in- disputably the language of international amateur radio. We

English with scores of foreign amateurs who as-

found

practice

have ourselves met and conversed in

December, 1936

9

Col ia

vledge of the language came study of YS7'! (What a respon- lering the way we hams are late our mother tongue! ips talked too much about our- upposed to be our privilege on Because of the unique nature of through which amateurs every- QST has been happily

perate,

Announces Annual Award

to be Given America’s Outstanding \mateur Radio Operator

\

AM

r

S. PALEY, president of the Broadcasting System, has an- a permanent award to be that individual who, radio, in the opinion of an im-

Awards, has contributed most American people, either in re- il development or operating

er ot

illv to

s designated the American Radio is the permanent custodians of it will be engraved each year

e winner of the award. A smaller

presented to the individual se- vinner by an impartial board amateur radio

authorities on

en have been selected to serve on

Award, it was announced by Mr.

ber 17th. The members of the Admiral Cary T. Grayson, chair- rican Red Cross; C. P. Edwards,

for the Canadian Department Prall, chairman of the unieations Commission; J. H. f the radio section of the United ent of Commerce’s National Bu- is, and A. E. Kennelly, professoi trical engineering at Harvard

ning S.

of the board are experienced

iteur radio activities and their

s will be followed by Columbia

annual award of merit to the itstanding amateur operator.

is taken because Mr. Paley felt

service which amateur operators

» stricken communities during the

the early part of 1936 was only of the very great contribution to radio communication as it ex- the purposes of the award only the United States and Canada d eligible. Such an arrangement

privileged to contribute substantially to the ad- vance of our art. Carrying the torch in many an uphill struggle, endeavoring always to conduct ourselves in terms of the greatest good to the biggest number, we have participated in many profound changes in amateur radio. We renew our pledge to strive ever onward to even greater things, and with your continued help we'll do it! K. B. W.

will make possible a thorough and fair survey of accomplishment without regard to national boundaries but within a single geographical unit.

When Mr. Paley announced the original plan for the award he expressed the hope that mem- bers of the board would not look upon their duties as being in the nature of selecting the winner in a contest, but would endeavor to recog- nize outstanding work and experimentation done by amateurs and acknowledge meritorious service to the American people and to the advancement of radio communication.

“In the development of major industries, as in the growth of sports,” he said, ‘“‘the amateur pre- cedes the professional; and we in commercial broadcasting owe a debt of gratitude to those thousands of experimenting enthusiasts who first broke the ground in the limitless field that is radio to-day. The great progress that the ama- teurs have made in the past 20 years has been an inspiration to us in our particular sphere of en- deavor. In establishing this annual award, I wish it to be an acknowledgment of the valuable con- tribution which amateur radio operators in the United States and Canada have made to radio science and communication, as well as to the public service which they have rendered in times of emergency.”

Mr. E. K. Cohan, Director of Engineering of the Columbia Broadcasting System, a member of the American Radio Relay League since its earliest days, made the announcement of the award, on behalf of Mr. Paley, at the Chicago Convention of the A.R.R.L. before thousands of amateurs assembled from all parts of the United States and Canada.

The exact nature of the award itself is at pres- ent in process of determination. Seven young sculptors of distinctive merit have been selected to submit their concepts and interpretations of a design for the trophy. Each is giving very consid- erable thought to the design in an effort to develop something distinctly in the spirit of amateur radio communication.

Inasmuch as it will take several months to collect and examine the data and recommenda- tions on which the award will be based, it is not anticipated that the selection of the winner will be made prior to March 15th.

QST for

p

' 1

mod

plin

An Inexpensive Five-Band Low-Power Transmitter

A 20-Watt Output Rig Suitable for C.W. or Plate-Modulated ‘Phone

By George Grammer,* WIDF

ELECTING a design for a low-power trans- mitter capable of operating both c.w. and KY 'phone on all regular communication bands snot altogether easy. When it becomes necessary to balanee cost of tubes, apparatus, and power supply against simplicity, ease of operation and powel eutput especially modulated power out- put), some careful figuring is required in order to each a satisfactory conclusion.

Probably the great majority of low-power

ansmitters average a& power input of about thirty watts. At this power level a very effective transmitter could be built up using a small trans-

iitting pentode as the output tube—but a 500- volt plate supply would be required, and there would also be the necessity for special arrange- ments should plate modulation be used. Further- more, it is doubtful if any appreciable saving in apparatus would result, since to cover a number of bands with one crystal practically the same num- ber of tuned circuits is required regardless of the tube line-up.

It planning the transmitter to be described, therefore, it seemed to us that the most econom- cal way to get effective performance, both c.w ind plate-modulated "phone, on all five bands was to use inexpensive receiving tubes, provide as many stages as might be necessary to give adequate excitation for the final amplifer on all bands, and use straightforward, time-tried cir- cuits. Although there are four stages in all, the transmitter is fundamentally simple both in

design and operation, and its performance has justified the reasoning behind it.

As we have intimated, the necessity for phone operation was a consideration in the design of the set. The description of the modulator, however, will be left for a later issue, the present article being confined to the transmitter itself, an an- tenna coupler, and the power supply.

rHE TRANSMITTER CIRCUIT

The circuit diagram is given in Fig. 1. The crystal oscillator tube is a 41, used in the standard pentode circuit. The output of this tube may be fed either to a 41 doubler connected as a high-z triode, or to a 41 neutralized amplifier-doubler also used as a triode, but with the screen tied to the plate. The doubler stage is used only when it becomes necessary to operate the final amplifier on a frequency four times that of the crystal. The final stage uses two 42’s in push-pull, used as tri- odes with screens and plates tied together.

Considering now some of the individual fea- tures of the practical circuit diagram, it will be observed that parallel feed is used on all three driving stages. This was done because, since it was deemed desirable to build the whole trans- mitter on a metal sheet to obviate grounding difficulties and unwanted interstage couplings, it permitted mounting most of the tuning condens- ers directly on the n etal bas? and eliminated the need for the insulation which series feed would have required. Parallel feed has the incidental advantage that there is no danger of accidental

A LOW-COST 20-WATT FIVE-BAND TRANSMITTER USING RECEIVING TUBES Built in breadboard style, this rig has four stages, one of which can be cut in or out as needed, and can be plate- modulated on any regular communication band on which radiotelephony is permitted. The antenna-tuning and cou- bling apparatus, a separate unit, is at the right.

December, 1936

nser shaft and the metal base Series feed is used in this case, the rotor of the ris grounded so that the d.c

load to which they made for tapping the plate ible for feeding into either may follow the oscillator. ts obtamimng maximum out- without overloading uble-throw switch, Sw,

position, the oscillator output r grid and the plate output of nto the grid of the third 41 for purposes of

oss the grid coupling con- tech is in the upper position, nected to the driver and the s grounded. Since the doubler triode, its plate current value under these conditions

cathode-biased ‘4, Which is by-passed bv ¢ s to hold down its plate cur- vhen it is not excited, since to the plate the uw is rather nection could be used here, nethod is preferable for mong them being the fact is more suitable for e grids of the final stage impedance step-down.

ised in the final stage

leak, Rs, citation; a pair of terminals also are provided for the use of additional fixed bias, if this is deemed desirable. Keying is in the amplifier eathode circuit. In the amplifier plate circuit, a

is used to give automatic bias with ex-

pair of terminals is provided for the introduction of modulation; these must be shorted for e.w. operation. The amplifier is cross-neutralized in the usual way.

Jacks for reading plate current are available in the plate-feed circuits of all four stages.

One last point about the circuit diagram: By- pass condenser (jy, connected between positive B and ground on the plate-supply side of the doubler plate choke, mav not be absolutely necessary, but in the practical transmitter made some im. provement in the pertormance of the doubler, Its probable funetion is to ground any r.f. whieh might leak by the plate chokes, all of which meet at the common positive high-voltage lead. It will be noted that all of the tubes in the set are oper- ated at the same plate voltage

THE PRACTICAL TRANSMITTER

The transmitter is built in breadboard fas! 10On, the baseboard measuring 26 by 8S! by ls inches

1

Runners along the ends, 1! inches high, provide room underneath for mounting miscellaneous parts. A sheet of thin aluminum, 24 by 6 inches, runs along the front part of the baseboard: all ri. parts are mounted above or below this sheet, which serves as a ground.

The order of parts above the base is as follows Starting at the left, first in line is the socket for the ery stal oscillator. Next, to the front, is the socket for the oscillator tube; continuing in line are the oscillator plate condenser, (;, and coil, L;. To the rear, directly in back of the oscillator tube, is the doubler plate coil, Lo; to its right is Ce, with its shaft pointing to the rear, and then the doubler

AN VIEW OF THE TRANSMITTER WITH THE 1.75-MC. COILS IN PLACE

The location of the various components is discussed in the text.

QST for

tube socket. The doubler cut-out switch is next in line, to the right of the doubler tube and LZ. Next, to the front, is the driver neutralizing condenser, ( with the driver tube directly behind it. To the right of the driver tube is its plate coil, Ls; in front of L; is the driver plate tank condenser, (3. These are

followed by the two tubes = of the final amplifier, then S

the final plate tank con- 7 denser, C4, and last, the ba plate tank coil Ly. Inspection of the photo- graph will show the place-

mete

ment of the few remaining = parts above the baseboard. | eo T The plate blocking con- Tei + densers, Cs, C7, and Cw, &

for the oscillator, doubler 7 3A r und driver tubes respec- = ' tively, are mounted by

their wire leads close to the

plate prongs on the tube

sockets. The doubler and

driver grid condensers, (

and Co, are likewise close FIG.

to the proper socket prongs and to the movable arms of the switch to which they ire connected. The grid leaks, FR and Ry, are

mounted close to the con-

volt. “6, C7 —250-upfd. mica. Ss Co—100-ppfd. mica.

250-uufd. mica. densers. The final amplifier cathode by -pass condenser, (13, is between the two tube sockets. The oscil- lator feedback condenser, marked C in the dia- gram and shown dotted between oscillator plate and grid, is of very small capacity and is made by bringing a short length of No. 14 tinned wire near the lead between the oscillator tube grid prong and the erystal socket. It can be seen in the top-

“4—Split-stator condenser, 100 u ‘'s—O0.0l-pfd. paper, 400-

¢ 4 Cho, Cii~—-0.002-ufd. mica, ¢ <

‘3a, Cra—O.002-pfd. mica.

connected to the plate circuit is about 1!9 inches long. This condenser may not be needed, although the grid-plate capacity is so low in the 41 that it

may be difficult to get a low-frequency crystal,

I—CIRCUIT DIAGRAM OF THE LOW-POWER TRANSMITTER

C—Feedback condenser (see text).

Ci, Co, Ca—100-pufd. midget variable (National ST-100). ¢

<

ufd. per section (National TMS-100D).

oo Ci7—15-nyufd. Rs—7500 ohms, | 10-watt. midget (Cardwell Re—600 ohms, 2-watt. ZR-15-AS). RFC—R.F. chokes.

R,;—50,000 ohms, 2-watt. J—Single a circuit

Re—50,000 ohms, 2-watt. jacks.

Rs—10,000 ohms, 2-watt. M- 0-100 ‘ae milliam-

R4—50,000 ohms, 2-watt. meter, small size.

especially one ground for 1.75 me., to oscillate without it.

All above-board wiring is of No. 14 tinned cop- per wire. Grounds are made directly to the metal sheet by the shortest possible connections. The is a standard product which comes furnished with a fibre cross piece. This has been

removed and replaced by one home-

switch, S

made from bakelite in the interests of better insulation for the r.f. which the switch must carry.

Terminal strips for the various con- nections are mounted along the rear edge of the baseboard. The plate milli- ammeter, mounted on the small bake- lite panel fastened to the baseboard with angle brackets, is at the rear center, with the plate jacks on either

WIRING AND PARTS BELOW THE BASEBOARD

Chiefly bypass condensers, r.f. chokes and resistors. The only r.f. components are the neutralizing condensers for the final stage.

view photograph. A connection is brought from the stator plates of C; to an unused prong on the crystal socket, and the wire soldered to the same prong. Separation between the two wires is about 1/16 inch, and the wire

‘é condenser is

side. The latter are mounted under- neath the board, and project into holes through the base so that the meter plug goes in vertically. There is thus no danger of shock from touching the jacks.

The arrangement of parts underneath the base- board is shown in another photograph. By-pass condensers and r.f. chokes are mounted as closely as possible to the above-board circuits to which

December, 1936

13

hy

“ondensers for the final stage

rneath

}

pie,

the ‘ctions to made aS

None

| parts of the wood; the

inted

by running

the Isolan-

I

es

ikelite lug

held

are

rt tubular

r shafts

in the

readily be

by means

lrilled large enough to allow he plate feed connection fo

through a jack-top porce-

nd ral rule

re-

stor

}

ne four-prong socket on the

series or parallel with the

to the top of the , the driver tank on porcelain standoffs (the re National Type GS-1 wit!

ed). This is necessary to

that ih

;

;

vund leads are short. Since ts on top of the board are means of machine screws board rather than by wood yuund connections are avail- ate-current jacks, holes are etal parts and the jacks rt wood-screws.

strips except for hn go direct to ground. To leads are allowed to touch holes through which such

Lb ise, since both sides

gh r.f. potential because

mounted onal

FIG. 2—THE ANTENNA COU- PLER CIRCUIT DIAGRAM

Ci, Co—250-yufd. variable (National TMS-250).

Li—12 turns No. 14 bare wire, diam- eter 2 inches, spaced to occupy length of 134 inches.

Lo—Depends upon antenna system, if used. See text.

Sw—Double-pole, single-throw midget knife switch.

Some amateurs may prefer this method to

inductive coupling between pickup coil and final- amplifier tank coil. The coupler baseboard meas- ures 9 inches wide by 84 inches deep; the runners underneath are | hand edge of the baseboard can slide over the

4 inches high so that the left-

transmitter baseboard without touching it. The left-hand runner is 1 4 inches from the edge of the baseboard. The pickup coil, L, in

Fig. 2, is 4- by 2! 9-inch platform of bake- lite which projects off the edge

of the board and is in turn mounted on a wooden riser which brings the axis of the

pickup coil to the same height as the axis of the final tank coil the transmitter.

Coupling coils can readily be the unit about so that the spacing

the changed. The general view of the set shows moderately-close coupling between the two coils

Should link coupling be pre- ferred to inductive coupling, tli pickup coil may be omitted fron

the two

varied by

between

moving antenna-coupling

between two coils can be

the antenna coupler, the antenna coil and its link being wound on a four-prong form and plugged into the socket on the base. Identical links would then be used at both transmitter and coupler end

tie

inductive coupling shown, especially if it is desir- able to locate the antenna coupler some distance

from the transmitter.

base ~

This avoids

wood, a

NA COUPLER

of ante nna coupli gy ior

eT low-

7 specially

type of antenna is going illustrated in the photo- outfit, particularly adapt- nna systems involving a

ned

i i

of a pickup coil, a pair of switch for connecting

I ductance,

e circuit diagram is given

ch as to permit

or high-power, it

when it is

feeders. It is essen-

n also is made for the

Is quite

not

under full load.

the transformer.

should it be ohms might be

sired, although

discharge through the tubes in the transmitte

variable

“any precaution which is not |

POWER

conventional in design.

The particular transformer specified about the right power capacity and voltage out put to run the whole rig without difficulty, being loaded to about rated capacity stages are working.

The fibre strip on the series-parallel swit: should be replaced by a bakelite strip, just as was done with the switch in the transmitter.

The two tuning condensers are mounted o1 half-inch wide bakelite strip 7 inches long, which in turn is mounted somewhat above the wood.

possible leakage through thu

ird to take

SUPPLY

The power supply needs little comment, sinc

Inexpensiv'

receiving-type components are used throughout

has

just

all

an 83 or 83-\

foul

when Using either

rectifier, the output voltage is approximately 380

bleeder is used, the chiet

No

reason for its omission being to avoid overloading

A light bleeder of about 50,000

used to discharge the condensers when the transmitter is out of operation, if de- normally

the condensers will

when the primary power! is shut off

QST for

| ivoid the expense of a& separate filament

rimer, the filament winding on the powe! transformer is used to supply the heaters of the tubes in the transmitter. During stand-by periods between transmissions, therefore, the power sup- ply must be left ‘‘on’’ in order to keep the tube heaters up to temperature. The simplest switching

met! od is to open and close the

t eielt t

The excita- , than with sue

imes the erystal frequency tion for the final is lower, of course cessive doubling in each stage, and this procedure is therefore recommended for e.w. work only, not for "~phone. However, it offers a ready means for working the builder is the holder of a Class-B license, opera-

four bands with one crystal. If

connection between supply and

mitter, a system which, while

negutive

the powe! trans-

per ectly satisfactory from an

standpoint, place s

ope iting quite a stram on the filter con-

dense rs during stand-by periods

when the power supply is de-

livering no current. Electrolytic condensers with ordinary surge ratings will not stand up under

PL, Leekcce |

UUW

this treatment; con- densers with high surge ratings

used. The particular

special

ust be

mm ti Bi Z- -

“ft ty!

condensers specified have been found to be satisfactory in this We do not recommend for

service the paper electrolytics because, although

they are satisfactory from the voltage standpoint, a paper replacement for an 8-ufd. electrolytic has

replacements

considerably lower capacity and the filtering is

inadequate.

OPERATION

Considerable flexibility is possible in the

ethod of operating the transmitter to get output Recommended combinations

n various bands.

ire given in the table below:

1 Os Doubler Driver implif Vv f y. M Freq. M Freq. M Cut BR: 175 Cut ou $5 $9 7 14 14 it out 7 > g 5 Cut out 7 7.0 7.0 14 14 14 28 zs ( t out 1.0 1.0 Cut out 14 14 14 23 25

this table it ean be seen that the “‘doubler’’

as a doubler or quadrupler,

be used either ind the “driver” as either a straight amplifier on doubler. For working on the band next above that in which the crystal frequency lies, it is recom- mended that the driver be used as a doubler rather than to use the regular doubler and feed the driver as a straight amplifier; the excitation to the final stage is about the with either method and eutting out the doubler is simpler

same

from the operating standpoint With quadrupling in the second stage, quite good output can be obtained from the final stage

COMPLETE SET OF COILS FOR ALL FIVE BANDS Note the flexible center-taps on the final-amplifier tank coils in the fore- ground. The G. R. plugs on these leads are inserted in a jack-top feedthrough insulator on the baseboard.

COIL DATA Freq Diameter Length No Wire Tap M Inche Inches Turns Size 1.75 Lh 1% 55 24 26 & 35 $5 1% M46 29 IS 20 & 20 7.0 16 1% 15 18 9 & 15 Use 1; for same f equelr 7.0 7

14.0 14 1% S 18 None

1.735 l by lo oo 24 Center

" thle lo 40 IS Center

7.0 L\% lhg 1S 18 Center

14.0 Lhe 14 10 18 Center

28 .( 1% l i 18 Center

4 l 22 2% t IS Center 2k6 ~% 32 16 Center

7.0 214 22 16 Center

14.0 2 2% 12 12 Center 28.0 2 234 LF) 12 Center NOTE l s are counted from lower (ground) end of coil Highe ups on Ly go to grid of driver through Sw; lower

é Le and L3 are nd on Hammarlund bakelite plug-in forms, four prong Lat 1.75 Me. is wound on bakelite tubing; for 3.5, 7, and

t Mec., the coils are Barker and Williamson Nos. SOA, 40A

ler, also through Sw. Li,

i of dou

d 20A respectively, with taps soldered to center turn.

r 28 Me. has turns cemented to celluloid strips. Turns on

all coils should be spaced eve nly to fill the le ngth spec ified we

tion on 160 and 10 meters on ’phone, and on ¢.w. on all bands, can be carried out satisfactorily with only two erystals. The frequency of the first should be between 1,800 and 1,950 ke., and that of the second between 7,000 and 7,075 ke. or between 7,125 and 7,200 ke. These frequencies will be satis- factory for doubling into the successively higher- will avoid the Class-A

Trequency bands, and

‘phone assignments

December, 1936

15

‘ING

ADJUSTMENTS

complicated process, although ed out with care. Connect the | key, and connect jumpers | bias and modulation terminals.

lliammeter of about 0-50 or

SI

VHOLI

PPLY

TAKES CARE OF TRANSMITTER

r-type components are used. The rec-

THE

ble, it may be connected to easure grid current in the vecessories for tuning are a in stick whittled at the end ver for adjusting the neutral-

e use of such a tool rather rewdriver unwanted nd a ’phone plug which is left

avoids

to get the oscillator working. nd the proper oscillator plate ypen the doubler switch, Su, plug in the oscillator plate- he dummy plug in the driver his will open the driver plate the tube’s drawing excessive

ng the adjusting process. The

to perform the same job for