?Ro1essional-Serviceman-Adiotrician HUGO GERNSBACK Editor

Dec adio afit 25 Cents for the ?ro1essional-Serviceman-adiotrician HUGO GERNSBACK Editor

Wen who have made radio: SirOliverLodge www.americanradiohistory.com -.MM/ 11 ---soimems-- ;3o 1á H/ 9,pe1 10' St1" 10 Str 1.1.,,'.04 1' 1

%.1..i WHAT'S N EWS IN RADIO? A. C. SHORT- WAVE RADIO I'II.IITII /l \S PILOT Endorsed by Professionals Power lacks The original idea be- No.K -111 for S ..0 hind the Pilotrons was 171 -A Tubes to make a line of radio Thorough filtration of tubes for a select group direct current output, of professional radio makes hum inaudible. engineers, custom set - Self-contained rectifier tube. Hlghlp compact. builders, radio research- Delivers tip to 220 volts. ers, and others whose C plete. toady for use. Espe.lii l. recommended standards are consider- for the A.C. Super-Wasp. ably higher than the PILOT SUPER-WASI' general public's. To No. K-112 $19.50 win endorsement from for 245 Tubes radio's fussiest folks, two 2.45's Kit Power Easily hn ndlcs 4r 0 had in posh -poll pins five or K -115 Pack Pilotrons to he is 227 and 224 types. Extra outstandingly superior! Variable resistance 'n- The constantly nlou cling of full 3 delivery 4s ears rated voltages front the Hear dozens of stations you never knew demand for Pilotrons various Ut Ps. Delivers up existed . . . short -wave broadcasts from required the purchase to 300 volts. Ultra-com- foreign countries . . . strange music of pact. Compete, ready for an additional tube use. surprises by the score the thrill of factory. . . Now, the trans -oceanic reception is now yours, plus general public. learning the convenience of A.C. operation. from radio technicians, insist: on Pilotrons. en- Special Note -The Battery-Operated dor -i it by professionals. Super -Wasp, Kit K -110, will continue to be available. Cus- 9.50 ItADUO S tom Set - Builders' Price 82 11I1:I:EST 500 PILOT vu.1 -E brings you membership Push-Pull in Radio International OUTSTANDING Guild, including the AMPLIFIER official organ. Radio [Nor 2.15 Tubes] FEATURES Design -a construction Here's an am- $39 1- Complete kit -c;lo be assembled in a quarterly that sparkles A putier big v 1111..// single evening! with the latest and enough and greatest radio and short- p o w e r f u l 2- Employs the specially developed Pilotron enough for movie "Talk- 227 -the only :\.C. tube suitable for wave developments! irs" and public address short -wave detection! Current issue. together systems. Wherever ro- with Membership Pin, guiretnents dente nil max - Utilizes super -sensitive grid limon nmplification, free 3- screen tube. Card and Certificate,will from any hint of ilistor- 4 -Tunes from 14 to 500 meters. promptly sent on re- lion, this Pilot outfit is be recommended. All A. D 5- Operates from any ABC power pack of ceipt of remittance. ( and C voltages self -con- proper type. tained. Complete In RADIO DESIGN PUR. CO. semi-kit form (K -113). (Pilot K -111 is recommended, S16.50) Dept.l01, 103 Il,.ar, B4lya.N.Y.

Prices Quoted are for Custom Set -Builders in U. S. A. Get Pilot's Latest Catalogue front nearest authorized Pilot Dealer or write Direct to Factory. EILOT RADIO &TIJBE CORP. WORLD'S LARGEST RADIO PARTS PLANT -- ESTABLISHED 1908 323 BERRY STREET / \ BROOKLYN, NEW YORK ev S L \\ ql, J9 e NMI" 1.tSii sievlo 4rs 441bOG- gQ vtt0<.t g=j9/ c1e pe4ßco° a, ..i _d -4'_4 9 6 ° eo1e vFeo1$°1Oet. ólei °14 ò .,00< o L*9. . , a:e4fltllo!' .

www.americanradiohistory.com December, 1929 RADIO -CRAFT

et this .. CATALOG This big book of 148 -pages -rich from cover to cover with radio bargains -is yours for the asking. It contains all the latest radio devices and improvements - sets, accessories, parts and kits - profusely illustrated. No radio need is overlooked. Everything in this big book is available at wholesale prices, and many items are spotlighted as Specials at truly astounding reductions. To be without this book is to miss your greatest buying opportunity in radio. Every page points the way to money-saving. Never before have such startling values been offered -made possible by our tremendous buying power and low cost of operation. Quick deliveries and expert cooperation assured. to all our clients. A trial order will make you a regular customer, just as it has thousands of our pleased customers. Clip the Catalog Coupon, and mail it today! SCREEN -GRID 7rice-Savina ao Models COUP" . Store Screen Chicago Salvage Stock Marvelous offerings in new, Humless, 130 Grid A. C. all -electric and battery operated sets; Dept. so. State Chlcago,Dt. 609 charge and postpaid) me of Bargams. a wide range of beautiful consoles, from the small your send Book of Radio table model types to the most ornate and artistic of your new 148-Page radio furniture; dynamic speakers of tremendous volume Name ...... and richest tone; accessories, parts and kits in wide variety ...... -in fact, everything that is standard, as well as every. Address...... State...... thing that is new, in Radio. Get this book today! City...... CHICAGO SALVAGE STOCK STORE World's Largest Radio Store 509 So. State St, joeor. sao Chicago, Ill.

www.americanradiohistory.com 242 RADIO -CRAFT December, 1929

H. CERNSBACK. President S. GERNSBACK. Treasurer VOLUME 1 J. M. HERZBERG. Vice- President NUMBER 6 I. S. MANHEIMER. Secretary adios a t R. D. WASHBURNE, for the C. P. MASON. Technical Editor Associate Editor Professional- Serviceman- Radiotrician

HUGO GERNSBACK, Editor -in -Chief Money in Automobile Radio Contents of this Issue By HUGO GERNSBACK PAGE LEAVES FROM SERVICE MEN'S NOTEBOOKS ONE of the important new developments in radio that has By RADIO -CRAFT Readers 245 come about lately is the automobile radio set. From a LETTERS FROM SERVICE MEN 246 purely experimental stage, the car set has now been devel- MEN WHO MADE RADIO -Sir Oliver Lodge 247 oped to such a stage that, during the next few years, a tremendous NATIONAL LIST OF SERVICE MEN REPLY BLANK 247 new outlet for radio sets and radio parts will have been created. SOME PRESCRIPTIONS OF A RADIO DOCTOR And, incidentally, those who get in on the ground floor will, as usual, reap a rich harvest. By Paul L. Welker 248 WHAT IS RADIO'S GREATEST NEED FOR 1930? * * * * * By Service Men 249 AN important point to be remembered, not only by radio en- RADIO SERVICE DATA SHEETS 250 thusiasts but by the entire radio trade as well -is that the A MULTI -METER AND TESTER -By Louis B. Sklar 252 radio car set is an ADDITION to the natural consumption of radio SHORT -WAVE CRAFT -The Coast Guard's Best Short Wave sets; for the simple reason that the man who owns a radio at Receiver By S. R. Winters 253 home cannot take that set and install it into his car. It means R. an entirely new, as well as a different set. Of late, the car set C. A. SHORT -WAVE TELEVISION WORK 254 has taken the public's fancy; and several large manufacturers have SHORT-WAVE STATIONS AND THEIR SCHEDULES 255 announced their intention to equip their cars regularly with such VACUUM TUBES FOR RADIO RECEPTION -Part III sets for the coming season. Foremost among them is the Dodge By C. W. Palmer 256 Company. A COMBINATION WORK -BENCH AND TEST BOARD A radio set in a car today is a necessity, because it enables By A. Kronberg 258 one to keep in touch with what is going on while traveling between cities, and even within cities. For the apprehension of RADIO -CRAFT KINKS 259 criminals, it is a most important adjunct to any police department. THE COOPERATIVE LABORATORY -By David Grimes 260 * * * * * THE RADIO CRAFTSMAN'S OWN PAGE -By Himself 262 PRACTICAL LITERATURE FOR RADIO READERS 263 AT one time, it was the custom to build such car sets behind the dashboard. This was a most cumbersome arrangement, NEW RADIO DEVICES FOR SHOP AND HOME 264 and will not prevail in the future. The new sets that are now be- SOLVING THE PROBLEM OF CITY AERIALS 265 ing installed in cars work on entirely different principles. The THE DEVELOPMENT OF THE MODERN SOUND REPRODUCER set is installed in a metal cabinet, similar to a tool chest, which is By O. C. Roos 266 attached right on to the running board. A flexible shaft goes to INFORMATION BUREAU 270 the dashboard, where the shaft connects with a single knob which is used as a tuning control. The shaft, by the way, is of the variety that dentists use to connect their motors to the dental drill. Aside from the one tuning knob, there is also a filament switch; these constitutes all the controls for the car's radio set. In Forthcoming Issues: The operation is simplicity itself; the switch is turned on and a station is tuned in. There is no volume control, and there is no Tri -Chromatic Television Herbert E. Ives necessity for having one; because the volume is controlled simply Notes for Radio Service Men Bertram M. Freed by detuning a trifle. This makes for great simplicity. While, Interference in the future, some refinements may be added, yet even the pres- -Its Origin, Location and Elimination F R. ent method is a good one. Bristow During the coming year, we will witness an epidemic of Experiments with 14- Centimeter Waves Ernst Gerhard radio sets for cars, which the various manufacturers will put out Servicing the Freshman "N" Harold Weiler complete and ready to install. Radio Sets and Parts Salvage Clyde A. Randon * * * * * A Novel Scanning Disk Paul L. Clark OF course, these sets will not install themselves; so some- one will have to do the installing -and here is where the service man and radiotrician will reap a rich harvest. RADIO -CRAFT is published monthly. on the fifth of the month preced.ng tlrir It is conceivable that, by the end of the next five years, every of date: its subscription price is $2.50 per year. (In Canada and foreign car will come already equipped by the automobile manufacturers countries. $3.00 a year to cover additional postage.) Entered )une 24. 192. at the postoffice at New York. N. Y. a second-class matter under the act nil with a radio installed all ready to operate. But, for the next few March 3, 1870. Application pending for s transfer of second -class entry to the many iostoffice at Mount Morris, III. Title registered U. S. Patent Office. Trade, years, there will be cars not so equipped; and it is here that marks and copyrights by permission of Gernsback Publications, Inc., ' the service man and the radiotrician will be able to make a good )'ark Place. New York City. Copyright 1929 by G. P.. Inc. Text and illustrations of this magazine are copyright and must not be reproduced with- deal of money in the installation of such sets. out permission f the copyright owners. Vie are also agents for SCIENCE RADIO- CRAFT, from time to time, will present articles on this WONDER STORIES,t AIR WONDER STORIES and SCIENCE WONDER QUARTERLY. Subscriptions to these magazines may be taken in combination new and fascinating subject. with RADIO- CRAFT at reduced Club rates. Write for information.

Published by TECHNI -CRAFT PUBLISHING CORPORATION Publication Office: 404 No. Wesley Ave., Mount Morris, Illinois Editorial and Advertising Offices Western Advertising Office 96 -98 Park Place, New York City 737 North Michigan Avenue, Chicago, Ill. L. F. McCLURE, Western Advertising Representative.

www.americanradiohistory.com December, 1929 RADIO -CRAFT 243

the4O tacyWays tiMake$3°°qnliout.-- THE four Below plans InYour Spare Time shown are but a are a few of sample of the many the reports ways in which our mem- ín $3.00 F4Li0 from those now bers are making an hour upwards, spare time cashing in on the and full time, from the day they join "40 the Association. If you want to get Easy Ways" into Radio, have a business of your Clears Frank J. Deutch, Pa.- "Since own, make $50 to $75 weekly in $3,000.00 joining the Association I have your spare time, investigate the cleared nearly $3,000.00. It is almost impossible for a young fellow to fail, opportunities offered the inexper- no matter how little education he has, if he ienced, ambitious man by the As- will follow your easy ways of making money." sociation. $1,100.00 In J. R Allen, Calif. - "Have 6 Weeks done over $1,100.00 worth of Our Members Earning business in the last 6 weeks. Next month I am going to open up a store Thousands of Dollars of my own. I never knew that money could Every Week come so fast and easy." The Association assists men to $25.00 a Week N. J. Friedrich, N. Y. - "I cash in on Radio. It makes past ex- Spare Time haveaveraged$25.00aweek perience unnecessary. As a member for the last 7 months even of the Association you are trained though I am not a graduate but just learning." in a quick, easy, practical way to Training Lands R. C. Kirk. N. C.- "Your install, service, repair, build and training has been very Him Job valuable to me. I landed a rebuild sets -given ure -fire money- job with the big department store out here a making plans developed by us- few weeks ago becauro I had my member- helped to secure a position by our ship card with me. There were a large bunch Employment Department. You earn of applications ahead of me." while you learn, while you prepare yourself for a big -pay Radio position. The Association will enable you to ACT NOW buy parts at wholesale, start in busi- If You Wish NO -COST ness without capital, help you get Membership your share of the $600,000,000 spent annually for Radio. As a result of For a limited time we will give to the Association, men all over the the ambitious man a No -Cost Mem- country are opening stores, increas- bership which need not-should not ing their pay, pass - -cost you a cent. For the sake of inglicensed operator making more money now, and examinations, land- having a better position in the ing big-pay posi- future, mail coupon below now. tions with Radio You'll always be glad you did. makers. Radio Training Association of America Mail Coupon Today for the Dept. RCA -124513 Ravenswood Ave., Chicano. nl. Gentlemen: Please send me by return mail full details of FREE HANDBOOK your Membership Plan. and also a copy uo Áaalp oCost It is not only chock -full of absorbing information about Radio, but it shows you how easily you can increase your Nana income in your spare time. Mailing the coupon can mean $50 to $75 a week more for you. Address Radio Training Association of America 4513 Ravenswood Avenue Dept. RcA -1, Chicago, Illinois Cur State IMO ...eeefl J

www.americanradiohistory.com t RADIO -CRAFT December, 1929

CIE New Ifoisture Humidifier to â. Carbon Eliminator Man with Car for all Makes of Cars, Trucks, Tractors and Spare or FILM Time Engines $350 to $1500 a month An amazing Scientific Humidifier has been patented throughout the 1 man $4,939.66 in 33¿ months. Another $1,656.60 In 58 days. World that beats any ever got out. It makes engines run ALL THE 55,150.00 in 5 months to another. TIME with the same wonderful efficiency they do on a cool moist night. It gives MORE BIG MONEY can be-IS being made. pep and power, HIGHER top speed, eliminates hard carbon, and gives AMAZING mileage. Motors Fords report 28 to 42 miles per gallon. Other makes (both American and Foreign) report Fitting With Vix marvelous increases of % to double One man sold 8 first morning. mileage. Some of the best records are: Another sells all 3 men can install. Milts Miles Mlles Mlles Another's profits as high as $100.00 Buick .28's Essex 32 Nash 30 Pierce Arrow 22 a day. Cadillac 2113 Ford (Model T). 42 Oakland 31 Pontiac 31 VIX sells itself by 8 STARTLING Chevrolet 41 Ford (Model A). 40 Oldsmobile 3414 Rao 26¡i Hudson demonstrations BIG, STUNNING, Chrysler 30'¿ 231 Packard 213 Studebaker 29 ASTOUNDING -DEMONSTRATIONS. Dodge 31'4 Hupmobile 24! Li Plymouth. 29 Whippet 41 41?j Successful VIX men make MORE MON- Durant) Marmon 213, Graham- Paige 23)4 Willys- Knight 29 EY than they ever made before. And Hundreds of Other Wonderful Records on ALL American and Foreign Makes Try This New Principle ree T Gas Saver AT MY RISK Try this wonderful VIX Moisture Humidifier and Carbon Eliminator AT MY RISK on YOUR. OWN CAR to prove that VAPOR MOISTURE (drawn from Radiator to Engine) gives you that wonderful night driving effect ALL THE TIME with MORE mileage from gas and oil- eliminates hard carbon accumulation - gives MORE power, a SNAPPIER, PEPPIER motor. FASTER acceleration, a SMOOTHER, UIETER running engine and HIGHER top speed. VIX will PROVE ITS MONEY SAVING MERIT on your own car by 8 DEMONSTR.ATIONS conducted by yourself AT MY RISK -the most SENSATIONAL, most ASTOUNDING, most CON-- i VINCING DEMONSTRATIONS you ever saw. If you don't find from your tests that it does MORE than I claim, return it and it COSTS YOU NOTHING. I want wide- awake, hustling, County, State, Province and National Agencies everywhere, part or full time, to make 1350 to $1500 per month filling the great DEMAND for this wonderful invention wherever introduced. Write for my FREE TRIAL and MONEY MAKING OFFER. Use coupon below. WALTER CRITCHLOW Inventor and Manufacturer,e62AStreet, WHEATON, III, U. S. A. Pictures here and at top show Model "B" VIX attached to my own New ModelAFord. This car is wonderfully im- FIOEAV!IMailNow proved in performance with the VIX Moisture Humidifier. So is every Auto, Truck, Tractor. WALTER CRITCHLOW III Taxi, Bus, Marine, Sta- INVENTOR tionary and Aircraft En- and MANUFACTURER gine, both American and 862A Street, Wheaton, Ill., U. S. A. all Foreign makes. Please send me without obligation or charge i your FREE TRIAL and MONEY MAKING GUARANTEED TO VIX OFFER. r 1t /4 to 1/2 Gas Name Carbon Cleaning SAVE Engine Repairs Address or Costs You Nothing Town

www.americanradiohistory.com llcìcmbcr, 1929 RADIO -CRAFT Leaves from Service Men's Note Books The "Meat" of What Our Professionals Have { Learned by Their Own Practical Experiences of Many Years 1 By RADIO -CRAFT READERS $25.00 Prize Winner about three -quarters of an hour to do; and it PROTECTING THE A.F. AMPLIFIER is building up quite a reputation for us. We By C. O. Merwin READJUSTING THE DYNAMIC - have found on numerous visits that we had SPEAKER CONE been recommended by a friend who had one " A F. TRANSFORMER shot again!" By Benjamin J. Spotts of these sets serviced by us. "Why?" is the first question an owner of the set asks after he has had this very THE writer has been called, on numerous thing happen over and over again, and the occasions in the past three months, to cost of maintenance of the set mounts higher repair dynamic reproducers in electric sets and higher. and "please take out the rattle." As I have The writer has been running a small radio a "Majestic 72" myself, I decided to sacrifice laboratory in what is said by many manufac- my own speaker to the cause of improvement, turers of audio transformers to be the worst and find out what was the matter. locality in the United States (Southern Flor- Here is what was found (and I am wonder- ida). Upon our returning the transformer to ing yet why the radio engineers have not pub- the factory, the same stereotyped correspond- lished it is, of course, if they have found -that ence ensues: "We are sorry that the trans- it out): the cause is atmospheric conditions - former developed a defect after you had pur- the heat and moisture in the air. chased it. We are replacing it free of charge." The dynamic- speaker diaphragm is securely Obviously, the customer of a very fine custon. held at the periphery or rim of the cone, with built set will start to register a heavy kick a ring of chamois skin, or some other similar Assembling receiver data in loose -leaf books, after such a thing occurs about four times substance. Warm weather, following a period classified by makes and indexed. a year; even though the replacement costs him of dampness, causes this material to harden. nothing and the community set builder is out and pull the paper of the cone slightly toward FILING RADIO CONDENSING AND his time and service charges. the top or sides. Sometimes the paper itself, SERVICE DATA We have been worn dog -eared here with after absorbing moisture, becomes dry and dis- By Fred McElwee this trouble; so much so, that we were com- torted. Under strong vibrations while in op- THE writer's method of compiling serv- pelled to find some remedy. Obviously it eration, the center of the cone, which carries ice data books may be of some help to wasn't all caused by moisture leaking in, as the voice coil, touches the field magnet, as the professional service man; he has acquired the manufacturers would have it. If such were indicated in the illustration (Fig. A). I found the case, why then didn't the secondaries go out this fact by the use of ordinary automo- as well as the primaries? What was the bile cylinder gauges of the feeler type. $25.00 EVERY MONTH difference? Why simply this; the primary car- The remedy I have found is to loosen the ries D.C. which the secondary did not. Take reproducer's clamp nuts at the outside rim, Will be paid for the most interesting story by a professional reader, containing his out the D.C. in the prima,) and then see what which holds the chamois skin or leather; care- practical experiences and something of value will happen. We invented an indirect method fully rub the skin between the fingers until to most other service men. It will appear of coupling and ran test after test. We have it becomes again soft and pliable; and then on this page; together with other helpful which at had transformers last as long as three years put it back, very loosely, in the rim. In the contributions, will be paid for the regular rates. Send in your story; in any with the indirect method of coupling; and case of the Majestic, or any other speaker hav- shape so long as it is both understandable then switched them around to the direct method ing a bakelite or some such "spider" held to and interesting. Address the Editor, RADIO - and had them go out in two weeks. This the field -magnet case by a small screw, I make CRAFT. proves conclusively that the major number of the hole which passes this screw a little larger. "blown" primaries are cursed b) D.C. surge.': The frame may then be adjusted accordingly. a library which has been prepared from serv- static encourages this sort of thing wonder- In only one case out of thirty -seven did I find ice data, received from set manufacturers and fully in this part of the country. the paper so badly distorted that I had o clipped from radio magazines. A burst of static will cause the plate cur- use a new cone. This complete job takes on y A loose -leaf note book is used for each of rent to jump as much as 50 milliamps. when the popular makes of receivers which we directly connected! One can visualize what service. I use a paper punch and make holes is happening at the soldered connection of the in all the manuals, service data sheets from RADIO -CRAFT, blueprints of all the models, etc. On the first page of the book (a separate one is used for each make) I prepare an index, listing the page where each model may be found. I number each page in the book; and include also a few sheets of blank paper for notes and service data about the particular set which I have been servicing. There is a set of these books in each serv- transformers ice car, and one is kept in the shop. In the A Southern custom builder finds connected in the usual manner very subject to shop, also, we keep a data book with in- burn -out from "static." The connection above formation on tubes, rheostats, power pack con- prevents this entirely.

1 densers, amperites, etc. Any service manager can prepare books like small wire and the larger one within the trans- Fig. A these at small cost; and he or his service former. This connection pulverizes in time; At upper right is shown how slight a distortion men will always have their service data right and the winding gradually breaks down, be- is needed to from normal adjustment (left) where they can find the information at a comes noisy and then opens. Where two dis- cause rank. It is corrected by softening the copper. are chamois ring, as shown below. moment's notice. similar metals, such as solder and

www.americanradiohistory.com 246 RADIOCRAFT December, 1929 brought together and heated, a minute current is started; this causes a slow oxidization .01A '12A 2MF '71A 4 MF. 135.7.1 of the weaker metal. The whole becomes 0 UT PUT porous and the resistance rises; and this oxid- o ization when once started keeps right on- SEC PRI and that is generally what happens to the III o audio transformer. C-4iV. 2MF PRI. T1SEC. OUTPUT Fig. I shows the indirect method of cou- .. CHOKE FIG.2. TA+ I C -IAV. A+ pling which we use; not only does it give a markedly better quality to the reproduction The three transformer- coupled stages above were designed to prevent transformer primary burnouts, (the low notes come through splendidly) but on the principle of Fig. 1. Keeping the plate current out of the primary also minimizes distortion. it permits of a third stage of audio easily. Fig. 2 shows a sketch of a three -stage ampli- Some time ago, the writer came up against tubes and the receiver, and found everything fier which we have used for years with splen- a case of this nature in his own demonstration O.K. It was then found that this noise could did success. The plate current rarely exceeds room. Having set up a "Silver" receiver in not be produced with the aerial disconnected 25 milliamps, and there is all the volume one a particularly nice corner, I proceeded to gar- (this receiver uses a small screen aerial fast- can stand in the average home. It will be nish the top with a small sign easel and a ened to the inside of cabinet top). noticed that the plates of the detector tube medium -sized antique lamp belonging to Friend To make a long story short, I soon found and the '01 -A are returned through 1 /10 -meg. Wife, and so left it. that the antique lamp (being made of brass resistors. This system requires only one tap After using the receiver several hours I be- in two sections) had considerable capacitative to be taken from the "B" battery bank. A came aware of the fact that a very fine imi- coupling with the aerial in the cabinet; and D.P.S.T. switch should always be used; so tation of static could be produced by tapping poor connections, due to tarnish (oxidization) that the "B" current is cut off when the "A" the side of the cabinet or walking across the between the upper and lower sections of the is cut. A protector tube shoulsl be used be- floor. Of course I immediately rechecked the lamp, had produced the "static" effects in the tween the "A" supply and the "B"; "A-1 -" set. is connected to "B-" through a 40 -watt elec- I now use only a basket of paper flowers for tric -light bulb. This point cannot be too decoration; and, in my journeys through my highly stressed; for by -pass condensers some- city, I wonder how many of the nicely - times do break down. If such trouble should jointed aerials and lead -ins I see are static occur, the protector tube lights up, saving the machines? tubes and a lot of loss of religion. Moral: make it all of one wire and play (To prevent circuit feed -back the 40 -watt safe. lamp should be by- passed with a condenser of To avoid "seeing stars" always discharge 1 mf. capacity. -Editor.) the condensers in the power unit with an insulated screw driver; unless the condenser is UNDESIRABLE ANTENNA EFFECTS of the electrolytic type, when it is desirable PRODUCED BY LAMP to discharge it at a slower rate. By W. H. Scheppele Last week, I heard a young fellow -who NO doubt, every radio man is interested doesn't know a grid from a stove bolt -calmly in the reduction of interference, man- assert that from now on he isn't going to made static, etc., encountered in the operation service battery receivers any more; only All - of receivers of the very sensitive types in use Electrics for him, because there isn't so much danger of burning out the tubes when he today; and has had, or will have, some unusual Electricity is wholesome. rcr b.r rs, but not en- experiences along this line. joyable in chis manner. works on them. Letters from Service Men Opinions and Comments on Present Trade Conditions

RADIO AS A SIDE -LINE (According to a recent report of the Depart- state there isn't any "secret;" knowledge, ex- ITHINK your registration idea is a good ment of Commerce, outside of the cities of perience, and imagination are the foundation; one. I have been in the radio game since more than 10,000 population, more than 73 something you have to work for to get. about four years ago; at that time I took a per cent of the radio business is transacted by Knowledge of what goes on inside the coils, radio the- course through the Radio Training Association dealers with whom it is a .ride -line. More condensers, and tubes, according to of Chicago, and gleaned a lot of other informa- than eight per cent of reported radio sales ory; the practical application as shown visually tion from magazines, etc., library books, and were made by automobile dealers, and more by inspection and meters; experience that cer- others I got my chance with a Philco- equipped than four per cent by hardware dealers. What teaches you just what to expect from a "Radiola 28." The work was so satisfactory, portion of the servicing of the country is done tain location and the complete radio installa- on an imagina- in comparison with the trouble the owners by full -time radio workers, and u -hat portion tion you are working -plus a you experienced on other occasions, that these peo- by those skilled mechanic with whom it is a tion that changes you into "bug" and you ple told others. Result, more work; and so profitable side -line, is one of the questions mentally crawl through the wires until interferes with my business has increased. I advertised, too, toward the solución of which the RADIO -CRAFT find the leak or obstacle that radio. Perhaps this in a local paper, which helped. By always NATIONAL Lim. OF SERVICE MEN will be a the normal action of a giving dollar -for- dollar service, I always get guide. Have you filled out a copy of the is the "magic secret" referred to. the return call, at a later date. questionnaire which appeared in the two pre- No two sets are alike; no two customers vary in different local- I have meters, car, and all that is needed. vious issues of RADIO- CRAFT? If riot, it is are the same; conditions a variation in service men due to I have built various sets, and in all that reprinted for your use, in this issue on page ities; even and time, have never worked for store or radio 247, opposite.) a difference in knowledge, experience, shops; but for myself, in my spare time. imagination makes it a mighty hard proposi- Why? Because I work at the carpenter game; tion to give any cut -and -dried system of test- and, in spare time, at radio. I would accept ing and checking radios. A TIP TO THE R.M.A. a position where I could work at radio on One store sends its service man around with part time; evenings, Saturday afternoons, etc. JUST what is your system of testing a radio? a pocket full of tubes and a Beede socket But the thing is that I make more in carpen- Until a friend of mine asked that ques- meter; another service man has a Jewell, ter work, with radio on the side, than I tion I don't suppose I ever gave a thought Weston, or Supreme Set Analyzer. Would could get at a full -time radio job. that I had a "system" of testing a radio. But, you expect the same system of testing with JOE KoMO, if I must explain the magic secret- all this varied equipment? No. Chicago, Illinois. In the first place I want to emphatically (Continued on Page 278)

www.americanradiohistory.com December, 1929 RADIO-CRAFT 247 Men Who Made Radio -Sir Oliver Lodge

THE THIRD OF A SERIES

WHILE the inventor is nowadays the Oliver Lodge is in his seventy-ninth year; responding activity which takes place in elec- most spectacular figure in the de- for over half a century he has been a prom- trical conductors. It was Lodge who demon- velopment of a great new art, such inent figure in the scientific world. Among strated the possibility of radio communication, as radio, there is always in the the countless lines of investigation he has fol- experimentally, as Marconi did its commercial background, behind the inventor, the man of value -just as Henry created the telegraph "pure" science. The mathematician and the and Morse made it of practical utility. researcher into the by -ways of Nature pre- The discoveries of Lodge in the matter of pare the way; often many years before any the properties of an electric current in a liquid, practical benefit is extracted from their work and the phenomena of "ionization," have con- by the inventor who turns it into a new, every- tributed in no small degree to the building up day necessity of life. In no branch of human of highly -complicated modern electric theory; endeavor has this been so apparent as in the with its marvelous implications as to the theory application of electricity. The scientists made of the universe. Similarly, the researches of thousands, and millions, of painstaking ob- Lodge into the actions of light-which is, servations; the mathematicians made millions after all, merely radio of invisibly -short wave- of most complicated calculations, all in the lengths -are valued steps in the history of hope that, some day, mankind could profit by modern science. The genius of Lodge antici- . their labors. "What use is electricity?" de- pated by many years the commonplaces of pop- manded a practical man of Franklin, a century ular electricity today; the moving -coil or dy- and a half ago. "What use is a baby ?" re- namic speaker, for instance, having been de- turned old Ben. scribed by him more than thirty years ago. Among the greatest of the scientists whose As one of the most distinguished scientists life work has been to contribute to the crea- of the present day, his fame and honors are tion of radio as a separate, and most impor- international. A great teacher as well as a tant, branch of electricity, is the man whose great investigator, he is a man whose wide thoughtful face appears upon the cover of this sympathies and zeal for the spread of science issue of RADIO- CRAFT. He it was who brought have left their mark upon every field of his ac- the prophetic calculations of Maxwell and the tivity. The Grand Old Man of Radio laboratory work of Hertz to his own genera- is still vigorous; although for some years other tion; and he has lived to see radio, which lowed in that time, that of the oscillations fields of inquiry have made his name most he adopted when it was-so to speak -an of electricity in a conductor is the most im- familiar to the public at large, it is undoubtedly orphan child, become an honored member of portant with respect to our subject. While upon his pioneer work in the fields of electri- every home. More than that, it is the an- Hertz was discovering radio waves in air, cal oscillation and radiation that his greatest nihilator of space and the unifier of nations. Lodge was determining the laws of the cor- permanent fame will rest. Attention: Radio Service Men RADIO-CRAFT is compiling an international list of names of qualified service men throughout the United National List of Service Men, States and Canada, as well as in foreign c/o RADto- CRAFT, 98 Park Place, New York, N. Y. countries. Please enter the undersigned in the files of your National List of This list, which RADto -CRAFT is trying to Radio Service Men. My qualifications are as set forth below: make the most complete one in the world, Name (please will be a connecting link between the radio print) manufacturer and the radio service man. Address (City) (State) RADIO -CRAFT is continuously being soli- Firm Name and Address cited by radio manufacturers for the names (If in business for self, please :o :late) of competent service men; and it is for Age Years' Experience in Radio Construction In this purpose only that this list is being compiled. There is no charge for this Professional Servicing service to either radio service men or radio Have You Agency for Commercial Sets? (What Makes ?) .... manufacturers. We are hereby asking every reader What Tubes Do You Recommend of RADto -CRAFT who is a professional serv- Custom Builder (What Specialties ?) ice man to fill out the blank printed on this page or (if he prefers not to cut the Study Courses Taken in Radio Work from Following Institutions page of this magazine) to put the same information on his letterhead or that of his firm, and send it in to RADIO- CRAFT. Specialized in Servicing Following Makes The data thus obtained will be arranged in systematic form and will constitute an What Testing Equipment Do You Own official list of radio service men, throughout the United States and foreign coun- Other Trades or Professions tries, available to radio manufacturers. This Educational and Other Qualifications list makes possible increased cooperation for Comments the benefit of the industry and all concerned in the betterment of the radio trade. (Dec.) (Signed)

www.americanradiohistory.com 248 RADIO -CRAFT December, 1929 Some Prescriptions of a Radio Doctor In this first article of a series by an "Old -Timer," some common ailments of Magnavox, Radiola and Stromberg- Carlson receivers are diagnosed. i By PAUL L. WELKER

IN the course of diagnosing and repairing with the load and with different receivers. the ills of radio receivers, there are many If there are no A.C. meters on hand, there is kinks and easy remedies which cannot be no simple way in which to ascertain the cor- learned must be ob- rect value of the resistor required to reduce ú from books; these < TO tained from personal experience. It is the the potential to 110 volts. If an A.C. meter SET purpose of this article, therefore, to hand on is available, it is placed across the input ter- R to the serviceman a few of the troubles en- minals to the set and the variable resistor STEP DOWN countered during a period of servicing, with is connected in series with one side of the 220 V A C TRANSFORMER LINE 2:1 RATIO an explanation of the remedies used. Many of line as shown in Fig. 1. FIG.2 the ills cited are common to a particular type of set and, if the serviceman knows the remedy, .LAMP:9AAÇK4T;, aIPTAi"TPxtx 6 MR,. The most efficient way to obtain 110 volts from the trouble is easily fixed. rlkTlP r4M[NStila txS¿XS r x xcsl°A 220 is to use a step -down transformer. Note - quS .. : p..,,.r t it doesn't work on 220 -volt D.C. 110-Volt Operation from 220 to,l. Several cases have been encountered where When all was in readiness, and the tubes in- the customer had purchased a -operated serted, the set refused to work. A careful socket .".' 110 -volt A.C. receiver while supplied with check showed that the receiver was in perfect ll, nvOka 220 volts, or had moved to a section having condition. It was noticed that the filament was provided a 220 -volt A.C. supply. rheostat ( "volume control ") There are two possible methods whereby the with a pin which prevented it from being .Let turned to a full "on position. This pin was set may be used on the 220 -volt line. Un- "7,, - doubtedly the first remedy which suggests it- .1:KSI "S L POST AxC.'PORS... removed, as well as the fixed resistor found Wt protected self is the use of a resistor in series with one 10.°11 g.o.C1wS" under the set near the front panel, side of the line. This method would be by cardboard. Both sets functioned well after this had been done. wholly satisfactory were it not for the fact The positions of tubes, hum balancers and that the value of the resistor to be used varies other parts of the Stromberg- Carlson "636" are shown above. Increasing Response Certain types of receivers, such as the R.C.A. An optional method of reducing the line - models 16, 17 and 18, Knight, Graybar (which voltage is illustrated in Fig. 2. Here use is are the same as the Radiolas) and others, use made of a step -down transformer having a a resistor across the antenna and ground in ratio of 2 to 1. The secondary is connected the first stage; so that the gang control will across the set input. not be affected by the size of the antenna used. These sets are all of the single -dial type and Magnavox Receivers the response at the upper end of the broadcast spectrum is less than that at the lower end. In two cases the serviceman was called upon A simple remedy is to take a coil (which if A fundamental circuit for operating 110 -volt to fix old -style Magnavox receivers. Both tuned by a variable condenser will cover the apparatus from a 220 -volt line; the resisto must dissipate as much current as the set draws needed new tubes besides a few minor repairs. (Continued on Page 277)

PHONO. PICK -UP AUDIO / JACK. FILTER CHOKE -0 HF .ÓNIt .a,SF_

O OUTPUT CHOKE. PIN JACKS.

2.9V ON-OM HI -LO SNITCH. WITCH

LO HI 2.7V.

o DIAL o 4.5 V. LAMD, = .01 MF o

rNMF. 0 9MF 1011F. FIG.3

4.5V. 5014. CHOKE.

Circuit diagram of the Stromberg- Carlson "Models 635" and "636 ", indicating all values. The circuit is, obviously, a neutrodyne; and the service MIN will find little trouble in making tests and replacements, with the aid of the picture above. Manufacturer's changes in parcs of the circuit, in some sets of these models, are shown in the continuation.

www.americanradiohistory.com December, 1929 RADIO-CRAFT 249 What Is Radio's Greatest Need for 1930? The Radio Dealer and Radio Service Man Talk Back to the Manufacturer, and Tell Frankly What Should be Done to Make for Progress and Better Business.

CAREFUL SELECTION OF DEALERS WHAT ARE GOOD MEN WORTH? GOOD MEN NEEDED IAGREE heartily with the opinion advanced by WHAT Radio needs in 1930 is less humbug. IHAVE read every issue of your magazine. and As to what is Mr. J. E. Smith regarding the needs of radio for Leading chain and other radio stores in this think very much of its contents. need of Radio in 1930, I like Mr. J. E. Smith's the year 1930. city advertise a sale of tubes, such as RCA and the as there is a whole lot to it. What the If there are any manufacturers who think this not Cunningham. When you ask for them, they try to article, the radio trade needs is more good service men. We true, let them take a service kit and go out serv- sell their own pet tube. They tell you that have firms selling radio sets here at 35 down. You icing sets. After a few experiences with disgruntled RCA and Cunningham tubes are inferior, so that get no service, or practically none; and this turns set owners who think they have been "gypped" be- they cannot guarantee them. The suckers, as these for this people against a set when all it needs is a little cause a franchised dealer failed to install the set in harpies consider the general public, fall adjusting. the proper manner, for lack of experience or knowl- hokum and pay more for an inferior article. One service man from dealer told the edge of radio, or after it was installed, was unable The cry has gone up that the run of serv- customer that the line -voltage was only 109 and it and keep a satisfied customer. every ice men is very poor. What inducements are to repair that this isn't enough to operate an 8 -tube set. manufacturer should know that a dissatisfied customer given the trained man in the service field? That is just a sample of some of the stories I is a liability; but on the other hand a satisfied He is offend the munificent sum of as much as get here. ARDEN L. CLARK, customer is a booster and a good sales advertise- $30 week; he can furnish a car, as high if 514 Pike Ave., ment. as $42. Out of the extra $12, he must pay for Massillon, Ohio. So, for the future the radio manufacturer must gas, oil, storage and repairs. He must furnish his establish a system whereby a greater cooperation own testing instruments, and work long hours for can be brought about between him and his dis- less money than building -trades laborer. "BOOSTER" OR "KNOCKER," WHICH? tributor, franchised dealer and customer. This can Yours for better conditions, INOTE that many of the leaders in the radio be done by having competent and qualified men FRED ROACH, industry tell of radio's dire need for service install and service their receivers and also keeping New York City. men in 1930; but do these same manufacturers at- in contact with the customer for a period of time 3034 Third Ave., tempt to cooperate with the professional service after selling the set. The distributor will also man, unless he has their agency and sells their have to exercise more judgment in selecting dealers, particular receivers? unless he can take over the responsibility in re- Can the average music shop or service station gards to servicing and proper installation. You secure from the manufacturer wiring diagrams or an't expect this of grocerymen, plumbers, etc. IN our October issue, a formidable service sheets? Not on your life; unless, as before The manufacturer must also realize that the av- array of the best -known radio stated, you are selling their sets. him service he knows erage service man is rendering leaders in this country, at a request Illustration; a customer brings in a receiver for little about, by keeping for him a satisfied customer; repair; it is of a make entirely different from the and he ought to cooperate with him by keeping him from the Editor of RADIO- CRAFT, three for which the dealer has the agency. We will informed in regards to new apparatus, etc., through gave their viewpoints and opinions as presume the cause of the trouble is obscure. Rapid magazines such as yours. the most diagnosis is necessary, and can be greatly facili- F. LYNN, to what, in their minds, are JOHN will need tated by wiring diagrams, showing ohmic resistance Jermyn, Penna. important things that radio values, etc. in 1930. Every service man is hampered and limited by the What avenues are open, TOO MANY PARTS DESIGNS The Editor, in the same issue, ask- manufacturer's attitude. ed the radio professionals to reply to to secure information? Such publications as RADIo- THE crying need for Radio in 1930 is standardiza- CRAFT and a few worth -while books (and among tion of those small parts that do so much of the radio leaders, giving their view- these the only real one, in fact. which I have been the work in a broadcast receiver and give way so point as to what the radio industry able to secure is Rider's Trouble -Shooter's Manual. often. Consider the various shapes and sizes of needs most for 1930. He was virtual- Here is hoping that more of such high -grade, com- means of mounting by -pass condensers and the divers with but the mon -sense books arrive on the market). them. If a by -pass condenser of 0.5 -mf. capacity ly swamped their replies; The manufacturers who survive, and thrive to breaks down, the (dealer's) service man usually takes best ones are printed on this page. any material extent during the next five years, will the set back to the store to replace the defective part be those who are open -minded enough to realize that with the peculiarly- shaped one furnished by the man- the service man in the field can be quite a factor ufacturers. He generally hasn't it in stock, and waits as a "booster" or a "knocker" in response to their for the jobber who distributes that set to send one attitude toward him. out. A standard -sized one could have been installed EXAMINATIONS FOR SERVICE MEN Accept my thanks for the many helpful articles in the set owner's home, and everyone would be reading through the magazine, I read your I have secured from your good publication. satisfied. interesting article on the demand for service men. G. M. JENKINS, and IN Compare the shapes and sizes of the "B" Though I have for some time been free -lancing, the Jenkins Music Shop, and Silver "C" resistors in the Philco, Crosley thing is of interest to me. 354 East 43rd St they? receivers. They have to be that way, don't I began on Yaquinna Bay, Oregon, in 1912, served Chicago, Ill. Oh, yes! These parta could be made with standard with the army in 1916 -18. The government gave lugs, just as easily mounting holes and soldering me two courses, one at the College of Hawaii, and NEWS, NOT HISTORY, WANTED es tubes with standard bases. the other at Fort Kamehameha service schools. I of the important needs of the Yours for easier servicing, IN my opinion, one came back to Portland, Ore., in 1920, and started 1930 is closer cooperation be- L. SOLOMON, radio industry for my first radio building there next year. I went to and the service man in the 716 Washington Ave., tween the manufacturer work as radiotrician for the Bush & Lane piano complicated Braddock, Pa. field. Radio is developing into more company, for whom I worked three and a half circuits; and changing so rapidly that a service man years; and again for a year as specialist on their becomes familiar with a certain model, only to find worked on and successfully re- BATTERY SET STILL IMPORTANT new sets. I have that there is a newer one with increased complica- paired between twenty -five and thirty different tions. THERE are approximately 7,000,000 farm homes makes. and have built A.C. sets for custom trade. Just recently, I wrote to a prominent radio manu- in the United States. In this vicinity, about I have successfully combined dynamic and magnetic facturer. about some of his sets, only to be referred 21% have battery -operated sets, and only about speakers, assembling them in a manner to prevent to some textbook or some radio journal. What I A.C. sets. 2% acoustical distortion. I have used test apparatus needed was the service sheets with the electrical This year all -electric sets have had their boom made by manufacturers, and now have my own, values of each part, and full data on testing. and small -town sales. The great majority in city built up principally of Jewell meters. Until the manufacturers are ready to stand by homes are not equipped with electric -light of farm But I have on my mind more than this there the men who are in the field helping to keep their current. About 90% of the farmers who have are too many would -be radio men and junior grad- sets working 100% efficient, the radio industry will electric -light plants have radio sets already. uates, whom the dealers out here hire because they not move forward as rapidly as it should. Basing my assumption on the foregoing facts, can get their services for from $15 to $20 a week - In 1930 we will see the radio infant, Television. are between five and a half and six million there anything to get by cheaply. I have listened to some growing rapidly. What radio needs in 1930 is for homes that are in the market for battery- farm of the arguments of these would -be service men to manufacturers and service men to work shoulder to radios and, in view of this, I consider the operated customers that would -if Marconi were dead -be shoulder. The manufacturer should prepare his serv- most urgent requirement of the radio industry to- enough to turn him over in his grave. ice data and mail them in advance of putting the day the creation of a battery- operated radio work- believe that every service man should be re- sets on the market. This gives the man in the ing at peak efficiency with a minimum number of I to pass a examination as to his real field a chance to become familiar with the new tubes and a minimum consumption of battery quired stiff ability and actual experience as a journeyman radio circuits, and be ready to render proper service when current. for less than $40 the sets are placed on the market. The ultimate standardization of radio parts and servicer. I have never worked why have sought Another need is for the installation of a voltage would also prove very beneficial to the radio a week in this line, that is I circuits for myself. regulator to be built into every radio set; which and serviceman. However, at present, we new territory and am working retailer the goal of will save many a tube from going into the scrap a pleasant dream of what If this registration is a step toward will just consider this pile prematurely from fluctuation in the power supply atore for us. efficiency, I am forever for it. the future has in Iines. DELBERT MYERS, A. I. R. E. H. H. NORDNESS, ROLF N. JENSEN, Whalan, Minn. Emmett, Idaho. Sweetser, Indiana.

www.americanradiohistory.com T Radio Service Data Sheets 44+++++44+++++++++++++++++++4444+++++++++++++++++++++++++++4. ++++++++++++++++++++++++++++ DAY -FAN FIVE "5044"

The circuit used in this receiver is reflexed. Thus, pointer to approximately the correct point for that signed for selectivity conditions not as stringent as V2 functions as an amplifier of both radio- and station, and tightening the lock -nut. The condenser those of the present day, and it is not as easy now- audio -frequency currents. With SW1 in position on adjustment may require centering the rotor plates in to obtain interference-free reception in congested dis- 1, the audio output of V2 is fed to the reproducer; relation to the stator plates. A lock -nut on the end tricts as formerly.) A suggestion for obtaining in position 2, V5 is introduced as a third stage of of the rotor shaft is available for this purpose; it is additional selectivity is to connect a compact air - A.F. amplification. dielectric variable condenser from 6 to 11, Units R.F. Choke 1 R.F. Choke 2 and AN2ENNA GRODsD 90.22ís -f1 -a -a adjusting it to cause regeneration. It may be R.F.T. 2 are iron -core instruments in radio - mounted at a convenient point on the panel. frequency circuits. If regeneration on the longer waves is insuffi- A Continuity Test of the receiver should cient, it may be necessary to reduce to .001 - check as indicated below. The reference mf. the capacity of the by -pass condenser, numbers appear on the "Tube Layout." connected from the plate of V4 to "A -." Trrminaf7 Correa Came if Wrong Still stronger regeneration may be obtained by Plus 90.2 High resis. Open or shorted connecting a radio- frequency choke coil be' R.F. Choke 1 or tween the plate and AFT1 primary lead of open lead V4. A safety measure recommended for these Plus 90-6 High resis. Open or shorted receivers when operating from "B" batteries R.F. Choke 2 or is the of a fixed condenser of .01 -mf. open lead insertion capacity in series with the variable regen- Plus 22(í -11 High tesis. Open or shorted eration condenser mentioned above. A cau- pri. of AFT1 or this installation is to keep leads open lead tion regarding as short as possible, and to shield these new Plus 90 -15 High relis. (Sw. 1 on 2.) tests of this particular Open or shorted leads. The voltage were with a Weston AFT2 or open model receiver obtained a lead Student Galvanometer Model 375. With a 7,000 -ohm series Plus 90-19 High relis. (Reproducer 41/2-volt battery supply, approximation of this value is plugged in and loosened, the rotor an dstator plates are centered. and resistor is used. (An then tightened. If one or 'secured by the use of the secondary of a "replace- SW 1 on 2.) Open or two of the plates remain "Sw 1" is the "Speaker shorted reproducer or out of alignment, they may be centered by careful ment' A.F. transformer.) lead bending of the plates. If difficulty is experienced in Switch," getting Minus "A " -1 Dead short Open RFTI sec, or distant stations while locals are on, it will The Reflex Circuit open lead be well ro check the length of battery leads. Those An explanation of the paths which the varying Minus "A -5 Dead short Open RFAT3 or open which are too long will pick up sufficient energy from " currents follow may be an aid to lead the locals to cause these signals to "ride in" on top R.F. and A.F. the faults which may be encountered in Plus "A Dead short (SW2 closed.) Open of distant station programs. The solution is to keep deterfining " -C3 of this type. stator lead battery leads as short as possible. receivers The R.F. input is amplified by VI ; R.F. Choke Minus "A " -16 High resi$, Open or shorted RFT2 A peculiarity of this particular receiver is that an 1 forces the R.F. signal to pass through RFT2 to sec., AFT1 sec. or open antenna length of less than sixty feet will not (con- ; here another plate -circuit impedance (AFT2 pri. lead. V2 trary to usual practice) result in greater ease of tun- or the reproducer) keeps back the R.F., which con- High Open or shorted AFT2 Minus "A " -20 relis. ing through local stations ; a length of more than tinues to V3, via RFAT3, and then to V4, being sec. or open lead 100 feet is also inadvisable. The explanation lies again blocked by R.F. choke 2. The A.F. output Open RFTI pri. or Aerial -ground Dead short in the "selector coil" of this receiver. With an of V4 is reflexed" through AFT1 back to V2; open lead " antenna shorter than sixty feet, sufficient energy is and the A.F. output of V2 either actuates the Shorted .001 mf. cou- Minus "A " -2 Open not received from the distant station to allow the reproducer or is passed on through AFT to VS (the pling cond. selector to be turned to a point where the local sta- option being determined by SW1). Consequently, Open pri. Minus "A" -tap Dead short part of tion is cut out, and at the same time the distant VI is the first R.F. tube; V2 is second R.F. and 3 RFAT3 or open lead of RFAT3 station is brought in. In other words, a strong first A,F.; V3 is third R.F. ; V4 is the detector; and open) Shorted Minus "A " -1S Open (Swt signal from the distant station as well as from the V5 is the second A.F. Plus "A" -tap .001 -mf. coupling cond. local allows the user to select either station by pro- Other reflex receivers made by Day -Fan are the Open pri. part of 3 of RFAT4 Dead short per use of teh selector. Selectivity in this receiver "OEM -11" 3 -tube; "OEM -7" 4 -tube; "OEM -7" 4, RFAT4 or open lead depends to a major extent on the setting of the rube "Super- Selective;" and "OEM -12" 4 -tube. A Plus "A "-6 Open (Sw2 closed.) Shorted RFTI primary coil P in relation to S; reduced word picture distinguishing one from the other fol- .001 -mf. coupling cond. coupling increases the selectivity but at the same time lows. The OEM -21 receiver has two stages of tuned Minus "A " -11 Open Shorted .001 -mf. by- the sensitivity, within certain limits. However, the R.F. and two of A.F. amplification. pass cond. service man may install a small variable condenser The "OEM -7" receiver has one T.R.F. stage fol- "Off logging" may be due to the pointers having of the mica -dielectric type, inside the cabinet, and lowed by another T.R.F. stage reflexed for first slipped, or to the rotor and stator plates of the tun- connect it in series with the antenna lead to the RFTI A.F. The second A. F. is a separate rube. The ing condenser not being in correct register. The primary. By adjustment of this unit and of the "Super -Selective" varies from this model only in former may be corrected by tuning to a particular inductive coupling, a point of optimum selectivity and the looser coupling, through the R.F. transformer; station, loosening the pointer lock -nut, setting the sensitivity may be obtained. (This receiver was de- as does the "OEM -12" from the "OEM -11."

RA CHOKEf REFLEXED RFT2 .001 : TUBE .001 DET. RFTI MF MF. VI V2/ AFT2 R FAT 3 V3 RFAT4 V4 AFT( V5

0C (o° C3 ' C

Mai 111

.0001 - MF. ts - .001 WIZ MF.

SW 2

A+B- B+90V. REPRODUCER -- g+22(/2V.

250 RADIO -CRAFT December, 1929

www.americanradiohistory.com Radio Service Data Sheets 8 ++++4-444++++++++++++++++4++++++++++++++++++++a-+++++++++++++++4-14++a44+44++++++++++++++++

C.irD CROSLEY MODEL 601 C`l.9

The circuit used in this receiver incorporates the that it is necessary to remove indicator dial, pulley This set is not critical to antenna lengths, and will Hazeltine neutralization system. Tubes VI w V5 and both belts if center condenser must be replaced. give good results with a short indoor antenna. A are '01As; V6 may be either a '12A or '71A, the To remove this indicator dial, or to replace belts, total length of from 50 to 100 feet for the antenna latter being preferable. To take chassis from "can," take out three screws attaching indicator dial to and lead -in combined is recommended for average remove the three knobs; remove the escutcheon by center pulley and remove dial. Loosen screws which conditions. If locals cause interference, an aerial taking out the drive screws; remove two cap screws of 25 to 50 feet, including lead -in, may give better in front and two in rear, using socket wrench or results. The recommended lengths may be exceeded. pliers; raise rear of case until it clears coil shields; of course, in many instances with excellent results. then slide the case forward until it clears the shafts Local conditions must govern the choice of antenna of the tuning controls; and lift off. A total an- Color Code length. A good ground should be used. tenna- and -lead -in length of 50 to 100 feet is recom- Black "A "B-," "C+; There are four binding posts on the set, two for mended, except where a shorter length reduces inter- -," Blue "B-I-45" the reproducer, one for the aerial, one for the ference. For best results, ground must be connected White "B+90 ground. Battery connections are made to the cable to only one point, the ground binding post. Con- "; Red "B+Power attached to the set, in accordance with the color nection to the "A" battery may result in burning "; Brown "C -41/2" code in the preceding column. out a resistor; if set is being tested in the service Green "C-Power"; The use of '01As throughout is recommended by shop, care must be taken that only one ground con- Yellow "A-1-," the manufacturer, with a '71 power tube; though a nection is made to the let. Study of the schematic '12 may be used to economize batteries. Á separate circuit will show why this is necessary. The vol- "C" battery is recommended for the first audio ume control regulates the filament current of the EJIIIIIIIIII IIIIIIIIIIIIIIIII11111111111111111111111111111111111111111111111IIIIIIIIIIIIIIIIIIIIIIIIIIII11111111111111IIIIIIIIIIIIIIIIr. (brown lead) stage. first three tubes; the "acuminators," or trimming condensers, resonate the secondary circuits of V2, Lack of sensitivity, critical operation, motorboat- control tension of belts and take off belts. Put new and V3; the variable capacity in shunt with the ing, distorted reception, may often be checked to belts in position with drive pins on pulleys through tuning capacity in the grid circuit of V4 is an "align- an open R4 leak. (Most of these effects may be holes in belts. Tighten tensioning screws. To re- experienced ing" condenser which is adjusted at the factory if the leak has too high a resistance; place detector by -pass condenser, or grid- leak -and- replace and has no panel control. To balance receiver, leave it with a leak of two to three megs. resistance.) The tube layout of this receiver is as bottom attached, balancing with case on or off. follows: Looking at front of set, first R.F. tube socket is in Tune to a strong signal near 210 meters (using head- left corner, second R. phones at output) and insulate filament of V3. front; R.F., left, rear; third F. is next, followed by the detector; first A.F. socket Insert long -shank No. 4 socket wrench (insulated Test Continuity is right rear and second A.F. or power stage is front handle) through balance- condenser hole in chassis (Two test prods and a 10 w. lamp in series with right socket. Note that a wavelength of about 210 (third from left, as seen from front). Tune set the 110 v. circuit.) meters is recommended for neutralizing the receiver: for loudest response and balance for minimum signal but that one of about meters is recommended with wrench removed. Repeat operation with V2. Otherwise 300 Contact Correct for balancing the aligning condenser. If condensers using second balance condenser from left; following light Open wire or LIB Gnd-A CI, C2 and C4 should short -circuit, there is no dan- to VI and balance condenser at extreme left. The Open LIA or wiring Gnd-V1G ger of shorting "B" batteries or burning out tube "aligning" condenser is directly in front of V4. To Gnd-V2G Open wire or L4 filaments (as would be the case with sets using adjust, tune to strong local with "acuminators" at Open wire or L7 Gnd-V3G neutralizing circuits which obtain the neutralizing about middle setting; remove V3 and tune receiver Gnd-V4G no light Shorted C5 or R4 potential by tapping to a point on the plate- circuit until maximum signal is heard, adjusting right acu- Gnd-bk. light Open wire, RI or R2 coil) ; for the neutralizing potential in this rec- minator as required. Insert socket wrench on align- Gnd-whi. no light Shorted C3 eiver is obtained from the plate circuit inductively ing condenser and adjust for maximum signal, with Whi-VIP light Open wire or L2 by means of coils L3, L6 and L9. The effect of a wrench removed. Replace tube and adjust right acu- Wh i-V2P Open wire or L5 low -resistance short in Cl, C2 or C4 will be broad minator for maximum signal, slightly changing set- Open wire or L8 Wh i-V3P tuning, circuit oscillation and weak reception. If the ting of station selector if necessary. Acuminator Whi-VSP Open wire or T2 pri. leads to L3, L6 or L9 are reversed, it will be im- should then be at or slightly above middle position. Blue-V4P Open wire or Tl pri. possible to neutralize the receiver ; this fault will oc- To replace R.F. transformer, remove case and bot- wire Blk-V4F Open or R3 cur only if the receiver was partly re -wired during tom from receiver. With set upside down, remove servicing, and is readily localized by following the copper can to chassis over (With Headphone and Battery,) two nuts holding coil through the neutralizing process. Start from the de- to be replaced, and lift off can. Unsolder R.F.T. Connect: tector tube and work toward the antenna; the stage leads and remove two nuts holding R.F.T. to chassis. Gnd -V2G; rotate station selector; if click C7 shorted; upon which a "zero point" or silence -point cannot Solder leads to lugs and replace can. necessary If adjust left acuminator; if click 01 shorted. be obtained is the faulty one. Noisy operation replace a tuning condenser, case to remove Gnd -V3G; duplicate above. Clicks show shorted during manipulation of RI indicates poor contact. as described, also underside chassis nuts hold- Co or C10. (Instead of the variation of resistance being smooth, ing condenser shield to bottom of chassis, and Gnd -V4G; Clicks show shorted CII or C12. it is being effected in relatively large jumps.) The remove two screws on in front panel holding shield Green -V6G; no click shows open wire or T2 sec. remedy is to clean the resistor and sliding contact place. Press shield gently back it clears the until Brown -V5G; no click shows open wire or TI sec. with sandpaper. This must be done carefully, to top edge of the front panel, raise vertically, and prevent taking out the spring tension of the slider remove. leads and loosen screw which Unsolder IIGI IIIII I:I IIIIIIIII IIIII II!IIIII IIIIIIIIIIiIIllllll.!811111111IIIIIIIIIIIIIIIIIIIIIIIII IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII arm, when the arm will no longer make contact controls belt tension. Remove belt from condenser with the wire. A short in condenser C6 will cause pulley and remove pulley. Take out three screws the set to "go dead," as far as broadcast reception attaching condenser to front panel, and remove con- condenser mounting. unsolder leads, remove sup- is concerned; in this case, a test from detector plate denser. Attach new one to front panel by three porting screws, place new unit in position and re- to filament will show a lower resistance than if the screws provided and replace pulley and belt, tighten- solder leads. A 3- mcgohm grid leak is recom- resistance of the primary of Ti were effective, in- ing latter. Solder leads and replace shield. Note mended. stead of shorted out.

CI C2 C4 L2 Cl L5 C9 L8 V1 V2 V3 T2 v6 o o oq o o LI A ó ó O LIB APERIOOIC L3 L4 C8 L7 LIO C 2 L S. ANTENNA COUPLER O R4

C3 R3 RI SW

Y YELLOW WHITE BLACK BLUE BROWN GREEN REO')

December, 1929 RADIO -CRAFT 251

www.americanradiohistory.com 252 RADIO-CRAFT December, 1929 A Multi-Meter and Tester An Inexpensive Arrangement Which Will Function as Continuity Tester, Ammeter, Milliammeter, D.C. or A.C. Voltmeter.

By LOUIS B. SKLAR

DURING the last few months there radio -frequency transformer, or in any part have appeared on the market a of the set where a test for an open or short number of radio set testers and an- circuit is required. alyzers. The writer, however, wishes to present to radio workers a radio tester of a Parts Required new type, which requires only a few parts and can be built for a sum within the reach of The parts required for the tester are as everybody. The parts used, in most cases, can follows: A view of the apparatus built by the writer be found in the workshop. 1- Readrite 0 -to -25 scale D.C. milliam- in a convenient carrying case for use on calls, meter (1) well as in his workshop. While some of the features of this tester as are not new, the writer claims, however, orig- 1 -0 -to- 200 -ohm rheostat wound with heavy inality in the arrangement and design of the wire. 1- Electric plug for 110 volts A.C. (10) etc. various electrical circuits, so thst a maximum I- Electrad 0- to- 12,000 -ohm wire -wound re- Electric bulbs, binding posts, jumpers, the of performances can be done with a minimum sistor (3) Fig. I shows a schematic diagram of the number of parts. Some of the tests which 1-Electrad 0-to- 6,000 -ohm wire -wound re- tester; each unit is numbered according to can be made with this instrument cannot, as sistor (4) list above. We will go through, in detail, 1. far as the writer knows, be performed with 1 -Pilot UX socket, sub -panel type (5) each test mentioned, starting with No. 3 -Pilot UY sockets, sub -panel type (6) any commercial tester on the market. This set- Using the Tester up may be used as follows: 1 -Sign light receptacle (7) 4 -Small disconnecting switches (8) To get the plate -milliampere reading of any (1) To test the plate milliampere output of tube in the set, place one end of plug 9a or 9b any tube, A.C. or D.C. type. By a special (depending on the type of tube to be tested), arrangement, described later, the tubes can in the socket of the radio set and the other be tested even when the power supply of the end of the plug in socket 6b; place the tube receiver is not functioning; to be tested in socket 5 for a four -prong tube a five tube; the mil- (2) As a milliammeter; or in socket 6c for -prong liammeter will then give a reading for the (3) As an ammeter, having one or more plate current of this particular tube. different ranges; (In making this, as well as any other test, (4) As a D.C. voltmeter, of three different it is advisable to keep all disconnecting ranges; switches open; close them only when the test requires. Adhering to this rule will avoid voltmeter. (5) As an A.C. This feature burn -out tubes and injury to the meter.) was particularly designed so it can be used This test for plate current of a tube can as a check for 110 house cur- the -volt A.C. be performed only if the power supply is in rent; but, by proper tapping of the resistor good condition; should there be a defect in used for this purpose and calibration with a the "A" or "B" supply, it cannot be made. standard A.C. meter, it can be used as an A.C. The neat panel appearance of the Multi- Meter. Without the use of the "A" and "B" supply voltmeter for other purposes. of the radio set, a test is made as follows: - (6) As a tube rectivator to "rejuvenate" any 1-Testing plug, 4- contact plug on one end Put plug 10 into the house -current socket. type of tube which is "revivable." and 5- contact plug on the other (9a) Place an electric lamp of suitable size (the is given in Table 1) (7) To test for an open circuit or "ground" 1-Testing plug, 5- contact points at each size of lamp for each tube in the primary or secondary of an audio- or end (9b) in receptacle 7 and close switch 8b. When the electric lamp is lighted, insert the tube to be tested in socket 5 or 6c (depending on tube EXTRA WIRE FROM SCREEN-GRID TUBE CLIP CLIP FOR S.G. to be tested) open switch 813 and close switch TO CAP ON TUBE TO BE TESTED TUBE CAP 8c the reading of the milliammeter will in- r ; CUP dicate the condition of the tube. (Cables 9a TUBE TO CAP and 9b are not used in this test.) BE TESTED (The purpose of closing 813 before inserting 0- 10 M. A. PLUG SOCKET socket is to bring the IN TESTER the tube in the tester filament mazda lamp to its BUS WIRE SOCKET IN/ tungsten of the U i RADIO SET resis- maximum temperature and maximum tance, allowing only the proper current to flow through the radio tube; should you place the tube before the lamp has reached its high temperature, there will be a sudden rush of current with a possibility of burning out tubes.) J Changes of Scale 2 `111smoswee WIRE CABLE Tests Nos. -3 -4 are very simple, and there 5 need SCREEN GRID TUBE i is no need for explanations. All you SOCKET IN TESTER. for these three are two jumpers, which can be made from a piece of duplex wire and four clips. The voltmeter multipliers which are Fig. 2 tapped from the 12,000 -ohm resistance were Methods of testing screen -grid tubes, "Plug socket in tester" is 6B; "screen -grid tube socket in tester" is GC B (Continued on Page 272)

www.americanradiohistory.com December, 1929 RADIO -CRAFT 253

The Coast Guard's Best Short Wave Receiver

Details of a New Four -Tube High- Frequency Set, with K.F. Screen -Grid Stage, Used by the Government Services.

By S. R. Winters

ASHORT -WAVE radio receiving set able on the market, may be used in their stead. may be cut down in one of three ways-in- installed on the Coast Guard Cutter The tuning controls are provided with a creasing regeneration beyond the critical va- Chelan and more recently used on the variable ratio vernier drive, and a small vernier lue, reducing the input coupling, or by mani- U. S. S. Utah during a South Amer- is found on the tuning condenser of the de- pulating the plug and jack system. ican good -wilt tour demonstrated such extreme tector compartment for fine control of the beat sensitivity as to equal the performance of a note. This vernier is situated between the de- The Audio System 6 -or 7 -tube outfit. Designed by the General tector- tuning and regeneration dials on the All of the battery leads in this receiver Electric Company, this high -frequency set em- lower part of the panel. are provided with radio- frequency filters, and ploys only four tubes. There are three tuning controls and in by the application of an audio filter -system to the amplifier two or more receivers may be operated from one battery supply. Without the audio -frequency filters, however, "cross talk" would develop when using more than one receiving set. The use of the output of this receiver is a variable factor-that is, it may be tapped for use in a number of ways. For instance, head telephones may be plugged into either the detector stage or the jacks of the first or second audio -frequency stages. Or, the primary winding of the output transformer (external plug and cord) may be inserted in the detector stage, first audio -frequency or second audio -frequency jacks and the head telephones plugged into either of the two up- Panel appearance of the set used by the Coast Guard, with two tuning, and one regeneration, controls. per head -telephone jacks. The output transformer supplied with this set has a 3 -to -1 Details of Tubes and Coils addition to these are the following knobs which step -down ratio. When employing type 10 Input audio tubes the output transformer is intend- The use of a screen -grid tube compensates are manipulated as needs justify: type ed to work into a 1,200 -ohm transmission line, for any apparent deficit in the number of tubes coupling, filament voltage on the '22 tube, and when type 'OlA tubes are used this out- employed. This four -element tube is employed the filament switch, and a stage change plug put transformer functions best in a 3,000 -ohm in the stage of tuned radio -frequency amplifica- and jack system. Regeneration and wave- increase with dial setting. transmission line. The input to this receiver tion and this together with a regenerative de- length may be a doublet, a transmission line, or an tector and two stages of transformer coupled To intercept a continuous -wave signal, aerial and ground connection. audio -frequency amplification complete the regeneration is maintained near but slightly The power plant for this ultra- sensitive 4- circuit. The four-element tube is of type '22; above the point of oscillation as the tuning tube receiving outfit is quite elaborate. If the regenerative detector is a high -mu tube of control is manipulated. Simultaneously, the type '10 vacuum tubes are employed in the set, type UX -841; and the two stages of audio - input tuning is kept in resonance by noting requirements are: Plus "A", 8 -volt frequency amplification use type '10's. How- the increase of background noise. The extreme the power sensitive setting of regeneration represents storage battery; minus "C ", 18 volts grid ever, the type of tubes employed is a flexible the detector, plus 67% volts; four -ele- factor and instead of those just outlined the minimum of regeneration which will permit biasing; screen -grid, plus 45 volts; radio - high mu tube type '40 may be used in the the detector to oscillate and a beat note to be ment tube's perceived. Radio telephone signals are best frequency amplification, plus 135 volts; audio - detector stage; and a type '01A in the audio - plus 250 volts. If frequency amplification stages. tuned in by keeping regeneration in close frequency amplification, proximity to and slightly under oscillation. type '01A tubes are used in this receiver, This ultra-sensitive short -wave receiver is The volume of the output of the receiver the power requirements are as follows: Plus designed to cover a band of wave -lengths from 12 to 80 meters but this limit may be ex- tended to 250 meters by the addition of tuning coils not ordinarily included in this particular design. As.now constituted, there are four sets of interchangeable inductance coils-embracing, respectively, 12 to 18 meters, 17 to 28 meters, 26.5 to 45.5 meters, and 45 to 80 meters. Each set of tuning coils contains two units-one for insertion in the compartment devoted to the stage of tuned radio -frequency amplification and the other coil is plugged into the detector compartment. To facilitate the interchange of different coils, each set bears its wave -length range, engraved thereon. Any standard kit of coils of good design, obtain- Rear view of the receiver, removed from its cabinet and shields. Two coils cover each of four U'.uhington, D. C. correspondent RADIO- CRAFT. bands from 12 to 80 meters; they are of the plug -in type shown in the foreground.

www.americanradiohistory.com 254 RADIO -CRAFT December, 1929

01A

FIRST AUDIO T '01A CN1 Ó (PSI E

o o 19

B+ISSV. (1.22#V C-4=V 590V.

Schematic circuit of the four -tube receiver designed for the U. S. Coast Guard and the Air Service. Note the liberal use of by -pass condensers; 01 -mf. capacity is used, and the filament connections are made at the tube sockets. All leads must be as short as possible; condenser ground leads less than two inches. Bias for the screen -grid tube is obtained from resistor 12; ail shielding is grounded to "A -". Interesting combinations are possible with the little unit shown at the right. Units 22 are .005 -mf., with center connection grounded; detector jack 18 is by- passed by .002-mf.

"A ", 6-volt storage battery; minus 4% volts an indication that it has burned out. If the the Air Corps, United States Army. Captain grid biasing; detector, plus 67% volts; 4 -elem- audio amplifier oscillates, it is a sign that the Paul S. Edwards, the radio officer, sensed the ent tube screen -grid, plus 45 volts; radio -fre- "B" batteries are exhausted or their energy is extreme sensitivity of this circuit and indicated quency amplification, plus 135 volts. In the running low. A one- or two -microfarad con- that it would qualify as standard equipment denser across use of either type of tubes, the minuses of the battery will temporarily cor- for the Air Corps aircraft short -wave receiver rect this condition but the "B" battery should development. Subsequently, when the new the "A" and "B" batteries and the plus of preferably be replenished. Coast Guard Cutter Chelan went on its so- the "C" battery and ground are joined to- Used by Air Corps called "shake-down" cruise, it was noted that gether to the minus "A" binding post. The When this high -frequency receiver was this receiver eclipsed the performance of stand- filaments of all of the tubes are connected in originally designed, it was subjected to pre- ard Coast Guard radio outfits although the parallel and the failure of a tube to light is liminary trials in the flying radio laboratory of former employed fewer tubes, R.C.A.'s Television Work on Short Waves cSThe R.C.A. Experiments at W2XBS on a 100 -kc. band between 143 and 150 meters are discussed in this article.

WE are so accustomed to thinking of the standpoint is quite a different thing from the the actual demonstration and then to compare Radio Corporation of America only in laboratory or experimental product. these experiments with the later developments connection with their commercial receiver and Recently, a demonstration of television was of the same laboratory. accessories business, that many short -wave given to a small group and at the end of the workers fail to realize that the experimental seance, Dr. Goldsmith told his guests that the Television Demonstration laboratories of this organization are working demonstration they had observed was, from a The first consideration will be the trans- practically "night and day" on the problem of purely technical standpoint, of an obsolete mitter. A line telephone connection was set successful television. form of television technique! up to convey verbal directions and conversa- And successful television from a commercial It will be of interest to learn first, about (Continued on Page 274)

Looking into the shielded cabinet of the short -wave receiver used on the "Chelan." This receiver is a piece of standard commercial engineering; but the constructor may readily duplicate the circuit with parts available to bim. While coil data are not given, any short -wave kit may be used. Note how primary of first R.F. coil (at the left) is partially shielded from the secondary. The three -connection panel strip at left of larger compartment permits leads to the screen -grid tube compartment to be rigidly shielded. R.F. chokes of the pancake variety are used.

www.americanradiohistory.com December, 1929 RADIO -CRAFT 255 Short -Wave Stations of the World Kilo- Kilo- Meters cycles All Schedules Eastern Standard deter cycle s 14.50 20,680 Argentina. after 10:30 -.... Monte Grande, 37.80 7.930 -DOA. Doeberit z, Germany. 1 to 3 p.m. p.m. telephony with Europe. Reichpostzentralamt. Time: Add 5 Hours for Greenwich Berlin. 14.84 22.220 -DGW, Nauen. Germany. 2 to 9 p.m. 38.80 7,770-PCL, Kootwijk. Holland. 9 a.m. to 7 Telephony to Buenos Aires. Mean Time. p.m. 15.00 19,990 -....Mexico City, Mexico, 12:30 to 2:30 39.98 7.500-AFK, Doeberita, Germany. p. m. -TFZSH, Reykjavik, Iceland. From 15.03 19,950 -LSG Monte Grande. Argentina. -EK4ZZZ. Dantzig (Free State). 9 a.m. to 1 p.m. Telephony to Paris and Nauen (Berlin). 40.20 7.460-YR, Lyons. France. Daily except Sun.. Kilo- 11 :30 a.In. to 12:30 -DIN, Nauen, Germany. Meters cycles p.m. 41.00 7.310- ....Paris. France ("Radio Vitus ") Tests. 15.50 19.350 Nancy, France. 4 to 5 p.m. 30.50 9,130 -NRH. Heredia. Costa Rica. 10.30 to -.... 11:30 p.m. Amando Cespedes Marin. 41.50 7.220 -....Zurich. Switzerland. Sat. 3 to 5 -FW3. Paris, France. From 10 a.m. Tel- Apartado 40. p.m. ephony tu Monte Grande (Buenos Aires). 4L70 7,190-6AG, Perth, 30.75 9.750 Agell. France. Tues. and Fri.. 5 to \Vest Australia. Between -... 6:30 and 11 a.m. 15.74 19.060 -PLE, Bandoeng. Java. Broadcasts Wed. 6:15 p.m. 8:40 to 10:40 a.m. Telephony with Koot- 42.12 7,280-0Z7RL, Copenhagen. Denmark. Irreg- wijk (Amsterdam). 30.91 9.700- W2XAL, New York. N. Y. ular. Around 7 p.nl. 16.10 18.620 --GBJ Rodwin. England. Telephony with 3L00 9.680 -7LO. Nairobi. Kenya, Africa. 11 a.m. to 43.00 6.870 -EAR 110. Madrid. Spain. Tues. and Sat.. Montreal. 2 p.m. Relays G5SW. Chelmsford, fre- 5:30 to 7 p.m. quently from 2 to 3 p.m. 43.50 6.900 18.620 Kootwijk, Holland. Daily from 1 -IMA. Rome. Italy. Sun.. noon to 2:30 16.10 -PCK, .. Monte Grande. Argentina. works p.m. to 6:30 a.m. Nauen after 10:30 p.m. irregularly 43.86 6.830 -VRY, Georgetown, 16.35 18.350 -WND, Deal Beach. N. J. Transatlantic British Guiana. Wed. telephony. 3L23 9.600 -LGN, Bergen. Norway. and Sun.. 7:15 to 10:15. 44.00 ith 31.26 9.590 -PCJ. Hilversum. Holland. English pro- 6.820 -XC 51. San Lazaro, Mexico. 3 a.m. and 10.38 18,310 -GBS, Rugby. England. Telephony 3 p.m. New York. General Postoffice. London. grams Thurs. and Fri. from 7 to 9 p.m.. Sat. from 5 to 7 a.m. Other languages. 45.00 6,660 -.... Berlin. Germany. t6.50 18,170 -CGA, Drummondville. Quebec. Canada. Thurs. 1 to 3 a.m., Fri. midnight to 4 Mar- 45.20 6.635-WSBN. SS. "Leviathan." Telephony to England. Canadian a.m.; Sat. 1 to 7 a.m. N. V. Philips coni Co. Radio, Eindhoven, Holland. 47.00 6,380- CT3AC, Funchal, Madeira Island. Sat. after 10 p.m. 16.80 17,350 -PLF. Bandoeng, Java ( "Radio Mal- 31.28 9.580- VK2FC. Sydney, Australia. Irregularly 49.02 6,120 New . with Holland. -W2XE, York City. Relays \VABC. abar') Works after 4 a.m. N. S. W. Broadcasting Co. Atlantic to Broadcasting Co. 16.88 17.770 -PHI. Il wizen, Holland. Beam station -VPD, Suva, Fiji Islands. 49.34 Dutch colonies. Broadcasts Mon.. Wed.. 6.080- W2XCX, Newark. N. J. Relays \VOR Thurs.. Fri. 8 to li a.m. N. V. Philips 49.40 6,070 -UOR2, Vienna. Austria. Testing Tues. Radio. Amsterdam. and Thurs.. 8 -10 to 9:10 a.m. Wed. and Sat. after 6 16.90 17,740- HSIPJ, Bangkok. Siam. Broadcasts 9 p.m. a.m. 49.50 6.060- WSXAL. Cincinnati. Ohio. Relays to 11:30 WLW. 17.20 17,440 Nauen. Germany. -.... -W9XU, Council Bluffs. Iowa. Relays 17.34 17,300 -W2XK, Schenectady. N. Y. Tues.. (NOTE: this list it compiled from many KOIL. Thurs.. Sat.. 12 to 5 General Elec- 50.00 p.m. 6.000- EAJ25, Barcelona, Spain. Sat. 3 to 4 tric Co. sources, all of which are not in agreement, 18.40 16,300 -PCL, Kootwijk. Holland. Works with and which show greater or lets discrepancies; Moscow. State -RFN, Russia. Tues.. Thurs., Bandoeng from 7 a.m. Netherland Sat. 8 to 9 a.m. Telegraphs. in view of the fact that most schedules and -SAJ, Karlsborg, Sweden. 18.80 15.950 -PLC, Bandoeng, Java. Afternoons. many wavelengths are in an experimental still -Eiffel Tower. Paris. France. Testing 19.56 15.340- W2XAD. Schenectady, N. Y. Broadcasts 6:30 Thurs. stage; that daylight time introduces confusion to 6:45 a.m.. 1:15 to 1:30, 5:15 to Sun. 2:30 tu 5:40 p.m., Tues.. 5:45 p.m.. around this wave. and Sat. noon to 5 p.m., Fri. 2 to 3 and that wavelengths are calculated differently 52.00 5.770 p.m. ; besides relaying \VGY's evening -AFL. Bergedorf, Germany. program oit Mon.. Wed.. Fri., and Sat.. in many schedules. We shall be glad to 56.70 5.300 -AGJ, Natlen, Germany. Occasionally evenings. General Electric Company. alter 7 p.m. receive later and more accurate information 19.60 15.300-.... Lyngby. Denmark. Experimental. 58.00 5,172- ....Prague. Czechoslovakia. 20.00 14.990- TFZSH, Iceland. from broadcasters and other transmitting or- 60.90 4.926 -LL, Paris. France. 20.50 14,625-W8XF. Pittsburgh, Penna. ganizations, and from listeners who have 62.50 4.800 -W8XK. Pittsburgh. Pa. Relays KDKA after 6 p.m. Works with 5SW 5 to 7 22.20 13.500 -....Vienna. Austria. authentic information as to calls, exact wave- Beach, N. Transatlantic p.m. Tues. and Thurs. Westinghouse 2..38 13.400-WND, Deal J. Electric Cu. telephony. lengths and schedules. We cannot undertake 61.22 to 62.50 meters -4.800 to 4.900 kc. Television. 22.69 13.050- W2XAA- Houlton, Me. Transatlantic to answer readers who inquire as to the iden- telephony. -WBXK, Pittsburgh. Pa.; WIXAY. Lev - a ingtuu, Mass.; W2XBU. Beacon. N. 23.3; 12.850 -W2XO. Schenectady. N. Y. Antipodal tity of unknaun stations beard, as that is 1.; program 9 0.111. Mon. to 3 a.m. Pues.: matter of guesswork; in addition to this, the -WENR, Chicago. III. nuon to 5 p.m. on Tues., Thurs. and 65.22 to 66.67 meters-4.500 to 4.600 kc. Television. Sat. General Electric Co. harmonics of many local long -wave stations -W6XC, Los Angeles. Calif. Relays EGO -W6XN, Oakland. Calif. can be heard in a short -wave receiver.-- Editor.) 67.65 4.430 -DOA, Doeberitz. Germany. 6 to 7 a.m. to 4 p.m. An- Tues., Wed.. Fri., 12:30 2 to 3 p.111. Mon., Wed., Fri. to 3 2.111. Tues. tipodal program 9 p.m. 70.00 4.280 Also after 9 p.m. General Electric Co. -OHK2, Vienna, Austria. Sun.. first 15 minutes of hour from 1 to 7 p.m. 24.50 12.240 Ste. Assise (Paris) France. Works -FW. 70.20 4,270- RA -19. Khabarovsk, Siberia. Daily ex- Buenos Aires. indu -('bina and .1 ava. On cept Wed. front 4 9 a.m. to 1 p.in.. and other hours. a.m. 80.00 24.68 12,150 Rugby. England. Transatlantic 3.750-FSKR, Constantine, Tunis, Africa. Mon. -GBS- and Fri. Phone to Deal. N. J. (New Yorke. 31.38 9.550- . Zeesen. Germany. Projected new station. 84.24 3,560- OZ7RL, Copenhagen. Denmark. Tuesday 2 ;,10 11.940 -.. Zeesen. Germany. Tests of new and Fri. after 6 p.m Super -power broadcasters. 31.48 9.530.-W2XAF, Schenectady, New York. Mon.. 25.40 11,800 -W8XK -East Pittsburgh, Pa. Relays 'Ines.. Thurs. and Sat. nights, relays 98.00 1060 -.... \Iotala. Sweden. K I)KA after 6 9,m. foes. and Thurs. %VGY from 6 p.m. General Electric Co. 101.7 to 105.3 Ineters -2,850 to 2,950 kc. Television. Electric Co. front 5 to 7. Westinghouse -W9XA. Denver, Colorado. Relays KOA. -W3XK, Silver Spring. Md.. 8 to 9 25.53 1I.75í)-GSSW- Chelmsford. England. Relays -. ...Helsingfors, Finland. except Sunday; WPY, Allwoud. N. J. 5X X, Darentry 2 to 7 p.m.. experimental 104.4 2,870 -6WF, Perth. Australia. transmission from 7 to 9 p.m. and 7:30 3L56 9,500- VK3LO. Melbourne. Australia. irregular. to 8:30 a.m.. and tests with \\'2X0 12 Broadcasting Cu. of Australia. 305.3 to 109.1 meters -2,750 to 2.850 hr. Television. to 1 p.m. Mon. and Thurs. Silent Sat. -OZ7RL, Copenhagen. Denmark. Around -W2XBA, Newark. N. J Tues. and Fri. and Sun. British Broadcasting Co. 7 p.m. 12 to 1 a.m.;- W2XCL, Brooklyn. N. 25.40 11.710 -C3RX. Winnipeg. Canada. 5:30 to 8 p.m. Y.;- WBXAU. Pittsburgh, Pa. :-W1XB, 32.00 9.375-CCA, Drummondville. Canada. Irregular. Somerville, Mass.; W7XAO, Portland, daily. Sun. 1 to 2 0.111. Relays CJRW. James Richardson & Sons. Ltd. Canadian 'Marconi Co. Ore. 26.22 11,430 -DHC, Nauen. Germany (Berlin) Week- -EH9OC. Berne. Switzerland. Mon.. Tues.. 109.1 to 113.1 meters -2.650 to 2.750 kc. Television - days after 5. Sun. after 9 p.m. Sat. .3 to 4 p.m. W9XR, Chicago. Ill. 26.70 11,230 -WSBN. SS. "Leviathan" and A. T. & -JB. Johannesburg. South Africa. 2 to 6:45 136.4 to 142.9 meters-2.100 to 2.200 kc. Television. T. telephone connection. I,.II1. -W2XCR, Jersey City, N. J. 3 to 5 p.m.. 270q 11.100 -EATH, Vienna. Austria. Mon. and -OZ7MK, Copenhagen, Denmark. Irregular 8 t 10 11.111. except Sat. and Su11.; Thurs.. 5:30 to 7 p.m. alter 7 p.m. WBXAU, Pittsburgh, Pa.; WIXB, Som- erville. Muss. W2XCW. Schenectady. 27.27 11,000- .. Posen. Poland. Mon. and Thurs. 5 32.50 9.230 -FL. Paris. France (Eiffel Tower) Tinte ; N. Y. tu 6 p.nn. New station testing. signals 3:56 a.m. and 3:56 p.m. 142.9 to 150 Ineters -3.000 in 2.100 kc. Television. 27.80 10,780 -PLR. Bandoeng. Java. Vnrks with Hol- -VK2BL, Sydney. Australia. land and France weekdays from 7 a.m.; -W2XCL. Brooklyn, N. Y.. Mon., Wed.. sometimes after 9:30. 32.59 9.200 -CBS. Rugby. England. Transatlantic Fri., 9 to 10 p.m. ;- W9XAA. Chicait . 1 II. W2XBS, New York. N. Y., frame 28.00 10.710 -VAS. Glace Bay. N. S.. Canada 5 a.m. plume. ;- (0 litres deep. 72 wide. 1,200 R. M.I'.;- to 2 p.m. Canadian Marconi Co. 33.70 8.900- Posen. Poland. Tests Mon. and WIXAE, Springfield. Mass. ; -WBXAU. 28.20 10,630 -PLE, Bandoeng. Java. Tests with Aus- Thurs. 6 to 7 p.m. tralia. Pittsburgh. Pa.; W6XAM, Los Angeles; 28.50 10,510 -RDRL, Leningrad. U.S.S.R. (Russia) 34.50 8.690- W2XAC, Schenectady. New York. -W2XBU. Beacon. N. Y.;- W2XBW, Washing- 2&80 Sydney. Bound Brook. N. J. ;--W3XK. 10.410- VK2ME, Australia. Irregular. 35.48 8,450 -WSBN, SS. "Leviathan." ton. I2 e Daily except Sun., 8 tu 9 On Wed. after 6 a.m. Amalgamated p.m. ;-WPY. Allwood, N. J. Wireless of Australia, Pennant 11111s. N. 37.02 8,100 -EATH. Vienna. Austria. Mon. and S. W Thurs. 5:30 to 7 p.m. 30.00 9,995 -... Posen, Poland. -HS4P, Bangkok. Siam. Tues. and Fri 30.20 9.930 -W2XU. Long Island City. New York. Fri. 9 tu 11:30 a.m. (Standard Television scanning. 48 lines. 910 R.P.M.)

www.americanradiohistory.com 256 RADIO-CRAFT December, 1929 Vacuum Tubes for Radio Reception The Third of a Series, of Articles Explaining Tube Char- acteristics, Design, and Functions, and Methods of Manu- facture and Testing; in which Power Tubes are Described. By C. W. PALMER

WE have considered, in previous in- Plate voltage, 135; current 6.5 milliamperes; current, the filament circuit should be shunt- stallments, general -purpose tubes Grid bias, 221/4 volts; ed by a 15 -ohm resistor with an adjustable which operate on direct-current Plate resistance, 6600 ohms; center tap. The plate and grid returns are (battery) or A.C. filament supply, Amplification- factor, 3.3; made to this tap, which is then adjusted to the together with some of the special -purpose Undistorted output, 110 milliwatts. 7000 "valves," including screen -grid tubes. In this BOO 6 The '12A Tube issue, we will give the characteristics of the 6000 "power" tubes, beginning with the smallest and Next in order is the '12A type tube; the 1750 4 I = ending with the latest. original design was known as the '12 tube, a 5000 The first tube is the '20 type; this was and had a filament which required half an ,.. 1000 .. 3 developed as a companion to the '99 dry-cell ampere to bring it to the correct temperature. 4000 Later, the tube was changed by the substitution of a new filament, which needs only one 3000 half the current of the older type. It 77 The '12A tube, although it was designed be- 2000 fore the era of electric sets, is suitable for prtwl .0 to 3.0 3.0 10 1 100 vim a storage battery, PATE CURRENT u LUANPRES operation, not only from but with a step -down transformer as the filament Fig. 4

supply. Also, because of its high amplifica- The '71A gives less amplification, but more out - is put. than the '12A. Its plate resistance is very 6+ tion- factor, it a very good general -purpose Ac .a.wnl low. A2 tube; even though it was not designed for this purpose. The internal capacity is com- hum is heard. the paratively small, permitting its use as a radio - point where the least (If has a center -tapped Fig. 3 frequency amplifier. step -down transformer resistor is not necessary; for the Alternating current through a filament requires winding, this r is then used for the a center -tapped balancing resistor to take out tap on the transformer hum, beside the grid -bias resistor. 52 grid and the plate returns.) This is RI, Fig. 3. 46 Filament voltage, 5 volts; current 0.25 -am- tubes, so that better quality than was possible u pere. with the latter could be obtained. This tube W 40 Plate voltage, 90 to 157 volts; plate current has a small amplification- factor and, for this s 5.5 milliamperes at 90 volts, 7 ma. at 135 volts reason, is suitable for use only in the last 7, 52 and 9 ma. at 157 volts; Grid bias, 4% volts audio stage of the set. Its filament is different s at 90 plate volts, 9 volts at 135 and 11 volts from that of the '99 tube, in the amount of at 157; current required to supply the correct heat. The Plate resistance, 5300 ohms at 90 volts, '99 tube requires only six one -hundredths of 5000 at 135; an ampere; the '20 tube needs thirteen (132 Amplification -factor, 8; Undistorted output, 120 milliwatts at 135 milliamperes). It may be operated from dry 6 a2. volts, 300 at 180 volts. cells, if so desired; but more economical oper- 4 a ation results from the use of a storage battery. 10 The Old Favorite MO M 41 OM M O O N a0 M. Y E0 40 400 With a 6 -volt battery, a resistor of 20 ohms S PATE POTENTIAL is next in line; this is should be connected in the negative lead, in The '71A tube the Fig. 1 power tube ever order to reduce the voltage across the tube to probably the most popular operating as the '71, with the correct value. The characteristics are: A convenient chart of the comparative made; it was first produced tubes. It does not in- conditions of the power on Page 279) Filament voltage, 3.3 volts; current 0.132 - dicate comparative outputs. (Continued ampere; O When used as a power tube, the '12A is most suitable for small sets; the undistorted 3200 6 6000 3200 6 output is not very great and in large sets, 2600 T be 2000 7 where the volume is high, the tube will overloaded. Since it has a comparatively high 2400 6 6000 2400 , 6 6000 et amplification factor, (8), the volume of a small set, however, will be greater than if a 2000 I? 2060 s tube such as the '71A were employed. 1600 z 4 4000 Fig. 2 shows the main characteristics of 1600 4 4000 a the '12A. The amplification- factor is the 1200 3 A C. 1200 § 1 horizontal line at the top; it will be noticed that this is not straight, as would be the 600 1 2 2000 600 32 2000 II,- A case if the "Mu" of the tube were exactly 400 1 400 constant. It is interesting to note that the mutual conductance increases with an increase 0 0 N 100 ISO 200 250 300 40 60 So 100 120 in plate voltage, while the plate resistance PLATE VOLTAGE PATE VOLTAGE decreases. If a graph were made with grid Fig. 2 voltage, instead of plate voltage, as the Fig. 5 horizontal factor, the two volumes would also The characteristics of a '12A -type tube. With The '10 rube has both high amplification and the aid of graphs such as these are receivers increase and decrease in the same manner. high output. Its efficiency increases rapidly as designed. When using the '12A tube with alternating the maximum voltage is approached.

www.americanradiohistory.com December, 1929 RADIO -CRAFT Characteristic Data of Radio Vacuum Tubes Ampli- Mutual N. Undistorted Filament Supply Plate Supply Pl.t. notion Conduct. 'C" Max. Typo RadioCnit MILLI. Resistance Factor .nc Bi.. Output MANUFACTURER T..d. Moo Numb.. Dedcaation - B... VOLTS AMPS. VOLTS AMPS. OHMS MU. Month m VOLTS Milliram

Radio-Victor Corporation of America R.C.A. UX120 '20 Small 3.3 .132 90 3.2 7700 3.3 428 16.5 X Std 135 6.5 6600 5.5 500 22.5 110 E. T. Cunningham, Inc. Cunningham CX220 '20 3.3 .132 90 3.2 7700 33 428 16.5 135 6.5 6600 3.3 500 22.5 110 Sonauon X120; Champion UX120; Sylvania SX120; Gold Seal GSX120; Perryman PA120; KenRad 120; Ce -Co E; Ra -O -Vac RX120; same claracteristi s as UX120 and CX220, above)

Radio-Victor Corporation of America R.C.A. UX112A '12A Large 5.0. .25 90 5.5 5300 8.0 1500 4.5 50 X Sid. 135 7.0 5000 8.0 1600 9.0 120 157 10.0 4700 8.0 1700 10.5 195 180 10.0 4700 8.0 1700 13.5 300 8.0 1500 4.5 30 E. T. Cunningham, Inc. Cunningham CX112A '12A . " 5.0 .25 90 5.5 5300 135 7.0 5000 8.0 1600 9.0 120 157 10.0 4700 8.0 1700 10.5 195 180 10.0 4700 8.0 1700 13.5 300 Sonatron X112A; Speed 112A; Champion UX1I2A; Triad T112A; Sylvania SX112A; Perryman PA112A; Km -Rad 112A, Ce-Co F112A: Eveready -Raytheon Ra XII2A; DeForest 412A; Ray -O -Vac RX112A; Dutton D112A; Gold Seal GSX112A (same characteristi s as UXII2A and CX112A, above).

Radio-Victof Corporation of America.. R.C.A. UX17IA '71A Large 5.0 .25 90 10 2500 3.0 1200 16.5 130 X Sid. 135 16 2200 3.0 1360 27 330 157 18 2150 3.0 1400 33 500 180 20 2000 3.0 1500 40.5 700 27 E. T. Cunningham, Inc. Cunningham CX37IA '71A 5.0 .25 135 16 2200 3.0 1360 330 157 18 2150 1400 33 500 180 20 2000. 1300 40.5 700 Champion Radio Tube Works Champion UX171A '71A " 5.0 .25 90 3.0 16.5 135 27 180 40.5 Sylvania Products Co. Sylvania SX171A '7IA 5.0 .25 90.180 10.20 2200 3.0 1400 16-40 Cable Radio Tube Co. Speed 171A '7IA 5.0 .25 135 -180 16 -20 3.0 1500 27.40 Gold Seal Electric Co., Inc. Gold Seal GSXI7IA '71A 5.0 .25 90 10 2500 3.0 1200 16.5 130 135 16 2200 3.0 1300 27 330 180 20 2000 3.0 1500 40.5 700 Ken -Rad Corporation Ken -Rad 171A '71A " 5.0 .25 180 20 1950 3.0 1525 40.5 Ce-Co Mfg. Co. Ce -Co J71A '71A " 5.0 .25 90-180 9-20 2500 3.0 1200 16.45 Eveready Carbon Co Eveready- RayX. '71A " 5.0 .25 90 10 2500 3.0 1200 16.5 130 Raytheon 171A 135 16 2200 3.0 1300 27 330 180 20 2000 3.0 1500 40.5 700 DeForest Radio Cos DeForest 47IA '71A " 5.0 .25 90 11 2500 3.0 1200 16.5 135 16 2200 1360 27 157 18 2150 1400 33 180 20 2000 1500 40.5 French Battery Co. Ray -O -Vac RX171A '71A " 5.0 .25 180 3.0 Diatron 171A '71 " 5.0 .5 90 16.5 . Diamond Electric Co 135 27 180 40.5 Triad Mfg. Co. Triad TI71A "1A 5.0 .25 180 20 2000 3.0 1500 40.5 Arcturus Radio Co Arcturus 071 ` IA 5.0 .25 180 20 2000 3.0 1500 40.5 Radio-Victor Corporation of America R.C.A. UX210 :10 7.5 1.25 250 12 5600 8.0 1330 18 540 350 16 5150 8.0 1550 27 925 425 20 5000 8.0 1600 35 1540 E. T. Cunningham, Inc. Cunningham CX310 '10 " 7.5 1.25 250 12 5600 8.0 1330 18 340 350 16 5150 8.0 1550 27 925 425 20 5000 8.0 1600 35 1540 Snn.iron X210: Champion UX210, Sylvania SX210: Sneed 210A: Perryman PA210: Ken-Rad 210: Gold Seal GSX210 Ce-Co L10, Evereadv.Ravrheon RavX210: DeForest 410: Ray -U -Vat -11X210; patron 210; (same as UX210 and LX310, above).

Radio -Victor Corporation of America R.C.A. UX2S0 '50 7.5 1.25 250 28 2100 3.8 1800 45 900 350 45 1900 3.8 2000 63 2350 450 55 1800 3.8 2100 84 4650 E. T. Cunningham, Inc. Cunningham 0X250 '50 7.5 1.25 250 28 2100 3.8 1800 45 900 350 45 1900 3.8 2000 65 2350 450 55 1800 3.8 2100 84 4650 Champion Radio Tube Works Champion UX2S0 '50 7.5 1.21 250 28 3.8 900 350 45 3.8 2350 450 55 1800 3.8 2100 45 Sylvania Products Co. Sylvania SX250 '50 7.5 1.25 250 28 3.8 45 450 55 84 Cable Radio Tube Co. Speed 250 '50 7.5 1.25 250 3.8 2100 45 450 53 84 Perryman Electric Co., Inc..._ Perryman PA250 '50 7.5 1.25 Ken-Rad Corporation Ken.Rad 250 '50 7.5 1.25 450 55 1800 3.8 2100 Gold Seal Electric Co., Inc Gold Seal GCX2S0 '50 7.5 1.25 250 28 2100 3.8 1800 45 900 350 45 1900 3.8 2000 63 2550 450 55 1800 3.8 2100 84 4650 Ce-Co Mfg. Co. Ce -Co 250 '50 " 7.5 1.25 250 28 2100 3.8 1800 45 Eveready Carbon Co - - Eveready- RayX '50 7.5 1.25 250 28 2100 1800 45 900 Raytheon 250 350 45 1900 3.8 2000 63 2300 450 55 1800 2100 84 4600 DeForest Radio Co ..,.. DeForest 450 '50 " 7.5 1.25 250 28 2100 3.8 1800 45 350 45 2000 3.8 2000 63 400 55 1800 3.8 2100 70 450 55 1800 3.8 2100 84 French Battery Co. . - Ray -O -Vac RX250 '50 " 7.5 1.25 450 3.8 Diamond Electric -Corp. Diatron 250 '30 " 7.5 1.25 250 -450 45-84 Triad Mfg. Co. Triad T250 '50 7.5 1.25 450 55 1800 3.8 2100 84 4650

Radio-Victor Corporation of America R.C.A. UX245 '45 Large 2.5 1.50 180 26 1950 3.5 1800 34.5 750 St'd. 250 32 1900 3.5 1850 51.5 1600 E. T. Cunningham, Inc. Cunningham 0X345 '45 2.5 1.50 180 26 1950 3.5 1800 34.5 750 250 32 1900 3.5 1550 51.5 1600 Champion Radio Tube Works Champion UX245 '45 2.5 L50 180 34.5 250 51.5 Cable Radio Tube Co Speedpeed 245 43 2.5 1.50 180 26 3.5 33 250 32 1850 50 Perryman Electric Co., Inc...... , Perryman PA245 b45 2.5 1.50 180 26 3.5 34.5 250 32 51.5 Gold Seal Electric Co.. Inc... '.. Gold Seal GSX245 '43 2.5 1.50 180 26 1950 3.5 1'800 33 750 250 32 1900 3.5 1850 50 1600 Co ' DeForest Radio DeForest 445 .'45 2.i 1.50 '180 26 2150 3.5 1350 33 . 250 32 .2000 3.5 1750 50' Arctunu Radio Tube (',o...... _ Arcturus 14S '45 2.5 1.50 2S0 42 1800 3.5 1900 50, 1800 Ken-Rad 245. same characteristic, as UX245; Ray-O -Vac RX245, Diatron 24S. same diaracteristia as GSX245-

www.americanradiohistory.com RADIO-CRAFT December, 1929 A Combination Work Bench and Test Board A Workshop Necessity which is Easy and Cheap to Build, with Suggested Instrumental Layout 1 d for General Use. By A. KRONBERG

FOR the workshop of the experimenter, 2x4 -four 30" lengths, two 381/4", two 141/2", as well as that of the service man, a two 101/2. (One more 381/4" and two 101/4" good work bench, a test board and a lengths of 2x4, indicated in Fig. 3, are op- toolrack are real necessities. These tional) ; may be combined into one unit which places 1 small vise; all tools, testing apparatus, etc., within easy reach and thus saves both time and labor. 1 "Ant" and 1 "Gnd" binding posts; and 2 As, in the near future, a great many A.C.- bakelite strips, 11/4x3/4", for mounting operated sets will have to be taken into the them; shop for replacements, should The frame supporting the rabletop. this combination 1 duplex flush receptacle and plate for A.C. appeal to the service man who wants what outlet; he wants when he wants it. 15 feet duplex lamp cord; 10 carriage bolts and nuts, 3" long; The test -board should be equipped with ac- 16 flat- or round -head screws, 2 "; curate meters; as those of the cheap kind do 16 flat -head screws, 21/2 "; not give accurate readings, because of the excessive current drawn. The workbench TEST BOARD should be equipped with ground aerial and 10 pieces ceiling lumber, 2" wide, 44" long; connections, an A.C. duplex outlet, and a and 4 cleats, 2 "x2 "x26 "; vise; as shown in Fig. 3. 1 bracket lamp and pull -chain socket; 1 Hoyt voltmeter, 0 -100 -500 scale (resistance, Material Needed 1000 ohms to 1 volt); The parts and lumber required for the con- 1 Hoyt rotary volt-ammeter, 0 -10 -100 ma., struction of the combination here described 0 -10 -amp., 0 -10- 200 -volt, D.C.; and illustrated are as follows: 1 Hoyt A.C. voltmeter, 0 -3 -9 -150 scale; 1 Jewell capacity meter, 11/2- 15 -mf.; WORK BENCH 3 bakelite panels, one 6 "x12 ", two 6 "x6 "; The first 8 carriage bolts and nuts, four 3 ", four 2 "; Lumber: 2 boards 44 "x10 "x1"; 4 boards step -the foundation unir on which the workbench is built. The bracing f rame of 12 phone -tip jacks; 6 "x3/4", 44" long, 10 2 fits two two 181/2"; pieces Fig. snugly inside. 12 round -head screws, 13/4 "; and A sufficient number of galvanized cleats, shaped to hold tools (as in Fig. 3) with screws to fasten them to test -board.

Construction of Table RACK BRACKET LAMP The longest FOR 42:!B fir=y two thin boards (44x6x3/4 ") TOOLS CAN BE are fastened to one end of each of the 30- PLACED inch legs (2x4) on the 2 -inch sides; leaving HERE a space of 3/4 -inch outside each leg, to overlap the end boards. The latter (181/2x6x3/4 AND ") are now fastened, as shown in Fig. 1, to the GROUND ends of the sections just completed. Keep BIND NG- - their ends tight against POSTS the lips of the front and back strips, which extend just far enough beyond each leg to overlap the end boards. Use two 2 -inch screws, on front, back and end boards, for fastening to each leg. Then fasten the two 101/2 -inch lengths of 2x4 to the end ql boards, between the legs; keeping their top sides A.C. OUTLETS flush with the tops ll of the end boards, and using two 3 -inch carriage bolts to each piece. They may also be tacked to the legs, by driving nails in slant - lll ingly from the top and bottom of the ends. Lay out the two longest 2x4 pieces (381/2" III lengths) with their two -inch sides up; nail the 141/2" lengths across and inside them, as .II shown in Fig. 2; and bolt this frame inside the top of the foundation. FIG.3 The top of this - frame should be flush with the top edge of the boards, and it should fit very snug. A little of the front 2x4 should be cut away at the bottom, left, to give a place for the The completed workbench with its backboard for tools and instruments. Those listed in the arritle A.C. receptacle. were used by the writer; but the builder will, of course, select his own to suit his purposes and pocketbook. The dotted cross -brace is not essential, but strengthens the table. (Continued on Page 281)

www.americanradiohistory.com December, 1929 RADIO -CRAFT ÁD10 CRAIFT INKS

The two readers of RADIO -CRAFT who send in the greatest number of ingenious Kinks each month will be awarded, each, a copy of "The Radio Amateur's Handbook," a work well known for its value; in addition to the space rates paid for all articles printed.

A USEFUL SERVICE LAMP A galvanometer (or a low- reading milliam- closing the circuit with the battery in series. meter -which is practically the same instru- These instruments are very sensitive and deli- By Victor A. Ulrich ment, in principle) is the ideal device for cate, and may be damaged even with a small AVERY handy device for looking around testing; and very valuable information may run down battery. corners and in crannies of deep consoles be gained through its use. By varying the resistor, we may readily ad- is illustrated. It is an inexpensive arrange- With a small "C" battery and a variable just the pointer to any desirable place on the ment. high resistor in series with the instrument a scale, and the instrument is then ready for use. number of different tests may be performed. The same procedure as in the case of phone testing is followed; but instead of hearing Be Careful with Instruments clicks we watch the deflection of the pointer. This combination is exceedingly helpful for testing windings in audio- frequency transformers and, by taking readings, we may de- the approximate transformation -ratio AN INEXPENSIVE ELECTRIC SOLDER- termine ING IRON of the windings and establish the identity of the primary and secondary when these are By Bernard T. Ring tests of re- not marked. Other comparative AN inexpensive, low voltage electric solder- as one becomes sistance may be performed, ing "iron" that will work on a 4, 6, or 12 -volt storage battery, or on a toy transformer The lamp thus connected may easily be carried up to 25 volts can be made by following these in a servicer's kit; and guarantees him good constructional details. light to examine connections. The parts required are one screwdriver handle; one piece of brass or copper tubing, 3g- The parts required are an automobile dash- in. dia., by 6 in. long; three clips; two gas board socket, a six -volt lamp for same, a tips; some flashlight battery carbons and a couple of connection clips, some wire, and a single strand of lamp cord about five feet block of wood. long. If a particularly bright light is desired, with We may segregate the construction into a slightly increased current drain, gas -filled, seven operations, as follows: high candle -power headlight bulbs of the (1) Enlarge the hole in the handle of the same voltage may be used. screwdriver until it is about 33-in. dia. and By following the design shown there will 2 in. deep; then, bore a hole all the way be no danger of short- circuiting the connec- A galvanometer (or milliammeter) rakes the through, 3/16 -in. dia. tions of the lamp or those in the set. guesswork out of servicing. All data sheets (2) Thread the brass tube at one end so lamps are based on the assumption that the service be (Fig. 1A). As most experimenters know, may man has means of measurement. the gas tip can screwed on. be operated from either an A. C. or a D. C. (3) Solder one end of the single -conductor voltage. lamp cord into the end of the brass tube which source of the correct more familiar with the possibilities of this not If a iron or a valuable instrument for radio testing. is threaded. soldering is not a few short pieces of Care should be taken, when making the torch available, IN bus bar made into a "V" shape and twisted UTILIZING A GALVANOMETER necessary connections to the instrument, that TESTING WORK around the point with the end of the lamp the resistance is at a maximum and of a By J. M. Conesa value of at least 100,000 ohms, when first (Continued on Page 281) ELECTRICAL meters are the eyes of the

radio experimenter and service man, for IIIII!II!IIIII!JIIIIIIII!IIIIIIIIII!II!IIVI!fl!II!IIIII!II!Illl spotting trouble, and I am a close adherent HANDLE WIRE CUP and zealous user of these valuable electrical T h e electric soldering GS TIP GRASS 706E CORD devices. I know of many a service man who iron shown will work still depends upon guesswork, a pair of from either direct or al- current, up to phones with a battery, or 110 -volt line with ternating CARBON TIP 25 volts; its construction CLIP WIRE a lamp in series, as the only means of locat- is simplicity itself. An CORD ing faults, disregarding other factors and insulating handle, shown CLIP ignoring the actual cause of the trouble. For at B, a brass rube A. and a gas tip C are the essen- SCREW GAS SOLDER WIRE IN THIS END most service men are interested only in shorts tials. It is well to paint TIP HERE -A- and breaks in the wiring; and anything else is the brass tube with in- 1!19811 sulating compound, or immaterial to them. BRASS TUBE 6' LONG 3/8 DIAM. PuSH THIS END INTO HANDLE tape it; so it cannot be A continuity test is all that is required in shorted by other things -C- most cases, but there are instances where during the soldering partial breaks or shorts occur and a phone process. Changing tips very little information, is done by unscrewing or lamp test yields the gas tip, taking out if any. the carbon tip and in- REMOVE GAS INSERT CARBON TIP BATTERY BRASS In radio circuits we are dealing with un- serting another. FLAME TIP THROUGH HERE AND CARBON CAP SPREAD SCREW ON TO TUBE seen conditions and we must depend on some FIG 1 instrument by which we may visualize faulty conditions.

www.americanradiohistory.com rl) RADIO -CRAFT December, 1929 The Cooperative Radio Laboratory

This Month the "Lab." Delves into the Intricacies of the Design of an A.C. { Electric Receiver Employing the "Hybrid- Tube" Circuit Previously Des- cribed, with Band -Pass "Tandem Tuner" and '45 Power Stage. i DAVID GRIMES Director

IT is but natural that we should adapt our tuned by a variable condenser in the well - INPUT TRSEC, '45 - .... , hybrid-tube circuit to alternating cur- known manner. But, in series with this coil, rent operation. During preliminary ex- is the tapped primary L3 of the succeeding 2Mc. I perimental stages, it is well that as many tuned transformer; this primary of six turns II REPRODUCER difficulties be dispensed with as possible; so is tapped at the center. From the tuned straight battery circuits were first employed. secondary L4 of this second coil onwards, the But, now that most of the wrinkles have been operation is similar to that experienced in ironed out, we can proceed with some degree standard tuned- radio- frequency circuits. 1500 fJ of assurance to electrify the receiver. It will 1" w8 SOURCE he of interest to you to know that this is Controlled Selectivity FICA. in many large research AC. 11111* the procedure followed The operation of the tandem tuner is rather 2.5V laboratories. Furthermore, there are still many unique; it is a rather new commercial appli- The in a power experimenters throughout the country who alternating "s'gnal" currents cation of an old technical idea. It is a system tube circuit are shown by wavy arrows ; the would rather operate on the steady voltages for increasing the selectivity without cutting direct plate current by straight arrows. obtainable from batteries, and who do not off the side -bands, or otherwise affecting the object to the extra care they demand. quality adversely. Such devices are sometimes Fig. 2 is obtained. The strength of the elu- 1 is as a covers Fig. given starter; this the called "band- pass" filters; an idea of their sive station is increased, and the increased with entire over -all circuit details. This action may be obtained from a study of Fig. selectivity permits the suppression of the in- method of introducing a subject is rather a 2. A little explanation is in order on this, terfering local. The answer is satisfaction. departure; it is customary to work up to the even though some information has been given whole with fear and trembling; but there By the way, it must be obvious to some are many of you who are sufficiently well of you that this coupling will vary over the .. +'27 versed in the art to proceed with better AUDIO COUPLING wavelength band according to frequency, even though the number of taps is left fixed. In facility if all cards are placed on the table. tt V3 CATHODE other words, the degree of coupling on the Hence Fig. 1. We will develop the various 74. 2 MF G. the short ideas by describing the operation of the cir- -` three -turn primary is greater on 2 250 ta cuit, starting with the antenna. In this way, AL.AS'A' broadcast waves than at the 500 -meter setting. IMF. -pass will perform you will be able to recognize the functions This means that the band VOLTAGE somewhat irregularly throughout the tuning that have already been explained in previous RESISTOR 'B- present band -pass issues in connection with battery operation. range, but this is true of all FIG.3 111111111+ filters. There is a very fertile field for the The signals are picked up in the antenna experimenter in making such a device fairly and are brought down to the earth through the Plate current in a heater -cathode tube follows uniform at the various frequencies encoun- specially- tapped antenna primary winding, LI. the path above (conventional direction indicat- tered in broadcasting. It should be as im- The coil has five taps on it, arranged "geo- ed) ; "C" bias equals the voltage drop in the resistor. portant as the uniform- amplification R.F. cir- metrically," at the second, fourth, eighth, six- cuits which have been so valuable. Perhaps teenth, and thirty- second turns; the full con- a rotating primary in place of the taps will structional details of this coil have been cov- before. You see, we have added to the tandem -tuner primary the tapped feature which do the trick; this has been suggested by ered in past numbers of the "Cooperative David Moscowitz of Newark, N. J. Laboratory." Then the signal is resonated in was not shown before. It is quite important; the first winding L2 of the tandem -filter cir- for it permits increased selectivity under cer- cuit; this is the usual secondary of 100 turns, tain extreme conditions where a sacrifice in Use of A.C. Tubes tone quality may be tolerated. For all ordinary operation the filter is set There really isn't as much to this A.C. elec- with the maximum primary of six turns. This trification as appears on the surface. The LOOSE COUPLING F00 SUPER- SELECTIVITY. from the use a gives a performance indicated by the flat- unusual features that arise of top curve shown in the heavy line of Fig. 2. separate heater and the cathode are about the The width of the curve at the top is about only departures from standard practice. Cer- tainly, the "B" eliminator end of the A.C. CLOSER 5,000 cycles-just sufficient to pass the pro- COUPONS circuit is old; there is no difference here in FOX gram without discrimination. Now, there are 'BAND- any respect. We will therefore devote our PASS" locations and times when greater selectivity TUNING. time to a description of the filament and "C" tc than this must be had, if that desired station is to be brought in through the maze of lo- bias circuits. -s cals. Such a condition exists, in many places Heater -type tubes are used throughout the in New York City, in connection with WLW, entire circuit, with the exception of the last n, has the Crosley station in Cincinnati, and WOR, power tube; experience taught the en- FREQUENCY the Bamberger Station in Newark, N. J. With gineering profession that this is the only real APPROXIMATE' BANDPA55' CURVES the selectivity shown in the flat -top curve, it way to eliminate the hum. The fact that the FIG. 2 would be impossible to work through WOR to cathode requires several seconds to heat up bring in WLW. Here is where the tapped to the proper operating temperature, and as The characteristics of the hand -pass "Tandem feature comes into play; by reducing the pri- many more to cool off again, makes it free Tuner" whose construction is described. The mary to half its normal turns, the peaked from any rapid variations in filament or heater heavy line shows the tuning effects with close coupling; and the dotted. the sharpest cut -off. selectivity curve shown in the dotted lines in currents such as are encountered in 60 -cycle

www.americanradiohistory.com December, 1929 RADIO-CRAFT

'24 then to make the grid negative with respect to the cathode is to connect the grid return directly back to "B-." If this is difficult to see, just figure that we are making the cathode positive with respect to the grid, L.4 .g. which is equivalent to making the grid minus with respect to the cathode. C VOLTAGE RESISTOR- - It is essential to calculate the amount of FIG.5 SDURI1I1UwI NI both the "plate" currents in order to determine the value of the biasing resistor. With a The "hybrid- The A.C. screen -grid rube requires lower va- 180 volts on the plate and 70 volts on the tube" combination may be used lue of resistor, to give its lower grid bias. without a bias, screen -grid (the values recommended for best also, as shown here. Experiment will probably find the best value with any par- operation) the resistance works out at about ticular crystal. alternating circuits. The necessity for such a 450 ohms, which gives a little more than precaution in the last audio stage is not para- 1% volts, negative bias on the grid. The allowed to impress mount; for the amplification here is not great any voltage back on the resistor is by- passed by means of a good husky grid or bucking feed enough to cause any trouble. -back will once more oc- R.F. condenser; so that R.F. currents flowing cur. It is extremely All of the heaters are connected to one important here; for the in the plate circuit will not impress R.F. volt- effect seems to be very much 2% -volt winding of the power transformer, more pronounced ages back on the grid. This would constitute -the signals being practically while the filament of the last power tube is killed. One a feed -back circuit; and, unfortunately, it microfarad capacity has run on raw A.C. from a separate 2% -volt been found satisfac- gives a bucking action and the amplification is tory; such condensers winding of the power unit. It might appear need not be of the greatly diminished. Ample by- passing is best quality, as the voltages that all of the tubes could be connected to across them are necessary, extremely winding, because the same low. the same filament Audio Amplification voltage is used throughout. Some success has The condition for obtaining the "C" bias obtained along these lines; but it is and reducing the hum in the last (power) am- been Fig. 3 should be fairly clear in view of the on plifier are a little different from those just much better to keep the power amplifier above explanation. The difference between the discussed in connection with the heater a separate winding. If this precaution does R.F. tube and the audio grid -biasing system tubes; you must remember that we are using raw nothing else, it enables us to place the proper is entirely one of design and not theory. The same A.C. on the filament of this power tube. "C" bias on the last tube and, at the plate current is passed through a biasing re- Fig. 4 will serve to illustrate the new time, keep the other heaters at ground po- sistor on the way from the cathode to the conditions. In the first place, the grid return tential. This statement may not be exactly "B-" return. In this case, we have some- must he we have brought, eventually, back to the middle of the clear at the moment; but wait until what less current to contend with, because we bias circuits. filament; otherwise the alternating pulsations covered the "C" do not have the extra flow of the screen - in the A.C. filament will be impressed on grid; and the plate voltage is less on the the "C" Bias Resistors grid -resulting in a bad hum. By returning CARBORUNDUM the grid to the exact neutral center of this Fig. 5 next be studied; this shows a C RYSTAL --- should circuit, the back -voltage on the grid, caused R.F. amplifying tube cir- L '27 section of the first from the alternating currents in the filament, cuit. It is necessary to understand this ac- Ca 'HYBRID , TUBE is completely neutralized. We must, there- tion quite thoroughly in order to make the SHIELDED GRID LEAD fore, put a center -tapped resistor across the for the "C" bias. proper circuit connections filament of this tube. Then, in the second inspection of the drawing will A superficial place, we are interested, not only in keeping currents flow in disclose the fact that "plate" the hum from the grid, but also in placing regular plate circuit and, also, the TO COMMON - ' 1 t both the ROTORS IN GANG on the grid the proper biasing potential ARRANGEMENT. (WITH BIAS.) FtG.6A to screen -grid circuit; because the latter operates enable us to obtain good quality. with a positive potential in the same manner In the circuit of a '27 tube in the ' hybrid - This is done in the manner already des- as a regular plate. These two currents com- tube" hook -up, there is a 41/2 -volt bias on cribed. The resistor is placed bine in the electron stream in the tube and the grid through the crystal. It is best applied between the by a battery, to insure against hum. center tap and the return. The flow together through the hot cathode back "B-" plate current of the power tube is considerably to the negative end of the "B" supply. Now, more than that experienced in the if we place a resistance in series with this audio amplifier. Hence, we are obliged to ordinary amplifying tube; so we return path between the cathode and the increase the value of the biasing resistor in do not require as much resistance "B-," the total electron current must pass order to secure the proper voltage on the grid for a given potential bias on the grid. Thus, in spite through it. This current will create a voltage of this tube. This value, in the case of the of the fact that about 50 volts are required on the drop across the resistance and, since the cur- amplifier, works out to be about 2,250 ohms. grid of the power tube, we calculate that only about 1500 ohms rent is flowing from the cathode down through The by- passing condenser in this circuit must are needed in the plate the resistance, the voltage drop will make the be much higher than in the R.F. stage, because return. This is less than the value required cathode positive compared with the "B-" we have audio currents to consider in the plate in the first audio am- end of the resistance. All we have to do circuit. These audio currents must not be (Continued on Page 282)

--- IMr 225 " ANTENNA II CARBORUNDUM HYBRID TUBE ISO

CRYSTAL-. 55 bol IGOT. DOT. oQ,o 15EAD .01511r. V

Lt C3 B-

2 MT L, ET, ant. CINttR 2 TAME - pp 32?TAPPED 500 I RE PRODIICCR TWIST

- BANOPASS 5WircH WI ST SMT 2.SV.AC. 200.000íJ ``I1000D00Ò} óT.AC. FIG.1 110s1 AC.

The complete circuit of the A.C. model of the "hybrid- rube" receiver. By means of the band -pass "Tandem Tuner," together with the high amplification of a '24 screen -grid R.F. stage, selectivity and sensitivity are readily obtained. Constructional values are shown ; it is necessary to locate the power equipment so that its field causes no hum in the receiver.

www.americanradiohistory.com 262 RADIO-CRAFT December, 1929 The Radio Craftsman's Own Page

In these columns will be found letters of RADIO -CRAFT readers from every quarter of the globe. Here old friends will renew acquaintances of long standing. }

TO REACTIVATE OR NOT? USING OLD APPARATUS A "BIG KICK" IN RECEPTION Editor, RADIO -CRAFT: Editor, RADIO- CRAFT: Editor, RADIO -CRAFT: I am just in the midst of the pleasure of reading Many of your readers have "A" eliminators and I like this magazine; it's just the kind I wished your October issue which is the first number I have are progressing to A. C. operation; they will want to have, because it explains every detail in the hook- seen, and I am enjoying it very much. However, I to find some use for the "A" unit, or must sacrifice ups, and for the other good features it contains. wish to register my exception to Mr. Palmer's state- ir. I contemplate using mine to operate two or more I built a "Candy -Box Special" short -wave set and ment in his tube article: "Reactivation of a filament dynamic reproducers in one baffle. Would be very coils, and have had good results. I listened to 2ME, is a confession of abuse, either through sheer care- much interested in your views on this. Sydney, Australia, between 6 and 8 a. m., Eastern lessness or pure ignorance of the meaning of cor- Tom R. ANTWIS, Daylight Time, on Sundays, June 16, 23, 30 and rect use." Sarasota, Florida. July 7. That station was doing duplex work with As a mere experimenter, I do not care to pit (This is perfectly practicable with the dynamics CGA at Drummondville, Canada; on June 30, it re. my beliefs against any radio engineer's; but I do which are designed for 6 -volt D. C. excitation of the broadcast CGA, and on July 7 I heard the Thanks- are giving services not believe this statement to be correct. I use a home - field coil. The later models, of course, built in Westminster Abbey, London, from constructed four -tuber; with a stage of tuned R.F. with their own rectifiers to operate from the lighting Sydney. The announcer said that CGA picked up before a regenerative detector and two stages of trans- current; but the method suggested offers a slight 5SW at Chelmsford and relayed it to 2ME. I have former- coupled A.F. The filaments of the R.F. economy for the constructor who bas a superseded written Sydney for verification, but I am waiting for and the two A.F. stages are controlled by amperites. "A" unit on hand. Editor.) it for this occasion. NICK GAUG, The R.F. stage occasionally gets light in volume and Astoria, L. I., New York. cranky in tuning. In such cases I invariably find (There are several thrills in short -wave listening, it (per my tube checker) the plate emission of this will be seen, as compared with ordinary broadcast THE letters of encouragement and praise tube to be low, and in need of reactivation -which DX, for the listener whose location it good and which our readers have been showering it gets promptly. Things are then O.K. This does whose installation is right. The wonders of short- on us have been very welcome to the Editors not seem to check up with the statements of Mr. wave transmission have not yet begun. Editor,) of RADIO -CRAFT, and they take this op- Palmer. R. S. TALCOTT, portunity of acknowledging the great number 224 Eureka Ave., Wyandotte, Mich. to which it has been impossible to reply HOW'S YOUR GROUND? much as they have liked (Even the recital of his experience by our cor- personally, would Editor, RADIO- CRAFT: respondent does not lead ut to alter the judgment to do so. This is YOUR magazine, and it Often in the middle of a program it is disturbed expressed in the article to which he takes exception; will welcome every letter which exp a by a crackling sound which sometimes lasts for min- based, as it is on the experience of all rube- labora- definite wish for a certain line of editorial utes at a time. Such was the case in my radio and tory engineers. A "thoriated- tungsten" filament will information. I often attributed it to local electrical storms. How- continue to supply electrons until the thorium is We trust to make this Experimenter's page ever, I noticed that, whenever anyone went into one exhausted sufficiently to bring it to the end of its the stamping ground of those who like to of the rooms on the second story, we would witness useful life; u-hen rejuvenation restores functioning follow out their own ideas and do something the same disturbance. After tracing the trouble I for bat a short time. When, hou -ever, the tube is little different. What have you found out found that the ground was connected to the radiator operated at a plate voltage too high -or a grid bias for yourself that will help along other ex- in the room and the bed upstairs was rubbing against too low -'the plate current draws too heavily on the perimenters? Write to the Editor of the radiator. Changing the ground to the water -pipe filament emission [not plate emission, for the plate RADIO -CRAFT and tell your story in your reduced this disturbance to a minimum. emits nothing) and the tube is temporarily paralyzed. own words. V. K. CONCANNON, It may then be reactivated, and this operation may 213 -34 112th Ave., Queens Village, L. I., N. Y. be repeated several times; though the proper remedy is to correct the operating conditions, so that the ONE OF MANY GOOD WISHERS tube wi!! give more satisfactory results during a A REAL "B" ELIMINATOR Editor, RADIO -CRAFT: longer life. That Afr. Talcott's tube keeps requiring Editor, RADIO- CRAFT: reactivation suggests I wish to thank you for your magazine; find that the circuit values should Sometime ago I had been listening to a program of I be changed, as it one of the best that can be put out, and aro regards this stage.- Editor.) music from WLW and, as I was going to retire. I telling all my radio friends I pulled out the plug which attached my "B" about it. I am getting my copies from the news company. eliminator to the 110 -volt line. I was using the I shall be glad to do all I can your magazine. EXTRAORDINARY DISTANCE WORK headphones at the time and the filaments of the for I am getting the parts - tubes were still burning. I was greatly surprised for the new "A.C. Screen Editor, RADIO -CRAFT: Grid Peridyne" described to find that I still heard the program of WLW, in September RADIO -CRAFT I wonder if there arc any fans who are inter- and will build it. ested in listening to stations as i had not yet removed the headphones. Al- on the other side of JOSEPH REBELLO, JR.. the world that operate though the reception was very faint, it was quite on our own broadcast band? 94 Amour St., New Bedford, Mass. I have had such hopes distinct. Turning the dial I could get several other for several years, but never we wish that we could print all the letters of realized them until last winter. stations; KDKA coming in quite plain. so that I I have verifications friendly cooperation that reach us but. fortunately, from three stations in New Zealand, could get the announcements clearly. Of course the and four in they are too many in number. They are appreciated, eliminator was still connected to the set, but it Australia; besides hearing other stations, of which however.-Editor.) six were in Japan. (Original verifications enclosed was not connected to the pou-er line. It uses an -Editor.) '80 rectifier tube, while the receiver is a Zenith 4R I have two sets which bring them in; one with set with three tubes. I was using a storage "A" AN INDUSTRIOUS EXPERIMENTER five tubes and the other with six. Their success battery. E. R. PRINCE, Editor, RADIO -CRAFT: does not lie in the circuit, which is simple, but in Logan Avenue, No. Parkersburg, W. Va. I would like to express my gratitude at this time the tubes. I use UX -199s or their equivalent as the (It is possible for a tube to operate with low for your much -needed publication. R.F. amplifiers and detector. with a resistor to pro- plate current on no more voltage than an "A" bat- I do a good deal of experimenting, and would tect them from the "A" battery. The audio stages tery will furnish; since the potential of the filament like to tell you of my success with a small outfit. use a 201A and a 11M. I find the 199s much ranges all the u -ay from "A +" down to "A -" I built a three -tube regenerative receiver without more sensitive in the R.F. and detector stages; they and there may therefore be fire volts on the plate a blocking tube, until I got it working well. I are one of the reasons for such extreme DX. Also, as compared with the low- voltage tide of the filament. used a variable tickler and found it too "ticklish "; static does not hurt my ear drums when I am The "Solodyne" which came out some years ago installed a variable resistor (old potentiometer) using them; as it does with 20IAs in these stages. operated without a separate "B" battery.-Editor.) across the tickler coil, and made things smoother. Sometimes f can put a station clear across the Then I put in a blocking tube, untuned, and Pacific on the loud speaker; I get them best from used different types, to find: the '01A a good dis- t a.m. to 6 a.m., Central Standard Time. Among THANK YOU: WE ARE TRYING tance- getter, but very critical : the '71A not so those most often received Editor, RADIO -CRAFT: are 2YA, Wellington, good on distance, but it almost eliminated the N. Z., and 2BL, Sydney, Australia; which I get You sure are putting out the stuff that the average whistle down to 225 meters. Now, I use a '22 three or four mornings of each week. They always fan wants. We have our radio for broadcast receiv- screen -grid and CeCo detector, with 135 volts "B" come in during a falling barometer; but hardly ever ing. and it stays put; but we want to try everything on the plate of the first, and 90 on the second. The during a rising barometer. My aerial is 100 feet new that comes out and you seem to be trying to first audio stage is an 'OlA and the last a '12A. long and 30 (eer high; for a ground, I have four give us the right dope. Finally, I did away with the original 3- circuit tuner pipes driven in. E. M. WELLING. I am in touch with about twenty fans and we all and wound a coil with a fixed tickler. Crawford, Nebraska. waited patiently for the first issue of RADIO- CRAFT, My log shows stations from 199.9 meters to (/Ife, Welling u -ill probably be besieged with in- as we have been stung so many times subscribing to 545; I am situated about 45 miles quiries for his hookup; but, at he very correctly furniture catalogues (called radio magazines) that from San Francisco and have no interference. observes, it isn't the circuit that gives such unusual we had to be shown. When it did come out, there In the winter I receive, almost every night, reulrt. There is no doubt that his location it an were not enough to go round; simply just couldn't WLAC, Nashville. Also, while demonstrating to my have excellent one, while the tame set at most points be found in San Francisco, so we loaned them out. friends, I received stations every half would bring in nothing beyond the Coast. At for We all had our orders placed with local newsdealers point on the dial for five points, with surprising selectivity. tubes, u-hile he finds the '99s best, it may be of for the next number, and we are sure well pleased No shielding is used anywhere. interest to our readers that the finest transatlantic with it. Keep up the good work and the fans will have commercial receivers use amplifiers as large as 'los in back you up, J. R. HRCOtYRr, I coupled my tickler's variable resistor t, the R.F. stages.- Editor,) San Francisco, Calif, (Continued on Page 286)

www.americanradiohistory.com December, 1929 RADIO-CRAFT 263 Practical Literature for Radio Readers Available from Many Sources, and Giving Information That Is Worth Having

Servicing Power Amplification Short Waves INSTRUCTIONS FOR SERVICING RADIO RE. THORDARSON POWER AMPLIFIER MANUAL. HAMMARLUND SHORT -WAVE MANUAL, CEIVERS. Several editions, with data for the use This book of 64 pages carries, in addition to a list of 1929, Data for short -wave receiver design, screen - of different testing units. Contains tables giving the the apparatus designed by its publisher, with circuit grid tube circuits. list of transmitting stations, etc. characteristics of standard receivers of the principal diagrams and values, a general chapter dealing with Calibration curves for coils, hour- conversion chart, commercial makes, tube test data, etc. (Jewell Elec- the design, building and testing of amplifiers, tube etc. I0 cents. (Hammarlund Mfg. Co., New York trical Instrument Co., Chicago). data, etc. It should be upon the shelf of every custom City). builder in these days of increasing demand for am- THE DIAGNOTRICIAN. Issued by the "Supreme SHORT -WAVE APPARATUS, Second Edition. Mississippi, com- plification to operate multiple -radio and public ad- Service League" of Greenwood, This booklet, while more in the nature of a catalog, dress systems. 25 cents. (Thordarson Electric M /g. posed exclusively of owners of "Supreme" testing contains diagrams, with constants, etc., of short -wave articles, as Co., Chicago). apparatus. Includes general and special transmitting apparatus up to ten watts, as well Radio as well as supplement sheets for the "Supreme AUDIO -FREQUENCY TRANSFORMERS. A book- receivers and operating information, instruction in the of 51.00 Manual," with which its stated subscription let containing a discussion of the characteristics use of frequency (wave) meter, etc. 25 cents. necessary from an per year is combined. to obtain fidelity of reproduction (Radio Engineering Laboratories, Long Island City, TUBE DATA-The CY-324 and the CX -345. The A. F. channel, of the characteristics of push -pull N. Y.) new tubes are the most important developments circuits, reproducers, etc.; and diagrams and two NOTES ON SHORT -WAVE RECEPTION. of the past two years, and these booklets, sup- specifications for the construction of amplifiers and With power a push - an account of methods used in plementing the "Cunningham Tube Data Book," units from single '71 -type output to tuning in foreign pull '50s. (Ferranti, Inc., New York City.) stations on a "Thrill -Box" screen -grid receiver. which carries data on the complete previous line, are (Ab- bott Research Laboratories, Malden, Mass.) essentials to intelligent operation and experiment with the new A.C. screen -grid and the medium - RADIO DESIGN. The fall issue of this meaty amplifier of this season. Inci- magazine for constructors voltage super -power IT will be the purpose of this depart- and experimenters intro- dentally, the new data sheets are furnished in a duces the new A.C. shore.wave -Super-Wasp" de- smaller size with handy loose -leaf cover. (E. T. ment to list, as it comes to hand, all signed by the Pilot Mfg. Co., with which Radio Cunningham, Inc., New York City). literature which will be of help to Design is closely associated. The P.227 tube was the custom builder, the service man, or designed for use as the regenerative detector of this Custom Building the amateur experimenter and set build- set. The 96 pages of this quarterly, which has CUSTOM -BUILT RADIO. This, perhaps the er, from the standpoint of conveying been enlarged, contain much in the way of wrinkles finest book yet issued for a similar purpose, is and practical hints, as well as data. 50 cents a technical and business information year. (Radio Design Publishing Co., Brooklyn, N. Y.) worthy of notice for the unusually attractive il- worthy of their reading filing for It is worthy and lustrations in rotogravure and colors. TELEVISION -THE EYE OF RADIO. A book- Hand -Made:" reference. Some of the items described of its text, "The Finest Things are let which, without technical contents, contains a and illustrates the possibilities of custom -building are issued for free distribution; and for discussion others of television from the side of its future de luxe, for clients who desire cabinets to harmonize a small amount is charged, to commercial value. It is illustrated with pictures of with fine interiors. (Scott Transformer Co., Chicago). limit the requests to those to whom the the Jenkins system, including views of a home tele- THE RADIOBUILDER, A monthly publication information will be of real value. We visor whose design is being worked out. (Jenkins dealing with the products of the company issuing invite all manufacturers and distributors Television Corp., Jersey City, N. J.) together with Technical Data Sheets. The issue issuing new material of this practical it, Parts Accessories before us describes the new line of factory -made kind to send advance copies to this and "Silver" receivers which have been added to the office, to ensure its early listing in BULLETIN No. 101 (of the Elkon Division, P. R. Mallory & kits well known to custom builders. Incidentally, R: \DIO- CRAFT. Co.) "General Data on the Elkon the company announces that it no longer manufac- Rectifier." The theory and construction of the tures "private brands," but has concentrated upon dry electrolytic rectifier, now coming into wide use its own trademarked products. (Silver -Marshall, for so many other purposes besides the battery Inc., Chicago.) LOUD SPEAKERS. An engineering bulletin which charging for which it was at first developed, are analyzes the performance and characteristics of re- set forth herein; together with diagrams of circuits Experiment and Design producers, with special reference to audio quality; and data on the operation of the devices. ( Elkon, HIGH -FREQUENCY STABILIZATION. A brief and gives valuable instructions as to their selection Indianapolis, Ind.) (quartz - and comparison. Unlike most commercial synopsis of the history of the piezo -electric literature, TRUVOLT DIVIDER MANUAL Data on the crystal) oscillator since its fundamental principle was this contains no advertising. (International Resistance application of resistance in power circuits to obtain discovered by the Curies, and of its various dis- "Durham " -Philadelphia, Penna.) A Co.- com- varying voltages, with tables and formulas sufficient coveries and practical applications; together with in- following it, is "Dynamic panion bulletin, Loud for the a and care of this deli- design of "B" unit. IO cents. (Electrad, formation on the construction Speakers," by the same writer. Inc., New cate apparatus, which now has so important a York City). function in transmission and other work. (Adam Constructional Information THE GATEWAY TO BETTER RADIO. A dis. Hilger, Ltd., London, England.) COPPER SHIELDING FOR RADIO. This is the cussion of many features of set design operation, and GENERAL RADIO EXPERIMENTER. In the product of a cooperative association of producers "kinks' for the constructor and servicers. A very July -August issue of this little magazine for the interested in following up every possible market. thorough discussion of the effects of resistance in advanced experimenter, we find an article on "The The booklet contains a little explanation of the different circuits, and of the merits of different Importance of Mutual Conductance in Testing Vacu- principles of shielding design; and practical advice, methods of applying control with resistors of different T. Burke. It is accom- um Tubes," by Charles with diagrams, for the constructor who undertakes ranges and current carrying capacity. 25 cents. by circuit diagrams. A second panied formulas, and to be his own sheet metal worker. (Copper & Brass (Clarostat Mfg. Co., Brooklyn, New York). article describes a new meter designed to measure Research Association, Neu' York City.) an -frequency AEROVOX CONDENSER the power output delivered by audio WHAT SHALL I BUILD? Like all radio edi- AND RESISTOR a system. MANUAL. This is well amplifier, as in the case of public -address tors, the writer of this book tells the constructor to described in its sub -title, "How and the by "A helpful manual on the proper Why Fader" Horatio Lamson, choose for himself. Fifteen popular receivers are use of condensers discusses a new device which permits of and resistors in radio receivers power- control described, ranging from four tubes to fourteen; the and supply sound and smooth change over, as units, with detailed specifications amplification superheterodyne type predominates. In addition, the of Aerovox con- from one movie film to (General densers and resistors." -two large talking another. booklet offers data on other circuits if requested. Thirty pages of Radio Co., Cambridge, Mass.) rl'he practical data. ( Aerovox Wireless Corp., Brooklyn, Remler and Frost lines of parts are illustrated. N. Y.) (Herbert H. Frost, Inc., Chicago, Ill.) Merchandising SOMETHING LOWER PRICED, Etc. A r THE CROSLEY BROADCASTER. "Boy, page Interference chute addressed particularly to the manufacturer in- is of first page Aladdin!" the heading the of the FILTERETTES, monthly. A small periodical de- terested in cutting costs on mass production. De- Sept. 1 issue of this semi- monthly "house voted organ," voted to methods of locating and remedying inter- to a discussion of bakelite- socket construction which is illustrated by a view of the new plant and design, and especially ference or "static" caused by electrical appliances and the subject of tube -prong of its publisher. The Broadcaster, unlike many other contacts. "Sixty per cent, of the service power lines, etc. This subject is one of increasing troubles house organs, makes it a point to carry several help- developing in sets," it is stated on the authority of interest to service men. Free distribution. (The ful hints for dealers in each issue; as well as a manufacturer, "are due to faulty contact of Tobe technical data, such as the current "Advanced Radio Deutschmann Corporation, Canton, Mau.) sockets;" and the advent of modern A. C. tube Course." (Crosley Radio Corporation, Cincinnati, O.) RMA BETTER RADIO RECEPTION MANUAL. design has made this matter more and more im- MERCHANDISE. This is not a radio periodical; The purpose of this book is explained in its sub -title, portant. A large line of stock sockets, plugs and but the issue before us is devoted to another exposure "Home -Made Static and How to Avoid It." It adapters is shown in concentrated form. (Alden of "gyp" store methods, now possible only in 9. contains trouble- shooting advice, filter diagrams, Manufacturing Company, Brockton, Mas.) large city, typical cases of substitution, misrepresenta- choke -coil constructional data, etc.; and was pre- THE AMPERITE BLUE BOOK, An explanation, tion, and downright dishonesty on the part of a pared by its publishers as a cooperative measure to in connection with the self -adjusting rheostat, of chain of radio scores in Philadelphia. Fortunately, better the radio industry by improving general recep- tube action, with characteristic curves and diagrams we may assume, most radio men nowadays either tion conditions. Its distribution has been very large. of a number of well -known receivers. A convenient are honest or believe that honesty is the best polity, Price, 25 cents. (Radio Manufacturers Association, guide for the experimenter and set builder. 15 cents. (Better Basinez, Barran of Philadelphia.) Inc., New York City). (The Radial! Company, New York City).

www.americanradiohistory.com 264 RADIO-CRAFT Deccnlbcr, 1929 New Radio Devices for Shop and Home In this department are reviewed commercial products of most recent interest. Manufacturers are requested to submit descriptions of forthcoming developments. }

"PICKLE- BOTTLE" COILS FOR In the head of this stripping plier are set S-G TUBES two independent components, operated by the hand -grips; one comprises a cutting blade IN the set below there are a two-wind- which moves toward and away from a fixed ing coil and a three- winding coil. (The blade, and the other a serrated gripping sur- primaries are placed at one end of the second- face which moves toward and away from a aries.) The former has a primary for the fixed gripping surface. The wire is placed in the slot of proper size and the plier is grasped in the hand. The result is that the two gripping surfaces close

on the insulation; and the two cutting surfaces Your radio dial is your log ; settings are ob- clip through the insulation, but do not nick tained immediately at predetermined points. the wire. Continued pressure causes the gripping surfaces to move away from the cutting of celluloid markers, stations up to seventeen in number. These settings may be made exact for those stations by the regular method of tuning; and then the exact adjustment thus A kit of coils designed for efficient screen -grid broadcast-set construction. found is indicated for future use. In operating the "Master Tuning Selector," the usual procedure is to turn the volume knob aerial and ground, and a secondary which is to minimum, then the selector knob until the designed to "look into" a screen -grid tube. pointer indicates that the desired station set- The highly amplified output of this R.F. tube ting has been reached; and then bring up the connects to the primary of the second coil unit; volume to the desired level. This method is and the secondary of the latter to a standard quiet and avoids noisy blasts, howls, and detector tube (a '12A is recommended for D. similar tuning annoyances. in the detector is The "Speakerelay" may be u..d in this manner C. operation). Regeneration to balance reproducer quality. Only a few minutes are required to attach then obtained by means of the tickler coil pro- the instrument to almost any receiver. vided for its plate circuit. All coils are wound stripping the cut -through insulation This item lists for $3.75, in the same direction. edges, thus from the wire. "low- loss" coil com- The constants of this If it is so desired, the wire may be clipped 22 D. S. C. wire bination are as follows: No. entirely through, by placing it between two THE "SPEAKERELAY" primary, 10 turns, used throughout; antenna cutting edges provided, instead of in the nick second tapped at the 5th for closer tuning; intended only for insulation- stripping. UNDER this name the Fisch Radio at the 10th; both Company, Bronx, N. Y., are offer- coil primary, 30 turns tapped This tool is ruggedly built, easily oiled; the of primaries, 2 ing a simple little "accessory" to the secondaries, 58 turns; diameter cutting and gripping surfaces are replaceable 2% inches; radio set. It is essentially a glorified inches; diameter of secondaries, and may be resharpened; and it may be easily diameter of tickler coil, 1 inch; tickler coil single -pole double -throw switch; this will ex- has 30 turns; tuning capacity, .0005 -mf. For plain the circuit arrangements which appear circuits requiring various primary impedances, in these columns. The points from 1 to 6 in ten, twenty or the full thirty turns of the sec- the accompanying diagrams are the connections ond primary coil may be used, to give the op- of the "Speakerelay. In Fig. 1, the arrange- timum performance. ment permits the use of either one or both re- -pitched The list price of this matched coil combin- producers. If one is low and the other high -pitched, interesting combinations may be ation, made by the Eastern Coil Co., Brook- obtained; their quality depending upon the lyn, N. Y., is $7.50. particular program and station being heard. Another and less obvious arrangement, Fig. 2, produces a "tone- color" effect by shunting This connection of the same device permits the a reproducer with the two capacities shown. THE "E -Z WIRE STRIPPER" most pleasing "tone modulation." (Continued on Page 274) A CLEVER device, the "E -Z Wire Stripper," is being offered by the tooled to fit any particular wire condition. It Pyramid Products Co., of Chicago and is heavily nickeled, and weighs twelve ounces. Los Angeles. Its particular merit lies in The length is 7% inches; the price, $5.00. an extraordinary ability to strip heavy insulation from wires rapidly and cleanly. "MASTER TUNING SELECTOR" TO the growing group of station- select- ing devices has been added a product of the Master Engineering Co., Chicago, Ill., called the "Master Tuning Selector," which is illustrated in these columns. By means of a rack -and -pinion movement, the rotary motion of the regular tuning knob is transformed into a lateral motion. This The automatic operation of these pliers makes lateral drive carries a pointer across a "full- Appearance of the "Speakerelay" selector switch, stripping heavy wire an easy job. vision" scale on which are indicated, by means uses of which are shown in Figs. 1 and 2.

www.americanradiohistory.com Dcccrnhcr. 1929 RADIO -CRAFT 265 Solving the Problems of City Aerials The RCA "Centralized Radio" Sys- tem Enables All Receivers in a Build- ing to Operate from One Aerial at Once.

Typical view of a New York City roof, with "Centralized Radio" System FEW people, except those directly con- The R.C.A. "independent" (yet interfering) aerials. work of in- cerned with the practical To serve the greatest number of receivers large cities, Neatness of equipment stalling radio receivers in with maximum efficiency, the Radio -Victor and improved ap- can realize the serious difficulties, of pearance of building; obtaining suitable antenna connections in a High efficiency of signal pick -up and trans- "multiple dwelling" or apartment house, which fer; have arisen as a result of the universal interest Low cost per outlet group. now taken in radio reception. A look, however, at the roof of many a building of this kind Details of the System that it bears a literal "forest of will show A well -designed aerial, properly installed do its neighbors on every side. aerials," as and lightning -protected, has its lead -in con- the eye can perceive, in all directions, As far as nected to an aperiodic (untuned) stage of extend. The service man the copper strands radio -frequency amplification (called the "cen- navigating the maze; the becomes adroit in tral coupling and plate- supply unit," or must be another Sherlock Holmes to installer "RFC ") located as close to the antenna as is at which to fasten locate a possible point physically possible; this in most instances, one more wire" to serve another radio "Just means placing this shielded unit in a pent- listener, house An "FPO" outlet mounted in the wall of a on the roof. One '80 and one '26 -type room furnishes all connections for a receiver. tubes are used in the "RFC "; the "B" eliminator for the "RFC" and one to eight "RFXs" Corporation of America has developed its is also incorporated in this unit. One aerial LINE TFRMWAL "feed" VNIT(RFT) "Centralized Radio" system. will up the eight "RFC" units. From the "RFC" runs the three -wire No. 19 In this design the signal is picked up by a single aerial and brought to room outlets,

each of which has antenna and ground posts R F R OUTPUT R.FTRANS OUTPUT R TRAN! L2 SW. RFO L FI L. TRA NS. FILAMEN TRANS ANT. 6N0.

The system, in the order of its operating units, '26 The "RFX" or outlet unit feeding the individ- UtOK,' COIL ual receiver. The "RFT" unit appears only in UNIT the last "RFX" on the line. to which any standard radio set may be connected. '80 trans- CONDENSER This system of program pick -up and BLOC Almost over night, it seems, all this has fer has many advantages over the ordinary been swept into the discard; and the antenna arrangements, as follow: tangle takes its place with the crystal detector, Total absence of inter- action between re- CONNECTOI PANEL the little -horn reproducer, the loose- coupler, ceivers; and the other relics of a day when we knew Elimination of electric- equipment interfer- no better. A single copper wire may now ence, ordinarily picked up by the lead -in; The "RFC," or first unit of the system supplies serve the antenna needs of eighty receiving Ease of installation and maintenance; plate current also for coupling units. sets. No moving parts; "triple twisted," rubber-covered R.F. transmission line, which also carries "B" potential from the "RFC "; this line is called a "riser." At every twenty feet, there is placed in this a ANTENNA '26 ANT. "riser" "loading -coil unit" ( "AFL "); the purpose of which is to prevent the radio -frequency current being by- passed to ground. V- (Such coils often consist of 100 turns of No. R1 CN 3 f6 32 enameled wire on a half -inch bakelite ó form; two forms spaced about 11/a inches being required.) Next follows the "extension coupling unit," C- or "RFX "; it is an aperiodic stage of radio - RFx ---. RF C l RFR frequency amplification using a '26 tube. Its (B +) potential is taken from the middle lead of L "B" the "riser." One "RFX" is required for each radio set; one riser will feed ten "RFXs." (Therefore, one aerial will serve for eighty Schefatic circuit of a "Centralized Radio" system. The "RFC" within dotted lines at the left radio receivers. An additional aerial is re- aerial; through "risers" containing "RFL" loading coils, it may be one of eight connected to one quired for each group of eighty outlets.) feeds up to ten extension coupling units, or "RFXs," like that at the right. Each of the latter is connected to one receiver through an "RFO" outlet in its room. (Continued on Page 282)

www.americanradiohistory.com 266 R ADIO-CRAFT December, 1929 The Development of the Modern Sound Reproducer The Combination of the Old Principle of Multiple Diaphragms with that of the Electrostatic Speaker 1

Has Made Possible a Remarkable New Design. r By OSCAR C. ROOS

MUCH interest has been aroused in flow; these ripples are amplified in the usual Early Reproduction Experiments the radio industry by the proposed manner. The advantage obtained is that the We may begin advantageously by consider- new electrostatic reproducers, and glow, unlike a mechanical diaphragm, has no ing the small electrostatic telephones used as especially among the manufacturers inertia or natural period, and responds in- headphones in France a generation ago, and who desire a product that will compete with stantly to all impulses; but the instrument is abandoned because of their lack of sensitivity. the more complicated electrodynamic unit; as far too sensitive for use under ordinary con- (Two stages of A. F. amplification would have well as among the dealers who wish an ap- ditions. done the trick, but amplifiers were not then paratus capable of doing all that the higher - The "glow -reproducer" reverses the "glow - available.) These diaphragms were small priced dynamics can accomplish, yet built to mike's" action, as a diaphragm reproducer does sell between $35 and $40, instead of twice that of the ordinary microphone; it has a INSULATOR CHARGED24 NORN that sum. weightless cylinder of glow- discharge in open t\ttttt\\\\\ NEGATIVENEGAT GO A Leaving aside reproducers which employ the air, under a direct- current voltage of 3,000 to CO ]O WiPE ROD DGE OF principle of magnetostriction in their opera- 20,000; and the diameter of the glow varies LOW CYLINDER DISCHARGE tion, it may be said that there are now being with the audio modulations imposed on this Y developed two types of electrostatic reproduc- current, creating sound waves. Unfortunately, B i2- ers which are in fidelity of tone superior to it will be seen, this is not yet a commercial F:jr2 available, and capable of possibility (due to the potential required). anything previously 'Glow Discharge" loud speaker; "B" voltage giving, with increased size, volume sufficient Its construction is diagrammed in Fig. 2. 3000 -20000 volts. for the largest theatres. "Piston" Action in Diaphragms movable membranes, 1% to inches in diam- Perfection in the Laboratory 3 There are two other ways, speaking gener- eter, and gave out weak but distinct repro- interest state It may be of passing to that ally, of creating sound waves electrically, and ductions of the transmission; they were satis at pres- the most perfect of all reproducers each has its good and its bad points. First, isfactory for telegraph receivers of high -power curiosity, as in its present a mere laboratory the small diaphragm such as employed with "buzzes" but did not supersede the printing ent form it is yet unsuitable for commercial distribution. This is the "glow- cushion," or CEILING reversed "glow- microphone," under investiga- 0 ROPE ROPE tion in Germany by Dessauer and Brenziger, F 11 as well as in England, and in the American W V1 laboratories of the Westinghouse company. NETTIN OM 11 The "glow-discharge" microphone consists i) PLANE SOUNiii EAR PHONES din,= TA- in diameter, II WAVES of three electrodes, to % -inch As < separated by about 1/16 -inch of air through LOUDSPEAKERS ÑW 1 which a high- tension electric discharge is main- _ D 11 tained (Fig. 1). The air waves caused by the resistance of the "glow," 21.2,1t sound change AIR % 1 and thus create ripples in the direct- current WAVELETS FLOOR //J / /I / /// Fig. 3 Fessenden's early experiment using a bank of ear-phones to give a p ane sound wave in an auditorium.

horns; and, secondly, the large or cone dia- receivers. From these we may note develop- phragm driven mechanically From its center ments, not of the electrostatic phone, but of with a piston motion. the diaphragm. The electrostatic loud speaker, it is true, The horn came into popularity with the generally employs a flat surface as developed original dictating machine; diaphragms as by German designers like Vogt and Massolle, small as % -inch (in diameter) were used, but rather than a cone; but the flat diaphragm the average was about an inch. The horn had may be considered as a flattened stiff cone, and resonance points, as well as a megaphone ef- will exhibit even more piston action. That is, the shape of a cone helps it to remain rigid FRAME while it is moving at low frequencies; and the electrostatic diaphragm as designed by Massolle vibrates in even greater degree with a large portion of its surface moving always together, parallel to itself. Unfortunately, this ideal piston action cannot be maintained at A B high frequencies with any large diaphragm, no matter how driven. b /--- After analyzing the behavior of both the horn and the cone diaphragms, we shall see C how they act in multiple; and will then more readily understand how a combination of them will advance reproducer design, especially spalNG where the use of the baffle board is mechanically a disadvantage. In fact, the presence of the latter is today the grave drawback of high - Fig./ Fig. A. Rear view of commercial reproducer powered apparatus; though it is not abso- condensers and showing the parallel -connected lutely essential, as the author will show in a the high voltage D.C. supply. (Photo courtesy Reversed "Glow Discharge" speaker used as Columbia Woodworking Co.) later discussion. a "Mike."

www.americanradiohistory.com December, 1929 RADIO -CRAFT ookcTraiucd Mciii et Me - _n 5 Rici

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www.americanradiohistory.com 268 RADIO-CRAFT December, 1925

feet, to distort the effect on the human ear electrostatic reproducer, in which every part of the treble or higher notes from separate sources which is a "non- linear" sound detector and re- the diaphragm, which ranges from six inches must interfere with each other. Every listene, sponds with different degrees of efficiency un- to six feet in diameter, is subjected to the who observes carefully in an auditorium with der strong impulses than under normal sound same pull. Yet it does not move as a flat a hemispherical sound reflector, on a concert intensities. There was little, therefore, to be piston unless the attracting plate is cone - stage, recognizes that at certain seats in the done with the horn except to give it an ex- shaped and concave toward it; thus making orchestra and lower mezzanine there are such the pull least at the center and progressively strong reinforcements of certain notes, with greater toward the rim. Even here there is a any given orchestral "setting," that the sounds change -over point; which may be raised in fre- seem to come to the listener from a source a H quency to any desired extent by stretching the foot away, instead of seventy or so. diaphragm radially, short of rupturing it. This stage of development is shown in the forms known as the "Statophone" or "uni- CELLO STATIONARY SOUND WAVE ON ass CYCLES PER S. D lateral," with "single displacement" from DI original diaphragm position (Fig. rirmkalik .41710 RADIAL 6), and the C SOUND 01/1,114.40;: 4111k WAVES "Oscilloplane" or "bilateral" with "double dis- AI STATIONARY SOUND D placement," as in Fig, 7. We shall later re- VIOLIN WAVE ON 384 CYCLES PER SECOND fer to the former in connection with a possible ORCHESTRA STAGE development in combination with the other Flg 6 family of speaker diaphragms -the "fly's eye" The production or better, "mesh-unit" type, of "Tartini's tones" is illus- Left -General type of unilaterally- driven con- trated above. denser- speaker such as 'Statophone" made in Germany or "Kylectron" made in America, Multiple Diaphragms for Volume showing position of moving diaphragm under Interference of Sound Waves "B" voltage. Right -General type of bi- later- The development of the last named grew The reason is indicated in Fig. 4; since ally- driven condenser -speaker, such as Oscillo- out of the use of several reproducers in "ser- sound travels at a speed of plane made in Germany. ies-multiple" arrangements. Fessenden did about eleven hundred feet a second, the length of this back around 1904 and demonstrated the the wave produced by a musical instrument ponential curve to obtain even propagation advantage of a large "fiat" wave of sound sounding "middle C" is little more than four of sound. Even after this had been done, the over a spherical wave to distribute energy in feet. If such a wave is directed against a wall, "barrel" effect remained, and it is only in late an auditorium more evenly and with less and reflected, the reflection encounters sound years that attempts have been made to com- acoustic distortion. For many years the im- waves pensate these acoustic resonance points by seated later from the same instrument; and shunting the "motor" unit driving the dia- it is possible that "stationary" or "standing" phragm with circuits tuned to audio frequen- waves will be set up. We may have also cies- sometimes as high as seventeen in num- "diffraction" patterns, showing points of sound ber. This method of leveling off sound reinforcement at right angles to the former "peaks" is obviously not attractive from a com- lines, for the same note; and finally, very mercial standpoint. strong tones of simple frequency ratio (such In the opposite course of development, ex- as 3 to 2, for their fundamentals) give beat( perimenters (Pathé, Lumiere, Brown, Hopkins or "Tartini's tones," the principle of which is and others) went from the small diaphragm, illustrated in Fig. 5. which acted more or less as a piston, to a Thus we may have interference of two kinds large stiff diaphragm, cone -shaped to increase -on the same note or on different notes; in its rigidity, and acting as a very short, wide- the former case the action may take place angled horn. This still acted as a piston up without the presence of a reflector. When we to the "change -over frequency "; above which ask why listeners are not more annoyed than most of the energy is present in the form of they are by these phenomena even in the dis- waves in the diaphragm, theoretically radial, Method employed to prevent radial vibrations producing concentric zones of reinforced vibra- but in practice irregular figures arranged fan - tions in unilateral E. S. L. S. The surface is wise around the cone, in patterns theoretically touched eccentrically by damping circles- c -c -c. duplicating each other. plications of this experiment (Fig. 3) re- CENTER OF FASTEN- mained unused and it was not until about ING CONE CENTER Or 1922 that an English publication suggested RECEPTACLE a,"s CONE that a closed room may be more agreeably filled with music from many sources than from FIXED 000000 one. (This has no relation to the "binaural" VENT HOLES IN n FIRED ELECTRODE° O effects which have been since used to give a TO CENTER OF DIAPHRAGM ° doubtful illusion of the position of the lis- 6-go tener in the midst of the actual studio.) The One of several different schematic arrangements suggestion is based on the well -known fact by which a metal foil diaphragm may be stretched that, in a closed space, the volume or density radially by variable mechanical adjustors. Com- of sound is increased by the use of several pare method of tightening tympani or kettle - An early form of reproducers, and the sound is noticeably unilateral speaker, using mul- drums in orchestra or "banjo." tiple grains embedded in a movable diaphragm. strengthened in locations where it would other- The latter is made to move parallel to itself by As more power was used, the effective wise be weak. The drawback is that there the "bulge" K, in the fixed electrode F. "change-over" frequency was lowered and so, are always developed in the room a set of when the super- dynamic was used with more points-different for each frequency-where tortion of single tones-let alone the whole than 800 volts on the plate of the output gamut -we see that it is because of the very stage, it became necessary to make the moving complexity of the actions; when the whole system lighter and yet stiffer -the latter char- range of tones is used, so that no one stands acteristic in all cases most important. The out during a performance, the oddities are increased lightness made easier instantaneous not so apparent. These considerations apply damping; which is absolutely necessary to only to notes which are perceptibly prolonged avoid "blasting" and give fidelity because am- and, as this is the exception, not the rule, in plitudes, following a musical or speech sound - the treble-we are still further freed from worry over curve, change in intensity from 1 to 99% the theoretical defects of a mul- in a hundredth of a second! tiple- diaphragm system planned to give better sound distribution over a small auditorium. Early Electrostatic "Speakers" Stationary sound waves producing reinforcement Fessenden endeavored with more or less suc- and annulment on one cello tone-middle The next practical development of the pis- C- cess to produce a plane or flat -front wave from every half wave-22 - inches-outwardly from Eon was diaphragm the circular plate of the stage. A is player; C, the reflecting surface. (Continued on Page 283)

www.americanradiohistory.com December, 1929 RADIO-CRAFT 269 What Radio Design and liadioInternational Gild Offer the Radio Minded! Here is what you get fo r 50e per year ..

FIRSTYou will receive immediately the current number of Radio Design. This issue contains the latest up- to -the- minute construction articles (including the sensational A.C. Super - Wasp), short -wave data, radio in aviation, etc., written by engineering authorities- Robert Hertzberg, Robert S. Kruse, David Grimes, John Geloso, Zeb Bouck, and Alfred A. Ghirardi.

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www.americanradiohistory.com 270 RADIO -CRAFT December, 1929 4- NFORA,ATION u R EA 1.1

SPECIAL NOTICE TO CORRESPONDENTS: Ask as many questions as you like, but please observe these rules: Furnish sufficient information, and draw a careful diagram when needed, to explain your meaning; use only one side of the paper. Lift each question.

Inquiries can he answered by mail only when accompanied by 25 cents (stamps) for each separate question. We cannot furnish blueprints or give comparisons of the merit of r.mmerial products.

The reader asking she greatest number of interesting questions, though they may not be all answered in the same issue, will find his name at the head of this department.

Highest for the current month: E. R. PRINCE with 5 interesting questions.

"CHARGED" PANEL -"BLAIR" CIRCUIT .0001225 -mf. in the antenna lead will greatly increase varied until a spark signal is heard ; if there is no selectivity. Circuit oscillation is controlled by the spark signal within this range (2498 meters) a .0005 - (33) Mr. Fred Bower. Hastings, Mich. rheostat in the filament circuit of the R.F. stages. mf. variable condenser may be connected from de. (Q.) Is it possible for the metal panel of a rec Jack 31 is for headphones, and J2 is for the rector plate to antenna, and varied until there is Myer such as the Freshman "Masterpiece" to become reproducer. "charged" ; so that a shock is felt when the panel Condensers C4, CS and C6 may be .001 -mf. Re- is touched? sistors R4, R5 and R6 may be 100,000 ohms; if type - 1000 RANSORMFR (A.) If the "B-{-" of the receiver becomes '40 tubes are used as V4 and V5, resistors R5 and 6l G grounded to the metal panel, a shock will be felt OSCILLATOR R6 may have a value of about 250,000 ohms. Re- T1 when the panel (or chassis) and any instrument -- sistors R7, R8, and R9 may be about 1 megohm; if J t L connected to the "A" circuit are touched simultan- VS V6 is a power tube, R9 may be 250,000 to 500,000 FIXED OR B+ locate the at which eously. The solution is to point ohms; with a "C" bias of the proper value to VARI LE PRI. SEC the 'B" circuit is grounded and "clear" the ground. balance the "B" potential applied to the plate of FREQUENCY A simple way to do this is to connect an old head- the power tube. phone in series with the "B-{ -" lead, where it comes out of the current supply unit. Upon com- ó MATCHING pleting the circuit through a lamp, by bridging the "STROBODYNE " -R. E. 29- MATCHING o CD a TRANSFORMER. lamp from the panel to the "A" circuit, a click INTERMEDIATES L will be heard. This continuity click will disappear (34) Mr. W. A. Beavers, Washington, D. C., and when the grounded instrument has been located by T3 Mr. Everett M. McIntyre, Bridgeport, Conn. PRI SEC. the process of removing wires, one at a time, from (Q.) What is the intermediate frequency used TRANSFORMER B+ panel-mounted instruments. in the Lacault "R. E. 29" receiver? UNDER (Q.) Please print the schematic circuit of the (A.) This frequency is 120 kilocycles. TEST C -A+ "Blair" receiver. This is a resistance-capacity- (Q.) Are the same intermediates used in the "R. T2 BC+ 45V. coupled receiver made some time ago by the Blair E. 29" receiver as were used in the "Screen -Grid 4v Radio Laboratories. Strobodyne ;" and if so, where may they be ob- (Q.35) Arrangement used in a manufacturer's tained? laboratory, to determine the relative value of (A.) "Strobodyne" intermediates may be used in A.F. transformers. A tuningfork oscillator is the R. E. 29 ; we believe they are obtainable from shown. the Estate of R. E. Lacault, 1931 Broadway, N. Y. C. (Q.) How can a ser of home -made intermediates circuit oscillation (to obtain this oscillation it may be matched? be necessary to reduce the capacity of the fixed con- the (A.) It is presupposed that the design is ap- denser in shunt with headphones). When a proximately correct for the desired frequency. The whistle is heard, as the beat -frequency between a problem, then, is not to match the coils exactly to CW signal and the circuit under test becomes audible, a given frequency, but to match one set o/ coils to the reading of the variable condenser in shunt to the secondary is noted. and the second intermediate - the other. The best method involves the use of a calibrated, A.F.- Modulated, R. F. oscillator. Its frequency transformer is substituted for the first. The condenser is again the same signal output is transferred to a detector tube, the inter- shunt varied until mediate- frequency transformer being introduced be- is recognized. Then, turns are removed from (or added to) the secondary coil until the variable con- single arrangement to match R.P. tween the two units. Maximum deflection on a Q.34) A denser's reading is exactly the same as it was when transformers. Long -wave transformers are milliammeter indicates resonance ; which is obtained (I.F.) the same signal was heard with the first transformer under test above. by varying the number of turns on the secondary. Varying the adjustment of the long -wave oscillator in circuit. This is a very accurate method ; the only until the meter indicates a current will show whether requirements are care and common sense in applying (A.) This schematic circuit appears in these there are too many or too few secondary turns. it. In this arrangement, a code station is com- columns. The exact values of the parts used are A more simple method is to connect antenna and mandeered to supply the A.F.- modulated R.F. long - not available, but they are approximately as indi- ground to the primary winding, and a detector tube wave signal (the spark signal) ; or she R.F. signal be cated. The radio -frequency transformers and vari- to the secondary ; one side of the coil connecting to may the code transmissions of the C.W. station; able condensers may be any standard equipment. the grid condenser and leak, and the other side to the A.F. modulation being obtained by the heter- odyne method as mentioned Many variations of this circuit are possible; for "A +." A pair of headphones, shunted by a .001 - above. instance, the inclusion of tubes of high- plate -im- mf. fixed condenser. are connected in the plate cir- To facilitate rapid comparison, a circuit, shown pedance (such as the '40), in the resistance-capacity- cuit of the detector tube. A .0005 -mf. variable con- in these columns, has been developed. coupled stages. Also, a fixed condenser of about denser is connected across the secondary coil and (Continued on Page 285)

V1 VZ V3 Ca va CS VS C6 V6

R6 C IV 1 M1111111111111111111 11 Schematic (Q.53) circuit n/ the 123 31 J2 Blair receiver. Tu-o stages of T.R.F. Rl are followed by three of resistance - rapacity coupled A.F. 45-67 V A- A+ 60-70V 90-135V. B+ B+ B+

www.americanradiohistory.com December, 1929 RADIO-CRAFT WHOLESALE PRICES For Dealers, Service Men, General Repairmen and Set Builders! . Our new, HUGE LARGER PAGE SIZE (8" x 101/2 ") WHOLESALE CATALOG No. 19, 2nd Edition, enjoys the enviable distinction of (Uú WHOLHALE (TL being universally accepted by the RADIO F 05 -7 TRADE in the same manner that a school treas- PG°30CtS ures the Dictionary and Encyclopedia Britannica 4a2.g -or the home, the Bible and Almanac!! Those .... ,-' "in the know" regard our catalog AS THE R OFFICIAL ORGAN OF THE 1929 RADIO SEASON!!! This FREE CATALOG is literally a most valuable ENCYCLOPEDIA -YOU cannot well E afford to be without one -and, you do not have ASCO to. Your request for one is all that is needed! In these many years we have been in the Radio E Mail Order Business, we have learned to GAIN , AND RETAIN THE GOOD WILL OF OUR CUSTOMERS. In this, our DETERMINED GOAL, RADIO SPECIALTY COMPANY OF- FERS TO SHIP PRACTICALLY ALL ORDERS _ IN FROM 6 to 24 HOURS -OFFERS YOU C 100% MERCHANDISE ON A STRICT t MONEY -BACK BASIS IF NOT SATISFIED - AND OFFERS YOU ALL MERCHANDISE AT

I / , ^ PRICES! A ABSOLUTE ROCK BOTTOM NET T Our Catalog Lists More ih.. p Completely Assembled `r ,' J '//:FT. t % All- Electric A. C. Receivers 98 PARK PLACE, NEW YORK than any other Radio Catalog! A ; , Available in chassis form, or mounted in - - láik` table or console cabinets, with and with- \ , ; out built -in loud speakers. L Il . 1 j a;,, ' ,V th44 _. OUR ROCK BOTTOM NET PRICES o . - FOR THESE SETS WILL o a . ASTOUND YOU! - \//D In this new catalog there are also listed / large assortments of CAMERAS, HOUSE- RASCO HAS IT HOLD ELECTRICAL APPLIANCES G AND ELECTRICAL TOOLS OF EVERY -_ - DESCRIPTION. sir HERE ARE TWO OF OUR BIG BARGAINS Order From This Page-Send Money Order -Check -or Postage Stamps RASCO REPLACEMENT AUDIO TRANSFORMERS DUO- MAGNETIC CONE SPEAKER CHASSIS Can be moaned in either of three positions, that is, ling down, or standing up No other magnetic speaker chassis is so strongly with the core parallel With the bate on which it is resting, or standing np uith constructed ! Note the heavily ribbed, sturdy "spider core perpendicular to the base. Other replacement transformers can only be mount- leg" white -lead casting! The entire frame work is ed two ways. There are six specially designed feet to provide the most convenient one piece a beautifully molded job! A Duo-Mag- choice of mounting, and any of them can be re- netic cone speaker unit is bolted to the rear mount- moved at will, should you so desire. Thus. it is ing plate of the chassis, and the Burtex "ribbed" logical to conclude that our Replacement trans- cloth cone is fastened between two heavy rings of formers can be installed in ANY receiver, either cardboard -these rings are held in place by either custom or factory built, no matter how small a screws and nuts, bolted to the frame of the chassis, space there may be available, whether such or by being pressed up against a baffle mounting mounting is to be above, or beneath, a sub - hoard. Although this speaker can be used as illus- panel, or baseboard. The coils themselves are trated, it is strongly recommended that it be used in of the first quality, and are only found on the conjunction either with a baffle board or mounted most costly Transformers. The core is the within a box, a cabinet, or speaker compartment highest grade silicon steel, and of ample pro- space in any console. The tone quality is comparable portions. A happy combination of electrical to any speaker selling for many times its trivial cots. values in both the core, and coil, assure maxi- T'ill stand all the s alome any radio set can ''gire mum amplification possibilities-more than sufficient volume, yet with no trace it." Will work satisfactorily with a D.C. or an A.C. set -with 90 volts applied of distortion! The silicon steel stampings are very rigidly bolted together by a through it, or even as high as 500 volts! No blasting! No distortion! No generous size bar which is attractively nickel plated. 21/2 in. long by 11/2 in. rattling! You will he most impressed with its splendid performance! Overall high by 2t4 in. wide. dimensions: Diameter 9 in., width of mounting ring yZ in., depth (rear of unit to No. 7900. Your net Cost $0. O8 mounting battle hoard plate) btu in.: diameter of unit mounting plate .0/2 in. No. OM. COMPLETELY ASSEMBLED. Including DUO -MAGNETIC UNIT TERMINAL STRIP MODEL and cord. AS ILLUSTRATED. Your Special The primary and secondary leads are spaghetti covered, and unusually well Net Cost $Ú ?5/ 7 soldered to generous size lugs. Strip is bakelite and properly lettered. i.1 No. as''. MOUNTED IN A CABINET OF EXTRAVAGANT Q No. 7950. Your Net Cost $ BEAUTY. Your Net Cost $ 9.44 98C Park Place RADIO SPECIALTY CO. New York City BUY FROM RADIO'S OLDEST MAIL ORDER HOUSE

www.americanradiohistory.com 272 RADIO -CRAFT December, 1929

A MULTI -METER (Continued from Page 252) ______r ; C 6 or 's calibrated for a "Readrite" 25- milliampere i meter. If the radio fan wishes to use a dif-

ferent type of meter, the resistance of the 6b multiplier will have to be changed in propor- 6 milliammeter. -- tion to the resistance of the t The resistance of the instrument used is about 300 ohms; on shunting the meter with jl a 0 -to- 300 -ohm rheostat, and proper calibration I Trfrftarrr for various settings of the rheostat, the milli- Ad ammeter can be made to read up to half an awe t ampere with fair accuracy. Higher readings can N4 éc be obtained if the shunt resistor will carry WANWVWWWNA Ir! i ) the current without overheating. 8b 4 r r to ao Vacuum Tube Voltmeter TRANS. ; TRANS sEC. ; i rams)-à Test No. 5 -In the first test the grid of the n. tube was not in the circuit; on closing switch r. Ba, and putting a potential, A.C. or D.C., on k. ' v`_i r' the "K" binding posts the reading of the L._ meter will increase proportionally to the voltage impressed on the "K" terminals. KI-KI, J e- o+ÿ v. 6 ; K2 -K2 K3 6, Kt K3 !lt9 M.A. 110V b1ASLnc. D and K3 -K3 use different resistors and, RES. TRANS. ELIO. 100V 110V OV 10V F16.1 300V by proper calibration with a standard meter, the milliammeter can made to read ac- be The complete connections of the Multi -Meter arranged for the tests described in the article. A curately up to 400 volts A.C. In case you do standard tube is recommended for voltage tests. Units 6a, 6b and 6c are type UY sockets; 5 is a not get a reading on the meter when A.C. type UX socket (in the tester). Cables 9a and 9b Inuit be low resistance. is impressed on the "K" terminals, reverse the testing leads. an open circuit in the primaries or secondaries This instrument has been used by the writer Test No. 6 -This tester functions as a tube of transformers; also for the grid -bias resistors for several years as a tester for radio sets and reviver. The procedure is the same as in the and grid- suppressors. These tests can be per- also in his electrical laboratory. The radio second test. A.C. is used to light the Ilament of formed by using plugs 9a or 9b from the fan building this instrument will find it a the tube for the "baking" period. For the radio -set socket (of the particular transformer very useful unit in his laboratory or radio "flash" period a larger size lamp is used. The to be tested) and socket 6a. Binding posts workshop. size of lamp required for the "flash" period for "C," "P," "G," "F" and "F" are the testing various radio tubes is given in Table I. points. The dotted lines and the dash -and- Testing Screen -Grid Tubes Test No. 7 -When the tester is connected dotted lines illustrate how these points reach as outlined in No. 2, keeping switch Sc open, the parts to be tested through the flexible The schematic circuit (Fig. 2) illustrates binding posts K4 -K4 can be used to test for cables of the plugs. how the screen -grid tube can be tested for plate FREE.' COMPLETE COURSE in Radio and Television Through Courtesy of Organized Labor A better understanding of the theory and mechanics of radio and television is essential to the fullest enjoyment of these two great inventions. To meet this imperative need ORGANIZED LABOR is supplying a complete course in Radio and Television FREE OF ALL COST to all who are interested. This great educational project is conducted in connection with Radio Sta- Lion. W CFL at Ch'tcago -t h e on y station b ut'I t, omone d an d contro Il e d b y Luch wage earners. This Free Correspondence Course includes: Theory of Radio and Television Transmission and Reception, Radio and Television Construction, How to Locate and Remedy Radio Troubles, How to Service Your Own Radio Set, Short -wave Adapters, and many other important subjects. Just the Thing for Beginners and for Boys This splendid correspondence course is distributed WCFL RADIO STUDY CLUB, FREE through the WCFL RADIO STUDY CLUB. 625 South Wabash Avenue, Chicago. Membership in the Club, with first year's dues, is Send me your Radio and Television Course. These $200, and includes an annual subscription to WCFL lessons are to be sent to me FREE and without obligat- Radio Magazine ing me in any way. -the only magazine fighting for the preservation of the Freedom of the Air, the most Name important subject now before the vast radio public. Special discounts also are available to members of Street WCFL Radio Study Club Postoffice State 625 South Wabash Ave., CHICAGO Age Occupation

www.americanradiohistory.com December, 1929 RADIO -CRAFT

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www.americanradiohistory.com 274 RADIO-CRAFT December, 1929

and screen -grid current values. To get the If LW happens to be an odd wattage, use R. C. A. TELEVISION WORK plate current reading all that is required is a combination of 2 or 3 standard lamps in (Continued from page 254) an extra wire from the cap of the tube to be parallel to give the nearest watts required. tion. This tested to the clip which goes to the cap of This can be accomplished by putting in a could have been transmitted on one of the experimental the same tube when the tube is in the radio multiple socket in the receptacle. phone wavelengths, set. but it was not considered necessary for the To get the filament -to- screen -grid current LATEST THINGS IN RADIO occasion. Picture transmission was on the allotted wavelength band between 143 emission, a slight change in the wiring of the (Continued front page 264) and 150 meters. meter is required; it also requires another 0 These condensers may be readily connected Instead of confining to 10 D.C. milliammeter. into the circuit by mounting them on pieces the modulation to the customary audio limits To do this proceed as follows: Open up of bus -bar to fit into the tip -jacks of the unit. of ten kilocycles, the modulation the wire running between the grids of the The "Speakerelay," primarily, affords a covered a band of about 100 kilocycles. "plug" and testing socket as illustrated. Place This was nearly a 50- kilocycle swing each side one binding post at each end of the break, of the assigned carrier frequency of experimental station and connect the two binding posts with a W2XBS. The antenna piece of bus bar. When it is desired to make at the receiving end three miles away (experiments the test for screen -grid emission, remove the are being conducted daily to points far bus wire and insert the meter in its place. It as as 20 miles away) accounted in part for the clear and satisfactory will readily be seen that the meter is in the reception. screen -grid circuit and therefore registers the The arrangement is attributed to Dr. Conrad current passing through it. and other engineers of the Westinghouse Elec- tric and Manufacturing Company, who designed a "radio frequency transmission line" TABLE I form of lead -in which has proved highly prac- Wattage Fil. Current of of Lamp Res d.. tical. The effect of Radio Tube In For Normal For "Flash" Period the design is to reduce Amps. Current When Reactivating Tube to a minimum pickup of "strays" of all types. .06 10 15 In general, the idea consists of a stage of .25 30 75 to 100 radio frequency amplification located at the .5 60 75 to 100 antenna. The output of this R.F. amplifier is 1.05 120 conducted to the receiver through a shielded 1.75 200 cable and it is called the "transmission line." The switch- points as they appear in the "Speak - has high erelay." 1, 2, 3 and 4 serve as tip -jacks and It been found practical to use as as To find the size of lamp for any radio tube switch- points; 5 and 6, soldering lugs ; ten broadcast wave and ten television wave not T. hole listed above, use the following approximate for "tie- cord" of phone lead. amplifier units, each unit being connected to formula: convenient means of determining the respec- a different radio set, without objectionable in- LW= I(E -Et) tive merits of two reproducers under substan- teraction or loss of signal strength. where, LW - size of lamp in watts required. tially similar conditions; other uses will sug- These "booster stages" may be used for I = rated current of radio tube. gests themselves at once to the technician. operation on short wavelengths with even Et = rated voltage of radio tube. The mechanism in encased in polished black more success than on the regular broadcast E = line voltage, A.C. or D.C. bakelite; and the instrument retails for $2.00. wavelengths. In this particular instance, due

Size 9 "x12" F 11 S. GERNSBACK'S L L RADIO ENCYCLOPEDIA Y L The First Radio Encyclopedia Regular L Price U Ever Published s $2.00 T R EDITED by SIDNEY GERNS- The works contains 1,930 definitions, Our A BACK, Author of "Wireless 549 photographs, drawing and dia- T Course in Twenty Lessons" -"One grams. Special E T h o u sa n d and One Formulas" - D "Practical Electricity Course"-"The REMEMBER THIS IS A REAL Price Radio Educator," etc. ENCYCLOPEDIA -NOT A DIC- 1930 Definitions TIONARY - and very few of the $1.49 S. GERNSBACK'S RADIO ENCY- things described and illustrated in this CLOPEDIA is the only standard work volume can be found in any diction- SEND NO MONEY ever published in America attempting ary, or any other encyclopedia. to classify alphabetically the countless Just Pay Postman words used in the highly specialized The book contains as a supplement (Canada or Foreign send check or science of RADIO. The ENCYCLO- a classified cross index designed to Money Order of $1.75). PEDIA is written in plain English so bring together radio references under that everybody can understand the one heading having relations in com- ISKOR PRESS, Inc., R -12 definitions and descriptions. mon. 286 Fifth Avenue, New York. No All circuits new and old are de- expense has been spared, cover- scribed by word and picture and every Send me one copy of Sidney Gems- ing over two years in compilation, to part and apparatus used in Radio is back's First Radio Encyclopedia in one make it worthy a place in your library. explained and made understandable by volume as advertised. I will pay post- means of photographs and drawings. man $1.49 plus postage on delivery. It is published in one volume-168 pages -size 9 x 12 inches, nearly an The volume is printed upon fine Name inch thick and nicely accommodates the paper -bound in full black Keratol, beautiful illustrations and the large, marbled paper Ay leaves and end sheets, Address easy -to -read type. with the title stamped in gold. Town and State

www.americanradiohistory.com December, 1929 RADIO -CRAFT 27.:.

to the shielding effect of tall buildings (the electrical values of which are effective within the broadcast frequency range), the shorter waves were received best. The NEW llFL Mastertone The R.F. stage units were powered by a current supply unit in a protected place on the roof, line current of 110 volts being wired LaboratoryMade Receiver to the unit and remote controlled. The television console included a special amplifier for the "television frequency range," a scanning disk and a neon lamp. The amplifier was in two major sections, a radio -frequency amplifier and an intermediate frequency amplifier; an audio amplifier was not used, the output of the intermediate frequency amplifier connecting to the neon lamp and delivering power sufficient to operate the lamp at full glow. The scanning disk is of 60 -hole size. Square holes are used for the increased amount of light which will pass through them. The disk rotates at a speed of 1,200 R.P.M. For proper definition, or sharpness, 20 complete pictures per second were considered necessary. The e picture appeared on a ground glass about five Completely Built and Assembled by inches square. The disk does not require manual synchronizing as a method has been developed which makes automatic, the syn- HFL Engineers -Shipped ready to Operate chronous "tracking" of the transmitter and electric line receiver disks. (Independent of All metal completely shielded chassis: 7" x 21" x 7! i ". Fits nearly all consoles. 11 tubes supply.) operating at peak efficiency (5-224; 3 -227; 2-245; 1 -280.) Single dial positive one-spot Newer Developments tuning; Humless AC Operation; Uses 5 Screen -Grid tubes, 5 Tuned R. F. Circuits; The laboratories associated with the Radio High Power Ss.,een -Grid detector, with 175 volts impressed on plate; Automatic line Dynamic field Corporation of America have developed an ex- voltage control inbuilt holds voltage against fluctuating; 100 -Volt DC Finest quality precision made parts. ceedingly compact and also portable "pick -up" supply incorporated; 3 stage Phonographic amplifier, unit. It has been termed a "television eye." Amazing Power Highly Developed Circuit It may be carried to any desired point of Startling realism! Unfailing accuracy! Its Intermediate employs 4 screen -grid tubes interest and the proceedings at that point great power and sweet tone awe and thrill, with 5 tuned filter circuits, easily adjustable frequency. Positive 10 transmitted to a companion receiving instru- setting new standards of performance to peak of tuned Kilocycle selectivity. Most highly engin- ment. By a means not yet made public, it achieved by H. F. L. engineers after two years of tireless research and tests under eered receiver ever built. has been found possible to practically ehm- The New Audio System inate the scanning disk as it is generally known. all conditions. Uniform amplification over entire musical The image produced may be seen with excel- Keenest Sensitivity scale. Operates with dynamic, magnetic or lent clarity on a screen about 15x18 inches. Unlike any ever known! Gets distant horn speakers without a bit of hum. distinctly with only The receiving end of the latest television stations clearly, sharply, The H-F -L Power Master design is so compact that the entire equipment wire screen or metal plate aerial built in power pack, but a specially does not require a greater space than is re- cabinet. Not an ordinary developed unit of the Mastertone, quired by the regular radio set of good con- built separately to simplify installa- struction. tion. Has oversized transformer, It may be pointed out that the television full wave type 280 rectifier tube. unit cannot supplant but must supplement a Built by Hand -Yet Low good radio receiver. The completed "job" in Priee- will probably include a short -wave pick -up and Quality-not quantity-the H -F -L amplifying system designed for the television Mastertone standard. One demonstration will convince you that unit and another one designed for proper op- its the master receiver of all times. eration of a receiver operating on the broad- Fully guaranteed. cast frequency band. Write today for complete Because of the unusually wide frequency description and price. band which must be simultaneously operated in with maximum efficiency at all points in that band, the so- called "short -wave adapter" HIGH FREQUENCY ILABORATORIEf will not prove suitable; pictures can be re- 28 North Sheldon St- Dw.I Chicago, Ill. ceived, but the image is highly distorted due to lack of the higher frequencies filtered by ATTENTION the circuit as designed, and to uneven ampli- - fication which often exists. It is not evident RADIO SERVICE MEN A New. Startling Revelation to the ear but this distortion in the audio spec - by a Paramount Authority trum, may be "seen" when it is transposed to the visual spectrum. LOVE AN DMARRIAGE Leading manufacturers often con- By W INFIELD SCOTT HALL, M.D., Pa.D. About the future relations of Television sult us for the names of competent Unfolds the secrets of love and sex relationships and Broadcasting, Dr. Goldsmith has this to fully and frankly. Gives intimate details of such say: vital subjects as Companionate Marriage and Birth "It should he emphasized that ordinary service men who are actively en- Control. Why muddle along? Learn now about the broadcast receivers cannot receive television gaged in radio work. sex and love instincts, how to select a mate, etc. images, and vice versa, so that television and Decide today to have Illustrated ordinary this new. precious knowl- telephone broadcasting are separate We want every reader of RADIO - edge, it you are a young and distinct services. Accordingly, owners or man or young woman, if CRAFT who is engaged as a ser- engaged or married, if prospective purchasers of broadcast receivers parent or teacher, or if need not be concerned that television will vice man to read page 247 of this a man or woman of 45. CLOTH, 366 PAGES make their broadcast receivers obsolete. A issue. You will find the few min- complete Only $2.00 service requires both a broadcast set utes We pay postage for voice and music, reading this page well worth and a separate television C. WINSTON CO.,39 Winston Bldg., Philadelphia image receiver." while. JOHN

www.americanradiohistory.com RADIO-CRAFT Decembers 1929 INTERNATIONAL PROGRAMS RADIO technicians will find the art enter- New,/ ing a new cycle as rebroadcasting assumes FLECHIIILIM greater proportions. The Great Lakes Broadcasting SUPERIOR CONDENSERS Company, the NOT Adapter Universal Broadcasting Company, and the Pa- MERELY BETTER, BUT cific- Western Broadcasting Federation have THE BEST! gor the made arrangements with foreign countries to rebroadcast their transmissions. 245 The last -named concern is negotiating with sure the radio stations of 119 countries and prov- inces, and announces an almost complete pro- POWER TUBES gram- interchange agreement between certain stations in Germany, Great Britain, Norway, Turkey, Italy, Spain and Japan. These relay transmissions will be handled on short waves not yet decided upon, with relatively high antenna power. Engineers of the Federal Radio Commission, realizing these demands for channels, suggest an international division of time on a basis Uncased filter condensers, dipped in of so many days a week, or so many hours a pitch, impervious to moisture and in day to each station, according to the Associated every respect, a Superior Condenser. Press. Rated at 450 V DC, equipped with wire leads and unexcelled for repair, They point out this will a variety afford replacement and constructional radio of foreign programs for listeners throughout work. Available in .1, .25, .5, 1, 2 the world. In this country, for example, the and 4 mfds capacity at very attractive fan would be able to hear an orchestra in Ber- prices. lin on Monday, a speech in London on Tues- day, melodies from Madrid or Buenos Aires on Wednesday, and the description of an in- Bring your pres- ternational tennis match in France Thursday. ent s e t up -to -date using the New 245 Super Power Tube regardless of what INCREASING "WIRED WIRELESS" you now have. No rewiring necessary. This adapter makes the job simple; EXPERIMENTS at Freeport, Ill., with the any one can hook it up in a few minutes' wired wireless" system he has devised, time. Greater volume, finer clarity an amazing and ability to reproduce low notes according to Gen. George O. Squier, have are the features gained through the the use of shown that a five-watt transmitter output is new 245 tube and this adapter. Re- wiring of your set is necessary if you do sufficient to "saturate" 6,000 telephone lines, not use this adapter. You simply cannot or "cable pairs," with modulated radio -fre- do without it. Our highly develop- quency current sufficient for satisfactory use ed "A" filter con- The Famous Flech- All Orders Must Be Accompanied with special receivers. The radio -frequency densers are the best theim Midget Conden- By a Deposit of 20% carrier, of course, cannot be heard in ordinary you can obtain, for sers are well known "A" eliminators or among radio men who telephone receivers. dynamic Io s p e a k e r appreciate accurate ca- M1rQ1O Os The receiver designed for the purpose has fields. I n 1000 pacity, minimum rf three tubes; an A.C. screen -grid radio -fre- mfds at 12 volts; impedance and a high quency stage, a power detector, and an audio 2000 mfds at 18 value of resistance to volts and 4 0 0 0 DC. Electrostatically sRUkiyÍ IN stage with sufficient output for a dynamic mfds at 12 volts. shielded. Service Corp. speaker. However, since only three carriers may be put at once on the telephone wires, The devel- 1072 Atlantic Avenue, opment in conden- the choice of programs with this apparatus is Brooklyn, N. Y. sers, today - type limited. Its operation is automatic; as it is HV, rated at 800 V pretuned, and only the pushing of a switch is DC, (550 rm necessary to start it and to in the RAC max.), having tune optional the finest electrical I/LCCN.x.xl programs. 'characteristics, and In Cleveland a similar system will be in the smallest physical operation this fall over electric -light wires. dimensions. F o r the portable, receiver, transmitter or 0 BETTER TRANSMITTER SITES power pack (espe- PATENTS HE importance of location in radio work cially designed for the 245). TRADE is indicated by the announcement -MARKS of the FLECHTHEIM SUPERIOR DON'T LOSE YOUR RIGHTS Westinghouse Company that the transmitters TO PATENT PROTECTION of KDKA and operated VOLTMETERS Before disclosing your invention to KYW, by that corpo- anyone send for blank form "Evt- ration, will be moved to more favorable sites DF..NCE Or CONCEPTION' to be signed in to increase If you and witnessed. order the effective area covered by them. Tests carried out by engineers haven't one LANCASTER & ALLWINE indi- of our 0- (Registered Patent Attorneys) cate that KDKA's power will be most ef- 300 DC, 0- 475 OLIRAY nLDG., WASHINGTON. D. C. Originators of forms "Evidence of Conception" fective at Saxonburgh, the new site about 500 DC or twenty -five miles northeast of Pittsburgh, at 0 -600 AC & DC met. an elevation of 1,300 feet. es, get one In the case of KYW, (removed twenty-two today. Most miles from Chicago), its aerial will be sepa- essential to rated from the efficient the transmitter building some dis- service man. SONG WRITERS! tance, and placed over a "natural pond "; Substantial Advance Royalties which presumably will serve in are paid on work found acceptable for pub - lieu of the Send For Latest Catalog tion. Anyone wishing to write either elaborate counterpoise -ground of buried wires theic neiwish may submit A. M. FLECHTHEIM work for free examination and advice. often used. Wooden masts, 110 feet high, Pastezperienesunneressary.New demand created by "Talking Pictures ". fully de- will avoid the absorption of the wave, and & Co., Inc. scribed in our free book. Write for it Today- Newcomer Associates consequent loss of field strength in certain 136 Liberty St., New York, N.Y. 751 Earle Building, New York, N. Y. directions, which metal towers cause.

www.americanradiohistory.com December, 1929 RADIO -CRAFT PRESCRIPTIONS OF A RADIO START tó PLAY DOCTOR Very First Day/ (Continued from Page 248) Pleasant, band) and connect it across the an- Easy broadcast to Lessons tenna and ground. (It may be convenient en Show You try this coil in series with the resistor.-Edi- How! tor.) If the coil is provided with a primary, OF this should be ignored and the secondary alone THOUSANDS used; the primary winding may be removed three - A lifetime of rich, wholesome fun. 5 days' if desired. Coils obtained from an old free trial in your own home. A year to pay. dial tuned- radio- fìequency set were used and, whole world seems different when you learn to since they were of the basket -wound pattern, 1'IIEplay and now you can play the most spectacular of No long wait- RADIO all instruments -the Deagan Xylorimba. took up little space. ing. No finger or lip exercise. No tiresome practice. Start to play very first day even if you can read note of music right now. Soon you'll be the 'hit" of Carlson etery party. Maybe, like the Musical Ilallmans (Read- Hum in Stromberg- ing. Pa.) you'll make S6S a week spare timo. se! let's all about the free trial In one instance a Stromberg- Carlson set No. St Our Big Free Book fifer. the easy lessons, the JOB wonderful payment plan. No cost or obligation -send 635 developed a hum after a period of about in coupon today. six months' steady use. There are two "hum J. C. Deegan. Inc., Dept. 1939, 1770 Berteau Ave.. Chicago. Send without obligation, full details of Free Trial offer and e easy-payment plan of the Deagan ylorimba. Name Address

Radio repair mechanics earn from $1800 to $4000 Radio Operators $90 to $200 CHEMISTRY a year. a month (board free). IF you are interested in chemistry, you will Pick the job you want -see what be pleased to hear that a magazine written In ertain of the Stromberg-Carlson models, as only 9 months training will do! in plain English, containing a vast amount of expl fined in these columns, plate rectification is and the more emp oyed. This alters the detector circuit only MAKE big money in Radio. It's a information for the beginner from advanced student in chemistry is being pub- to the extent shown. big pay business. Salaries lished now. $2,000 to $25,000 a year are common. manufac- balancers" at the rear of the chassis, and these Broadcasting stations and Experimenter turers are now eagerly seeking trained Chemical when adjusted failed to reduce the hum. In- of interest- men ... Thousands of ships require is a Monthly Magazine chock -full dications were that the filament supply was men who know experienced operators. ing Departments, edited by grounded; undoubtedly the audio filament sup- how to state worth -while facts. Easy to Learn at Home With This ply, since the dial light went out when the Outfit Departments about: Magnificent Laboratory There are balancer" was turned as far as it would of America "Chemistry in the Home" "History of "hum The Radio Corporation - go in one direction and the "hum balancer" sponsors this marvelous, simplified Chemistry" - "Experiments in Chemistry" - Prepare for of Celebrated Chemists" of last audio tube when turned did not effect home training course ... "Biographies - success in every phase of Radio ... by "C.hemistry for the Beginner" - etc., etc. a balance. given will receive when actual experience with apparatus Send the coupon below and you This conclusion proved correct for, with this course...learn how to solve all information about this Magazine. the dial light bracket was examined, it was every Radio problem. found to be bent forward and one side of the Only Course Backed by CHEMICAL INSTITUTE OF NEW YORK, lamp socket was making contact with the Radio Corporation of America 16 East 30th Street, New York, RC -12 the '71A filament Gentlemen: dial and thereby grounding This gigantic organization sets the Please send me free of charge all informa- standards for the entire industry ... tion about ']I-A (2ND A. r) and sponsors every lesson in the are posted CHEMICAL EXPERIMENTER course. That's why graduates '26 I'll in newestdevelopments in Radio.That's TRANS Name why they are always in big demand. Money Back if Not Satisfied Address 3 '27 FIL. As a student you will receive an agree- G TRANS TWISTED ment signed by the president of this Town PAIR school assuring you of complete satisfaction upon completion of your 3 '7rA FIL. si training your money refunded. 2 TRANS. -or READ THIS FREE BOOK Free...evervthing you want to know about Ra- HUM BALANCER' dio ... 50 fascinating pastis of 1200;:: packed with pictures Choice POWER and descriptions showing lytl TRANS. brilliant opportunities in Newest thisfast- growing profession. See for yourself why R.I.A. training has placed thou. '60 FIL. sands of men in well paid t TRANS. RADIOI I positions- usually from 3 to 10 days after grad- q,gg;IV.e1. uation. Mail this cou- VALUES pon now and receive for our 1930 rata- T ¡r Fig. 3B your FREE BOOK. SENDlog. Filled with amazing valves \mac r,-; The power -transformer windings of the Strom. in screen grid radios, push puU 1::q berg- Carlson "635" and "636," showing how a audio, consoles, kin, parts. RADIO INSTITUTE ground in the filament circuit introduces hum. of AMERICA All standard makes gad 1s I l' . guaranteed merchandise. Dept. RC -12, 326 Broadway New York, N. Y. of set in question is WESTERN RADIO MFG. CO. circuit. The portion the Gentlemen: Please send me your FREE 50 -page W. LAKE ST. L IGA LO 'Li.. shown in Fig. 3B. This trouble has been ex- book which illustrates the brilliant opportuni- Q.,g ties in Radio and describes your laboratory - perienced also in the 636 type Stromberg- method of instruction. in Carlson receiver. (The change the detector Name. circuit of these models with plate rectification When writing to advertherr, please mention Address RADIO -CRAFT. is shown in Fig. 3A.)

www.americanradiohistory.com 278 RADIO-CRAFT December, 1929

Letters From Radio Service Men (Continued from Page 246) 44TH ST. The Manufacturer's Part The real answer to the question must come HOTEL from the R.M.A. Manufacturers must, in the Just East of B'way One of New York's near future, seriously consider the independent service station. Few of the stores selling New Hotels at Right Prices radios pay enough attention to their service department; thus forcing the customer to call A high class hotel in the very center in an independent service man when they want satisfactory service. It's up to the manufacturer of Times Square and within walking to see that these men are supplied with all the information necessary to intelligently repair the distance of all Shops, Theatres, etc. sets that have passed the usual guarantee, if the manufacturers want to keep in the good graces of the public. 300 Rooms -300 Baths Human nature is about the same the world over. When an independent service man writes to a manufacturer for a circuit dia- $2.50 & $3.00 per Day gram and continuity chart, and for answer is told it is not the company's policy to A Restaurant of Unusual Excellence furnish any except to their authorized dealers, that company loses money; because a lot Special Weekly Rates of high- priced advertising is going to be nullified in the circle of possible buyers that service man deals with. It's taken me quite a few years to make my collection of circuit diagrams, continuity charts, and other information of past and pres- Tempered Steel 1 00 ent sets, and in acquiring it I also have been 10 Tools in One Screw Driver $ snubbed by certain manufacturers, who forgot I would repair their sets regardless of whether Natt'e* they sent me the information I asked for or ASMALL but handy article which serves for not. every possible need of the all -round mechanic. Standard Service Diagrams Invaluable in any emergency. An excellent combination of utilities for Let the R.M.A. take this up. Have the the household -every necessity featured: individual companies furnish a light cardboard HAMMER - KNIFE - CAN- OPENER - Bottle sheet for each receiver; one side a complete High Carbon circuit diagram, the other side giving a con- SHARPENER - NAIL - WEIGH -SCALE -RULER Opener PULLER - BOTTLE - Knife Sharpener tinuity chart and what other information is -TABLE OF WEIGHTS OPENER - SCREW necessary for testing the tuner and power DRIVER- CORK-SCREW AND MEASURES. pack. Let one standard set analyzer be the Cork Just glance at the illustration and you will medium for making all tests and checks; Screw see how really useful this article is. The eventually all service men will revamp their "Ten in One Tool" is 10 inches high and old ones or buy a new one. Have these finely nickel -plated. Adjustable charts at one central distributing point and advertise that service The new tool is not only handy in the Screw Weigh any man writing under household, but every TOURIST, AUTO - Scale his own letterhead or that of the store he IST, CAMPER, PICKNICKER, BOY - 15 Pounds works for, can have them either free or for SCOUT, FISHERMAN, CANOEIST, etc., the cost of printing. Do this, and each manu- should carry in his bag one of these in- Table of facturer will save many more dollars than dispensable combination tools. No SHOP, ;5s Inch Weights it costs him; besides having a bunch of serv- OFFICE, STORE, GARAGE, FARM, Steel Rule and ice men (and they are many) boosting instead BOAT, should be without one. PRICE Measures of knocking. Not only that, but the manu- $1.00 POSTAGE PAID. facturer will have a check on these men who Be the first one to own the "Ten Tools in are such a "menace" to their slipshod dealers' One" in your own town. service departments. Most of the independents are giving better Send your order today, pin a dollar bill to Can coupon below and the shipment will go Opener service because they have dollars invested, forward to you the same day as received. where the average dealer has pennies. Out of the limbo of experimentation and guess- Only work, we (my son and I) are building up a GRENPARK TOOL CO. 10 Inches 245 Greenwich St., High profitable business, and are commencing to enjoy a reputation for good honest service; New York which, I believe, is what every service station should strive for. The money end will Grenpark Tool Company, R -12 Weigh Scale Mail take care of itself. 245 Greenwich Street, Hook How do I test a radio? New York, N. Y. Part of my "system" I've Enclosed find $1.00 for which please Coupon explained, but I send me prepaid your "Ten Tools in One." have also told you how we could have a real system that would increase the good will Name of the public toward the manufacturer, and Send for Yours save money for the customer, for in the end Add rev , it's always the customer who pays. Town State TO DAY D. F. MORRISON & SON, Elmira, N. Y. By "The Old Man" himself.

www.americanradiohistory.com December, 1929 RADIO-CRAFT 279

VACUUM TUBES FOR RADIO tube plotted against plate current in milliamperes. The value of "mu" and the curves RECEPTION for the plate resistance and mutual conduc- (Continued from Page 256) tance are plainly shown. The use of a graph Here's the gives a very clear and concise a filament drawing half an ampere, as in the of this type impression of the characteristics of the tube '12 type. It has a low amplification- factor and impedance, and for this under different conditions. Answer a very low output The first three tubes in the power -tube series reason it is useful only in the last stage of to every question about the principles, just described, have very definitely limited out- the set. The plate current of this tube is too methods, or apparatus of radio trans - values, beyond which considerable dis- high for the average loudspeaker winding and put mitting and receiving. A complete tortion occurs. Where more than a moderate therefore some type of output- coupling trans- course in radio operation in a Single signal strength is required, as in the case where former or impedance must be used in order Volume a large room, an auditorium, or an outdoor to protect the winding from breakdown. This is to be filled with either radio or phono- output-coupling device may be used to balance area, THE graph music, some means has to be devised the impedance values of the tube and speaker, to get a larger value of undistorted output. if desired, in the manner described some time It is comparatively easy to obtain a grid ago. swing sufficiently large to produce tremendous RAI 10 As in the case of the '12A type, the '71A volume, especially with the new screen -grid a bat- filament may be operated from either tubes. It is necessary only to obtain some tery or a step -down transformer. The un- this wide MANUAL device which will successfully handle is much distorted output of the '71A tube grid -voltage swing, and couple it to the speak- A New Edition described higher than that of the two tubes er, in order to obtain the desired results. Complete new chapters on aircraft radio equip- except where ment; Practical Television and Radiomovies with above and, with most receivers, radio in- volume instructions for building a complete outfit; extreme volume is desired, sufficient The Largest Power Tubes terference; 100% modulation; latest equipment of the can be obtained without overloading this tube Western Electric Co.; the Marconi Auto -Alarm Sys- the past year can be increased almost three The '10, '50 and '45 tubes are a series suc- tem; and many other developments of The output value All this information is added to the new edition and, times by using the "push- pull" system, with cessively designed with this point in view. The besides, the entire book has been brought right up to RADIO MAN- two of these tubes. last -named tube is the latest and, because of date with much new material. THE UAL continues to be the one complete and up- to -the- the comparatively low plate voltage required field. Fig. 3 shows the wiring of a push -pull am- minute handbook covering the entire radio it is becoming very plifier. It will be noticed that two resistors as well as the high output, types of sets. are connected between the filament and the popular in all three tubes are heavy, plate wiring; they are used to obtain "C" bias The filaments of these A Handbook to bring them to the and filament balance. RI is the filament -bal- and require high currents for For this reason, altern- ance resistor; it has a value of ten to thirty correct temperature. Students invariably used as the source of ohms, and the adjustable center tap permits the ating current is Amateurs The filament of plate and grid circuits to be connected to any supply in commercial practice. Operators tubes, the '10, requires 7.5 point on its length. In this way, these two the first of these Inspectors of 1'/y amperes. This tube circuits may be connected to the effective volts at a current factor than the center point of the filament circuit, with the has a higher amplification reason, it is more suit- result that the A.C. hum is reduced to a other two and, for this in channels where the grid swing Twenty big chapters minimum. able audio cover: Elementary is not very high. Its undistorted output also Electricity and Mag- other resistor R2 gives the "C" bias. The is lower than that of the others; and these netism; Motors and (We have explained the operation of these Generators : Storage Batteries characteristics place a limit on the use of the and Charging Circuits; The resistors in the previous issue of RADIO- CRAFT, tube. Fig. 5 gives the characteristics of the Vacuum Tube; Circuits Em- method of figuring the correct ployed in Vacuum Tube and given the tube plotted against plate voltage up to 300. no further explanation should Transmitters; Modulating value; so that Filament voltage 7.5; current 1.25 amperes Systems and 100% Modulation; Wave -meters; A 2150 -ohm resistor gives a Oscillators ; Wave Traps ; Marine Vac. be necessary. (A.C. from a step -down transformer); Piezo -electric drop at 20 milliamperes plate current.) uum Tube Transmitters; Radio Broadcasting Equip- 43 -volt Plate voltage, 250 to 450; ment; Arc Transmitters; Spark Transmitters; Com- this resistor is a The condenser shunting Plate current, 12 milliamperes at 250 volts, mercial Radio Receivers; Marconi Auto -Alarm; Radio piece of apparatus; for other- Beacons and Direction Finders; Aircraft Radio Equip- very necessary 16 at and 20 from 400 to 450; currents in the plate and 350, ment; Practical Television and Radiomovies; Elimi- wise the signal Grid bias, 18 volts at 250 volts, 27 at nating Radio Interference; Radio Laws and Regula- grid circuits must pass through the resistor, tions; Handling and Abstracting Traffic. 350 and 35 at 425 volts; in a reduction of signal An immense amount of information never before and this would result Plate resistance, 5600 ohms at 250 volts, available including detailed descriptions of standard strength or a loss of quality. The only other equipment is presented. 5000 at 425; are the transformers, parts in the amplifier Amplification- factor, 8; usual type of push -pull Prepared by Official which are of the Undistorted output, 340 milliwatts at 250 No comment is necessary about these Examining Officer design. volts, at 350, 1540 at 425; is requirement is that 925 the author, G. E. STERLING. Radio Inspector instruments; the only The largest tube of the series is the '50, and Examining Officer, Radio Division. U. S. Dept. quality, in order to main- of Commerce. The book has been edited in detail by they be of the best which was designed to supply a very large in the output. ROBERT S. KRUSE, for five years Technical Edi- tain high fidelity amount of current to the speaker, and will tor of QST, the Magazine of the American Radio Re- lay League. Many other experts assisted them. Since its development, the '71A tube was handle a very wide grid swing without over- used in almost all the popular commercial loading. Like the '10 tube, this valve requires the appearance of the In Free Examination sets until recently; but 1.25 amperes for the filament at 7.5 volts. The new edition of The Radio Manual.' has just new '45 tube with its higher output value has this case also, alternating current is invariably been published. Nearly 900 pages, 369 illustrations. its supremacy to some extent. The This tube will Bound in Flexible Fabrikoid. The coupon brings the threatened used as the source of supply. volume for free examination. If you do not agree following are the figures for the '71A: give more than three times the undistorted out- that it is the best Radio book you have seen, return volts; current 0.25 -am- it has a lower amplification it and owe nothing. If you keep it, send the price of Filament voltage, 5 put of the '10; $6.00 within ten days. be given a wider pere: factor, however, and must Order On This Coupon Plate voltage, 135 to 180; current 16 mil- grid swing than the smaller tube, to obtain 135 volts, 20 ma. at 180; the same volume. The advantage is in its liamperes at D. Van Nostrand Co., Inc., Grid bias, 27 volts at 135 plate volts, 40t/z greater power -handling ability. has a very low 250 Fourth Ave., New York volts at 180. (When A.C. is used for the Like the '71A tube, the '50 Send me the Revised Edition of THE RADIO to supply, it is necessary to increase this A.C. plate resistance, and it is advisable MANUAL for examination. Within ten days filament I will return the volume or a device of the type which per- after receipt either bias value by one half the filament voltage use coupling you $6.00, the price in full. - speaker imped- send in this case, 2% volts.); mits matching the plate and (Radio Craft 12 -29) and cur- Plate resistance, 2,200 ohms at 135 volts, ances. Because of the high voltages special pre- Name 2000 ohms at 180; rent needed to operate this tube, using it. If a St. and No. Amplification -factor, 3; cautions must be observed in of the filter Undistorted output, 330 milliwatts at 135 short -circuit should occur or one City and State down, result might be a volts, 700 milliwatts at 180. condensers break the necessary to use the high- Fig. 4 shows the characteristics of the '71A fire. It is therefore

www.americanradiohistory.com 280 RADIO-CRAFT December, 192;

est grade of condensers in all the high -voltage circuits of both the amplifier and the plate - Orders - Inauiries supply unit; and it is advisable also to place CanYou Outguess fuses in both of the primary leads of the power Can be transformer, to prevent trouble. These fuses O.Henry should be rated at 5 so I+ about amperes, that they will melt very quickly. wiring !cured The of Can you look ahcad in an O. I leory by the amplifier should be done with extreme story and sec the unexpected denou- care and well- insulated wire must be used. ment, the strange twists of plot, the breath -taking finish? Try it? If you AIL Filament voltage 7.5; current 1.25 amperes; succeed you can out -think the best minds in the world, for the genius of Plate voltage, 250 to 450; O. Henry sets the wits of the brilliant Plate current, 28 milliamperes at 250 volts, people of all lands working at top ma, at 300, 45 at 350, and 55 from 400 to speed and still he amazed them all 35 He is the supreme master of the "trick" 450; ending. luring you into sudden laughter POLK' /REFERENCE BOOK while a lump still lingers in your Grid bias, 45 volts at 250 plate volts, 54 throat- making you gasp by a sudden and Mailing List Catalog at 300, 63 at 350, 70 at 400 and 84 at 450; livid flash of horror in the midst of a smoothly flowing tale. Gives counts and prices on over 8.000 Plate resistance, 2100 ohms at 250 volts, different lines of business. No matter what your business, in this book you 2000 at 300, 1900 at 350 and 1800 from 400 Stories of Wit and Pathos will find the number of your prospec- to 450. Gentle i O. Henry, but manly tive customers listed. strength s glows in every irilc Valuable Information showing how to Amplification- factor, 3.8; sentence: tender with the suf- use the mails to secure orders and In- fering; ever kind to the under quiries for your products or services is Undistorted output, 900 milliwatts at 250 log; clinch ling with the light- given. hearted- drawing always from volts, 1500 at 300, 2350 at 350, 3250 at 400 his unplumbed depths of un- \C'rlte for FREE Copy derstanding the sparkling cry- R. L. POLK & CO., Detroit, Mieh. and 4650 at 450. In push -pull, two '50 tubes stal of sincerity. A great Largest CIty Directory Publisbers In the will give over thirteen watts -sufficient to writer, yet the most entertain- World. Branches In Principal Clues ing and thrilling companion.o Mailing List Compilers- Business Statistics operate a battery of dynamic speakers for a Reading his stories is like Producers of Direct Mail Advertising theatre or public address system. The Master Story The Type '45 Tube Teller At Last!- a book containing all The latest of the power -tube series is the the rules of commercial and govern- new '45 type, now coming rapidly into favor. it ment radio traffic-and operating reg- It will give a power output between those of ulations. the '71A and the '50, with comparatively low The Only Book of Its Kind. plate voltages. It is designed primarily for Why nog to a more brilliant operation in domestic A.C. sets and, for this 1'y-teller titan you ever DO YOU new.a it is works immeasur- READ? Radio Traffic Manual and service, it incorporates a very sturdy fila- ably enrich the limited library. ment which, however, is made for a 2.5 -volt and grace the shelves of the F o r entertain- most crowded. ment? For es- Operating Regulations supply. cape from daily 53 BEST STORIES drabness? For The tube is designed to operate at plate romance. adven- By R. L. Duncan voltages from 180 to 250 volts maximum. In Less tban ture. thrills? To and C. E. Drew cents each sharpen your electrical characteristics it is similar to the 4 $1.97 wits or exercise You are now offered for the first your emotions? RADIO INSTITUTES '71A in that the amplification factor is 3.5, the time 53 engrossing living. selected Whatever your OF AMERICA stories, handsomely. and durably reason. O. Hen- plate resistance is 1900 ohms, and the mutual bound in leatherette, stamped with ry scores a last here is a conductance is 1850 at a plate voltage of 250. gold. 500 pages, all for the price hull's -e ye on ATbook for stu- of only one ordinary short novel. every point. dents, amateurs, and The '45 tube is not interchangeable with the radio operators who '71A, however, because of the lower voltage CUT PRICE COUPON contemplate entering required for the filament. When inserted in Grenpark Company. Dept. R.C: 12 the commercial field. 245 Greenwich St.. With the help of the socket designed for the '71A, a '45 will New York. N. Y. this little book -the burn out, if the filament winding of the power Please send me O. Henry's Best Stories at the only complete one of cut price of $1.97. I enclose stamps. check or its kind -you may learn quickly transformer does not go first. The '45 filament M. O. for the amount. (Check which). and easily all the government requires 2.5 amperes to bring it to the correct and commercial traffic rules and Name temperature; and a fluctuation of 5 %, above operating regulations. Address Duncan and Drew, the two well -known authors or below the rated voltage of 2.5, is permis- of "Radio Telegraphy and Telephony," have set sible with no ill effects. The last -mentioned City and State forth clearly and accurately the in 181 pages all - information on the subject that you will want. Every characteristic tends to reduce the effect of line thing from Morse Code and Conventional Signals to voltage changes which have been so disastrous the Issuance of Radio Operators' Licenses is included in detail. An excellent index in the back of the to tubes in some locations. book makes every topic easy to locate. One precaution must be observed in oper- $2.00 ating the '45 tube; the grid bias must never be PATENTS removed. If the "C" battery should become On Approval Coupon short- circuited, the plate current would in- John Wiley and Sons. inc.. Protect Your Ideas I 440 Fourth Avenue, New York. crease sufficiently to overheat the elements and Gentlemen: Kindly send me on approval Duncan and Drew's "Radio Traffic Manual." At the ex- would probably cause permanent injury. It piration of ten days. I agree to remit 52.00 or re is desirable to obtain the grid bias from a re- Write for Instructions, turn the book postpaid. sistor in the plate -return lead; it will be found free on request - - or Name that this compensates almost completely for send drawing or model Address changes in plate potential. By this we mean for preliminary exami Reference R.C. 12 -29 that, if the plate voltage either increases or de- nation of Patent Office 1 creases, the grid bias also increases or decreases, thus maintaining the balance. This is records TO NEW READERS because the change in voltage causes a prop- Promptness Assured with A few copies of the July, August, ortionate one in the plate current. When the Best Results September, October and November plate current changes, the voltage drop through issues of the resistor does so too (according to Ohm's OQd law) ; with the result that the "C" bias is RADIO -CRAFT altered proportionately. can still be had at the regular price of A very handy chart of plate- current values Carl Miller 25c each. Send stamps, cash or money for different tube charts has come to our at- PATENT ATTORNEY tention, recently, in the technical bulletin of order to: FORMER MEMBER EXAMINING CORPS, one of the large tube manufacturers; this is U. S. PATENT OFFICE RADIO-CRAFT reproduced as Fig. 1. It is very handy data for 265 McGILL Building WASHINGTON, D. C. 98 Park Place New York, N. Y. the service man to keep beside his set tester.

www.americanradiohistory.com December, 1929 RADIO -CRAFT 281

A RADIO WORK BENCH SKINDERVIKEN (Continued from Page 258) Transmitter Units The table may be stiffened as indicated in Fig. 3, if desired, by the use of a "spreader" 95c consisting of two 101/2" lengths of 2x4 at the bottom and a longitudinal brace of the same stock, 38%" long. The table is then completed by fastening on, for its top, the two widest boards (44 "x 10 ") with the 21/7" flat -head screws, counter- sunk in and mounting the binding posts. The duplex A.C. outlet may, perhaps, be more conveniently first attached to the frame. Two The Test Board for ` AUDIO To assemble the back of the bench is very $1.75 simple. The ceiling material used is grooved on TRANSFORMERS Have hundreds of uses. Every amateur should have one edge of each piece, and tongued on the other two or three of these amplifiers in his laboratory. Worthy of the A FEW USES FOR THESE UNITS to fit the groove of the next. Start six inches from the bottom of the cleats; and nail the HAMMARLUND SPEAKER /t ,:at first piece of ceiling to each cleat, with finish- ing nails through both grooved and tongued Name Plate sides. Each succeeding piece need be nailed DESIGNED primarily for the new "HiQ- only through the tongued side; and the tongue 30" Custom -Built Receiver, Hammar- fund Transformers are a revelation in am- is trimmed evenly off the topmost piece. The plifying power and tone fidelity over the test -board foundation may now be placed flush entire audible frequency range. BUrtW The large cross- section core of specially : e ./ against the back of the work -table, to which treated laminations permits high primary rLr1t`_. it is firmly bolted. currents without saturation. Completely shielded. Pigtail terminal leads for sub- The meters are taken from their mountings panel connection. (if any) and remounted in tO KAM, D[COVtD the bakelite panels; Four types: -First stage, Push -Pull Input, OD Lau0 tKANA .MIDUnCR- wires are run to the phone jacks, Push -Pull Output for magnetic speakers, ORID LEAR- -tip which are mounted in the panels Push -Pull Output for dynamic speakers. and, of course, Hear them! Try them! They will greatly .RADIOAMPLIFIER- designated on the outside of the panel above improve the output from any circuit. ''., , each. The panels then are fastened to the Details Write Dept. RC12 for test- board, using 1 -inch sleeves, or spools over ..i screws, between the board and each panel. HAMMARLUND MFG. CO. I . I -pNE $TAOS The final arrangement is indicated AMPLIFlCATION ,' in Fig. 3. 424 -438 W. St., York ' 33rd New

RADIO -CRAFT KINKS 3trl, sctfbli. nadld ."u p l 11 .w \ JI. (Continued from Page 259) ámmärluncl r. cord and then pulled through the will wa tube 11,164 t PRODUCTS make excellent contact. . D. Mt.w.D = -TALKI,IL UGMT _OETEROa (4) Pass the lamp cord through the wide -COOL . ;'. opening of the handle and pull through the

w-e. small hole (Fig. 1B). Q (5) Push the brass tube into the handle f°" :U71` 'w, ÿ` tightly. (6) Leave the brass caps on the battery N --- Im carbons. Rub the other end back and forth .w.._ -aALOWiM [WAIL AMDlanta.+ on a file to shape in any manner desired. 12 PAGE INSTRUCTION BOOKLET Take flame -spreader out of gas tip (Fig. containing suggestions and diagrams for innumerable uses, furnished with each unit. 1C). (7) Solder one dip to lamp cord and the WE PAY $5.00 IN CASH other two clips to another piece of lamp cord for every new use developed for this unit about 2 ft. long. and accepted and published by us. Operation: Connect the soldering -iron clip tur OUT 1930 cata- P. G. MICROPHONE TRANSFORMER SENDlog. Filled with amazing value. a A Modulation Trans- to one terminal of battery or transformer, con- in screen grid radios, push roll former specially de- nect one clip on other wire to other terminal. audio, consoles. kits, parts. signed for use with a standard makes and JE, the S k i o d e rviken Insert the carbon rod into the gas tip through guaranteedd merchandise. Transmitter Unit. the large end of the tip and screw on to Has many other WE TERN RA010 MFG. CO. uses. Pri- brass tube. mary resis- $2 Connect the other clip to object to be sol- tance, %- dered; or, if object is small, connect the clip ohm ; secondary, 55 ohms. FOR SALE AT LEADING DEALERS to piece of solder. Hold solder close to ob- ALUMINUM BOX SHIELDS Or Order Direct. Using Coupon Below ject to be soldered and touch with solder. $1.75. We BealBeautifulny sise mdordth,245,hounó"- SEND NO MONEY Pickle Bottle Antenna Coil When the postman delivers your order you pay him $1.95. for whatever you have ordered, plus a few cents ERRATA Readrite meters $.95 and postage. up. In the October issue of RADIO- CRAFT, page Full line of Pilot parts - PRESS GUILD. R -12 -29 lowest prices. 16- 18- R -E5sT 301Is r., NEW YORK, N. Y. 1 58 , the ground lead on the "B" side of the Please mail me at once as many of the following Speaker relay -one or two R.F. transformer primary in the plate circuit of speakers ar once. items as 1 have indicated. ..Skinderviken Transmitter Units at 95c. for 1; V2 should be removed. Instead, a fixed con- Full Stock of Ameetran $1.75 for 2; 32.50 for 3; $320 for 4. denser connects from the socket leads of the ....P. G. Microphone Transformers at S2. Genuine Baldwin Type "C" screen -grids V1 and V2 to phones, a necessity for When delivered 1 will pay the postman the cost of tubes ground. of the items specified plus postage. In the November issue, page 199, a fixed short- wave reception, $3.65 a pair. Name condenser should be inserted as a by-pass in Address the ground lead which is shown connected ELAN THE RADIO MAN, Inc. 89B St. EST. 1923 New York City State around resistor R2. Cortlandt

www.americanradiohistory.com RADIO-CRAFT December, 1929 COOPERATIVE RADIO 0014iles e I LABORATORY onaGallo (Continued from Page 261) "Trouble Shooter's According to a recent article by tho plifier tube where the required bias is in the president of the world's largest motor neighborhood of 6 volts. As usual, the re- research corporation, there is enough Manual" energy in a gallon of gasoline If con- sistor must be by- passed with a heavy con- verted 100% In mechanical energy to run a four cylinder car 450 miles. denser; 1 -mf. is sufficient, and it need not be a high -voltage expensive unit. By JOHN F. RIDER NEW GAS SAVING INVENTION ASTONISHES Shielding the Hybrid's Input Wiring Diagrams of All CAR OWNERS The only shielding that has been found A marvelous device. already installed on thousands of cara, has accomplish- necessary in this hybrid -tube circuit, on Well Known Receivers! ed wonders In utilizing a portion of A.C. operation, is in the grid circuit of the this waste energy and is producing Besides 22 chapters covering thoroughly the mileage tests that seem unbelievable. hybrid tube. The lead from the crystal to Not only does it save gasoline. field of trouble shooting, this volume contains but it also creates more power, gives the grid of the tube should be as short as the wiring diagrams of models, as obtained direct instant starting, quick pick -up, and eliminates carbon. from the factory, a wealth of hitherto confiden. possible and, even then, should be protected tial wiring information released for the first time FREE SAMPLE and $100 a Week from external fields by shielding, which should in the interest of producing better results from To obtain national distribution quickly, men are being receivers. You will find these diagrams alone appointed everywhere to help supply the tremendous de- be well grounded. The grid biasing of the well worth mand. Free samples (undated to workers. write torts$ the price of the book. The wiring to E. Oliver, Pros., for this free sample and Ws "detector" or hybrid tube is a real problem. diagrams are of new and old models, of receivers money making offer. Fig. 6 shows two sketches-with grid bias and accessories, and u to some of the set manu- WHIRLWIND MFG. CO. (A) and without it (B). In the latter case, facturers, all the models they ever produced are 999 -41 E. Third St., Milwaukee, WISC. shown in wiring diagrams! Here is the list of there is nothing to worry about. The grid receivers, etc., diagrams of which are published is merely grounded, and so is the cathode. in this most important and valuable book: To apply a bias, however, it is best to em- R. C. A. ZENITH ploy a small separate "C" battery. Such a 60. 62. 20, 64. 30, 105. 39. 39A. 392, 392A. 40A, 51, 35PX, 35APX, 352PX, battery should last at least a year, and it 16. 32, 50, 25 AC, atsrgtp- 28 AC, 41, Receptor 3S2APX. 37A, 35P, S,P.U., 17, 18, 33. 35AP. 352P, 352AP, 34P. prevents all manner of trouble from hum, 342P. 33. 34, 35, 35A. which the biasing resistor will introduce into FEDERAL 342. 352. 352A, 362. 31. Type P series filament, 32. 333. 353A, power the circuit. You see, the plate current of the type E supply ZE17, power sup- series filament. ply ZEl2. RADIO hybrid tube is so small that proper value for type D series filament. , 5-/ Model K. Model H. -' the resistor can hardly be figured. Operat- MAJESTIC VALUES i!!rd41 ATWATER -KENT ing the detector grid on a cut -off bias, and 1015, 12. 20. 30. 35. 48, 70. 70B. 180. power peek for our 1930 cata- 32. 33, 49, 38. 36. 37, 7BP3, 7P6, 7P3 (old inserting the 2- megohm resistor in the wiring) 8P3, 8P6, 78P6, SENDlog. Filled wich amazing values plate 40. 42. 52, 50. 44. 43. radios, push pull lead, should be sufficient reason for a 41 power units for 37. in screen grid min- 38. 44, 43, 41. audio, consoles, kits, parts. ute plate current. FRESHMAN All standard makes and CROSLEY Masterpiece. equaphase. guaranteed merchandise. G. G -60 -S power sup - With all the "C" biases thus determined, it XI, Trirdyn 3R3, 601. ply. L and I.S. GIS, K. is now an easy matter to follow 401, 401A. 608. 704, B K -60 -S power supply. WESTERN RADIO MFG. CO. the signals and C supply for 704. ® W. LAKE ST. CHICAGO ILL. through the rest of the circuit. The tuning 704A. 704B. 705. 706. STROMBERG- into the hybrid tube is accomplished in the STEWART- CARLSON regular manner. The .015 -mf. fixed con- WARNER IA. 2B. 501, 502. 523. 300. 305. 310, 315. 320. 524. 635. 636, 403ÁA Just Published! denser in this tuned grid circuit is inserted 525, 500, 520, power plant. 404 RA A sure way of pass- 710, 715. 720. power plant. merely to permit the second and third tuning 5335. 750, 801, 802. 806. ' Mg your Govern- condensers to be ganged. Ganged units usu- GREBE ALL -AMERICAN ment Examinations! ally have common rotors, which force all grids MU1, MU2, synchro- 6 tube electric, 8 tebe phase 5, synchrophase 80, 83. 84. 85, 86. 88, 6 to return to the same point, unless some pre- AC6, synchrophase AC7. tube 60. 61. 62, 63, 66. Deluxe 428. 6 and 8 tube AC power Here are all the caution is taken. This condenser is the pre- lack. caution. It completes the tuning circuit back PHILCO Questions Ph i l - to the rotor of the tuning condenser, but pre- leo -e ect rie. 82. 86. DAY FAN OEM7. 4 tube. 5 -5 tube Completely vents the coil from being short- circuited to KOLSTER 1925 model. Day Fan S 4-tube chassis used in 6 AC. power supply for Answered that point. Hence, the coil can be taken out tube sets, tuning chassis 6 tube AC. 13 power for 7 tube sets. power supply 5524 and 5525. to any part of the circuit for its proper bias; amplifier, 7 tube power motor generator and IN in this case, the small dry-cell battery. pack and amplifier. 6 filter. 6 tube motor gen- tube power pack and erator set. 6 tube 110 amplifier, rectifier unit volt DC set. 6 tube 32 K23. volt DC set.

How to Pass There are also wiring diagrams of Fada, Freed - U. S. GOVERNMENT SOLVING CITY PROBLEMS Eisemann, Colonial, Workrite, Amrad, Sparton and others. Radio License (Continued from Page 265) Size of Book 8y e x 11. -234 pages. Profusely illustrated with charts and full page diagrams. Examinations The "RFT" or balancing resistor shown in By R. L. Duncan and C. E. Drew the "RFX" in the schematic circuit is found RADIO INSTITUTES OF AMERICA only in the last "RFX" in the line; all the RADIO TREATISE CO. DON'T take any chances wich your examinations. other "RFXs" on that "riser" are connected Careful study of this book will insure success in 1440 B'way, N. Y. C. obtaining your Government Radio License, because it to alternate sides of the "riser" and without contains full particulars, questions and answers, on the use of this center-tapped resistor. the latest radio examinations by the government. Send No Money It will not only give you all the data, but through Within twenty feet of the "RFX" is placed will the question and answer method used in the text, the outlet unit" ( "RFO teach you how best to express yourself and put that "radio "); a snap knowledge into words. switch is provided here to control the filament 259 questions with complete answers show you just current for its "RFX." (A delicate relay opens RADIO TREATISE CO., what will be expected of you. Order a copy now and start studying! the filament circuit of the "RFC" on the roof, 1440 Broadway, $2.00 when the last "RFX" in the building is no New York City. longer being operated.) Send me John F. Rider's "Trouble Shooter's On Approval Coupon Manual" and I will pay postman $3.50 plus a John Kiley and Sons. Inc.. It is preferable to install the wiring (an Fourth Avenue, New York. few cents for postage on delivery. It is under- i entlemen: Kindly send me on approval Duncan all- conduit job) when a building is being stood that my money will be refunded if I am and Drews "Ilow to Passe'. At the expiration built; for it is then most convenient not entirely satisfied. of ten days I agree to remit $2.00 or return the to place hook postpaid. this conduit and all fuses, together with the Name Name "RFC," the "RFL5," "RFXs" and the "RFOs." Address Address In one building on 107th Street in New State Reference R.C. 12 -29 City York City, such a system serves the owners

www.americanradiohistory.com December, 1929 RADIO -CRAFT 2S3

of approximately thirty different types of radio receivers, including regenerative sets. How- ever, since each "RFX" acts as a blocking tube, there is no interference between receivers and reception is reported to be several 1V.Y.Iticu icu. Scnooí' den hundred per cent better than in a former test when individual aerials were used. An oddity of design will be observed in the Graduate info schematic circuit, in the grounding of portions of the circuit requiring connection to "B + ". 1 The necessary plate potentials, however, are many fields. obtained by this connection; since the "B +" lead from the "B" eliminator is grounded. In- stead of following the usual practice of grounding "B-" and insulating "B +," the reverse AVIATION method was adopted, as shown in the schematic ELECTRICITY diagram; the insulated "B-" leads ate part of the "risers" connecting the "RFC" and the "RFXs." One "B -" lead connects to the grid of each "RFX" tube, and the correct grid bias is obtained by the drop through the resistor R5. (In the same manner grid bias for the '26 tube in the "RFC" is obtained.) Another conduit, paralleling the first, con - . tains the power line from which the power NAUTICAL transformers and switches are tapped off. A ELECTRICITY separate transformer winding is used for the filament of each tube. Regular "junction boxes," such as are used in regular electric - light wiring, are placed at these connections. One filament transformer is located in each ELECTRICAL "RFC" and "RFX "; the power transformer, ENGINEERING filter- condenser bank, and resistor network are found only in the "RFCs." Because this "B" eliminator is standard, for the sake of clarity A full knowledge of electricity, as Here at the New York Electrical School it is omitted from the diagram. taught in the New York Electrical you learn, not by correspondence, but by Maintenance of such a system as this re- School, makes you independent, ACTUAL PRACTICE on full -size stand- solves itself merely into replacing tubes after gives you your choice of either a ard equipment. NO BOOKS used. Indi- they have run their normal life. BIG PAY job with one of the vidual instruction -you can start any day. designed Complete installations have been world -famous electrical compa- This School owns and occupies two seven - to operate in direct- current lighting districts, nies, or a business of your own. story buildings in New York -the city of as well as those where A.C. is available. ELECTRICITY is also a stepping- most opportunities. It is widely known stone to Aviation, Automobile En- as the country's oldest and foremost insti- gineering and other highly paid tution for trade training. That's why big DEVELOPMENT OF MODERN professions. companies eagerly demand our graduates. REPRODUCERS SOUND THE NEW YORK ELECTRICAL SCHOOL (Continued from Page 268) 21 West 17th Street, New York about seventy -two phones (as the writer re- members it) in a room with square ends, and length somewhat greater than the height; the This big 84 -pape booklet gives full Information about the New York Electrical School courses and pleture of the equipment available for only theoretical defect with this scheme, if a -TREE your personal use. Send for It TODAY. It's free. parallel -front wave advancing down the audi- MAIL TODAY ence were produced, would be the production The New York Electrical School of standing waves and these would be mini- 21 Vest 17th Street, New York mized by the mixture of all the notes with Please send me FREE your 64 -page booklet. It is understood that this their different damping, etc. request puts me under no obligation. It is hardly necessary to point out that low tones produce less interference of the kind Name described than the higher ones, in average rooms or a small hall. The difference- or "Tar - Address tini" tones may be just as bad if they are backed by long- sustained components like the "low C" and its "major third." However, all these effects are reduced or destroyed by the Ex Libris presence of fittings, furnishings, tapestry and the listeners themselves in a room. Beautiful Bookplates Construction of Diaphragms DO YOU TAKE PRIDE IN YOUR LIBRARY? We have seen that in a "unilateral" elec- APERSONAL bookplate. with your name on it in- like that in Fig. 6, there sures you against loss of your cherished volumes. trostatic loud speaker, The friend who borrows your book can't fail to be is in the scale of frequencies a "change- over" reminded that it belongs m you point above which the piston action ceases, A bit of the feeling of the great Old Masten is vibrates in distinct seg- captured for you in our artistic Duo -Tone Book- and the diaphragm plates, reproducing old woodcuts and engravings, ments or zones; the smaller the diaphragm, on antique -tint vellum paper. S2 up per hundred, higher frequency at which this takes your name imprinted. Send loe for specimen and the the illustrated catalogue of our unique new series. place. In the "bilateral" reproducer of Fig. 7, the ISKOR PRESS, Inc. change -over frequency is much higher, and a 286 Fifth Ave. (Dept. 9) New York higher voltage from the amplifier output is required to make this effect noticeable. In

www.americanradiohistory.com RADIO-CRAFT December, 1929

both types, the tighter the radial pull on the diaphragm, the better the quality of the reproduction. In the German models a secret aluminum alloy is used for the purpose, in The Most Outstanding Literary discs a foot in diameter and 1/200 of an inch thick; and separated, about 2/100 of an inch. It is tightened by the use of sixteen movable Success in the Magazine World cones, sliding eccentrically into conical hous- ings spaced around a metal rim toward which the diaphragm is pulled by grip on the foil The Twin Magazinesagazines of Scientific Fiction (Fig. 8). The mechanical pull exerted on the metal foil by these cones is extremely high. Temperature changes, within the room range, do not appreciably loosen it. Copper is too Science weak, and steel or iron are inferior in performance; but in the absence of the special (AIR alloy, experimenters may find it necessary to WONDER STORIES use copper -coated or otherwise processed steel. WOHrds An improvement on the single- diaphragm Stories reproducer has been obtained, as shown in Fig. 9, through dividing it into a number of segments by securing it in its "polarized,' or -the future in aviation . . . -colorful scientific fiction stretched position at rest, so that it is im- 100, 1,000 and 10,000 years stories by world's foremost movable along certain lines- eccentric circles and radii. This is done by the use of a stiff hence. authors .. . frame. Since the membrane is already convex toward its fixed armature because of the polar- Enlightenment-entertainment-there's izing voltage, the frame must be slightly con- HOURS of pleasant pastime are a world of it in science fiction, and vex also to fit against it. Furthermore, the well spent in reading stories that it's within the grasp of everyone. diaphragm must be strongly fastened; for, you like -stories that are educational will find plenty You of both in every half wave in the audio -fre- and entertaining- written by men SCIENCE WONDER STORIES - otherwise, with a vision of future flying. You stories by many of the outstanding quency cycle will pull it away from the frame, will read stories that reach beyond writers of scientific literature-auth- and the segments of the diaphragm will cease present day aviation methods-future ors who have spent years in study to be effective as such. As they are, they warfare- gravity nullifiers-cities in to attain literary success in this field. have different points of resonance and change- the air -trips around the world, and You can share their knowledge of over, so that they do not work together to gripping revelations to expect of science, and as well, benefit by their add distortion. (This is German patent aviation 100, 1,000 and 10,000 years contributions to the ever -widening de- 426,839.) hence. mand for interesting scientific fiction literature. Multi-Unit Systems Each issue of AIR WONDER Just read on to the very last word you the best stories and In this system, which has a number of small STORIES gives learn what each issue of SCIENCE in aeronautical scientific fiction, a test WONDER STORIES gives its read- diaphragms mechanically independent, we find on your knowledge of aviation, avia- ers- stories, science test, science ques- that the number used, ranges from eight (in tion news, aviation forum; letters tions and answers, reader's forum and "phantom music," using small speakers in from our readers and book review. book review. series -parallel) up to enormously large numbers. In some modern forms, using "goat - eye' vent -holes, and designed especially to Each issue of AIR WONDER STORIES and SCIENCE promote piston action, there are 675 sound or WONDER STORIES contains 100 pages, including full - air -vents in a mesh -unit, 8 x 12 inches; and page by Paul and famous artists, and a illustrations other 25c as many as 96 units of these are used to form 4 -color cover. Just send in the coupon below with one dollar and you will receive either magazine for eight Copy a "speaker" twelve feet square. months. At the newsstands The In the Reisz electrostatic reproducer, the number is immensely greater; here, as in Fig. 10, we have a dielectric or insulating membrane to which a countless number of gran- Regular ules of conductive graphite are cemented; in SPECIAL a 12 -inch speaker there must be millions of Subscription OFFER them. They are made to form a single con- Rates ductor by the fact that each is in sliding and $2.50 in U. S. Months $ 100 rolling contact with those next to it, while it 3.00 in Canada 8 adheres to the insulating membrane only at the bottom. This instrument is the best illustration of a perfectly loose set of pistons developed to date; but, plausible as its advance notices were in 1926, it does not seem to have STELLAR PUBLISHING CORPORATION Dept. RC -12 been a striking success, even in spite of introducing the refinement of spacing the middle 98 Park Place, New York. of its fixed armature further, from the diaphragm, and thereby permitting the latter to Enclosed find $ , for which my enter subscription for be nearly flat in its vibration over a consid- eight months to erable distance. The design of this speaker is Air Wonder Stories Science Wonder Stories based on extensive experiments, by Hollunder- mark, on the action of conducting granules between the plates of a condenser; and this type Name may yet be a competitor of others better known in the United Stales. Address (Part II of this article will go into further detail with the explanation of the latest revo- lutionary addition to the electrostatic repro- City and State ducer family -the "goat -eye" or "mesh- unit" type; it will appear in a later issue of RADIO - CRAFT- Editor. )

www.americanradiohistory.com December, 1929 RADIO-CRAFT 285

INFORMATION BUREAU this receiver is poor tubeprong contact. Clean the tube -socket springs with sandpaper, similarly clean the (Continued from page 270) tube prongs; and bend up the socket springs, carefully, by placing below them a piece of cord and Makes Any Tube Although 1, 2 and the antenna may all he con- pulling it up. Whether the latter performance is nected together, a refinement, an antenna switch, is necessary, may be determined by gently wiggling LONGERand indicated in the dotted enclosure. each tube; if the receiver suddenly stops operating, Last this is due to an open circuit which will be remedied by restoring good contact. Perform BETTE ZENITH "4R" - RADIOLA "SUPER" - (Q.) Please show a schematic circuit for taking By automatically FINDING A.F.T. CURVE-BRISTOL the "characteristic curve" of an A.F. transformer, keeping voltage "COMPARAPHONE" or for determining its comparative value. (A.) The circuit requested appears in these col- exactly right for (35) Mr. E. R. Prince, N. Parkersburg, W. Va. umns. As shown, it is of value only for obtaining each tube, AMPERITE length- (Q.) A Zenith receiver "Type 4R" works well on an approximation of the "gain" or voltage step -up ens tube life and improves re- three tubes but not on four. Testing has proved of a particular transformer, at 1000 cycles (1 Ice.). ception. Neverwearsout. Insist that the third A.F.T. is burned out (Why are there as compared to another transformer used as a stand- on AMPERITE. A type for three A.F.T.'s ?). .1 cannot get another transformer ard. However, the gain of a complete stage, includ- every tube -A.C. or D.C. $1.10 with mounting (in U. S. A.) REPRODUCER Ji TIP -JACKS FOR At all dealers, CONNECTION 3 BUTTON CARBON :'-STRIP TYPE PICK -UP. +r- AMPERITE (9rporwtlon 1'hls symbol 601 BROADWAY. NEW YORE In a radio diagram FREE-- "Amperire Vest means- Pork.t Tube (:hart.° Irrite I),,, . RC -12, PERITE SELFvie ADJUSTING "?,eastat

(Q.35) The Bristol "Comparaphone." Meant for amplifying the output of this arrangement, thus making it possible to tue a "magnet" pick-up, are shown.

to work properly, although remainder of circuit ing such a transformer, at other frequencies may seems to be U.K. Please suggest a remedy. not be in proportion to this value. Three stages of A.F. (A.) amplification were To obtain a true picture, it is necessary to make a greater selected to obtain volume than could be graph of the values obtained at other frequencies; this NTOLA1+1 with only two stages. obtained Your difficulty is is possible by using an oscillator adjustable to these due to the fact that all the A.F. transformers so far frequencies. Lightning Arrester tried have been of too high a "turns ratio." Use The constants for T3 a transformer with a turns ratio of about of T3 will be determined by the design of oscillator s two- toone. the and the characteristics of the tube selected as VI (dæ voltages indicated are for It is suggested a '12A or 71A tube be used that an '01A). The milliammeter should read nearly as V4. The necessary changes to use the former zero, until the oscillator is started. are indicated in the diagram; they are the inclusion of special "B" and "C" potentials for this tube, (Q.) Please advise me as to how a Bristol no change being necessary in the filament circuit. "Comparaphone" should be connected to eliminate a The odd location of the added "B" unit is oc- loud rushing sound when dynamic reproducers are casioned by the wiring of the "Stage Selector Switch." being tested. How could A.F. amplification be ad Resistors R are 3q -amp. ballasts; 11, L2 and L3 ded to this unit? $100 constitute a "3- circuit tuner," LI being tapped ; L2 (A.) This internment was designed to be used Guarantee Against Lightning Damage is tuned by CI; C2 may have a capacity of .0005 to with a carbon -type phonograph pick -up; too much Enclosed ìn Each Box. It Also Dissipates Accumulated Static Charges. .001 -mf. Units R limit the filament potential to 5 battery current or a poor pick-up will result in this At Your Dealer or Dirges volts, while the 30 -ohm resistor functions as a master rushing sound. The remedy is obvious. control of the potential below that value. CORNISH WIRE COMPANY A.F. amplification may be added, in the man- 36 Church Street, New York City (Q.) What might cause a "Radiola Superheter- ner indicated, in the schematic circuit which appears Maier: of Corwiro BRAIDITE Hook -Up Wire odyne" ( "Second Harmonic" semi -portable) to ap- in these columns. pear "dead" at times, operate well for a time, then As Ti has a lowresistance primary, designed for suddenly go dead? a carbontype pick -up, it may be necessary to change (A.) This is probably due to loose contact at this unit to obtain the desired primary impedance if the "cat' (catacomb). Closely examine all con- a magnetic -type pick-up is used. nections on the aluminum "cat;" this is grounded, The circuit changes required to add A.F. amplifica- and voltage tests may be made with one side of the tion are as follows: break lead at XI and run two meter grounded against it. A milliammeter in the leads, G and P, to the terminal strip indicated in "B -" lead will fluctuate, if there is a break in dotted lines. Run dotted connection X2. Wire the the "B" circuit, during the process of shaking the audio amplifier, following any desired arrangement leads of the set; a similar meter in the "A" circuit of parrs, and connect its terminal strip to the would check defective "A" connections. "Comparator" as shown; R is a twotube filament There is a loop built into the rear of this rec- ballast; CI has a capacity of about .0005 -mf. If a eiver, and it occasionally happens that its connections magnetic pick -up is used, the center tip -jack may be to the sec work louse. Another cause of trouble in disregarded. ARRY this Amazing new vest C p,dket. Ming etre n.00annb out showing it to .trske,pers, bookkeepers profesional men and other.. Atoms cl eanine up with tnis fast seller. Svelto. who STACIE SELECTOR 4 does any kind of figurine needs It tad will buy on .iaht. SWITCH e`11Y - PDX 4. SY Complete Adding Machine Only $2.95 VE -PO -AD duplicates work of tar. adding machine.. Sells for only $2.95. Add.. subtracts. multiplies-in a JOBS. Always accurate-never gent out of order. Over 200,000 ic um You make 100 -;, profit a err sale. Mani If You over had a chance to CLEAN OP BIG MONEY -here It iel

S Sample Ve -Po-Ad FREE Yoe don't need experience. Shapiro mad. OUT UT $175 his first week. Others make 160 to Sinn week as many Vo aan hoar- oovver 84.0n rofit for you. Grasp Write at offer il e il,tof FREE rVe Ad nce d a MONEY -MAILING PLAN. Do it á NOW. C. M. CLEARY 303 W. Monroe St. Dept. 5-A Chicago, M.

90.EA it comes to making sick radio, well, cr WHEN radios (Q.35) Schematic circuit of good better just the Zenith "4R" Receiver, ¡bow- A ing improvements. tteMeAlGtL-Cp` Q T /rErrt) there's a ,` Purpose^ For literature, write CLAROSTAT Mfg. Co. 595 N. Sib St., Brooklyn, N. Y.

www.americanradiohistory.com 286 RADIO-CRAFT December, 1929 LETTERS FROM READERS (Continued from page 262) the end of my condenser shaft, to try to keep the A set automatically below the point of oscillation ; and I am sure it can be done with the proper value of resistor. My next experiment will be a tuned Special stage ahead of the detector. I find that by -pass condensers in the proper parts of the circuit make a vast improvement in distant reception. Courtesy I certainly believe that the coming popular set will have fewer tubes than those used today ; as a few tubes will do plenty of work if the proper to all hook -up is found. - The greatest difficulty has been in finding the perfect variable condenser. A change of condensers will bring in stations, but lose others. while using the same coil for both. I make a constant study of condensers and coils and absorb everything I SHORT WAVES see published on that subject. I have secured my best results with all- battery Radiotricians THE SUBMARINER operation. Line -voltage fluctuation is bad in this will convert your receiver into a short wave receiver district. and sets "bloop" too easily. Eventually, I Professionals without any changes. Enthusiastic owners have written us from all parts of suppose, some means of good control of voltage, the world. Stations broadcasting music 8000 miles automatically, will overcome that difficulty. If you Engineers away have been received. Very little static on short waves. Latest improvements- shielded- vernier dial know of any at present, make mention of it in some 64 to 1 ratio -a quality product -on the market over of your issues. Mechanics three years. Keep up the good work on RADIO- CRAFT, and I Many Models am sure that, when any of the fellows get hold Consultants 16 -32 meters. AC or DC, $17.50. Interch ble coil. of your magazine, they will become steady sub- 12.160 meters, AC or DC. $22.50. J" model gives five times volume of other adapters. Price. 16 -32 scribers. Designers meters. $22.50. Interchangeable coil J" model. F. P. CORRIGAN, 527.50. Sent postpaid upon receipt of price or C.O.D. Rutherford Garage, Rutherford, Calif. If $1.00 accompanies order. Give name of set and Service Men tubes used, when ordering. J.M -P MFG. CO., Inc. (Mr. Corrigan iJ typical of a great many ex- Contractors who working things out for 3333 Fond du Lac Ave.. Milwaukee. Wisconsin. perimenters still enjoy themselves. The dial -nurser will get things out of Manufacturers three tubes that escape from the owner of a com- TO NEW READERS mercial seven- or eight -tuber who knows only that Dealers A few copies of the July, August, there is a switch marked "On" and "Of." Et cannot see why there should be "holes" in the September, October and November operation of any good condenser if the plates are in issues of good shape and rigid an their mountings, and there is no back -lash or lost motion in the dial. There are In order to make it possible for all RADIO -CRAFT numerous automatic voltage regulators on the market, some of which have been described in our "New Radio Technicians to read RADIO - can still be had at the regular price of Things" pages; and others will appear later. Some 25c each. Send stamps, cash or money are automatic transformers, which permit only a CRAFT regularly, each month, we certain voltage to exist between the secondary ends; have put into effect a special sub- order to: others are variable resistors -such as the regulator tubes -which take an input exceeding the needs of scription price. RADIO -CRAFT the set, and dissipate all but the proper amount of 98 Park Place New York, N. Y. energy.-Editor.) The regular price of RADIO - CRAFT is $2.50 per year (12 is- MAKE SHORT -WAVE STATIONS HEARD r RADIO -CRAFT: sues). The newsstand rate is 25 Editor, ' FW4, St. Assise, France, is working on 15.55 cents a copy. GOOD RECEPTION meters to Buenos Aires and 24.5 meters to Saigon, Indo- China, from 1 to 3:30 p. m. E. S. T. Friday, Any radio EASY Saturday and Sunday. The power is 15 kw. DHC professional, sending in of Nauen, Germany. with the same power, is heard a subscription on his letterhead, Thousands of working the same stations sometimes, mainly Thurs- users marvel at the day. Friday, Saturday and Sunday, on 26.22 meters. showing that he is engaged in some difference in recep- On the night of July 26, I heard a powerful tion with a Towns- ; capacity in radio work will receive end B" Power German station about 45 meters they gave time at Unit. Full, sweet 10:38 p. m. DGW on 14.837 meters is testing as a special courtesy tone, clarity, vol- around 7:30 a. m., E. S. T. ume and greater There is a station VPD at Samoa, Fiji Islands, distance are among on a wave of 20 and 30 meters. Nothing definite Eight Issues of the many advan- daily. has been received as to the correct wave, power or toges reported transmission schedules yet. RICHARD BOGERT, ónliy TOWNSEND 1416 Linden St., Allentown, Penna. Q "B" POWER UNIT (VPD indicates a British colony; Samoa and the 71adio;@ft\ 01 J Hooked up in a few minutes; Fiji Islands are quite distinct.-Editor) just plug into the light socket fessional -Serviceman bdiotr and forgot it. Delivers up to 100 volta on any set -D.C. or A.C.- any cycle. NEW MEXICAN STATION? for One Dollar Approved and passed by the rigid laboratory tests of "Point- Editor, RADIO -CRAFT: tar Radio" and "Radio News." Another new one is XPR or XKR in Mexico; Just pin a dollar bill to the coupon wavelength about 15 meters. This is a German Over 150,000 Now In Use! transmitter testing with Nauen and Doberitz between below and forward it with your let- There's no longer any 12:30 a. m. and 2:30 p. m. Eastern Time. All reason for putting up with is in German. I would like to terhead or business card. the expense and undepend- HAS ONLY announcing done able performance of "D" WORDS OF hear from anyone who knows something definite Batteries -when you can PRAISE about this station. He has powerful volume and with ; though there is at times own a good "B" Power Unit. Please send clarity, little fading for $6.85. Over 150,000 another Elimina-- powerful telegraphic interference. RADIO- CRAFT, Townsend "B" Power Unit., tor. MERLE A. HEATH, now in use-a substantial of lurr Elm.he Iowa. RC-12, 98 Park Place, proof of satisfaction. ' inators In constant 501 Oak Ave., Waterloo, use on a 5 tube New York, N. Y. over two Send Only Sí.00 set for Enclosed find for which please enter my Send nnme and addre_s years nd have $1.00 On only words of great subscription to RADIO -CRAFT for eight months. with only $1.00. arrival praise for It. An ANOTHER GUESS of Townsend Power Unit with it is pay postman plus accident Editor, RADIO- CRAFT: $5.85 my e a so n for my -wave set with a "B" postage. Try out ten days, another.n ther. I am working short Name then. if it fails to do J. Cassidy, power unit (I have tried several makes) and I al- everything we say, return 531 Sterling Place. ways have used one. If any of your readers say it and money paid us will Brooklyn. N. Y. they can't play their set with one, I invite them to Address be refunded. Make a play it. and they won't know REALreceiver of your set. bring it here and I'll the difference from batteries. I can also work this TOWNSEND LABORATORIES do on my City State Chicago, Ill. set with the charger on, which I can't 715 Townsend St. broadcast set. I have no shielding, nor do I use

www.americanradiohistory.com December, 1929 RADIO-CRAFT 2S7

phones, but a W. E. 18 -inch cone and a UX -245 AGENTS WANTED power tube for detector. I would like to hear from fans who are trying this tube for the purpose. FREE BOOK. Start little mail order business. FW, St. Assise, is now on 15.429 meters and will Hadwil, 27A -74 Cortlandt Street, New York. go to 24 in December. DIH, Nauen, works a new station in Mexico which I can't make out; it may Get our Free Sample Case -Toilet Articles, Flavor- be XDA, XEH, or XIH, but I think the latter. ings, Soaps, Specialties. Wonderfully profitable. PCL is off the air in favor of PCK. LaDerma Dept. SC, St. Louis, Mo. Co., J. R. MCALLISTER, Struthers, AIRPLANE SUPPLIES Ohio. (Some of the difficulties of co- ordinating reports MODEL AEROPLANE Supplies. Write for free of reception from reports of listeners alone a Ili be bundle of sample stock. Aero Shop, 3050 Hurlbut seen from the above letters. We shall be especially -from hook- Ave., Detroit, Mich. glad to hear from listeners who hare definite facts from the stations themselves.- Editor.) ups to "trouble- BUSINESS OPPORTUNITY shooting" - for the CAPITAL-An experienced dependable broker will FROM THE LAND OF THE WHITE aid in financing projects of merit. Amster Leonard, broadcast listener a n d Last Orange, N. J. "CHANG" Editor, RADIOCRAFT: the radio service SELL BY MAIL. Books, Novelties, Bargains! Large man - profits. Particulars FREE! D. Elfco, 521 South I have the pleasure to inform you that Siam is Dearborn, Chicago. now on the air every Sunday from 1400 to 1630 ABOOK for the amateur who builds his GMT, using the wavelength of 16.9 meters. This own receiver-for the man who has CHEMICALS is in nature of experiment, using a 20 -kw. the an bought a "store" set but wants to know Telefunken transmitter, Another broadcast station, how it works and BOOKLET OF EXPERIMENTS and chemical cata- experimentally conducted by the same department, how to make repairs, if Box necessary log, 15e. General Chemical Company, 397, uses a wavelength of meters with a 200 -watt -and for the radio dealer and Reading, Penna. 37 transmitter every Friday and Tuesday, between the service man who is called upon to do same "trouble- shooting" DETECTIVES hours. These stations invite suggestions from on all types of receivers. listeners, and will be glad to hear about results of reception in any part of the world. Just drop a DETECTIVES Earn Big Money. Excellent oppor- card to the Radio Chief, Royal Siamese Post and tunity. Experience unnecessary. Particulars Free. Practical Radio Write, George Wagner, 2190B Broadway, N. Y. Telegraph Department, Bangkok, Siam. Siamese national orchestral music played on native INSTRUCTION instruments, and national songs by our native sing- Construction ers are the chief features. They may sound rather I CATCH from 45 to 50 foxes from 4 to 5 weeks' strange and unintelligible; but is it not worth while and Repairing time. Can teach any reader of this magazine how to tune in and hear these novelties from the land to get them. Write for particulars. W. A. Hadley, of cinema -famed "Chang "? This powerful station By JAMES A. MOYER Stanstead, Que. in the Far East challenges every DX fan in the Director of University Extension world to cry his skill at hunting. I may add that and JOHN F. LEARN tattooing. Instruction catalog, dime. Miller, European programs are occasionally broadcast. WOSTREL X431 Main, Norfolk, Virginia. Instructor in Radio, Division of University ASANACHINTA, LEARN MARBLEIZING Concrete products all kind. C. Extension, Massachusetts Department Wood, Metals, etc. Resembles polished marble or 1275 -A Asdang Road, Bangkok, Siam. of Education onyx. Wonderful for garden furniture, table tops, 319 pages, 51/2 x 8, 157 illustrations etc. Write Cowell Institute, Grayling, Mich. ASKS S -W. CORRESPONDENCE $2.00 MISCELLANEOUS THIS is a practical, every-day book of sound Editor, RADIO- CRAFT: it hints and instruction on all types of receiving sets and apparatus. TOBACCO OR SNUFF HABIT Cured or No Pay. I enjoy your magazine, especially the Data Sheets It is written entirely and correspondence pages (of course we could stand from the standpoint of the amateur. No pre- 81.50 if cured. Remedy sent on trial. Superba Co., vious training in radio more short -wave stuff). I like the plain English engineering is assumed. T28. Baltimore, Md. A thorough understanding of this which is Also, at time, I up -to -date used throughout. this volume will enable the broadcast fan to add OLD MONEY WANTED want to take the privilege of asking short-wave cor- new long -distance stations to his "DX" log; to respondents, especially in Europe and other foreign improve the tone quality and reproduction of his $5 to $500 EACH paid for Old Coins. Keep ALL parts, to write to me. set; to identify and overcome trouble anywhere old money. Many VERY valuable. Get Posted. VINCENT, in the circuit; to build new sets, including those LEON which will enable him Send 10c for Illustrated Coin Value Book, 4x6. New York. to listen in on the new Guaranteed Prices. We buy and sell. COIN EX- Dannemora, short wave band; and to have a practical know- CHANGE, Room 10. Le Roy, N. Y. ledge of radio which will be a money saving STATEMENT OF THE OWNERSHIP. MANAGE- factor and promote a more complete enjoyment PATENT ATTORNEY MENT. CIRCULATION. ETC., REQUIRED BY THE of broadcasting. ACT OF CONGRESS OF AUGUST 24, 1912, Of Radio-Craft, published monthly at New York, N. CONTENTS Y.. for October I. 1929. Radio Essentials State of New York County of New York ss Antenna and Ground Systems Before me. a Notary Public in and for the State and Tool Equipment for Radio Work county aforesaid. personally appeared Irving S. Man - Instruments; Methods of Testing been sworn to law. PATENTS -Time counts in applying for heinter, who, having duly according The Theory of Vacuum Tubes deposes and says that he is the business manager of Radio- Frequency Amplifiers patents. Don't risk delay in protecting your Radio-Craft and that the following is. to the best belief. true statement of the Construction of Receiving Sets ideas. Send sketch of model for instruc- of his knowledge and a Resistance and tions or write for free book, "How to Ob- ownership. management. etc.. of the aforesaid publica- - Impedance -coupling for tain a tion for the date shown in the above caption. required Audio -frequency Amplifiers Patent' and "Record of Invention" by the Act of August 24. 1912. embodied in section 411, Impedance -coupling Hookups form. No charge for information on how to Postal Laws and Regulations. to wit: Construction of 4 -tube Sets proceed. Communications strictly confiden- 1. That the names and addresses of the publisher, Reflex; Tuned Radio -frequency Sets tial. Prompt, careful, efficient service. editor. managing editor, and business managers arc: Clar- Publisher, l'echni -Craft Publishing Corporation, 98 Park Superheterodyne Construction ence A. O'Brien. Registered Patent Attorney, Place. New fork City. Short Wave Receivers 343 - A Security Bank Building (directly Editor. litigo Gernsback. 98 Park Place. New York City. Construction of Loud Speakers across street from Patent Office), Washing- Managing Editor, R. D. Washburn. 98 Park Place. "A ", "B" & "C" Eliminators ton, D. C. New York City. "Trouble -shooting" Business Manager. Irving S. Manlieimer, 98 Park Place, New York City. 2. That the owners are: lingo Gernsback. 98 Park Place, New York City. Send the Coupon TODAY Sidney Gernsback, 98 Park Place, New fork City. D. Manheinter, 98 Park Place, New York City. 3. That the known bondholders. mortgagees. and other McGRAW -HILL security holders owning or holding 1 per cent or more STAMPS of total amount of bonds. mortgages, or other securities á: None. Free Examination Coupon STAMPS: 20 varieties 4. That the two paragraphs next above. giving the unused free. Postage 2e. names of the owner stockholders, and security hold- Toledo Stamp Co., Toledo, Ohio. ers. if any, contain s not only the list of stockholders and security holders as they appear upon the books of McGraw Hill Book Company, Inc. the company but also, in cases where the stockholder Ave., PHOTOGRAPHY or security holder appears main the hooks of the com- 370 -7th N. Y. pany as trustee or in any other fiduciary relation. the Gentlemen: name of the person or corporation for whom such Send me for ten days' FREE examination a 12 prints any size 50c and one on back of pocket trustee is acting. is given: also that the said two para- copy of Moyer and Wostrel's Practical Radio mirror FREE. Any size roll developed and 6 good graphs contain statements embracing affiant's full Construction and Repairing, $2.00. I agree to prints 25c. An Line Photo Service, knowledge and belief as to the circumstances and con- Altoona, Penna. ditions under which stockholders and security holders either return the book in ten days or send my who do not appear upon the books of the company as remittance at that time. trustees. hold stock and securities in a capacity other RADIO SUPPLIES than that of a Iona fide owner: and this alliant lias no Name reason to believe that any other person, association, or corporation has any interest direct or indirect in the Address RADIO SUPPLIES. Save one -half here. Aerial said stock. bonds, or other securities than as su stated fittings, 3 ft. Ensco Cone Speaker. Alcohol solder- by him. City and State ing torches, loudspeaker extension IRVING S. cords, speaker MANIIEISTER Official Position plugs, lightning arrestors, earphones, etc. Hill -Site, Sworn to and subscribed before me this 19th day of R. 5 -LL, Kewaunee, Wisconsin. September, 1929. JOHN fS. CONSIDINE, Notary Public. Name of Company.. R.C. 12-29 (My commission expires March 30, 1930.)

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