Radio Craft July

OVER 175 ILLUSTRATIONS

Radio Create - " Fashion Patterns! - NEW! . An Acoustic "Magnifier" Europe's Ras.,; Was - Making a Hi - Fi Tuner :vicing A. C. - D. C. Sets

www.americanradiohistory.com The Best Known Name and the Oldest Trademark in the Business

CAPITALIZE on the definite sales advantages of the RCA Victor name and famous trademark. Authorized RCA Victor Radio Tube franchises are available only through RCA Victor Instrument Distributors.

RCA presents the "!Magic hey" every Sunday, 2 to 3 P. M., E. D. LT., on the NBC Blue Network. VieZt RADIO TUBES RCA MANUFACTURING CO., INC., CAMDEN, N. J. A Service of the Radio Corporation of America

www.americanradiohistory.com RADIO -CRAFT for JULY, 1938

1)/nip/from %8a weehr f o .S0 -- a free Book storied me ínyord this GOOD MY/N RADIO

01,PLOYES HERE'S ONLY

factory. Pd 6y S.J.E. "I had an $18 a week job In a shoe "The training National limbo lust itute gave nie hadn't read about the (NAME AND ADDRESS probably be st it today If I was so practical I was sooft ready to make $.;. $10. opportunities in Radio and started training at home icing Radio seta." UPON REQUEST) sly u week in spare time sen SENT for them."

months later N. R. I. },btpia)meut De "N. R. I. Training look me out of a low -pay shoo ''When I finished training 1 accepted a jub as "Eight pertinent sent me to Station K VCR as Radio factory job and me Into Radio at good pa. a Radio store. In three weeks put serviceman with L am Radio Engineer at Station operator. Now Radio is growing fast. The field is wide open I I was made service manager at more than twice WSUL am siso connected with Telodsion Sta- I properly trained men." what I earned in the shoe factory." tion N9 %K.,, how I TrainYou at Home to BE A RADIO EXPERT Find Out What Radio and Television Offer Make S30, $50, Mail lile r .pun nu for my Book. "Rich Rewards in Many They're free to any fellow a Week I Also Give You Radio" and siunple lesson. S75 mer IS years old. My book points out Radio's spare Do you too want a better time and full time opportunities, also those coming in This Professional tells about Raio an ;Eansl RH Presidintla job? Do you too want to men trained.) shows t 1s11on ;i shows youa 131 from "si4. more money? Ra- are doing, earning; shows my Money Back "OVA=hli.hCd make Servicing Instrument what they or and full time op- Agreement. MAIL. COUPON in an envelope. pasta dio offers many spare time card- NIli\". portunities for good pay and more oppor- as partof MyTralning on penny post tunities will come with Television. J. E. SMITH, Get Ready Now For Jobs Like Those Here Is the Instrument every Radio expert needs and Pr.aldent, employ engineers, opera- wants -an All -Ware, All-Purpose. Set Senlring In- National Radio Institute. Broadcasting stations A.C. tors, station managers and pay up to $5.000 a strument. It contains everything necessary to measure Dept. CCX many and D.C. voltages and current: to test tubes. resistance: year. Spare time Radio set servicing pays adjust nd align may set. old or new. It satisfies your Washington. D. C. pay $200 to $500 a year -full time servicing jobs ,I. for riving yner . graduate f many $30, $50, $75 a week. Many Radio Experts I era Icing set. .11i 11. Ir.Irrli'r are operating full or part time Radio businesses. Radio manufacturers and jobbers employ testers. I. s inspectors, foremen. engineers, servicemen, pay- J. E- President, Radio Institute, ing up to $6,000 a year. Radio operators on ships SMITH, National get good pay, see the world. Automobile, police, Dept. SGX, Washington, D. C. commercial Radio. loud speaker systems. aviation, obligation. send me free a Sample offer good opportunities now and for the future. Dear Mr. Smith: Without soon. Men I trained u Lesson and your 64 -page Book, "Rich Rewards in Radio." telling Television promises good jobs Radio opportunities. and how I good in these branches of Radio. u about spare time and full time have jobs ran train for them at home in spare time. (Please write plainly.) Many Make SS, $10. $15 a Week Extra u In Spare Time While Learning Age The day you enroll I start sending you Extra N Name Money Job Sheets. They show you how to do Ra- I dio repair jobs; how to cash in quickly. Through- out your training I send plans and ideas that Address ' made good spare time money -from $200 to $500 hundreds of fellows. I send special a year-for City Strate ...... 11x1 Radio equipment, give you practical Radio experience --show how to conduct experiments. build mmmmmmmmmmmm circuits illustrating important Radio I.rtnciples. &m emu samm sae meems...... Please Say That You Sato It u'x RADIO -CRAFT

www.americanradiohistory.com IMF adio- raft Foe T

SERVICE MAN- DEALER - RADIOTRICIAN

111111111 R 11111111111111111 I I I I I I 11111111 I 11111111111111111 I I I I I I I II I I I I I I I I I I I I I I I I 1111111111111111111111111111111111111 I I I I I I I I I I 1111111111111111111 11111111111111111111I11 m 111111I11111111111111I I I I I111111111111111111111111 m 1111111111111111111111111111111 I I I I I I I I I 111111111111111111111111111111111

HUGO GERNSBACK, Editor -in -Chief Unified P.A. Equipment Harry Paro 28 N. H. LESSEM ROBERT EICHBERG Wax & Oil Condensers in Radio Service Work Associate Editor Associate Editor William Bailey 28 R. D. WASHBURNE, Managing Editor Operating Notes Y9

Useful Circuit Ideas 30

A Wired -Radio "Nursemaid" 31 CONTENTS JULY ISSUE - 1938, Introducing--A 5 -Meter Converter 31 Volume X Number I The Latest Radio Equipment 32

RADIO SERVICE DATA SHEETS: Editorial: Service in Radio Servicing..Hugo Gernsback 5 No. 229 - Motorola Model 8-80 (Golden Voice) The Radio Month in Review 6 Car-Radio 36 Radio in Pictures 8 No. 230-Ditto (continued) 37 Europe's Undeclared Radio War Michael Norton 9 Servicing Questions & Answers 35 Radio Creates Amazing Fashion Patterns Radio Wittiquiz 35 Andrew Halbran and Robert Eichberg IO The First IO Steps in Radio Servicing 49 Television Without Scanning? U. A. Sanabria 12 Hum in Public Address Installations 53 New Radio Service "Car" G. E. DeNike 13 Man Still Champion of the Air Dr. Irving Langmuir 60 America's Radio Colossus 13 Looking Ahead to Television Occupations Servicing Universal A.C. -D.C. Receivers Dr. Alfred N. Goldsmith 61 J. B. Straughn 14 Book Reviews 63 Service Men!- Repair Your Customers' Sets "Better Than New "! George W. Haider 16 Servicing Pushbutton Tuning Systems -Part II NEXT MONTH Charles Sicuranza 18 -

New Circuits in Modern Radio Receivers-No. IO TELEVISION NUMBER F. L. Sprayberry 20 Television is now undergoing its final polishing stage Modifying a Older Sets to Receive the 4 High -Fidelity prior to its presentation to the public in workable form. Stations Robert Cobaugh 21 Regular transmission schedules have just been announced How to Make a High -Fidelity Tuner C. W. Palmer 22 by NBC; August Radio -Craft will help you keep abreast of these new and important developments. "Bi- Fonic" Sound Magnifier Robert Livingood 24 Service Men, public- address specialists, radio set build- Matching Loudspeakers to Tapped Transformers ers and beginners also will find in August Radio -Craft A. Coblenz 26 many valuable articles to their individual liking.

111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111

Published by Radcraft Publications, Inc. Publication office: 29 RADIO -CRAFT is published monthly, on the first of the month preced- Worthington Street, Springfield, Mess. Editorial and Advertising ing that of date; subscription price is $2.50 per year in U. S. and Can- ada. (In foreign countries, $3.00 a year to cover Offices: 99 Hudson Street, New York City. Chicago Advertising additional postage.) Entered at the post office at Springfield as second -class matter Office: RADIO -CRAFT, 520 North Michigan Avenue, Chicago, Ill. under the act of March 3, 1879.

Foreign Agents: Text and illustrations this magazine London- Gorringi s American News Agency, 9A Green St., Leicester of are copyright and must not be Square, W. C. 2, England. reproduced without permission of the copyright owners. Puis -Messageries Davison, 4 Rue Faubourg, Poissonniers, France. Melbourne -McGill's Agency, 179 Elizabeth St., Australia. Dunedin -James Johnston, Ltd., New Zealand. Copyright 1938 Radcraft Publications. Inc.

www.americanradiohistory.com RADIO -CRAFT for JULY, 1938 TRAIN FOR RADIO IN 12 WEEKS BYMYQUICK, EASY "LEARN BY DOING" METHOD Prepare today to enter a real money -making field . a : _ ,: u le-:=116-- by my quick, easy way to learn Radio. Here in my school you are trained in 12 weeks for your start for a better job and a real future. You do actual work on a great outlay of Radio equipment. The remarkable "Learn-By- Doing" methods used in the great Coyne Shops train you in Radio, Television and sound equipment servicing. Not by books . Not by Correspondence ... But all under the individual guidance of skilled instructors, and only on similar kind of work you will meet out on a real job. My methods make it easy to learn-First you are told how to do a thing - then you are shown how to do it -then you do the work yourself. WHERE ELSE CAN YOU FIND SO QUICK AND EASY A WAY TO GET PRACTICAL TRAINING IN THIS GIANT INDUSTRY? ILL FINANCE YOUR TRAINING in the Coupon TODAY. LET LACK OF MONEY keep you from sending DON'T first and take more than a year to pay for it Learn how you can get training after your regular 12 weeks' after graduation. Make your first payment 60 days in take over a yeanto pay the balance of your tuition training period ends. Then fellows have used this method easy monthly payments. Hundreds of ambitious l THE COUPON TODAY. to get Coyne Training. FILL IN way to t your sw ll bring you the details of this amazingly quick AND y towards a good pay job. )Y'. C. 84.04 Radio - Television -Sound Equipment finest kind of Is in wonderful, modern daylight shops on the Your training at Coyne as a TELEVISION and SOUND EQUIPMENT. Television is sure to come RADIO, and Public Address Part Time Work While Learning commercial industry, whether this year or next. Talking Picture possible has been done to Systems offer opportunities for the trained man. Everything as profitable. Employment Service after Graduation make your stay at Coyne happy and healthful as well training, my If you need part time work to help pay living expenses while Electric Refrigeration Training Employment Department will help you get it. They will also give you Leto- time Employment Service after you graduate.

at No Extra Cost Included Coupon Today Training (Radio and Refrigeration) can be of great value to you. Mail This Combination for a Radio Sales and Whether you go into business for yourself or get a job working All the Facts the fact that you are trained in servicing Electric Refrigerators I'll Send You Service organization', Electric Refriger- be profitable to you. Many Radio Manufacturers also make Get the new "Coyne Opportunity Catalog." should employers. ators and men with this combination training are much more valuable to these giving all facts about Coyne Training. Photographs You can NOW get this training without extra cost. of Shops showing students at work on modern radio equipment under the personal supervision of Coyne No Advanced Education or Expert Instructors. Also details of my Part Time Employment Offer. Pay After Graduation Plan and Previous Experience Needed Graduate Employment Service. Yours without cost. trained the Coyne If you can read and write simple English and are ambitious you can be Simply Mail the Coupon. actual experience on a wide variety of up-to-date Superheterodyne sets. way -by receiv- s ssst oscillators, analyzers, and test instruments. You learn how to operate television F ing and transmitting equipment and how to install, test and service public address H. C. LEWIS. President. systems and sound picture equipment. Coyne training also helps prepare you to qualify Radio Division, Coyne Electrical School, Radio Oper- 1 Chicago. Ill. for a government license examination as Amateur Broadcast or Telegraph 500 S. Paulina St., Dept. B8 -80 give me all ator and to know Code and Department of Commerce rules. Send coupon for all details. Send me your big FREE Book about Coyne Training and 1 details regarding your "Part Time Employment Offer" and "Pay After Graduation Plan" of easy, monthly payments. 1899 H. C. LEWIS, President RADIO DIVISION Founded 1 NAME AGE I COYNE ELECTRICAL SCHOOL ADDRESS 500 S. Paulina St., ';Dept. Ba-sH Chicago, III. 1 I CITY STATE Please Say That You Saw It in RADIO -CRAFT www.americanradiohistory.com RADIO -CRAFT for JULY, I 9 3 8 A New Policy! FREE INSPECTION PLAN 2/044. caot Zwif a#14, ge4lAach Ma4.1all f1K 71viee .73a4p.' /Inecial

Perhaps you're new in Radio -or probably, in previous years This plan Is simple- there's no mystery or red tape -it you missed one of the Gernsback OFFICIAL RADIO gives you every opportunity SERVICE MANUALS. This is your opportunity to buy to inspect the Manual of your any edition you might need -get it in a way differently selection. It costs you only a few cents return postage if than ever before offered. Under a new policy -FREE you decide not to keep it. INSPECTION PLAN -you can buy any Gernsback Manual on Three Days' Approval. There are thirteen Manuals and books from which to choose-every man in Latest Volume 7 Manual Included Radio should take advantage of this privilege. Volume 7 of the OFFICIAL RADIO SERVICE MANUAL -the edition which stampeded the Radio industry this Here Is How It's Done! past year because it was published in a new way -in Order any GERNSBACK MANUAL illustrated and de- twelve monthly installments, is included under this new scribed on this page -the publishers will ship it to you policy. This volume is now complete-twelve install- immediately POSTPAID. When it reaches you, inspect its ments, totaling 1,800 pages, are bound in a hardcover bind- contents. If, after three days' inspection, you decide to er and just packed with information you need today -and keep the Manual, mail your remittance to the publishers. in the years to come- The coupon below gives you the If the volume proves unsuitable, return it postpaid. privilege of inspecting this Manual also before you buy it

* VOLUME 7 * * 1136 MANUAL * Newest of GERNSBACK * 1135 MANUAL Contains 1.200 pages * L lover 2.500 illustra- An authentic radio s mall i am tions) packed with serv- lipgeges ide f over 1.000 Od data ie data f 103030 ith more than oo , x'30 -37.3N ivers. ta. Diagrams of -37 1513 3,000 more urto-date than Ì.50o receivers. Shows 4)"CÇFICIAL- lllur tins-ccon.oR service_ guide pub- speaker connections.n_ ho. ,100 pages of ` power 'RADIO, SERVICE Featuresltii many old seta erial which radio tns. Alignmentprn- MANUAL Previously de- usee i included with scribed, early all-wave ,m diagrá s °i óf t0aÿ anti short-wave sets, auto. different lgges'for oO radios, r facturred sets. receivers. an Includes '. 000 different ilium- Assembly a diagrams data on P.A. amplifiers, ' atione. Round In hard, show relationship servic and each tube Infnonnotion ;chanism permits other. Sise - Ú x 12 FREE QUESTION AND pages to he removedre inches: hd cover. ANSWER SERVICE. Site and replaced. Siise- looseleaf binder. inches: flexible, 9 12 inches. -9 x 12 PRICE $10.00 .5 PRICE $7.00

1935 AUTO -RADIO * *1134 MANUAL 1933 MANUAL MANUAL Contains sou* * * * Manual, OVER 240 PAGES -over 2,000 illus. Th, Tfnpa:;e OVER 500 pages The schema(- with < ) illus. ILLUSTRATIONS 11:11. (rations, contains page Looseleaf OffICust A n Feature. ;ter of nperal- Minder- .hs'receivers. readings, I.F. Ing notesn t s - schematics Flex ibie Covers AUTO -RADIO transformer vlue snowing location of on chassis-values PRICE (Mitt MANNA( l rhe. v a loan parts $2.50 pc lad tube data 1 FREE peaks. QUESTION AND AN- nc ondens com- SWER SERVICE. A plete section on * 1933 AUTO -RADIO index makesakes it atrurtion of various easy find any tapes of test equipment. MANUAL * rvice plus OVER 250 PAGES problems. dMaster lodes deas foin radin OVER 500 diagrams Pub. a fished in 1p stallation ands °Ionery ic- Loosen afR Brotlee_ MANUALS. Sise-il Size -9 12 ble Covers 12 inches: flexible, Ing.flexible, xloose- ihes: PRICE 52.50 PRICE $3.50 $5.00

* 1933 MANUAL * * 1931 MANUAL * OFFICIAL RADIO Thisul lanualo contains The first of the famous Ì GERNSBACK MANUALS SERVICE HANDIBOOK guide of ra1931 -32rvre Official wiri-contains all available Here's the sensational elvers. With over ng diagramsf of book icing. Covers 1.000 pages and over Radio Servire n y eiver b00 topics. Contains illustrations. Manual manufactured since special section of 250 featuYr XDIO eis step-by-step 1927. and manY prior 1(IVICI pages f Operating Notes. that nipar- AN0.F00a The book ere Circuit enemas r-chatt ahocwlntn ti cular editionTc Theory Analysis: vacuum 550 (including Modern Servicingd tubes schematic lepaesl Test Equipment; Pratti -- color cod - ral Trouble Shooting: dg indicated - comen r- g1r. 5Sm0 immprtantl dite specialized Receiver d etal short-wave receiv- to radio vis the Installation ëta¡Cancel. ers RADIO SERVICEICE and public addresS in ion Data, Over ericing Si tthiis RRedition.tlshSSite 1.1100 pages -Over 1.000 12 (íp1ches: flexible, Inches flexible. illustrations: hard looseleaf covers. 9a12lr ers. Site O x 9 Inches. PRICE $4.50 PRICE $5.00 IncludmN supplements PRICE $4.00

OFFICIAL REFRIGERATION SERVICE MANUAL (Volum 1) - $5,00 This Policy Includes OFFICIAL REFRIGERATION SERVICE MANUAL I Volume 2) -$5.00 - OFFICIAL AIR CONDITIONING SERVICE MANUAL - $5,00 7 RADCRAFT PUBLICATIONS, Inc. RC -738 How To Get Any Manual You Need! 99 Hudson Street, New York, N. Y. After you have definitely decided which Manual you want, Please send me. POSTPAID for three till in completely the coupon at the right. Clip it to your (Name of Manual or Book) letterhead or paste on a penny post card and mail to the days' examination on approval. In three days I will remit to you the publishers. In a few days your Manual will reach you - full cost of the Manual or book selected, or return the volume to Don't lose time -send coupon, TODAY, to you postpaid. Name RADCRAFT PUBLICATIONS, Inc. Address 99 Hudson Street New York, N. Y. City State Name of company or employer (This offer is Used only in continental United L States.) Please Say That You Saw It in RADIO -CRAFT www.americanradiohistory.com adio@ffFOR Tt SERVICE MAN DEALER RADIOTRICIAN "Takes the Resistance out of Radio"

I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 11111 i I l'. I I I I I I I I I I I I I I I I I 1 1 1 1 1 1 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I l l l l l l l 11 I I I I I I I I I I I I I I I I I I I I I II I I I I I I II I I I I I I I I I I I I I I I I I I I I I I I I I II I I I I I I I I I I I I I I I I I I I I II I I I I I I I I I I I I I I I I I II I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I Vol. X, No. I, July, 1938 Editorial Offices: 99 Hudson St., New York, N. Y. HUGO GERNSBACK, Editor

l l n 11 1 1 1 1 1 1 1 uu u l l l I I II I I I I II I I I I I I I I II I n1111111111111111110111111111111111111111111111111111111111111111111111111111n11111111111111111I I I I I l l l u l l l l l l l l l l ml IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII II I I I I IIIIIIIIII IIIIIIII II IIIIIIII88888R888888888888888nn011

SERVICE IN RADIO SERVICING An Editorial by HUGO GERNSBACK

IN China, doctors, for untold ages, have been in the habit give his customer a square deal. It is much better for the of collecting a fee for keeping patients free from sick- Service Man to make no money at all on the first transac- ness. In China you do not pay a doctor when you are ill. tion because in the end he will get much further with the This is excellent psychology not only from the doctor's radio set owner, once the customer finds out that the Service viewpoint, but from the patient's as well, as no one likes to Man merits his confidence. be sick. It is much better to pay a small fee every month or Applying the Chinese doctors' and dentists' methods quarterly to a doctor who makes it his business to keep to Radio Servicing, it is soon discovered that such methods you well. will in the long run work out most advantageously to the In the United States, it is the custom, with dentists, par- Service Man. Suppose for instance that a Service Man his list. good dentists, to send their patients an appoint- has 100 customers or prospective customers on It ticularly for ment card every 3 to 6 months for a general cleaning of should not be too difficult for him to convince them that the teeth. In doing so, the dentist keeps your teeth not only a fee of from 50c to $1 per month (depending upon the value condition but he can discover the start of decaying of the set) the Service Man or his organization will keep in good of teeth and fill them before the damage becomes more serious. the radio set in perfect working order for the duration 10 such a method This, too, is good business for the dentist and the patient the service. In 9 out of cases, with the because the very because it saves the patient much expense in the end. It is Service Man must be "in the money" in small an easy matter to fill a tooth that has just begun to decay. nature of things, most repairs that come along are has a set was It is quite another matter when the decaying process has and inconsequential. Even if a customer that by lightning, Service Man could still gone so far that the tooth becomes worthless and must entirely demolished the would have enough come out. This means expensive bridgework, and special repair or replace it because he had treatments compared to the trifling cost of filling the tooth income to do so without any quibbling or fuss. attention was first necessary. In a running business, it is the volume that counts as at the time will Radio Service should not be any different in prin- well as the law of averages. Out of 100 sets, few need Now, of a than the two examples given. Up to very recently, very extensive or expensive repairs during the course ciple to Service Men have been extremely shortsighted in regard to year. Of course with this method it is perfectly natural their relationship with the people whose sets they service, find that once in a while a customer will take advantage of are now paying the penalty of this shortsightedness a Service Man, but again the law of averages works in favor and they in caused by having the public mistrust the Service Man and of the radioman because people as a whole are honest his work. The public has come to realize that many Service their dealings and the Service Man should experience little is a big point, Men have taken ruthless advantage of them and now the difficulty in this respect. Then also, and this average non -technical radio set owner does not place too remember always that a Service Man has a tremendous much confidence in radio repairmen. advantage over the average salesman. in get- Often when a Service Man was called in, he would im- The average salesman has considerable difficulty when there was really ting into people's homes whereas the Service Man is mediately run up a bill of $20 or more a wrong with the set except perhaps a loose connec- ACTUALLY INVITED into the home. Just imagine how nothing vacuum cleaner salesman would jump at such tion or even such a trifling thing as a disconnected aerial hard -working a chance to be invited by his customer, yet the Service Man binding post, yet the dishonest Service Man would tell the radio set owner that the transformer was burned out, new never takes advantage of this great opportunity. It means after awhile the public be- that in a large proportion of calls the Service Man can tubes were needed, etc. Of course Radio came and the result was that in sell the radio set owner many other things besides wise to such crude methods which can the end these radio Service Men were the chief sufferers Service. There are a host of electrical appliances themselves. was that the Service be sold to such customers, but of course you must be pre- What usually happened or samples Man who took advantage of radio set owners' ignorance, pared to show them manufacturers' literature was never called back a second time and he eventually had and this should not be a very difficult thing. customers left. In this manner the Service Man can double or triple his to go out of business because he had no more is In Radio business, it is always income, so why not try it? The Radio Servicing business Servicing, as in any other make it the Golden Rule that counts. No Service Man can expect only what you make it. It is only "bad" if you to live and prosper if he does not use up -to-date methods and so yourself.

: : : : : : : : : . . : : . : : : : : : : : : : , , : , : : , : , : , , , , , , 11111111111111111111.11.11111111111111111111.1111111111M : : : : : : , : . : : : : . : , : : . , , : . : 111.1111 .. : , , , , , , , , 1.1 P. , , , , , : , : : : : , : , : : , : : , : , , 11/111111111.11111.4 ; ; ; ; ; ; ; ; ; ; : : : : . 1.11.1110111111111 . /I , , , , , , , , , , , , , , , , ; , , , ; , ; , , ; , , ; , ; ; , , , , , , ; , ; ; , - : , , : . : , , : : , , , : , : , , : , : : , : : : : : : . , , , , , , , , ,,,,,,,

www.americanradiohistory.com IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII III IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII IIIIIIIIIIIIIIIIIIIIIIIIIIIIII11111111111111IIIIIIIIIIIIIII1111111111111111111111111111111111111111111111111111111111111 THE RADIO MONTH

IIIIIIIIIIIIIIIIIIII1111111111I1111B111R111111111111111R1111B1111111111t11111111111111R111111IIIIIIIIII Radio is now such a vast and diversified art it becomes necessary for Radio -Craft to present YOU CAN'T a survey of important general - SAY THAT! interest monthly developments.

I II I I I I I I I I11111111111111111111111111111111!i P 111111 THE censors and their f 1111111111111111111111111111I111111111111I I proponents continued to struggle along, last venience and necessity" gives it too month, losing out in much power over what may and what these United States but booming blithe- must not be said. William S. Paley, ly in Britain. President of the C.B.S., widely famed In the tight little isle, Pearson's as a public -spirited citizen, suggests Weekly patted itself gently upon the that listeners cock a suspicious eye at 0 back, last month, because a radio an- all attempts to censor the medium nouncer prefaced a program by saying which affords them so much entertain- that it was unsuitable for young chil- ment. "WIRELESS" ON HORSEBACK. L ncashire mounted police now carry 6 lb. radio se s, by which they dren. A mother wrote in to comment The amount of entertainment is, ac- can conduct 2 -way speech 2 to 5 miles. Orders upon this and to recall weekly cording to Dr. Jay B. Nash, 150,000,000 can be handled between police planes that the and cars. had suggested some such sort of pro- listener -hours per day. The good Doc- cedure. The B.B.C. also announced that tor, who is chairman of the Physical its radio dramatization of "Dr. Cali - Education Department of New York gari" would be similarly introduced. University, last month declared, "It is It's a nice little play-about a mad- the moronishness, the stupidity, the house! inactivity of it (radio), rather than the Here the estimable Christian Science badness, that gives us the greatest con- Monitor, last month, praised Britain's cern." The Doctor is to be complimented defense of "helpless creatures-children upon having made a contribution to the for one class," and quotes a letter from nation's language, if not to its thought, President Byrd of the U. of Maryland, for "moronity," not "moronishness," is in which he threatens to throw away his the word given in our Unabridged. 3 receivers if his two sons won't stop listening to blood- curdling programs. Other educators write similarly, one be- TELEVISION wailing the fact that his young neglect WINDS TO HELP RADIO PR GRAMS. Checking COMES ALONG graphed performance of Bell Ta wind-electric gen- their home-work for "the radio." No erator., atop Schooley's (N. J.) Mountain. one mentions (and, possibly, rightly TELEVISION progress so) that persons who cannot F ur booster stations control the is apparently similar to o Bell Tel's. "Fourth actions of their own children might find the movement of a T nscontinental Line" it a bit difficult to control one of the glacier t rough the South - - irresistible, sst will each use a country's major industries -and no one but awfully slow. nd- electric genera - else seems to want to control it. Any- r to maintain pow - Best sign of last month was N.B.C.'s for the new "J "- way, why not let the kids enjoy life? announcement of broadcasts to be run tepe carrier tele- They're much safer getting one lines which their thrills 5 hours weekly during the period of a will have broadcast in their own homes than they would be month. These were planned to include program facilities as sneaking up a back alley with the "Ten thrice -weekly well. A gasoline - hours of stills and charts operated generator Beautiful Art Studies Weekly" or a for engineers' check -ups, and twice - will automatically copy of "Sexy Stories." weekly evening take over if wind - hours of 'live talent and power fails; while an But censorship has its opponents, too. movie film. Pictures were to be 441 lines automatic device sig- One of these is the redoubtable Hugh on 46.5 mc., nals nearest "in- with associated sound on habited" booster sta- Johnson, who last month went on to say 49.75 mc. tion in event of fur- that even the F.C.Commission's author- The next most 4 ther failure. (Unit on important step of last test, above, is des- ity to decide whether stations are month was the provision of a number tined for Mohave operating "in the public interest, con- of aliases Desert.) for the cathode -ray and other tubes. Thus, a C.-R. tube used in an oscilloscope becomes an Oscillotron, while, if used in television, it changes its name to Teletron. An image emitter,

RADIO "WALKERS." The Tiret unit of a series of novel window displays sup - plied fo tube dealers consists of 6 colorful, comic "walking" figures with bodies representing receiving and transmitting tubes, television tubes, etc.

6 RADIO -CRAFT for JULY, 1938

www.americanradiohistory.com I I I I I I P I I I I 11111111111111111111111111111 I I I I I I I I I I I I I I 11111111111 I I 11111111111111111111111111111111I . IN REVIEW

11111111111111111111111I11111I11111111111111111111111111111111111111111111111111111111111111111111111 or tube which provides a standard video signal source as reported in April Radio- Craft, is a Phasmajector and an "electric eye" or PE. mosaic pick-up tube for use in television cameras is an Electromalux, and has nothing to do with refrigeration. The Du Mont Lab- oratories announced their adoption of AlBilATRAik these names. In Australia, the editor of a Sydney CAJPFINfivi V radio weekly became quite enthusiastic FRONT SEATS VISION% over an announcement last month that fas TO John Logie Baird, television inventor, V. fNIsH plans to erect a $50,000 station there. H.M His enthusiasm was not shared by TELEVISION 'NEWS Stuart F. Doyle, chairman of the Com- monwealth Broadcasting Corporation, ÿ9j0 ;NEWS who stated that television programs in but entertain- England are "anything TELEVISING THE BOAT RACES. Experience gained here, televising the annual Head of the River race the sales of teleceivers between rowing clubs from London and elsewhere, was used to good advantage in later televising the ing," and that Brattier and Broadcaster. 10,000 per year. Oxford vs. Cambridge boat race. Insert shows ads., reproduced by Wireless there are less than illustrating how the programs get a boost. "Unquestionably," says Mr. Doyle, "television will be a most interesting sporting events. Plans call for the use development in the next few years, and of mobile units. organizer to it is up to some brilliant work was commenced last way of making it commercial." In France, find a month on the installations of under- E. K. Cohan, director of engineering .:alo ,t,6g last month from ground high -frequency cables, capable for C.B.S., returned of up to 4,000 kc. These cables a trip to England and remarked that carrying that the will link Paris with Limoges, BordeauN British television was good, but will tele- was only curious, rather than and Toulouse. They carry public vision, radio broadcast and telephone interested. conversations simultaneously. The reason for such insular apathy may be revealed in a discussion of television which took place in the House of RADIO AND Commons last month. Member White said that receivers cost too much; Mem- EDUCATION ber Simmons added that telly had not been developed "either geographically or LEVELAND, Ohio, and that first-rate artists schools last month be- technically," work on a munici- were not being televised, which meant , gan that programs seemed amateurish. pal school -of- the -air. Member Morrison said that the service The sum of $42,000 has been allotted monopolized by London, and to this work, which will include special was being for chil- that it should be extended to Scotland, news broadcasts, broadcasts Wales and the Provinces. dren of pre -school age, dramatized Meanwhile Marconiphone last month school lessons, programs for parents, developed a 37 -tube teleceiver which special events broadcasts, etc. N. Y. last month issued uses a 3 -inch projection tube, working University STUDIO -TYPE TELEVISION CAMERA. By utilizing at 20,000 volts, to project an 18- x 22- an announcement of a summer school the ultra -sentitive iconoscope as the pick -up tube, and production of Fernsah, A. G. (Berlin, Ger.) produced a camera, inch image on a screen. And the B.B.C. to teach preparation for indoor television scenes, which measures only advanced plans to telecast the 1938 radio programs. Besides staging their IT x 12 s B ins. wide. The handle on the side of will visit N.B.C., the device is used for focusing. Twin lenses include Oxford- Cambridge boat race and other own shows, students one lens for focusing; both are "optically coupled." C.B.S. and other studios, will hear lec- tures, etc. The best student programs will be aired. (Continued on page 42)

IDlllllllllllllllll8pllllllp8p1118811111II1I1111111111111111R111111111111III1111R111111R1 E- NO CONDENSERS, Mr. Paul Ware's "inductance tuning system" (Radio- Craft, Feb., '38, "New Condenserless Tuning System Demonstrated! "), as a 2 -gang, complete unit looks as shown at left. -3 NEWEST ROBOT. A "psycho -radio robot," as the awesome thing is called, is the device, shown at right, which was recently exhibited at the Interna- tional Exhibition of Invention at Sheffield, England, last month. It answers questions and claims to read thoughts!

111111111111111111111111 I 111111111111111111111111111111111111111 I I I I I I I I I I I I I I I I I I I 11111111111111111

RADIO -CRAFT for JULY, 1938

www.americanradiohistory.com RADIO IN PICTURES

1111111111111111111 I I I I I I I I I I I I 1111111111111111111111111111111111111111111I11111111111111111111111111111111111111111111111111111111111111111111111111 I I I I I I I I I I I I I I I I I I I I I I I I I I 111111111111

i Photo -Sovuto)

RADIO AFLOAT AT NORTH POLE TINY TELEVISION -NEWS CAMERA Above, and at upper- right, show past of Soviet We see, at left, how American engineering has Russia's 4 -man expedition to the North Pole, on helped perfect European television equipment; an ice floe; icebreakers rescued the men last Feb- Zworykin's Iconoscope has been utilized ruary (photos to perfect rcached U.S.A. in April). Radio oper- a television pick -up camera only a foot square and ator E. Krenkel is shown (above) inside his radio a half -foot wide! The outdoor television -news re- station; Reaching (upper- right) for pedal on the porter finds in this one case all the video equipment sled- mounted power generator -the wind- driven he requires, plus a built -in sunshade power and dual -lens unit may be seen, partly, in background focusing device, all in a cast -aluminum this - case! (The for "furthest North" radio nation, is Ivan sound pick -up apparatus, of course, is not included Papanin, "Hero of the U.S.S.R." in this set -up.) A companion small -space television camera is illustrated on the preceding page, both cameras $35,000 SOUND DISPLAY ON WHEELS! being a product of Fernseh A.G. (Berlin, Germany). Note however that the studio -type camera A 2 -point 7,000 exhibition tour, miles, by 3 RCA is somewhat wider than the outdoor type and un- officials, a in special Pullman car (A, below), like the latter its television and focusing lenses are started last month. Point I: to show dealers the mounted in a parallel plane. many markets for sound products; point 2: to spec- tacularly show architects, engineers, building owners, entertainment operators, industrial managers, RESISTOR GENERATES INFRA and -RED RAYS! school administrators in 24 principal cities of At lower the United States, the features of new -right you see how a resistor dutifully helps sound equip- take its own picture ment. In addition to living quarters, this in pitch -blackness! Illustration "itinerant serves the dual purpose museum" sports a section (8) for demonstrating of demonstrating to ex- record perimenters how ¡njra- ,d rays may easily be and film sound and talkies equipment generated, interphones, school and other permanent and how well-made resistors will stand sound up under considerable systems; and a section (C) for overload. In the test, a showing portable 360 -ohm Continental sound equipment, various electronic devices, etc. Carbon ''Ultrawatt" -type resistor rated for a normal On the observation platform are mounted mile - load of 10 watts was connected across 118 range loudspeakers (arrow, in A, indicates volts A.C.; and then sus- one of pended over the face two) to serve up speech and music; same -type units of the voltmeter recording the line potential. An exposure of 30 mins. are finding application, na ,ruígea(ed tu ¡tas( homes hypersensitized on of Radio -Craft, in the direction of fire- fighters, Infra -red negative material recorded the invisible rays ship-to -dock communication, and so -on. radiated by the resistor (overloaded 386%), and their reflection from the face of the meter. (Do you remember ?: April, '38 Radio -Craft showed how invisible cathode rays helped visualize electron flow; and the Sept., '36, issue showed how invisible X-rays made visible inside opaque Containers, faulty wiring, defective Components, etc.)

RADIO -CRAFT for JULY, 1938

www.americanradiohistory.com LONDON BERLIN, (GERMANY) (ENGLAND) (MY5TERY-STAT W N

MADRID

SALAMANCA

EUROPE'S UNDECLARED RADIO WAR! An Englishman tells of the relentless radio propaganda war being fought on the Western Hemisphere.

NORTONIIIIIIIIIIIIIIIIIIIIII:IIIIIII.III:I.IIIIIIIIIIIImIt11111111111111111111111111111111tllllllllllll1111111111m

IIE use of "wireless" (radio) as a Europe. It has the same power as WLW, means that the jamming is not always national weapon began during the Cincinnati. Soon, however, the British successful. This is especially noticeable Great War. In 1916, when the Ger- Broadcasting Corporation is to build 2 on the short waves, where the skip dis- mans could no longer use their sub- powerful shortwave transmitters which tance effect may mean that you can marine cables, they communicated with will be the most powerful in the world. hear the transmission but not the inter- their military attaché in Washington by The Russians are fortunate in that ruption. On the medium waves, things radio messages in code, sent by indirect their time is 2 hours ahead of Central are different. Only a few weeks ago, a routes. Unfortunately for them, this European Time, so that after their own German told me that he tried to hear code soon fell into the hands of the programs, they can use nearly all their the speeches of Herr von Schuschnigg, British. stations for broadcasting to the rest of the former Austrian Chancellor, but Toward the end of the War, there Europe. that he was unable to because they were was so much use of codes that, when the The Germans have made great efforts jammed by the German authorities. news of the Armistice was announced to jam the Russian transmissions. Some The most exciting event on the short k from the Eiffel Tower, not in code, sev- German friends of mine had a town waves took place last spring when a eral operators refused to believe what house which they were compelled to mystery German station suddenly ap- they heard, thinking the enemy was lease to the secret police. The owners peared on a wavelength of 29.8 meters. playing a trick! discovered by accident that the police Some say that it must be outside Ger- Over here in England, radio sets were had installed a Störsender, or "inter- many, but nothing has ever been proved forbidden during the War, and it was rupting station." It was intended for about this station. From 10 till 11 every ~ rumored that listeners had secret an- the interruption of the transmissions of night, it gives anti -Nazi propaganda, tennas fixed in disused chimneys. This the Russian station of Minsk, a town talking, for example, of the "gruesome may have been true; but I know that a less than 50 miles from Russia's west- barbarities of the Hitler regime." A similar thing occurred in Germany just ern frontier. German told me that the first night after the War. In the occupied area, the The moment that the propaganda in after this station was first heard in Allies forbade the use of broadcasting German starts from the Moscow station, Berlin, half the population of the town and its reception within the area. Some interference begins. On the long waves knew about it. The station was said by German friends living in Cologne told it takes the form of Morse (code) or a the announcer to be in Berlin, but it me that they had an indoor antenna and kind of dynamo hum. On the shortwave could not be traced. so did many of their friends. The an- transmission, the German interference It was thought that the transmitter tenna was taken down when the set was is usually made by the continual playing was placed inside a car, and the vehicle not in use. of a phonograph record. The record is driven round the town; but when I The first radio propaganda on a big usually one of the waltz Ramona, but listened here in England, the signal scale was put out by Moscow. The Rus- the Germans do use one other record, strength seemed too constant for that sians now broadcast propaganda in and this is of a slow fox -trot. to be the case. After a time, the German about 15 different languages, and they I know several Germans who listen authorities caused such severe jamming have the most powerful transmitter in to the Russian transmissions. This (Continued on page 39) RADIO -CRAFT for JULY, 1938 9

www.americanradiohistory.com RADIO CREATES Mr. Halbran, applying to fashion an amazing and endless variety of patterns created by television facilities, has instituted an entirely new tool for the stylist! Mr. Eichberg's engaging description, of how these patterns -due to a pencil of light moving at lightning speed -may find application in many new fields, will interest Radio -Craft readers. As told to ROBERT EICHBERG By ANDREW W. HALBRAN

Fig. A. Mr. C. E. Burnett is here shown setting up and photographing 111111111IIIIIIIIIIIIIIIIIIIIIII1111111111111IIIIIIIII1111111111IIIIIIII111I1111111111111111111IIIIIIIIIIIIII IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII the complicated electronic designs discussed in the text.

TEXTILE designers and ulation of the controls! others who must pro- Once it has been observed, duce patterns in in- it may be altered slightly- finite variety breathed or greatly, for that matter a sigh of relief when engi- -by adjusting the biases neer C. E. Burnett of RCA's (voltages) and frequencies. Television Research Labo- Nice though a pattern on ratory produced a "radio a C.-R. screen may look, it kaleidescope" (as the writer is of little value, save to dubs it), the heart of which is the good study, unless it can be recorded in per- old cathode -ray -or "C. -R." -tube, as manent form. This is easily done by used in television and oscilloscope work. means of a camera. A photograph of (See "New `Resolution Tester' for the image is snapped, and that's all Cathode -Ray Tubes," Oct. '37 Radio - there is to it. The tube's controls can Craft. Editor) be readjusted and a new pattern pro- As you no doubt know, the patterns duced, while the films are developed appearing on the screen of a "C.-R." and the prints sent wherever they are tube may be governed by the voltages likely to do the most good. of various frequencies applied to the Mr. Burnett is seen with the com- horizontal and vertical scanning elec- plete set -up in Fig. A. On the screen trodes. Innumerable patterns can be there is a pattern which looks much made to follow each other across this like a series of small cream bottles; it screen, and any that appear to have might be suited to sports dresses for interesting (i.e., commercial) possibili- country wear or a milkman's uniform, ties can be halted in its mad dash and or to paper used to wrap butter, etc. anchored fast simply by proper manip- A slight turn of the controls, and the bottle -effect vanishes. The spaces between the horizontal rows of bottles grow larger and the bottles themselves are broken up, while a dotted effect, much like that which would result by weaving a heavy white yarn through t a dark background appears to link the larger white blocks. It's practically a Scotch plaid (See Fig. B.), save that

4Ca_..'VAIL

!MUTT

11ullouhu !N111

11L;I1, I I I I ,I;11 !VIII{I¡I1llilll lo RADIO -CRAFT for JULY, 1938

www.americanradiohistory.com AMAZING FASHION PATTERNS

the print is black and white, instead of to be the inspiration for a new pattern being in every color of the rainbow, of decorative stitching, used to edge with a few extra added for good meas- handbags and wearing apparel. But ure. As the illustration (Fig. BI) shows, that was not all! The building and it is an ideal pattern for a gay Tam metal industries are expressing their O' Shanter. And it is also highly suited interest in it, for they say it reveals for use in blankets, golf socks, sport the possibilities of a new type of joint. coats, skirts and sweaters -even for Linked lines are also the basis of the the background of the label on a bottle basket -weave pattern which the cathode - of Scotch! ray kaleidoscope produces. A designer Did you notice the dots between the of women's accessories said, "It will blocks? Re-tuning the radio kaleido- make handbags which are simply scope brings them out as the dominant fetching, my dear," and promptly drew motif. (See Fig. C.) They make an a sketch (See Fig. Gl.) to prove her excellent all -over small -figure pattern, words. Designers of draperies also plan suitable for silk dresses, scarves, neck- to make use of this pattern in black ties, and so forth. (See Fig. Cl.) It is background interwoven with heavy gold even said that they inspired a wall- thread. paper manufacturer and a producer of A little shift in the tuning controls china -ware. breaks up the design into separate dashes which combine to form waves. RADIO KALEIDOSCOPE CREATES Notice how the pattern in Fig. H is "ELECTRONIC SNAKESKIN" PATTERN! broken at the edge of the C.-R. tube's The "electronic snakeskin," used as a screen. A defect? Not at all! The break pattern for the shoe, may also be traced is utilized as a border for the lamp- to a slight re- tuning from the plaid. Its shade shown in Fig. Hl. It gives the effect is a deformation of the regular- logical finish to the design as a whole. ity of the blocks, with complete separa- The lines were quite regular in that tion between the vertical rows while cathode -ray pattern. Adjusting the fre- broken bands run between the horizon- quency robs them of their regularity tal rows. The pattern (Fig. D) may be and provides a new pattern -the zigzag printed upon or woven into the fabric effect of Fig. I. A designer of fans fell of which the shoe (Fig. Dl) is made, in love with it, with the result seen in and a manufacturer has already signi- Fig. Il. As the pattern effect is that of fied his intention of bringing out such a flash, and as it was produced by the a model! use of electronic apparatus, it might This finding of patterns through elec- be termed the fashion industry's first tronic means is by no means an entirely real Radio Fan. hit -or -miss affair. Research has proven But the comparatively simple pat- that given frequencies may be relied terns described are not all that this upon to produce patterns of a certain apparatus can produce. It can make sort. If, for example, a chain effect of (Continued on page 38) linked lines is wanted, the electronic designer looks at his frequency chart, sets the controls and -presto! -a pattern similar to that used on the bracelet illustrated appears. The basic pattern is seen in two different forms in the accompanying illustrations, Figs. E and F. The former, you will notice, is precisely the design employed in the bracelet (Fig. El) ; the latter, which is but little different, opened up an entirely new line of thought. It proved

á;..: i ;4. :; ..w I . ik .a ' ii .... kr .

RADIO -CRAFT for JULY, 1938

www.americanradiohistory.com Fig. 3. The electron image (light amplifier) tube of the future.

w...---=cs c --coa.._.. .t - - - - + -ifüif'i ( 111-111 1t1 MOt, --'-' .t.-:t i: :i ",r=c 17.1.1 iia{.-.i r 11' ,1.{ i:i.¡.i- _.__ - - t t J'{ it"" ' ' `i -..t..t1l.i 'a a. IS 1. , ._ caca,c.: ' .- ..il.j - "- - .. cr d " 1111i11ë1:E. 1 t '. i to -. ta t u t :1ii-iïiïïï1 1 Fig. B. The television receiver -projector the of future. F g. A. Artist's conception of the centrally- located television transmitting tower. TELEVISION WITHOUT SCANNING? Will telescopes and periscopes replace our present complicated television scanning apparatus? A well -known television pioneer leaves the beaten path and reasons -out a new television concept. Compare Mr. Sanabria's observations 11\ with those of another forward -thinking technician, Mr. W. E. Shrage, whose article, "Ultra- Ultra- Microwave 'Radio' of the Future," in the January 1937 issue of Radio - Craft, too, discards many hide -bound ideas.

Fig. I. Fundamental optics of the predicted television system. Extreme simplicity prevails. BBIIBiIBIIIIIIIIBIBIIIIIIIBIIIIBIIIInBIIllnllllllllBBIIIIIInIIIIBIIIIIIIIBBBIIIIIIIBIIIIIBIBIIIIIIIIIIIIIBIIIIU. A. SANABRIA

EVERY television worker has gazed, science has never displaced the regular himself agreeing with the majority in in his dreams, upon the El Dorado jerking mechanism (or has it ? -Edi- any controversial matter. He was con- of a television system without scan- tor); the flapping wing airplane which vinced that "The majority is always ning. The development of spot -by- takes off and lands like a bird has never wrong." He reasoned that basically, spot scanning systems with all of their been a competitor of the propeller and higher intelligence is a characteristic of associated difficulties often cause the rigid wing system. (Continued on page 57) tired engineer to think about a system Such illustrations are the thoughts of which has none of these objectionable the pessimist who represents the mod- scanning features. ern version of the man who thought that the automobile would never dis- AN ANALYSIS OF PROBABILITIES place the horse, or the commonplace ob- When we talk to a television engineer servation that "Yon can't stop a roaring about the possibility of eliminating train with wind" prior to the develop- scanning, he will usually pass off your ment of the air brake. In contrast with question with a smile of aloofness and the above examples we find many seem- imply that this possibility belongs to ingly ideal devices: the water turbine, fiction writers. One can point out numer- the steam turbine, the induction motor, ous examples in industrial history the circular saw, and hundreds of other which reveal that ideal systems in examples of how fuss and commotion theory are seldom resolved into practi- have been eliminated by the hard work cal devices. The gasoline turbine which of engineers who believed fundamen- eliminates reciprocating parts for auto- tally in the slogan, "We can always mobile engines has never been per- improve." fected; the continuous running film The late Clarence Darrow explained camera and projector without intermit- that he stopped to analyze carefully the tent movements for motion Fig. 2. A periscope in the home wi dow picks up picture accuracy of his thoughts when he found the transmitted television s gnal!

12 RADIO -CRAFT for JULY, 1938

www.americanradiohistory.com NEW RADIO SERVICE "CAR"

120 miles to I gallon of gas! That is economy which Service Men will readily appreciate. This Motor Scooter and side - trunk is a practical "buggy ", especially for suburban use.

G. E. D e N il

SINCE the day the Chesterfield cig- which looked like a motorized scooter, arette girl suddenly burst forth popularity of this mode of conveyance on posters throughout the nation, has risen by leaps and bounds. posed on a new kind of a contraption Throughout the country, spread the fad of getting about on these zippy little motor horses. It didn't take long for local merchants to realize that here was the ideal low -cost transportation AX S for light deliveries if 80711e sort of a RADIf? SHOp carrying device could be attached to the conveyance. Fg. A. Reproduction of the cover painting. The manufacturers of these Motor Scooters quickly grasped the signifi- down the transportation expense in- cance of this situation and set their en- volved in service calls. gineers to work, .developing the kind of models needed for commercial appli- LOW -COST TRANSPORTATION FOR cation. They soon produced several SERVICE MEN models -of which the best one for The maintenance of one of these Mo- radio Service Men is illustrated. tor Scooters is scarcely more than that The handsome trunk built into the of a bicycle. The Service Man can ride side -car position offers plenty capacity from 100 to 120 miles on a gallon of for the transportation of-test equip- gasoline, license costs are at a minimum ment, tubes, manuals, parts, tools, com- and it takes very little "elbow grease" plete small radio sets and large radio to keep the unit sparkling like new - chassis and speakers. which helps a lot to attract and hold Here indeed is the answer for the the attention of prospective customers. on page 54) Fig. 6. Adaptable to mobile P.A. systems. Service Man to his problem of cutting (Continued AMERICA'S RADIO COLOSSUS Here are some interesting and revealing facts, which seldom come to the attention of the general public, concerning Radio's largest and most far -flung organization.

This indeed is one of the most widely spread and owned corporations. In its has some of the finest the branches of America's Radio Colossus. structure this organization Some of brains in the country, some recent additions being former scenes of radio's largest vice- President of the United States, General Charles G. WHAT transpires behind the of the corporation? How does it thrive? What is the nature Dawes; and the eminent Engineer and President How does this large organization J. G. White Engineering Corporation, Mr. Gano Dunn. To of-its transactions? we will refer briefly fit into the commercial structure of our industry and coun- give an idea of its many ramifications which the layman to the principal events which have taken place since the try? These are some of the questions Meeting of would like to have answered. first of this year as outlined at the 19th Annual There are few companies in the United States whose the stockholders of RCA. ownership is more widely distributed than that of the Radio Corporation of America. Its stockholders are situated FINANCIAL TRANSACTIONS in every State of the Union. Since its business is essentially In accordance with its recently-established policy of con- one of widespread public service it is only fitting that its centrating its investments within the United States the ownership should be so widely shared. company, during the months of January and February, sold Altogether there are approximately 242,000 owners of its Japanese and Canadian stockholdings. Its holdings in RCA stock. Forty -three per cent of this total number (more the Japanese Company (Victor Talking Machine Company than 100,000), strangely enough, are women. More than of Japan, Ltd.) were sold for $2,000,000. This transaction, half of the total number of stockholders (approximately however, included an extension of licenses, resulting in con- 135,000) own 10 shares or less. Fifteen per cent of these tinuing royalties paid to RCA. Against this amount the in cash, the stockholders (some 35,000) own 1 share each and only 10 company thus far received $1,750,000 balance per cent own as much as 100 shares each. No single indi- of $250,000 falling due January, 1939. on. 59) vidual owns as much as ih of 1 per cent of the total stock. (Continued page RADIO -CRAFT for JULY, 1939 I3

www.americanradiohistory.com 25Z5 SPEAKER INPUT 25Z5 t , FILTER FILTER FILAMENT VOLTAGE -43 *C COND.\ COND. DROPPING RESISTOR 6C6 FILTER /K2 k ! _\ CHOKE 4 + K1 Ot- r 1 MF I FILTER \ ' COND. ` ,ON-OFFON-0FF INPUT FILTER kTY SW. i COND. SPEAKER n FIELD 115V. A.C. OR D.C. 'SPEAKER FIELD Fig. I. Typical circuit of a midget A.C. D.C. receiver. Fig. 2. Typical power- supply circuits of A.G.-D.C. sets. SERVICING UNIVERSAL A.C.-D.C. RECEIVERS By special permission of National Radio Institute Radio -Craft is pleased to present an outstanding article, of exceptional importance to the average radio Service Man, which appeared in a recent issue of N.R.I.'s house organ National Radio News. This article is of unusual value to the practical man not only because it describes time- saving procedure but also because it explains in detail just why this procedure is preferable. Service Men will do well to actually study this article. J. B. STRAUGHN ONE of the most common types of grade parts. Such a line of reasoning counter a magnetic speaker. receivers brought in for servic- seldom fails to bring in the job at a In some sets one or more dummy ing is the "cigar box" type uni- high enough price to give the Service tubes will be found, with only the fila- versal A.C.-D.C. receiver using a Man a fair profit. ments connected into the circuit. As T.R.F. circuit with 4 or 5 tubes. Sets Although this article deals primarily long as the filament circuit is not open, like these have been widely distributed with the servicing of "universal" -type the condition of a dummy tube is im- over the entire country and have been (or A.C.-D.C.) T.R.F. receivers for material; in fact, defective tubes are sold at extremely low prices. Since man- which circuit diagrams are not obtain- often used originally by the manufac- ufacturing costs must obviously be kept able anywhere, the procedures described turer to keep costs down while making down when a receiver complete with apply equally well to these T.R.F. re- the customer think he is getting a tubes is to sell for less than $10, low - ceivers when circuit diagrams are at larger receiver. grade parts are often employed. Break- hand, and will also prove of value in downs are frequent, and Service Men servicing universal A.C.-D.C. super- TYPICAL "UNIVERSAL" CIRCUIT are expected to make prompt repairs. heterodyne receivers. In Fig. 1 is shown Unfortunately for the customer, the typical signal it The signal circuits of a midget T.R.F. circuit arrangement of an A.C.-D.C. costs very nearly as much to repair one radio set are extremely simple. Gener- T.R.F. receiver. of these small receivers There are several as a larger set. ally there is one stage of radio- frequen- peculiarities which should be noted; When a customer hears the estimate of cy amplification using a 6.3 -volt super - these are: (1) the service costs, he chassis may not be generally exclaims: control pentode tube such as the 78, an electrical part of the circuit, in "Why, I can buy a new radio for less 6D6 or 6K7. The former two types have which than that!" case the ground symbols simply the same base and are interchangeable, indicate that the parts so marked are This is true, sad to say, but the while the latter uses an octal base. connected together ; (2) the screen -grid business -like Service Man will point out The R.F. amplifier feeds into the de- of the the R.F. tube gets the same potential that parts in the new receiver will tector, which uses a pentode tube hav- as the plate; (3) an external ground be no better than those in the old one, ing a sharp plate- current cut-off connection is and same not used because one side the trouble will undoubtedly characteristic. Interchangeable, type of the power line (which connects to the develop in a short time. On the other 6C6 or 77 tubes, or the octal -base 6.17 receiver circuits) is grounded; (4) the hand, if the old receiver is repaired, tube will generally be found in the small using first coils connected to the primary -class parts which the manu- detector stage. R.F. coil windings provide capacitative facturer could not afford to employ, The audio output of the detector is coupling in addition to the usual excellent results be induc- may expected. The fed by means of resistance -capacity tive, primary/secondary coupling. cost of service work on one of these sets coupling into the power output tube, The aerial for a midget set is usually should really be considered a part of which is generally a type 43 pentode. of flexible wire, the purchase price, permanently attached for the value of the This tube in turn feeds the loudspeaker; to the set and connected to the receiver receiver will be increased in exact pro- although a dynamic loudspeaker is more input value circuit through a small tubular portion to the of the new high- often used, you will occasionally en- or mica condenser. This aerial wire may be grounded to a water pipe or other external ground, in which case the R.F. signals picked up by the ungrounded side of the power line will flow through the primary of the 1st R.F. transformer, then through the antenna condenser and the aerial wire to ground. The R.F. signals passing through the primary induce a signal voltage in the secondary in the usual way. If the chassis is an electrical part of the circuit and the line cord plug is inserted in such a way that the chassis Fig. 3. A and 8 are different. pilot light hookup Fig. 4. The rectifier and filter circuit. connects to the hot (ungrounded) side 14 RADIO -CRAFT for JULY, 1938

www.americanradiohistory.com shock which the filament -supporting wires 6C6 of the power line, you may get a (DEI MERI Q when you touch the chassis if some part pass. A mazda No. 40 lamp with a minia- J.--\ of your body is grounded. If you get a ture screw base draws 0.15- ampere and - I A No. - - ) shock, reverse the line plug if the source has a brown -colored bead. mazda ,- - , a- : 1 is A.C.; this will connect the chassis to 46 lamp with a miniature screw base the grounded side of the power line. In draws 0.25 -ampere and has a blue bead, the case of D.C. power you cannot re- while a mazda No. 44 lamp with a . . verse the plug, for that would make bayonet base also draws 0.25-ampere a blue bead. A third type of polarity incorrect; you will simply have and has Fig. 6. The defector screen -grid obtains its bias to avoid standing on a concrete floor (a lamp, having a white bead and drawing from the cathode of the power tube. good ground), and avoid touching any 0.20- ampere, is infrequently encoun- grounded object while working on the tered. Replace burned -out lamps with envelope and connected to prongs on on. With either A.C. or new lamps having the same bead color the tube base. Oftentimes taps are pro- set with power prongs, D.C. power, never make a direct connec- and voltage rating (6.3 volts). vided, with connections to tube tion from the chassis to an external You will occasionally find 2 pilot to eliminate need for separate pilot ground, for this may short- circuit the lamps connected in series directly lamp shunt resistors; an example of a power line and blow the line fuse. across the 110 -volt line, with no shunt ballast tube having one tap for this pur- resistor across them. These will be 110 - pose is shown in Fig. 3B. TYPICAL A.C.-D.C. POWER SUPPLY volt Japanese lamps similar to those When a ballast tube burns out, al- having Figure 2 shows a typical power sup- used on Christmas trees. They are con- ways replace it with another ply circuit used for both T.R.F. and nected in series to operate at half- exactly the same number. This is neces- voltage, thereby having longer life sary because the tubes are made with superheterodyne universal A.C.-D.C. with sets. A 2525 tube is connected as a sin- while still giving sufficient light to many different ohmic values and the illuminate the tuning dial. many different arrangements of prong gle half-wave rectifier, but where very loudspeaker field coil is energized inde- Types of Filament Resistors. Various connections. Ballast tubes become of circuit, there types of filament voltage- dropping re- hot while in use, but as the heat is pendently the receiver in the will be a separate connection to each sistors are used in universal A.C.-D.C. above the chassis, critical parts sets. Many of the earlier models use receiver are not damaged. cathode and an extra filter condenser to connected directly across the loud- ordinary wire-wound resistors mounted Service Men are sometimes asked in the dotted under the receiver chassis. The chief replace line cord resistors with ballast speaker field, as indicated in- circle at the right in Fig. 2. disadvantage of these is that the heat tubes; space limitations make it The tube filaments in a universal re- which they radiate causes deterioration advisable to attempt this, for midget ceiver are wired in series, with each of nearby receiver components, chiefly receivers are quite compactly construct- filament requiring 0.3- ampere. The fila- the electrolytic condensers. ed. Incidentally, an ohmmeter provides ments of the type 25Z5 and 43 tubes Line cord resistors, having the re- the quickest way of identifying the vari- require 25 volts each, while the 6D6 and sistance wire embedded in asbestos and ous prongs on a ballast tube. require 6.3 volts. This placed in the line cord along with the Rectifier Circuit Variations. A single 6C6 tithes each 37 makes a of approximately 63 volts, usual 2 copper wires, are now widely 12Z3 rectifier tube or even a type total connected and means that the filament voltage - used because they keep the dissipated triode with grid and plate dropping resistor must drop 115 - 63, or heat entirely out of the chassis. Line together may be found in a circuit ar- 4. Since approximately 52 volts. Since 0.3- cords are easily identified by the fact rangement like that in Fig. ampere flows through this resistor, it that they have 3 leads instead of 2; the supplying field excitation to a dynamic an ohm value of 52 + 0.3, or resistance wire is connected to one of speaker would place too heavy a drain will have to find approximately 175 ohms. the line wires, the connection being on the rectifier, you may expect lamps are used, they are made directly to one of the prongs on a magnetic loudspeaker in a receiver If pilot The usually placed in series with the voltage- the line cord plug. The line wire which having this power pack circuit. limiting resistor. Each lamp is operated connects to this same prong may be 0.1 -mf. condenser connected across the re- with an ohmmeter, and al- power line tends to prevent interfer- at about 4.25 volts, and hence the identified way quired voltage drop across the limiting ways goes to the rectifier plates. The ence from entering the receiver by wire will go to the ON -OFF of the power line. Oftentimes a 2,000 - resistor is reduced by this amount. Two other line of pilot lamps connected as in Fig. 3A switch which is mounted on the volume ohm, 1 -watt resistor is used in place drop by control of the receiver. the more efficient but bulkier and more ?educe this required voltage inside 8.5 volts. (Although the lamps are rated When a receiver which uses a line costly filter choke, as indicated 4. at 6.3 volts, they are operated at 4.25 cord resistor is in operation, the line the dotted circle in Fig. volts to prevent burn -out on surges.) cord becomes quite hot, but this is nat- Sometimes you will find a circuit Pilot lamps are always shunted by ural and is no cause for worry. Never which uses two 12Z3 tubes connected resistors, for these lamps do not draw attempt to shorten the line cord when in place of a single 25Z5; the circuit filaments. it has a built -in resistance, for this will be the same as that in Fig. 2 ex- as much current as the tube the The shunt resistance will be equal to would reduce the resistance value and cept that the 2 diode sections of the shunt current (the difference be- affect the operation of the receiver. rectifier tube will be in separate enve- tween the 0.3- ampere filament current Ballast tubes are even more satisfac- lopes. The filaments of the two 12Z3 and the pilot lamp current) divided into tory than line cord resistors for fila- tubes will be in series and will together the voltage across the lamp or lamps. ment voltage-dropping purposes. These be electrically equivalent to the filament secured with either of a single 25Z5 tube. This gives the Pilot Lamp Color Code. On A.C. -D.C. tubes can now be an sets, only 2 types of pilot lamps are glass or metal envelopes, the metal en- set an extra tube and is therefore ordinarily used; these can be identified velope being the more popular. The re- advantage from a sales standpoint. The by the color of the glass bead through sistance element is mounted inside the (Continued on page 46)

INPUT FILTER COMMON IN- I NPU T FILTER wzoM PUT A+ó t-W TOZO MF rit - 1l - Ol6F Fit- ±TOI6MFR ` ;l 8T0L6MF J` ±.DATTHTOR FI ir "SPEAKER i E-f CATHODE 11 ± SMF. r-' + 4TO8MF. IF ` SMF. ;it COMMON ~PCÁTHODEE Fit--f11ETTt10DÉ5MF. L-__PUT TER L - SMF. I POWER TUBE AND DETEC- I CATFtlOE 5 MF. IOR CATl100E. \COMMON L NEGATIVE L-_--. pM pU ÑEGAñVÉ ' FILTER condenser blocks used in in the negative Fig. 7. Typical connection for the electrolytic Fig. 5. Another power -supply circuit with the filter choke A.C.-D.C. sets. plate -supply lead. midget RADIO -CRAFT for JULY, 1938 15

www.americanradiohistory.com SERVICE MEN! REPAIR YOUR CUSTOMERS' SETS "BETTER THAN NEW "! A Service Man of over 12 years' experience, and who for the past few years has personally supervised an average of about 1,500 jobs per year, gives you the benefit of his practical experience. Most important of all he shows you in simple, straightforward fashion wherein lie the moneymaking possibilities of radio service. GEORGE W. HALDER

I I I I I I I I I I I I I I I I I I I I I I 1 1 1 1 1 1 111111111 I 111111111 I I I I I I I I 111111111111111111111111111111111111111111111 111111111111111111111111111111111111111111111111111111111111111111111111111111111111111 i I I I I I I I I I I l A SAYS THE AUTHOR: MOST radio Service Men look upon - MODERN EQUIPMENT ESSENTIAL themselves as technicians of un- q "The extra preliminary work (herein t described) takes time, so does the proper The questionable merit who, as a radio service shop must, of . adjustment of the selectivity curves; -but e course, have a whole are very much underpaid, complete assortment of 1 t it makes for satisfied customers, you get testing equipment. very much abused and very much under- fewer i The days of a radio call backs, and you are perfectly f shop built around a single rated. They justified in i analyzer, and believe that they belong to charging more for your work. tube tester, an upper strata of humanity affiliated "Don't be 'price conscious,' cleaning f' are definitely over. Essen- and tial equipment is recognized as a good with the geniuses of the mechanical alignment as described herein is i industry. Why? Because, with the aid . worth $5 of anybody's money and when t A.C.-D.C. voltmeter, calibrated oscilla- you return the radio t tor, of several hundred dollars' worth of set to the customer modulator and cathode-ray oscillo- i you are proud of your work. Tell him what scope, scientific instruments, they can cause a i tube tester equipped with sound, silent you have done, explain it to him whiles and some sort of audio oscillator. Prob- radio set to once more give forth you install the chassis in the cabinet, tell f. ably the most important piece raucous sounds, which they proudly ex- i him about the oscilloscope. He may of equip- not ment, and the one that is seldom plain to the customer, is the same re- i admit to you that the set is any better, found a. in a shop is an ception he once had when the radio set + but how he will brag about it to his ; air compressor, with was new. friends! -and that is what makes good flexible tubing attached to an air nozzle, They believe by business; -a satisfied customer giving you e for blowing dust out of the radio chassis. that merely replacing t a punctured condenser, or an open re- free advertising every time anyone men- Compressed air is the only way of tions 'radio'!" y sistor, they have accomplished a miracle reaching into the trimmer condensers, and "repaired" a radio receiver. Proba- coils and switches, for the removal of bly the variable condenser plates pete with you dirt. Last, but not least, a bottle of are -and educate the public Russian (or dirty, the bearings dry and squeaking, to the fact that your work is worth the "mineral ") oil, and a the volume control noisy, the speaker difference. camel's -hair brush. rattles now and then, the resistors have No workman in any line of industry The first step is to remove all tubes, changed value up to 50% of their orig- is really expert until he is conscientious- wipe them off with a damp cloth, and inal tolerance, but what of that, their ly thorough on every job, until he has test these tubes thoroughly; if the tube job is done -the "radio" is once more an open mind ready to receive new tester is equipped with sound, rap the running. thoughts, and methods which might be tubes severely with a small rubber ham- So it is sent back to the customer, and an improvement on his methods, and mer to locate weak joints and shorts. the customer wonders why he had to pay until upon completion of a job he can With about 80 pounds of air pres- so much money to have a 25c part re- honestly say, "This job, barring the cus- sure, blow the dust off the chassis, and placed. The customer was probably told tomer's restrictions, is perfect, and as from between the variable condenser he would have his set returned as good as new." plates; 20 or 30 pounds pressure can good as new, and he finds that it is not It is not sufficient to just repair a be applied to the trimmer condensers, much better than before it stopped, so, set, it must go back to the customer's and coils without fear of injuring these and not without some justification, he home performing as good, or BETTER parts if a little care is used. This clean- calls the radio service business a than it did when he first bought it. This ing of the trimmer condensers is very "racket," and the next time he has means a satisfied customer, and a satis- important; dust collects between the trouble he calls the janitor, or some fied customer will talk, and word of multiple plates of these small condensers high -school boy, and probably gets an mouth advertising is the most powerful and due to speaker vibration will shift equally good job for one -fifth of the cost. type of advertising in the world. back and forth, sometimes expanding Of course there are plenty of shops the adjustment and at other times sift- THE "SCREWDRIVER MECHANIC" with full equipment and competent tech- ing out, thereby increasing the capacity, Service Men wonder why business is nicians in charge, who turn out perfect and this makes plenty of difference in not as good as it could be; probably an repair jobs, but on the other hand there the overall performance of the radio, analysis of their shop methods will ex- are countless hundreds of shops which due to changing the acceptance curve of plain a lot! Thousands of dollars' worth turn out very poor work, either through the intermediate frequency amplifiers, of business is lost every year to the part lack of ability, or probably the greater and of course causing the oscillator to time worker, and the screwdriver me- evil, insufficient knowledge of proper drift off frequency, and changing the chanic, who operates from his cellar, or servicing methods. dial setting. attic, repairing his friends' "radios," The author has been actively em- Probably the two things that impress and just as long as he can turn out as ployed in radio service work for over 12 a customer most is a clean chassis, and a good work as a professional shop, just years, for the past few years has per- tuning dial that is adjusted right on the that long will he continue to do a thriv- sonally supervised about 1,500 jobs a dot. If a local station is on an assigned ing business. Every dollar's worth of year, and naturally enough has de- frequency of 1,400 kc. -that is where work done by this type of mechanic rep- veloped a certain technique for the he has a right to find it, if a local low - resents a loss of $3 to $5 to a legitimate handling of these jobs. In the following frequency station is at 570 kc. that is shop. The only way to stop this loss is chapters he will endeavor to take the where the pointer should rest when the to turn out work of such excellent qual- reader through the servicing of a super- station is properly tuned -in. Of course ity that he can no longer hope to corn- heterodyne chassis, using his methods. the author understands that the radio 16 RADI 0-CRAFT for JULY, 1938

www.americanradiohistory.com set probably never did tune on- frequen- the chassis. The variable condensers get cy, but that is your job, it means a more their share on both end bearings, and on satisfied customer, who will be a booster the brass contacting strips, also put oil for you. under the brass strips where they con- Cleaning the loudspeaker calls for a tact the divisional shielding plates. On different procedure. First loosen the old or badly oxidized condensers it may cone centering screws, allowing the cone be advisable to scrape or sandpaper the to float freely, then connect 110 V., A.C. divisional plate before applying the oil. across the field coil, this will relieve the Next apply oil to the pins of every pole piece of any residual magnetism tube before inserting them in their and allow you to blow out not only dust sockets, this will clean the sockets; con- but any metal filings that may have nect the speaker to the chassis, and plug collected in the air gap. Air pressure for the line cord in the A.C. outlet, turn this purpose will vary from 30 to 80 the current on and measure the high pounds, depending on the type and size voltage from the rectifier plates to of the speaker cone. Do not be afraid ground, to determine if both sides of of blowing the voice coil apart; if it does the power transformer are equal and loosen under the strain of the air pres- of approximately proper voltage. Next sure, it needed repairing anyway and insert the rectifier tube and let the radio would have buzzed or rattled at certain set run while the balance of the tubes frequencies. Loose voice coil wires can are replaced; this allows the radio re- be cemented together again with speak - ceiver to be subjected to excessively er cement, but if there is an air space high voltages from the power pack for between the voice coil wires and the a short time, and if a part is definitely paper form upon which they are wound weak, it is much better to have it break it is best to replace the entire cone. Re- down in the shop than in the customer's assemble the speaker, using shims on home a week later. If tube shields are both sides of the voice coil, i.e., inside used, a little oil applied to the part that and outside. contacts the chassis ring will insure a good contact and perfect shielding. THAT BOTTLE OF "SERVICE OIL" Now we have come to the point where Now we come to that bottle of oil. the average mechanic begins work, but Most of you are dubious or openly skep- we know that tubes, contact elements, tical as to what value oil is in the serv- etc., are in perfect condition, and that if icing of a radio chassis. Sort of makes a noise or some other disturbance is a person think of greasing an automo- noticed after operation is restored to bile, but try this method once and you the chassis, that it is definitely a defec- will always use it. Remember, this oil tive part, and valuable minutes will not is not a common oil, it is especially be wasted in searching for a poor con- suited to our needs, it will pass no cur- tact in a wave -band switch or something rent, it will not detract from R.F. gain of similar nature. As far as the testing at high or low frequencies, it does not of a "dead" radio set is concerned, become gummy, and it does wonders in a probably anyone's method is as good as noisy or "intermittent" radio receiver. the author's. Usually the procedure is Did you ever have a noisy carbon to check for approximately 200 V. be- volume control in the grid circuit of tween ground and the plates of the A.F. a 1st -audio tube? Did you ever remove output and R.F. plates, then for proper the back cover plate of one of these screen -grid voltages and so on. Any loss controls, and notice the number of metal - shorted condenser causing voltage to-metal contacts that carry the con- is easily found, as is an open resistor. tacting arm on the resistance element to Replace any defective parts with suit- the center terminal on the case? Try a able replacements, making the part little mineral oil applied with a camel's - mechanically secure before soldering. hair brush to these contact points; don't After operation is restored, turn off the be too fussy-the oil will not harm the current, and quickly check the bleeder, resistance element, but be sure it coupling and bias resistors for toler- reaches 'way in to the center of the ance, replace any that deviate more circular contacting member. Now try than 204 from the original specifica- the volume control in the circuit. Quiet? tions. like better than a Just silk, probably ALIGNMENT new one. One -tenth megohm, or higher value resistance elements seldom wear Now we have reached the point where out, but the metal -to -metal contacts do we must align the tuned circuits. Never get dirty and oxidized. One application align a chassis while it is cold, always of this "service" oil takes care of these let the radio set under test run for at points for years to come, by preventing least 15 minutes before attempting any further oxidization. Of course if the alignment adjustments, this same ap- control has a defective resistance ele- plies also to the oscillator and modu- .nent nothing can effect a satisfactory lator. Set up the oscillator to a 10 kc. repair other than replacement, but this frequency- modulated signal on the I.F. only happens about once in 20 times. of the receiver and align the I.F. stages Every movable part in the radio set according to the manufacturer's instruc- -rheostats, potentiometers, waveband tions, but fiat-top those curves. Be switches, supporting bearings for definitely sure you give the customer at switch mechanism- should be treated least a 10 kc. band -width in the I.F. with a touch of oil at the bearing stages. He bought the radio set pri- point only; do not be too liberal, a little marily for tone quality, and real enjoy- oil applied at the right point is far ment of local broadcasts. Don't send better than having oil leaking all over (Continued on page 58)

RADIO -CRAFT for JULY, 1938 17

www.americanradiohistory.com SERVICING

Continuing the discussion from Part I, two typical electro- mechanical tuning systems are here described for the benefit of all Service Men. Pushbutton tuning is here to stay . .. get acquainted with it now, while it's yet new.

Fig B. Front view of the Stewart-Warner electro- mechanical pushbutton tuning mechanism . . . a marvel of mechanical ingenuity. PART II SICURANZA

MANUAL UNDER the general classification of Mechanical Sys- BUTTON LSWK. L700 KC. 900KC. OOOKC. 600 KC. SOOÏ 700KG tems of Pushbutton Tuning, we encounter some of ®T( * li. the simplest mechanisms in the smaller sets; while r wed- -- -1 in I j i- the larger sets, we find some of the most intricate .. .. and high- precision assemblies ever seen in a radio receiver. /he e i MECHANICAL BUTTON TUNING WITH MOTOR DRIVE L e J - 1- n- The Stewart- Warner, 15- T Station Magic Keyboard mechan- tiY ism is an example c_a c t_s,Sa csS c of mechanical button tuning with motor to T çP drive. A front view of the Keyboard assembly is shown in Fig. B. The C 1 complete mechanism is unusual in several re- spects and its operation and setting up differ ) radically from 7 T i' the previous examples cited. Figure C shows the rear view BROWN OiiOiER of the mechanism. YELLOW SIDE OF TUNING As can be seen, 15 stations may be set -up, from r SWITCH. the front VARIABLE of the receiver, without tools. Once the buttons have been DENSER r MOVING set up, stations may be tuned -in almost instantly because I CONTACTS I ®/ the dial pointer travels directly to the desired station. In previous I STATIONARY descriptions of motor tuning, it was seen that the I dial pointer often had to travel the full length of the dial, PADDER reverse and return to the desired station. By utilizing an eccentric cam of special design for each button, the driving Fig. 14. The Meissner pushbutton assembly; circuit -transfer type. motor is made to turn clockwise or counter -clockwise, depending upon which station -button is pressed. As with other modern systems, the station buttons do Tt PUSHBUTTONSJ not have to be kept pushed -in by hand. The button is pushed T in and all the other buttons are released automatically, so 1 T that even if two or more buttons have been pushed in at ^^^ - I -I------I I-----I--, one time, all are released by pressing down any other free button. In this connection, it is interesting to note that if BUTTONr two buttons are pressed -in together, the dial pointer will MANUAL move to the nearest of the two stations and stop. LII111I With other systems, the dial pointer will keep on moving I--I__, across the whole length of the dial, back and forth, until a third button is pressed, to release the two previously depressed buttons. Another unusual feature is found in the Manual tuning . changeover. In this system, there is no knob to turn when DENSER r7 7 ir. -T either hand or button tuning is desired. The slightest twist TRIMMERS of the tuning selector knob disengages the cam assembly, Fig. 15. A typical pushbutton assembly of the circuit -closing type. releasing any depressed button and extinguishing the light signal reading "Automatic" while the Band Indicator and Visual Tuning Indicator light up. The A.F.C. voltage is always turned off for hand tuning and automatically turned LEVER - RELEASE LATCH SPRING LEVER on for button tuning. Hand tuning is of the "spinner" type, effected by means of a weighted flywheel at the end of the tuning knob. This PIVOT knob does not turn when the set is button -tuned -as it PIN does in other motor systems.

SETTING UP STATIONS

LATCH To set up stations on the keyboard, use the following step - FULCRUM TOP AND BOTTOM ULCRUM- by-step procedure: MOVING RELEASE (1) Allow the set to warm up for 20 minutes so that CONTACTS SPRING all parts will reach a constant temperature. (2) Remove the large station tuning knob by pulling Fig. 16. Section sketch of a latch -type pushbutton switch. The latch keeps the button depressed until another button is pushed in. straight out, exposing a small set -up knob on the same shaft.

18 RADIO -CRAFT for JULY. 1938

www.americanradiohistory.com PUSHBUTTON TUNING SYSTEMS

(3) Grasp this set -up knob and pull it out as far as it will go, rocking it slightly so that the gears will mesh properly. (4) The set -up knob should next be tuned to the right (clockwise). The knob will turn rather stiffly and the dial pointer will travel over to the right side of the dial scale. After the dial pointer reaches the right extremity of the dial scale, continue to turn the set-up knob clockwise about % of a turn until a definite stop is reached. (5) Push any button you wish to set up for a station. There need be no relationship between the position of the button on the keyboard and the station on the dial. Be sure the button is pushed all the way in. You will note that as the button is pushed in, the word "Automatic" will appear illuminated on the small indicator at the right side of the dial, and the keyboard mechanism will instantly move the dial pointer to some spot on the dial scale, according to the previous setting of the mechanism. This need have no relation, however, to the station for which you desire to set the button. (6) Grasp the set -up knob again and tune the receiver to Fig. C. Rear view of the Stewart- Warner pushbutton tuning mechanism. the desired station. Tune carefully and watch the dimming reactor tuning indicator for the point of least illumination be so that the set will be accurately tuned to the station. slipping on shaft. If signal is not heard clearly it may (7) The depressed button is now set to the station and A.F.C. contacts on back or side switch not opening or A.F.C. should be labelled at once with the proper tab. The next not functioning. step is to release the button set -up, and this is done by Motor Continues to Run when pawl does not fall far simply pushing in the next button you desire to set -up. enough into station selector cam to cut off power to motor. (8) Then tune in with the set -up knob the next station Pointer stops at a different place each time for a certain you wish to receive for the button that is now depressed, button, due to pointer drivegears slipping out of mesh or again making use of the Visual Tuning Indicator to be sure on shaft. Mechanism not locked up tight or left -end bearing that you are correctly tuned to the station. bracket loose. (9) Continue to set up as many other buttons as desired in the same manner; that is, push in the button, tune in PHILCO AUTOMATIC DIAL the desired station, then push in the next button, and so -on. While it is true that pushbuttons are not used in the Philco (10) In order to release the button which last remains dial, nevertheless there are modifications of this same depressed (the last one you desire to set up), grasp the mechanism using buttons, employed by other manufacturers. set -up knob and push it back into the cabinet as far as it As used in the Philco sets, the dial may be set up to tune will go and then pull it out again. Do not forget to rock in 15 or more stations. The method to use in setting up the set -up knob slightly when pulling it out, to properly stations is as follows: mesh the gears. Remove the 2 -piece tuning knob and the 3 flat -head screws (11) Turn the set-up knob to the left (counter -clockwise) ; which hold the circular metal plate to the tuning shaft hub. the knob will turn rather stiffly and the dial pointer will The dial control screws and station tab slits are now exposed. travel over to the extreme left side of the dial scale. Con- Tune the set to the lowest frequency station, and press in tinue to turn the set-up knob to the left even after the (with a screwdriver) the dial control screw which is nearest pointer reaches the end of the dial scale. Apply a firm pres- to the bottom of the dial. With the screw pressed in, rock the sure until the knob reaches a definite stop. screw left and right until a click is heard. When the click is (12) Push the set -up knob back into the cabinet again and heard it denotes that the control screw finger has engaged put on the large knob that was originally pulled off. The in the tuning gate and the dial escutcheon will move the Magic Keyboard is now completely set up for operation. dial scale back and forth with the motion of the screwdriver. Tune the desired station as accurately as possible in and then release the screw. TROUBLE -SHOOTING THE "MAGIC KEYBOARD" with the screwdriver pressed (Continued on page 40) Some of the troubles which may occur in the Stewart - Warner models 1845 to 1869 -which use the Magic Key- board as follows: -are SCREW Button Does Not Stay In or Does Not Release: Kickout STOP pointer tip improperly adjusted. Kickout spring bent down INDEXING too far. Insufficient tension in Key stop bar return spring. FINGER Star wheel stuck or not moving freely on tuning shaft. Kickout tip jams against star wheel. Stuck or jammed pawl v 1 or key. REAR VIEW FRONT VIEW Pointer Does Not Move When Button Is Pushed: Reversing REAR to SEGMENT OF VIEW contacts on back switch not closing. Motor stalled due AUTOMATIC OVAL mechanical overload and clutch not slipping. Motor runs SNOWING SPUNEO due to slipping. Pointer BORE FOR but pointer does not move, clutch CONTROL drive gear slipping on shaft or out of mesh. Motor does not SCREWS hum and tuner does not move with button in, due to power contacts on back switch not closing. Power contacts on side switch not closing. Bakelite back switch operating cam binding on contact arms or out of position. Pointer Moves But Does Not Tune Station Properly: Due to improper setting -up of mechanism or not locked up tightly.

When no signal is heard it may be due to Mute contacts Fig. 13. Segment of the Philco automatic dial showing the splined bores fo not opening. Gang condenser drive -gears out of mesh or the control screws.

RADIO -CRAFT for JULY, 1938 19

www.americanradiohistory.com 25Z5 i 50 NEW CIRCUITS \I BALLAST TUBE BIAS AC. LEADS IN MODERN F 20n

D SW. D.C. MF. FIELD RADIO RECEIVERS A.C. A/ The details of the modern radio receiver cir- Ì5 V (A.0 -D.C) LINE D.0 375r- cuits that make them "different" from previous designs are illustrated and described each month by a well -known technician.

F. L. SPRAYBERR I IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIINo. 10

(I) MOST EFFECTIVE AC -DC POWER SUPPLY Crosley Model 647. Uses voltage -doubling for A.C., obtaining high voltage without a step -up transformer and switches field' in line -shunt connection for D.C. providing maximum D.C. available. In Fig. lA win be seen the familiar 2- section 25Z5 rectifier with the plate of one section connected to the cathode of the other section. The remaining cathode thus becomes the high -voltage positive lead while the remaining plate is the high -voltage negative lead. The no -load output voltage is double the A.C. peak input voltage, and the exceptionally large filter condensers (50 mf. each) are required, as they must store the complete power between them every half - cycle. They are alternately charged in parallel and simultaneously discharged in series by the load. For D.C. operation the field is shunted across the line in series with one section of the ballast resistor so that it will carry the correct current, leaving one rectifier section free so that no unnecessary voltage drop will occur in the high - voltage supply. The change from A.C. to D.C. operation is made by switching as indicated in the figure. (2) A.V.C. WITH POWER DETECTION ACHIEVED WITH NO DIODE OR ADDITIONAL APPARATUS Fairbanks -Morse Model 5A. Although very much simplified, the circuit has the advantages of diode operation and A.V.C. using only a triode. The 2nd -detector acting as in Fig. 1B as a power detector with a near -cut -off bias, half -wave rectifies the I.F. signal in the grid- cathode circuit resulting in the grid becoming negative in proportion to the signal strength. The top end of the grid return resistor thus becomes negative in proportion to the I.F. carrier strength in the circuit. A large condenser value (0.25-mf.) filters this to essentially pure D.C. and it is used for A.V.C. The positive I.F. pulses or alterna- tions carry the signal to the plate where the I.F. variations are smoothed out by means of the 0.001 -mf. condenser; the audio component then remains.

(3) HIGH -GAIN DIRECT COUPLING ACQUIRED WITH CONVENTIONAL TUBES Emerson Models AR -171, -65, -66, -73, -74, -76, -77, -80 and -85. The simplest possible direct coupling between the next to last and output stages is required in these sets with no auxiliary parts, ordinary plate voltage and conventional triode tubes. A type 76 input tube of the amplifier in Fig. 1C is arranged to draw its cathode current from the grid of the output tube. Its plate is directly connected to "B+" so that as its grid varies at A.F. the plate current variations will bring about cathode voltage changes. The load for this tube is the grid- cathode circuit of the output tube. The output grid must remain positive at all times and the tube must be fitted for operation at minimum distortion when thus operated. Grid variations of the 76 cause amplified cathode variations in it. Grid variations of the 6AC5G tube must identi- cally follow these variations of the '76's cathode (the two elements being directly connected) ; subsequent amplified signals then appear at the output plate. Fig. I. The heavy lines in the circuits are the points discussed in the text. (Continued on page 55)

20 RADIO -CRAFT for JULY, 1 938

www.americanradiohistory.com l - - - -CLEARED CHANNEL BROADCAST STATIONS -- - 1 MODIFYING OLDER SETS N2, N22 Ne 3 r- 15.000CVCLE MODULATION CLEAR RANGE 14- MONKEY CHATTER 2111-^I TO RECEIVE THE 4 o I _

10000 ICVCLES HIGH -FIDELITY BETWEEN CHANNELS-.1 -- HIGNFIDELITY BROADCAST STATIONS- -s NO I - - N° 2 MONKEY STATIONS CLEAR RANGERANI GE CHATTER -NJ Service Men are finding new earnings in modifying older sets to receive the programs 20.000 CYCLES BETWEEN CHANNELS of these superlative broadcast stations. Fig. 2. Crosstalk ( "monkey chatter ") may be heard between stations IO kc. apart if the modulation exceeds 5,000 cycles. per- sideband, as shown at A; (note that cleared -channel stations in practice are spaced 50 kc. apart and hence are unlikely to interfere). At B, this proximity has been reduced to ROBERT COBAUGI-- IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII nil by carrier allocations that are not less than 20 kc. apart. THE Federal Communications that they can profit by this situation. Commission announced on Decem- It may, in addition, mean the sale of ber 19, 1933, that it had allocated PROLOGUE a set of tubes and possibly an antenna 3 double -width channels of 20 kc._ installation. Although the older re- each in the 1,500 kc. to 1,600 kc. band In its January 1935 issue, in the article ceivers are not able to reproduce the for experimental high- fidelity broad- "Hi- Fidelity en Short Waves," Radio - extended tonal range that the newer Craft told that a new group of 4 stations casting. These channels are 1,530 kc., was blazing new trails with daily broad- type of receivers are capable of, they 1,550 kc. and 1,570 kc. casts covering about 91/2 octaves of the nevertheless will give good reception of At the present time only 4 stations musical scale as compared to the 600 -odd excellent program material available. throughout the entire United States "standard" broadcast stations which Ninety -five per cent of the radio sets are licensed to operate in this band! cover only 3 to 4 octaves. Practically all manufactured before the yr ar 1929 They are: WQXR, New York; KPMC, modern sets are designed to tune in were unable to tune above 1,500 kc. Bakersfield, Calif., both on 1,550 ke.; these stations, but many owners of older Approximately 15% did not even sets do not realize how easy it is for KXBY, Kansas City, Mo.; and, their sets to be modified to receive the reach 1,400 ke. due to large stray WBRY, Waterbury, Conn., on 1,530 kc. super-quality programs they transmit, capacities such as shielded grid leads, The 1,570 kc. channel has not been daily. etc. The improved design of radio re- assigned to date. The results of these ceivers in recent years has made it experiments have shown that high - possible to build sets with a tuning fidelity broadcasting is successful and range from 550 ke. to 2,000 kc. practical. (See "High- Fidelity on Short Waves," in January, ADJUST THE TRIMMERS '35, Radio- Craft, and the February, '35, issue, page 456, for Most sets are equipped with padding condensers and illustration and description of WQXR and the equipment trimmers having a range of capacity from 10 to 40 mmf. used to obtain and maintain a station frequency fidelity The most satisfactory way to extend the high -frequency characteristic substantially "flat" from 25 cycles to over tuning range is by adjustment of the trimmer condensers. 15,000 cycles. Editor) (See Fig. 1A.) The ratio of the trimmer capacity to the All of the new sets on the market and those built within main condenser capacity will determine the percentage of the past 5 years, take in this band. Some of these sets have error introduced into the original dial readings. The error an additional band from 1,500 kc. to 3,000 kc. for the recep- will be greatest at the high -frequency end of the dial and tion of police and amateur stations, and it is possible to will decrease toward the low- frequency end of the dial by use this second band to pick up these high- fidelity stations. reason of the increasing ratio of the large variable capacity However, about 20% of sets in use today are over 5 years to the smaller fixed trimmer capacity. Adjustment of old old, and do not include the 1,500 kc. to 1,600 kc. band. (Be- sets using 3- element tubes such as the type 26 tube is not low 1,500 kc., though, are 4 stations which are free from always satisfactory because of the poor selectivity of such the "crosstalk" -see Fig. 2-encountered on the higher circuits, especially at the high -frequency end of the dial wavelengths. Editor) where the C/L ratio is so low. Although a great number of new sets are being sold, there is a large number of people who, for one reason or other, REMOVE TURNS cannot or will not buy a new radio, but are quite willing In some cases where the set is not equipped with trimmer to spend a few dollars on their own in order to make possible condensers it may be necessary to take turns off each coil. the reception of these stations. Many Service Men will find (Continued on page 38)

ADJUSTING -- REMOVING TRIMMERS TURNS

p,0

Fig. I. Service Men are equipped to modify older set fo receive WQXR (New York), KPMC (California) KXBY (Missouri), and WBRY (Connecticut). As shown, the ¡ob may entail (A) trimming for higher frequencies, (B) carefully removing turns from coils, or (C) shifting the I.F. to a slightly different frequency.

RADIO -CRAFT for JULY, 1938 21

www.americanradiohistory.com HOW TO MAKE Latest developments in radio tuner design are incorporated in this new 4 -tube instrument -for the radio set builder, P.A. specialist and Service Man -for the faithful reproduction of local radio programs.

C. W. PALMERIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII

ceiver was chosen. This selector system consists of 4 tuned circuits coupled into 2 pairs of band -pass filters by means of "negative mutual couplings" and capacity in such a manner that a substantially constant band of frequencies is passed, over the entire broadcast band. In other words, if the coupling is such that a 10-kc. band is passed at 550 kc. practically the same band separation will be indicated at Fig. A. Mr. Palmer operating the completed high -fidelity tuner. 1,400 or 1,500 kc. In addition, the pass -band can be easily changed by simply varying the capacity of the coupling NIANY advances have been made in A.F. amplifier elements. desigrf in the past year or so-to mention' just a The tuned circuits are over -coupled and while this results few, the beam-power tube, negative feedback, volume in the usual curve of resonance peaks with a dip between, the expansion, infinite baffles, peri- dynamic and bass dip is less than 2 db. which is taken advantage of in flat- reflex baffles-each of which has its place in the develop- tening the over-all acoustic output of the set, amplifier and ment of really high quality reproduction of music and speech. speakers. (The last mentioned ordinarily has a dropping off Such an amplifier equipped with good tweeter (high - of output at high frequencies which are compensated -for, to frequency) and woofer (low- frequency) speakers in an some extent, by slight exaggeration in the tuner.) acoustically- treated auditorium or theatre is far better than that obtained with all but the best of modern radio receivers. INFINITE -IMPEDANCE DETECTOR This statement may bring the wrath of some well -known A new type of detector is attached to the R.F. end of the radio engineers down around the writer's ears, but it is receiver. This detector has been named the "infinite - true -as critical listeners can verify. And also true is the impedance detector" by the RCA Laboratory, where it was fact that a radio receiver is capable of the same high fidelity designed. This new form of demodulator displays improved as that obtained from audio amplifying systems, from the characteristics over the diode which -up to now -has been better stations-if certain existing conditions imposed by the considered in one form or other the criterion in detectors. listening public can be dispensed with. And these conditions The diode has the disadvantages of reflecting a definite - can easily be removed by any rabid seeker after high quality. and unfortunately rather . low- impedance back into the It was with these thoughts in mind that the writer set preceding tuned circuit, thus preventing selective charac- about to design and construct a tuner unit which -without teristics to be utilized. Also, it is capable of a maximum of being too complex -would have fidelity characteristics equal some 80% modulation, thus cutting off some of the modula- to those of a good, modern, Public Address amplifier. tion peaks of a deeply -modulated signal. And last but not First, a good deal of research was done among the com- least, it resulted in actual attenuation of the signal- instead mercial circuits, books and other sources of information on of a signal voltage gain as found in most detectors. "high fidelity." Many circuits were analyzed and some were Contrasted to this, the "infinite-impedance detector" re- built into bread -board setups to answer certain questions. flects very high impedance back into the preceding tuned Finally a combination of well -known circuits, some old and circuit -it thus permits full selectivity to be realized. It is some new, were chosen and built into a tuner which satisfies capable of practically 100% modulation -thus being a better all conditions. detector than the diode, and it produces a signal gain instead of loss! NEGATIVE MUTUAL COUPLING Some explanation has been given to the detector as, in First, the well -known "negative mutual coupling" system the writer's opinion the detector is the bottle-neck or weak of tuning which was used in the Western Electric 10A re- link in the chain of individual parts which make up a "hi -fi"

64(7 R.F2 - So MMF GC6G L7 C3!C4I L5lî r 1 r- jig! O.5- LB VOLUME 3I CONTROL X X - . '7 _J MF OA- ~ MF MP 600 01- ó I 'IF(EAH)/ ó MEG 200 i- "_J (ORIO)G ME 5W2 ,MF 000 05-MEG(EACH) m42i-ñ. GN S 25.000. (EACH) APPROX.- 20.0004E T 71MF L MEG. IMATELV AS MF. Tl1=+ 35oOn 7500a ` 25000. MF. 3.500 4.0001- TtINING (O2_ \01- LMF 0.1-MEG EE 605-- MF MF

Fig. I. Schematic circuit of the high -fidelity tuner which uses negative mutual coupling in both R.F. stages and bass -compensated volume control.

22 RADIO -CRAFT for JULY, 1938

www.americanradiohistory.com A HIGH -FIDELITY TUNER Tuned -Radio - Frequency Circuit Automatic Volume Control Negative Mutual Coupling Visual Tuning Indicator Adjustable Band -Pass Monkey- Chatter Frequency Infinite -Impedance Detector Trap Tone- Compensated Volume Controlled Flat -Top Response Control Individual Voltage Dividers

I I I I I I I I I I I I 1111111 1 1 1 1 1111111 radio set. However, no theoretical ex- receivers, may question the use of a planation of the action of the "infinite - T.R.F. circuit in this tuner. The answer impedance" detector will be given since to this question is that where constant an article probably will appear in this pass-band can be obtained in a T.R.F.- publication shortly, giving full data on type set, in a receiver that is designed this new and improved demodulator. particularly for "local" reception, and where a flat -topped response that is Fig. B. The chassis, neatly laid out and built. TONE -COMPENSATED VOLUME CONTROL readily controllable can be obtained, Following the detector is a form of there is no need to increase the corn volume control which has become popu- plexity of the set by introducing "fre- lar in Europe, but has been neglected in quency shift" (superhet.) circuits. the U.S. in favor of bass boosters, bass An examination of the circuit (Fig. compensators and speakers which ex- 1) of the set shows the various parts aggerate bass response. which have been discussed; plus a few This is the "tone- compensated" vol- which have not been mentioned, such as ume control which consists of a poten- the use of an untuned coupling circuit tiometer tapped part of the way down between the 2nd R.F. stage and the its resistance with an inductance, ca- detector, the use of a dual- triode in the pacity and resistance connected between detector circuit, one section of which is this tap and ground. the infinite-impedance detector and the The A.F. filter thus formed is tuned other the diode A.V.C. rectifier. to a low audio frequency -about 40 It will be noticed that individual cycles -to increase the low- frequency voltage dividers are used for the screen - gain on low volume levels where ex- grid feed circuits. This is done to avoid aggerated bass response is desirable further delaying the cut -off point of the (for instance, to compensate the falling R.F. tubes so that they will be as linear characteristic of the human ear to low - as possible consistent with the needed Fig. C. Under -side view of the chassis. frequency response at low intensities). remote cut -off action. On higher volume levels, bass com- The cathode of the 1st R.F. tube is pensation should not be necessary-or biased with a 300 -ohm resistor which desired -so that the bass boosters some- permits full amplification of weak input times employed should not be required. signals at this point. A 600 -ohm resistor Experiments verified this assumption is used for the 2nd R.F. stage, to pre- -at least as far as the writer's ears are vent overloading at this stage on large concerned. input signals. This difference is desir- The set is equipped with a small de- able due to the incomplete A.V.C. action gree of A.V.C. though no attempt is in the set. made to completely control the gain of The inductance for the compensated the R.F. end of the set-with the volume control can be made at home if thought in mind that complete control desired, or a 420-millihenry coil may be would introduce harmonic distortion. In As shown in Fig. 2, the coil obtained. F g. 2. Winding data for Inductance used in the conjunction with this partial A.V.C., a (Continued on. page 41) bass-compensated volume- control circuit. tuning-eye tube is included to permit accurate tuning to facilitate obtaining the high quality possible with the tuner. 6C5 6L6 SPEAKER The final unit of the set is a 10,000 - 5W. filter consisting of a tuned trap f cycle MEG 1 0QQ(9Q000 115vAC. in the output of the detector to eliminate the "monkey chatter" (cross -talk) 5Q0oo n 000 would otherwise be heard in any + 6.3v + which ...Jo/von& X % X X v of the metropolitan areas where the GNO. only 0.5- local stations are separated by MF; .-NVAAw SPEAKER 30HY. 10 kc. FIELD, CH. CONSTRUCTION From the above sketchy outline of the 5Q000n set's make -up and background it can 6L6 be seen that much effort and thought tiiMF, and selec- have been given to the design 8 go to make up 2.200n 10.000.0. tion of the parts which MF / MF. the tuner. (EACH) 50.O00n \(EACH) Some readers who have become used to the superheterodyne circuits which Fig. 3. Circuit of a high -fidelity amplifier which will do justice to the quality of the signal obtainable constitute 9 out of 10 of our modern from the high -fidelity tuner. RADIO -CRAFT for JULY, 1938 23 www.americanradiohistory.com "BI- FONIC" Not since the "infinite baffle" made its appearance has there been the marked pro-

BI -FONIC gress, in the principles of sound reproduc- HOUSI NG tion, exhibited by this new system IN ( TO - BUILT MATCH WHICH THE BACKWAVE IS UTILIZED. LARGE DYNAMIC unnuuunuuunuuunnnunnuuuuuunuuuumnuuumuuuuuunnuunuuuunumnunuuuuuuuununnunnm SPEAKER) THE job of a loudspeaker is to reproduce all musical instruments, the human voice and various other sounds, with as little deviation from the original as possible. To build a loudspeaker which would accurately reproduce one musical instrument is a man -sized job; to build a speaker which will accurately reproduce a whole symphony orchestra is truly asking for a Twentieth Century Aladdin's lamp. If we are to reproduce accurately the various musical instruments, is it not logical that we MUST use the same basic principles of tone generation in our speaker as are used in the various instruments? These fundamental principles are as follows: FIRST -Every instrument is composed of 2 elements. 1. The vibrating clement. (Such as the string of the violin, the reed of the saxophone, the string of the piano, etc.) 2. The phase -inverting and tone -developing element. (Such as the tone box of the violin, the sound board of the piano, the air column of a trumpet, etc.) SECOND -Every instrument has an air displacement in ratio to its place in the musical scale. For example, Fig. A in the string instruments, the violin, viola, cello A midget radio set, its output fed to a Bi -Fonic Reproducer, goes "hi -fi." and bass viol each operates in a different section of the scale and as they progress downward in frequency they get larger. The bass viol is not louder than the violin but its notes are much heavier. This same principle applies to any other SERVICE MEN!- Hare's your opportunity to "sell" that recalcitrant customer, family of musical instruments. whom you couldn't induce to purchase an entire new radio set, a new housing for his midget set's loudspeaker. The customer gets high- quality repro- THIRD-No instrument contains any means of absorb- duction he didn't believe was possible, and you make a profitable sale. ing the back -wave of the vibrating element. Where the back -wave exists, its envelope is inverted by being reflected from a soundboard, or by being resonated in a tube. Using these principles as guide posts, and having studied music for 9 years, the author started experiments in speaker

- VOLUME AND FREQUENCY RANGE - (STANDARD 12 -INCH DYNAMIC SPEAKER)

BETTER A VOLUME USING BETTER BASS INFINITE BAFFLE TREBLE REPRODUCTION REPRODUCTION 8° VOLUME USING BI -FONIC HOUSING.

45 100 7.800 CYCLES CYCLES ORLES' Ca Ls II C- I C, c CJ Ì 4 Tl 47 1 7 1 ri p ;! !!!

TOP OPENING FREQUENCY RANGE, USING OF TUBE AN INFINITE BAFFLE N2.I FREQUENCY RANGE. USING A BI -FONIC HOUSING

(CUTOFF FREQUENCY IS TAKEN AS 7D8. BELOW REFERENCE LEVEL)

Fig. C Fig. I Rear view of Bi -Fonic Reproducer, showing bars, and top of tube No. I. Increased volume and fidelity are achieved by using a Bi -Fonic housing.

24 RADIO -CRAFT for JULY. 1938

www.americanradiohistory.com SOUND MAGNIFIER

H F. ACOJSTIC HIGV- FREQUENCY BACK WAVE eat Ths LOADING IS REFLECTED BACK TO CONE ANY STANDARD IN-PHASE DYN ANNC REPRODUCER FIRST ROBERT TIMEIN ANY LIVINGOOD RADIO HIGH-FRE- PrBIIoAToriIIII!IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII1111111IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII QUENCY DISPERSERS. design, over 2 years ago, which have culminated in the creation of what he terms Bi- Phonic Reproduction (Herein- after spelled "Bi- Fonic."-Editor). See Fig. 1, which illus- vol- LOW FRE- trates the improved frequency response and increased QUENCIES ume this system achieves. TRAVELING DOWN TUBE LIG N'': NE.1 BASIC PRINCIPLES OF BI -FONIC REPRODUCTION PLASTIC - SPACE In the Bi -Fonic Reproducer, shown complete in Fig. A, a conventional cone acts as the vibrating element. The Re- LOW FRE- producer acts as the tone -developing element. Together LOW FP,. QUENCIES, indicated in QUENCIES 'RAVELING they consist of a box having a cross -section as TRAVE. UP TUBE cone ' NE.2 the phantom view, Fig. B. The surfaces enclosing the are broken up with a series of half -round wood strips. The surface directly in back of the cone, as shown in Fig. C, is composed of several series of alternate vertical and horizontal half -round strips of wood. A slot is left between the M.F feeds into the first of 3 ACOUSTIC bottom and back surfaces. This slot LOADING parallel "tubes" of equal length and cross- section, and constructed of wood, but having end -plates of "lignin plastic" (masonite) . Before explaining the theory of operation of the Bi -Fonic Reproducer, the author desires to stress that each of these theories was checked, in both theory and practice. LOW- FREQUENCY FIRST-In a body of air of given temperature and pres- BACK WAVE in a straight line and can be EXITS LIGNIN PLASTIC sure, sound travels IN -PHASE WITH (MASONITE) reflected like a ray of light. FRONT WAVE SECOND -The band of audio frequencies reflected can be controlled by regulating the size of the reflecting surface. Fig. B Phantom view of Bi -Fonic Reproducer: sound is reflected, not absorbed. THIRD -If 2 air columns of the same length material and cross-section are made to resonate at the same frequency, but 180 degrees out -of- phase, the resulting audio output-providing the tubes are laid side-by-side--is zero. PUBLIC ADDRESS SPECIALISTS! -Hari s a sound reproducing system which Using these theories, the following functions take place develops more sound output, for a given electrical input, than does any broadcast station monitor - in the Bi -Fonic Reproducer. preceding type of reproducer. Clubs, restaurants, (Continued on page 50) rooms, schools, all are good prospects for this system.

SPEAKER CONE SPEAKER CONE REFLECTED MEDIUM -HIGH FREQUENCIES (AND IN- VERTED) ANO IN -PHASE SOUND - ENVELOPE

i.Att 1 \ s ' r3 CONFoL$- ti 90N WAVE

TON WAVE ORIGINAL SPEAKER t2 SOUND - CONE ENVELOPE t3 }

HALF-ROUND VERY -HIGH FREQUENCIES HALF -ROUND VERTICAL HORIZONTAL r2.

Fig. 2 Fig. 3 - r4 -waves are reflected in whole Medium- frequency back -waves are partly disbursed. High -frequency back LOW- FREQUENCY PORTION OF ENVELOPE off the half -round blocks. Those which reflect into in order to reduce "cabinet resonance, so that reach the cone in phase -aiding. This re- only a portion of these waves is reflected back to the cone Fig. 4 in increased highfrequency response. (The the surface of the cone in phase -aiding. (The back - sults back -waves exit in phase -aiding. sound envelope practically 'folds' inside out.) wall has an air space 1/16 -inch wide!) Low -frequency 25 RADIO -CRAFT for JULY, I 9 3 8

www.americanradiohistory.com MATCHING TO TAPPED A. COBLENZ

One fact is obvious immediately. The watts power consumed at Z -1, or delivered by Za equals 3 x 0.5, or 1.5 watts. The watts power at Z -2 is 10 watts, and that at Z-3, twice 3 watts, or 6 watts. That makes a total of 17.5 watts, so that the amplifier can take care of the drain. 11 Now, TO wNAT NZ it can be shown mathematically, that OUTPUT SERIES AND 5NU r Z of any tap Watts sec. tap supplies TUBE i OR NEEDED TUBES) ARRANGEMENT R5 as LOUD5PEAKE Z of its load Total Sec. watts As it is unnecessary to just waste the additional 2.5 watts, Given a tapped output transformar (fad from a given output -tube arrangement), and a group of assorted type of loudspeakers. what would be your the primary will be designed to supply 17.5 watts. In next step to obtain rated performance from these reproducers? formula form: Zs P-t THIS writer believes (and his attitude is based on experi- -equals- mental verification) that, on the average, one out of Zo Ps 100 radio Service Men, radio operators, Public Ad- Where P -t represents the watts power consumed at any dress operators, and you can throw in a few engineers one tap, and Ps equals the power in the secondary, or sup- for good measure, can solve the following problem: plied by the primary,-17.5 watts. (The losses in the trans- It is required to calculate the taps on the secondary of former are neglected.) an output transformer, giving the impedance in ohms, to Or, Zs equals P -t x Zo /Ps. accommodate the following 3 groups of speakers: Thus, for tap a, its impedance is then 1.5/17.5 x 1,667 (1) Three Magnetics, 5,000 ohms impedance, 0.5 -watt equals 141 ohms, approx. (each); For tap b, Z -b equal 10 /17.5 x 10, or 5.76 ohms (approx.) . (2) Two- Standard Dynamics, 15 ohms impedance, 3 For tap c, Z-c equals 6/17.5 x 7.5, or 2.57 ohms (approx.) . watts (each) ; Now that's all very well indeed, but how do you know (3) One Large Dynamic, 10 ohms, 10 watts. you're right, and where does the reflected impedance shine Each group is to be placed across one tap. An amplifier in? And what is "reflected impedance" anyway? And what is provided with a peak output of 20 watts, whose tubes are do you mean by saying that the impedance of the secondary to face a reflected load impedance of 6,000 ohms, plate -to- tap is such and such number of ohms? One at a time, please. plate. And you must check back to make sure you're right! WHAT IS None of the radio men in the first 3 classifications whom "REFLECTED IMPEDANCE "? this writer approached with this problem could do it, and Definition: Reflected impedance is the resistance in ohms, only a very few had any notion what "reflected load im- at the particular frequency under consideration, which the plate pedance" means. The engineers hemmed and hawed, and or plates, of the output stage face, resulting from the load placed gave at best incomplete replies. Better yet, this writer went across the secondary. Please note that if the secondary load to several first -rate textbooks and manuals, but not one, is 0, so is the reflected impedance. as far as several hours of looking could disclose, had mention Now about this impedance question. When the impedance of this topic! of a unit is specified in audio work, some manufacturers While brochures and analyses on impedance matching mean that the impedance has been measured at 60 cycles, can be found by the dozen, none gives the necessary for- others 400, still others 1,000. That is, Z equals 2pi fL, or mulas or extensions of reasoning to include this subject, 1 =2pi fC, and therefore, unless f is specified, Z can be any- and the writer has yet to see a formula involving reflected thing from 0 to infinity! Following the practice of the impedance. It is the hope of this article to throw a little majority, in specifying Z at a low frequency, and letting of this spring sunshine on this much neglected topic. Every the impedances take care of themselves, as they will, for P.A. operator and Service Man is sure to run afoul of higher frequencies, and also from considerations of con- such a problem sometime or other. venience, f is considered as 60 cycles. However, even if not specified, all that is necessary is to bear in mind that all TAPPED -SECONDARY TRANSFORMERS impedances are measured in terms of the same frequency, (Note that this discussion involves only ordinary grade - and, as ratios of Z are most important in audio work, the school arithmetic; that the bases of ordinary sound con- frequency will cancel anyway. So, when we say the im- siderations here analyzed for the radio and P.A. practi- pedance of the secondary tap is x ohms, we mean that tioner are only those elements of the subject without which 2pi fL equals x ohms, f being 60 cycles, and L referring the technician cannot "get to first base. " -Editor) to the inductance when leakage, mutual inductance, etc., First the diagram (Fig. 1A) to see what we're talking are all figured in. Now to show you where the reflected about: impedance harps in! The legend for the diagram is: Every radio man knows (or should know!) that Np /Ns Z-1 -total impedance of the 3 magnetics in parallel, as Ep /Es (primary -to- secondary turns ratio equals pri- equal to 1,067 ohms; mary-to- secondary voltage). He also knows that Np /Ns Z -3 -total impedance of the 2 standard dynamics in as VZp /Zs (primary -to- secondary turns ratio equals the parallel-7.5 ohms; sq. root of the primary -to- secondary impedance ratio). But Z-2- impedance of large dynamic-10 ohms; do you know that the impedance a tap on the secondary Za- impedance of tap for magnetics; reflects into the primary bears the same relation to its Zb-impedance of tap for 10 -ohm dynamic; load as the impedance of the primary (as the tube plates Zc-impedance of tap for two 15-ohm dynamics; see it), bears to the impedance of that tap? Zp- reflected load faced by tubes, 6,000 ohms. Stated in formula form: Zr /Zo equals Zp /Zs. You will To begin with, there are 2 solutions. Both give the same note that Zp appears in this formula, and it might look result, and both fundamentally alike, but, in outer appear- like a case of circular reasoning. But it isn't. For each ance, rather different. tube, or tubes, for optimum efficiency, there exists a Zp and

26 RADIO -CRAFT for JULY, 1938

www.americanradiohistory.com Many heretofore unpublished "mysteries" LOUDSPEAKERS of input, output and reflected impedance are here divulged, by a N.Y.C. Police -radio TRANSFORMERS technician,for radio and Public- Address men.

I I I I I 111111 i l l l 111111 I I I I I I I I I 1111111 11111111 1111111 1111111 111111111111111111111 11111111111111 I I I I I I I I I I I I I I I 1111111 I I I I I I Ì 11111111 I 111111111111111111111111111 I I 111111111111111111111111 I I I I I I I I I I I I I l' CAN YOU SOLVE the loads on the secondary are always THIS PROBLEM? - sultant current, and increases thereby designed so that this is taken care of. "It is required to calculate the taps on copper and other losses. But, in power While each tap will not reflect, per se, the secondary of an output transformer, giving the impedance transfer, you only match to the com- 6,000 ohms, or Zp in this case, into the in ohms, to accom- ponent of the inductance which repre- modate the following 3 groups of speak- secondary, all combined together, their ers: (I) 3 Magnetics, 5,000 ohms im- sents actual power, its current in- reflected impedances functioning in pedance, 0.5-W. (each): (2) 2 Standard phase with the voltage, and the im- parallel, will reflect the correct im- Dynamics, 15 ohms impedance, 3 W. pedance of the entire inductance is not pedance. Witness: (each); (3) I Large Dynamic, 10 ohms, entirely effective in delivering power. Zra equals 6,000 x 1,667/141 or 10 W. Hence, the fact that 141 ohms is paral- 70,200 ohms (approx.). Each group is to be placed across one lelled by 1,666 ohms, or 7.5 by 2.57, Zrb equals 6,000 x 10/5.7 or 10,560 tap. An amplifier is provided with a does not of necessity indicate a mis- ohms (approx.). peak output of 20 W., whose tubes are match. In fact, this system to face a reflected load impedance of particular Zrc equals 6,000 x 7.5/2.57 or 17,520 6,000 ohms, plate -to- plate. And you must as given is quite well matched. ohms (approx.). check back to make sure you're right!" Now we'll just put these 3 in parallel, In "Matching Loudspeakers to EXAMPLE OF SEEMING MISMATCH and presto!, we get 6,000 ohms within Tapped Transjornrers," Mr. Coblenz To illustrate even more strikingly an 1 or 2 per cent, allowing for small in- gives you the solution to this and arrangement which the average radio accuracies in the arithmetic. many other problems concerning the man would immediately as I,:uhhing of .9.1'. irnpedanc.' condemn a glaring example of poor engineering A USEFUL NEW EQUATION involving a mismatch, consider the There is another method, a simpler haustive hours in the 42nd St. Library, following diagram (Fig. 1B). By actual one, although the one above is really Technology Division, has even hinted measurement, at 60 cycles, Zp equals quite neat, if you care to delve into the of its existence. That it is a logical 20,000 ohms, Zs, 5,000 ohms, and Z1, mathematics behind it. This second outgrowth of the well -known formula 1,500 ohms. method takes voltages, and ratios, as of turns -ratio and impedance -ratio is Every radio man knows that for follows: granted, but just in this form, so use- maximum power transfer from tube to Since E equals V Zp, the voltage at ful for these common computations, he output, the load Z must equal Rp. Now the primary, and that at the various has never seen it. what self- respecting power tube, in loads, is readily computed. Thus: common use, and delivering 2 watts or Ea equals V 1.5 x 1,667 or 50 volts "WATTLESS" or "QUADRATURE" POWER more, say, has an Rp, or rated load Z Eb equals V10 x 10 or 10 volts One more very interesting observa- for maximum output as given in tube Ec equals V7.5 x 6 or 6.7 volts tion. To such misguided, but well mean- charts, of 20,000 ohms? All right, you Ep equals V 17.5 x 6,000 or 324 volts ing, radio men who picture impedance say for "optimum fidelity" the load Now we'll just recall one of the for- matching as x ohms across x ohms, the should be twice Rp? Fine. Look at your mulas every radio man should know, sight of, say, 1,667 ohms across 141 tube charts, and see that for power shown above. Namely: ohms, as in tap A, or of 2.57 ohms tubes as common as 6L6, 10, 50, 45, V Zp /Zs equals Np /Ns equals Ep/ across 7.5 ohms, as in tap C, must be 2A3, 2A5, and, of course, for higher Es and obviously Zp /Zs equals a horrible sight indeed. It has been the power tubes as used in transmitters, Ep /Es author's experience that radio men pic- Rp varies from 1,500 to 5,000. Thus And away we go: ture impedance matching as ohm for (and the same tube charts will also Za equals 2,500/10,500 x 6,000, or ohm, and allay their objecting con- tell you this), for stated output, the 141 ohms sciences by saying, "Well, I'm talking load Z approximately equals double this Zc equals 100/10,500 x 6,000, or 5.7 impedances, ain't I ?" value. And what's worse, look at the ohms But please consider this: A pure in- secondary -Zs is equal to 5,000 ohms; Zc equals 45/10,500 x 6,000, or 2.57 ductance or capacity neither absorbs and load, 1,500. How awful! Well, it ohms, remarkable, my dear Watson. nor gives out power. It is only the corn - isn't awful, and there is no mismatch But to check, you must go back to ponent of current in -phase with voltage here; in fact, it's a mighty good match- our old friend shown above, namely that represents power loss, "the coming arrangement! Let's see: Zr /Zo equals Zp /Zs. ponent in quadrature" is what we call According to the little formula in- The author cannot refrain from not- wattless, or "quadrature" power. You volving reflected impedance as given ing, in conclusion, that this last given do not match impedances to that be- above, the impedance reflected into the formula he has never seen or heard of, cause it has no power to deliver. True, primary as a result of the load, is from any one, and no publication that the component of current in quadra- 1,500/5,000 x 20,000, or 6,000 ohms. has came to his attention, after ex- ture with the voltage increases the re- (Continued on page 51) Zp /y Zp zp fl / - ZI ZS Z1_ . % _- Za '- 1 1 Z2 - Zr ^ Z2

I 111-

\ I '''Z3 O o o Q

Fig. I. "Equivalent diagrams" of effective impedances. A -3 magnetic loudspeak rs, 2 stenda d dynamics and I large dynamic. connected to single tapped secondary; B- glaring example of "mismatched" impedances; C- matching a sorted speakers to multi -secondary transformer; D- showing importance of reflected impedances. In general, is indicates impedance of any one sec. tap; Zo, load imp. on or actos it; and Zr, reflected load imp.

RADIO -CRAFT for JULY, I938 27

www.americanradiohistory.com 6110-s7,4 PA . 8y/7,-- UNIFIED P. A. EQUIPMENT In this article the author answers 2 questions: (I) in what way does modern sound equipment differ from earlier apparatus; and, (2) in what manner does modern sound equipment help increase earnings?

HARRY PAROII, IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII ,IIIIIIIIIIIIIIIIIIIIIIII

AVING grown from an experi- the inevitable penalties of pioneering; ment to a mature industry, the and not all loss, for the P.A. man who Public Address business now re- undertook such deals was at least ac- quires that sales and merchandising quiring experience in a field which procedures, and even technical prob- (then) was not so well known. lems, be handled differently than they were only a few years ago. To main- PUBLIC ADDRESS GROWS UP tain a proper level of profit, the iden- Profits today are more substantial. tical Public Address job is done differ- The entire business is on a different ently than it was in the past, and on a basis. For one thing, there is more of it, far more business -like basis. and overhead, charged properly where i For example, it was common enough it belongs, is minimized by division in earlier days to spend $50 worth of among a much larger number of P.A. c.dec,i RA. time experimenting over a rental in- rentals and sales. Sales cost also is c9n, stallation that paid only $50 altogether. lower; there is more competition, but A job of that sort might be summed much less canvassing among a disin- r up this way: value of time, $50; true terested public inclined to regard P.A. value of equipment rental, $25; sales as an unreliable toy. The general public cost and overhead, $25; $100 worth of now knows and wants P.A. and com- value given, $50 payment received. By petitive features are provided by the considering his time and skill worth manufacturers of equipment at no ap- nothing, the P.A. man just broke even: preciable cost to the P.A. merchant, as by charging his P.A. overhead and will be seen. sales costs to other business activities, Above all, there is practically no such as Radio Repair or Sales, he need now for experimentation on the might delude himself with the fictitious job, except in extraordinary cases. In idea of a $25 "profit ". That was one of (Continued on page 52)

WAX & OIL CONDENSERS IN RADIO SERVICE WORK Given a defective radio set, with trouble traced to a defective wax- or oil- dielectric condenser, what steps would you take to determine the capacity, rating, or other unknown data, needed in making replacement?

WILLIAM BA ILEYIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII,

IN servicing radio equipment of modern design, let us ante; inductive and non- inductive sections; and whether the assume that faulty condensers are found without much unit is a "wax," "oil" or "electrolytic." trouble. We will deal strictly with the next step -that of determining the type of unit causing the disruption of oper- CHECKING FOR "WAX" OR "OIL" ation. For instance, there are (referring to the dielectric Many wax and oil units closely resemble electrolytic con- material) wax, oil, mica, electrolytic and air (trimmer) densers in external appearance. The Service Man should condensers. make absolutely sure which are electrolytic and which are In this article we will consider only the first 2 types, wax- or oil-impregnated units before attempting to make "wax" and "oil." It is obvious that there is a marked elec- any definite replacement. This can easily be accomplished by trical difference between these 2 types, although their physi- checking the leakage through the condenser. If the leakage cal appearances, as the illustration above of repre- is in the order of milliamperes, it is of the electrolytic type. sentative types shows, are not so different as to facilitate If in the order of microamperes, it is paper. their identity. In making tests, the Service Man should test for open - Of course, if the unit is plainly and properly marked, circuits, short -circuits or, should the condenser be of a dual there is little trouble today in securing the replacement, nature, shorted sections. Other possible conditions to be providing the set being serviced is one of reputable make. checked are: shorted section with ground; high terminal However, should this means of identification be lacking, it leakage; oil or wax leakage; and, overloading due to some then becomes the Service Man's job to find out the electrical high transient setting up a peak voltage, when the peak characteristics of the unit itself, namely: capacity toler- (Continued on page 54)

28 RADIO -CRAFT for JULY, 1938

www.americanradiohistory.com SERVICE MEN - OPERATING NOTES What faults have you encountered in late-model radio sets? Note that Radio - Craft will consider your Operating Notes provided they relate to CHARACTERIS- ANALYSES of TIC (repeatedly encountered) faults of a given set model. Illustrations are desirable. Payment is made after publica- RADIO RECEIVER SYMPTOMS tion of the Operating Note.

RCA Victor 121, 122. Intermittent re- denser from screen -grid to ground. Re- oscillator or at the I.F. amplifier. ception on these models has been traced place with a rating of not less than A peculiar motor -boating hum at the to open -circuiting 0.05 -mf. bypass con- 400 volts. extreme low- frequency end is due to an densers, employed as grid filters in the open input filter condenser. Inspect the R.F., 1st -detector -oscillator and I.F. Apex 7. In these receivers above grounding connection before removing secondary -return circuits. The inter- Serial No. 1,074,054 the oscillator 600 the unit. This condenser may blow, the mittent condition is characterized by a kc. trimmer has been omitted and is 80 -tube's plates will then get red -hot. sudden drop in volume and resonance replaced by a condenser of fixed value. The grounding plate at the rear of hiss. In one instance, an open -circuited Quite often this condenser will lose some (Continued on page 55) I.F. grid filter condenser introduced a of its original capacity and cause very certain amount of motorboating and weak reception from about 750 to 550 REPAIR oscillation upon the high frequencies. kilocycles. -(031W- When any one of these receivers is If this condition is encountered, re- serviced for the complaint of stations place this condenser with, approximate- ~lo being received at two points about 20 ly a 775 mmf., mica -type unit shunted by (EAF e kc. apart with distortion between these various small capacities beginning with CH) MF. two points, check the I.F. grid filter 20 mmf., until the right combination condenser for a short -circuited or leaky is found, or better still, add an 85 mmf. condition. These symptoms will be ap- trimmer in parallel with the 775 mmf. Fig. 4. Chevrolet Modal' 500,565; the dried -out parent only with the volume control condenser and adjust for maximum sig- 0-mf. electrolytics replaced with single 8 -ml'. unit. turned well up when this failure occurs. nal at approximately 600 kc. See Fig. 1 for location of these condensers. Atwater Kent 82. Noise when chassis BERTRAM M. FREED is tapped, similar to that of a micro - phonic tube. Coil shield over I.F. trans- RCA Test Oscillator Type TMV -97. former may be loose. This must be When this instrument goes "dead" you absolutely tight. It is wise to drill these will find the primary winding of the shields to pass an aligning tool. Replace modulation transformer "open" which shield, and bolt or solder it to chassis. is caused by electrolysis arising out of Check alignment of I.F. trimmers at the difference of potential between the 130 kc. Fig. 3. Sparton Model 913; open A.F. transformer core and the primary winding. bridged with resistor and condenser. Works OK. In replacing the transformer it is Echophone S -4. Oscillation not due to best to remove the difference in poten- dirty condenser wiping contacts or tial between the core and the primary faulty bypass condensers may be cured 58 2ND 1.F. 56 2ND-DET. winding by insulating the core and the by replacing the 0.5 -meg. resistor from mounting strap from the chassis by detector screen-grid to ground. This re- using suitable fibre washers, and by sistor is the smallest one mounted on wiring a jumper wire from the mount- the resistor panel and when open will C14 ing strap to "B +" so that the core is increase the detector screen -grid poten- 01-MF the same as tial by about 15 volts, thus producing (REPLACE at potential the primary THIS winding, thereby eliminating a source circuit oscillation and low volume. CONDENSER) SPEAKER FIELD of electrolysis. It is suggested that this VICTOR I. DUDLEY precaution be taken before the instrument goes dead. Majestic 15, 15B. A common com- TO LEO J. DRAUs plaint with these receivers is a dead RECTIFIER MF. set due to open I.F. transformer pri- 450V Airline 62 -106, 62 -107, 62 -121. Where maries. This is apparent by a lack of Fig. 2. Airline 62 -106; replace shorted 0.1 -mf. a condition of very low or no D.C. volt- plate voltage at the autodyne detector- tond with one rated at 600 W.V. age at all exists at the tube socket terminals, check for a shorted 0.1 -mf. tubular bypass unit connected from the plate supply lug of the 3rd I.F. transformer to ground. This condenser is rated at 400 volts and is really connected in parallel with the first filter condenser (16 mf.) at which point the voltage surge exceeds 400 volts each time the set is turned on. Be sure to use a 600 -volt replacement. See Fig. 2.

Airline 62 -134, 62 -139. Another short - lived tubular bypass condenser is found in these models. This is a 0.25 - mf. unit rated at 200 volts and is used Fig. I. RCA- Vicfor Models 121, 122; intermittent reception traced fo open 0.05 -mf. bypass condensers in parallel with a 6 mf. electrolytic con- in the grid -return circuits of the Antenna, R.F. and 1st I.F. circuits.

RADIO -CRAFT for JULY, 1938 29

www.americanradiohistory.com AWARDS IN THE CONTEST USEFUL CIRCUIT IDEAS FIRST PRIZE ...... $10.00 Experimenters: Here is your Opportunity to win a prize for SECOND PRIZE .. 5.00 your pet circuit idea, if it is new, novel, and useful. THIRD PRIZE ..... 5.00 Honorable Mention

loosened and then PLUG CABLE with the A.C. ripple still being reproduced the centering screws should ®mm he tightened. The voice coil will be perfectly a centered. J ® This arrangement is much more con- LO venient than the method of disconnecting Alter I MEGS. 6F5 condensers in the set in order to produce hum. SAMUEL H. BEVERAGE NOB BUTTON CLOSED TO TE 5T TOP CONTACT O-t FOR TEST MA. HONORABLE MENTION 33.5V t RESISTANCE- CAPACITY BOX. I have been =11111 BATTERY AND POTENTIOMETER a reader of your publication for a number of IN CORD COMPARTMENT. years and enjoy it very much. "- CALIBRATE I am herewith inclosing a diagram of what 1,000"- WITH KNOWN - I term one of the handiest pieces of equipment 11, "- ESSENTIAL INTERNAL CONNECTIONS POTENTIOMETER AC OR O.0 60 OF -EMISSION "TUBE- TESTER-'- VOLTAGE ti around our shop. As can be seen from the diagram any resistance value from 200 ohms to Fig. I. Any emission -type tube tester may be used as a vacuum -tube voltmeter. 2 mega. may be had by merely operating the switch ; but in addition to this, any one of these FIRST PRIZE -;10.00 values may be varied to any desired value by the use of the variable control in the negative TUBE TESTER AS V.-T. VOLTMETER. Al- leg of the circuit. The 3 decks make possible 110V-120V ó pry1 most any emission -type tube tester may be used it A.0 NEON to name a deck for low values of resistance, a as a fairly accurate vacuum-tube voltmeter. TUBE deck for -high values. and a deck for condensers; With the use of a 1 000-ohm potentiometer and DYNAMIC which means that the whole thing is in one box. a 4% V. "C" battery a wide variety of different SPEAKER with only one switch. See Fig. 4. tube types may be used. An adapter is made for NEON A neat, 3 scale dial plate can be drawn for TUBE BINDING POSTS the tube to be used with the grid circuit left FO the switch and the volume controls may be TEST open. connects to top cap, no adapter is LEADS If grid calibrated or the regular plates purchased for needed. I used a type 6F5 since it has a top cap them. which can be used as a- probe and the socket can When repairing a set I manipulate my con- be connected to a plug and cable for high -fre- 110V- denser switch for different values of condensers quency measurements. My instrument is a Su- 120V at different points of the receiver. You will be C preme 69D and the circuit is shown in the dia- surprised at how much improvement you can gram of Fig. L Calibration curves can be made make a Fig. 3. Neon bulb helps center speaker cones. in the receiver with few extra con- to suit the instrument used. densers. WILLIAM WILSON 003-MF j3WJ Another place where the condenser resistor IIi01 ME box saves time is in cases of open high -value / iO3-MF nsoo.., .. 50000" resistors. If you are in doubt about a resistor 75000" z00on SECOND PRIZE -$5.00 of high value and your ohmmeter will not measure that high, then set your resistor switch A 6E5 REPLACES PHONES ON CON- to the value needed and go directly across the DENSER ANALYZER. I have been a constant resistor in doubt, and also sometimes you will reader of Radio-Craft since 1930 and have all find an open resistor which is not color -coded the copies bound in volumes and the entire set and the service manuals do not give the value. is card- indexed. I believe Radio -Craft to be the From your tube characteristics chart or other finest of its kind ever to be published for the data determine what voltage or current you service profession. I should like to contribute should have, connect a volt or current meter to the following to the Service Men who built or the circuit and place the test leads from your bought the Thordarson Condenser Analyzer as I condenser resistor box across the open resistor know that the phone method of minimum hum and vary the resistor switch until you find a tIÓ-EPOyi was. and ie, tiresome to use. ÑÄVI ja. ,SAOgpn resistor that gives nearly the voltage or current Posxr urrlcP I conceived the idea that the "eye" tube (6E5 wanted, if necessary you may cut in the volume or 605) might take the place of the phones and control and bring the exact amount of resistance found that it works very well, and is very Fig. 4. Resistance- capacity box saves time. in. Also you can experiment with resistors in compact and light as I use a 2525 in a voltage - load circuits and greatly improve a receiver. doubling (traneformerless) circuit. I trust that You will find many additional uses for this Q others may find this an easier way to balance condenser -resistor box. PRUNES the bridge. See Fig. 2. E. A. MARCHANT SW OR H. A. WIRsCHIDia L MICROAM- METER HONORABLE MENTION J THIRD PRIZE -$5.00 HOME -MADE VERSATILE TEST METER. NEON BULB HELPS CENTER SPEAKER Here is my pet circuit of a very useful instru- 1 CONE. I like your fine magazine very much, ment which can be used in many different ways. 22.5V especially the "Analyses of Radio Receiver Am submitting it as a circuit short -cut in your BATT. Symptoms- Operating Notes," as I am a Service contest. See Fig. 5. Man. 1 have a kink which you may find a place First the 0-5 (or any other voltmeter with for. It is for centering dynamic speaker cones. suitable scale) may be used externally. Jacks 1 It consists of a 110-V. neon bulb in series with and 4 may be used to increase range of volt- II the speaker output transformer primary and the meter. Also 1 and 5 may be used for next high- A.C. line (see Fig. 3). A low- pitched hum will est range; adjustment of series resistors in each Fig. 6. Measures A.V.C. circuits accurately. be reproduced. The centering screws should be (Continued on page 40)

NEON 1 MEG. TOP VIEW 0-5 V. /BATTERY TUBE - OF METER III TR192 UNKNOWN 1 --I TEST SOCKETS ^ RESISTOR EXTERNAL 115V. STANDARD . AL- POLARIZING 115V D.C. A.C. GG5 R1- O 4-rvtEG VOLTAGES (VARIABLE) 5 1 252/ E LECTOROLYTICS rid B .OMOF 1OR MF. .05-MF ,0.5 ME 200V. F. + R2 R3 2008M V. 5 MF. OS MEG T- (4+ MF PHONES î 0.1- ',STANDARD 25Z5 VOLTAGc- 2 3 MF. 000BLING CIRCUIT"- Fig. 5. Versatile home -made test meter. Fig. 2. Affords visual indication of bridge -circuit balance in a condenser analyzer.

30 RADIO -CRAFT for JULY, 1938

www.americanradiohistory.com A WIRED -RADIO "NURSEMAID" Does Baby need a diaper change? Is Baby breathing normally? Every mother is a logical prospect for this "Nursemaid," which gives instant reports of remote happenings. Saves steps.

I I 111111! I I I I I I I I I l l l l l I I I I I I I I I I I I I I I I I I I l l l l l I I I I I I l l! I I I I I I l l l l l l l I t 1l l l l 1111 I1I I I1I I I1I11111 I1I I I1l l

HERE, illustrated above, is a varia- mother in the kitchen, perhaps-and sick room. Any attempt to obtain great tion of the wired -radio type of intercepted by the "Radio Nurse" unit volume by speaking loudly directly into inter -communicator, in which shown by inside view in Fig. B and by the Guardian Ear will result in serious only 1 -way operation is possible, which diagram in Fig. 2. The latter unit is distortion and speaker rattle. Radio -Craft has termed the "Wired- composed of a detector, audio amplifier To test or demonstrate the Radio Radio Nursemaid." and reproducer. Nurse elsewhere than in a home the This 2 -unit, super- sensitive sound Total amplification from microphone Guardian Ear must be placed in a amplifying system utilizes at the pick- to speaker is on the order of 500,000 soundproof box or separate room. This up end a "Guardian Ear" which con- times. This gain provides a measure of will prevent howling or feedback which tains a condenser -type microphone, sensitivity capable of amplifying the normally results from an amplifier speech amplifier, and modulator- oscilla- slightest sounds. Being purely a sound where the speaker and microphone tor circuit as shown pictorially by in- amplifier no attempt is made to attain units are in close proximity. side view in Fig. A and schematically high fidelity or high power output. This The R.F. carrier of 300 kc. is gen- in Fig. 1. The generated signal is con- device is NOT an inter -communicating erated by the oscillating S.-G. and ducted-from baby's room, let us say - system nor intended to be used as such. plate circuits and coupled to the light by means of the lighting circuit -to Its use is primarily for the nursery or (Continued on page 38)

INTRODUCING -A 5-METER CONVERTER

At long last we are able to announce a self - contained, add -on converter which enables any T.R.F. or superhet. receiver to tune -in 5 -meter experimental programs.

MOST radio sets today are capable of tuning-in not only the extended broadcast band of about 540 to 1,570 kc., but also one or more short -wave bands. Fig. A. It's now easy To tune -in 5 -meter music on broadcast sets! However, very few modern radio sets are capable of tuning- in stations below a frequency of about 30 megacycles (10 _REG,uLAR meters). r «JI ANTENNA An add -on unit which therefore is welcome, and which S.O. makes it possible to receive stations transmitting in the LC. s.ac 5 -meter (60- megacycle) region, is the 2 -tube "5 -meter converter" here illustrated pictorially (Figs. A and B) and by diagram (Fig. 1). ANT Of what use is this converter? -What sort of stations will this converter tune -in? -Does any special interest / f attach to the programs of these ultra -shortwave stations? / ONO. We will brief the replies to these questions. RADIO (1) A converter of the type here shown affords a par- 25Z5 6J8G SET ticularly convenient means of transferring 5 -meter signals NOTE: (S O to a wavelength slightly below the standard broadcast band. OSNE The converter is completely self -powered and is interposed AND CON- between the regular antenna and the broadcast set. Conse- VERTER.) quently it is unnecessary to tamper with the inside wiring of the set either to supply power to the converter tubes, T MF. or to connect the converter to the input circuit of the 5 7-11,F regular radio set. MF. I (Continued on page 49) Fig. I. A simple but effective converter circuit is used.

RADIO -CRAFT for JULY, 1938 31

www.americanradiohistory.com Technicians utilize this department to THE LATEST keep posted on the newer and better ways of doing things in Radio, Elec- RADIO EQUIPMENT tronics, and Public Address.

SET DESIGN to a ±10 db. level, has just been NOVEL announced. These units employ a INCORPORATES UTILITY permalloy core and are designed for (I615) frequency response of ±1 db. between 40 and 13,000 cycles! Dimen WHAT is said to be an entirely sions, 1jµ x 1't¿ x 2 ins. high. Sp, new thought in radio cabinet cial units are designed to order styling is here illustrated (top, ex- with (illustrated), or without. terior view; bottom, interior). The ernistic- styled magnetic shield. "miracle dial" is conically designed sit- to facilitate reading from any PUBLIC ADDRESS TUNER ting or standing position ; the scales and numerals are clearly calibrated KIT (1620) and the entire dial floodlighted. The (Meissner Manufacturing Co.) loudspeaker has been styled to HERE is a practical, sensitive P.A. match. Chassis utilizes 6 tubes and an A.C.-D.C. superhet. circuit for tuner you can build yourself and which` will give high- fidelity repro- American and foreign reception. 1 Has A.V.C., tone control, beam duction of broadcast programs. Fre- power tube, jewel band indicator. quency range is 530 to 1,600 ke. The Midget transformer is artistically mag- T.R.F. circuit uses shielded iron - netic- shielded. (1619) core R.F. transformers and 4 gang - NEUTRALIZING tuning condensers ; also provided are CONDENSER HAS A.V.C., separate output channel for headphone monitoring, manual audio MICROMETER gain, and tone control. Detector out- ADJUSTMENT (1616) put adaptable to any audio (power) amplifier input circuit. Incorporate.- ANEUTRALIZING condenser 3 -61(7, 1 -6116. 1 -6F8G, and 1 -5Z4 with a capacity of 2 mmf. range tube. Measures 8% square x 12% ins. to 8 mmf., and a precise means of deep ; this permits 2 units to be adjustment. is now available for the and experimenter. mounted in a single relay rack panel. radio amateur Tuner is self- powered, 110 V., 60 At last one manufacturer has altered Plates are 3 /16 -in. thick, and ground cycles. conventional receiver design in pre- and polished to provide for max- With this kit you can build high - senting the above illustrated set. imum breakdown voltage with min- (1615) grade radio reception into sound di,- imum spacing between plates. A tribution systems for schools, hotel, knurled lock -nut holds the movable other gathering plate rigid. and public places. IMPROVED ADD -ON NEW 70 TO 100 WATT RECORD PLAYER (1617) "TRANSPORTABLE" This P.A. tuner kit is priced low. SYSTEM (1621) Its frequency rance is 530 to 1,600 k . (RCA Manufacturing Co.) A T.R.F. circuit is used. (1620) MODEL R -93 -C, new low - (Wholesale Radio Service THEpriced record player, here shown, Co., Inc.) is designed to provide a good- quality THE 70 to 100 W. transportabl, record reproducer for new converts System, in a new line of coordi- to recorded music and for high nated sound equipment suitable for school and college student record en- the largest indoor and outdoor in- thusiasts. The Service Man easily stallations, is shown. Especially de- connects this unit into any elec- signed for easy removal to and from trically- operated radio receiver. De- various installations; the complete vice incorporates lightweight crystal system, including amplifier, 2 micro- pickup; tone arm is true- tracked; phone floor stands, 4 heavy -duty newly developed motor has bearings P.M. speakers, all cables, etc., is and supports cushioned in rubber for contained in 3 handsome. airplane quiet operation ; volume control and luggage styled cases finished in power switch are in one unit. Spanish brown leatherette with con- Vernier adjustment and permanent set- trasting dark -brown striping. ting are afforded in an air dielectric ADD -ON POWER STAGE The amplifier occupies its own neutralizer for transmitters. (1616) case and features 4 beam -power (1618) tubes. A.V.C. and automatic volume (Allied Radio Corp.) expansion, cathode -ray "eye" output indicator, complete mixing and fad- Portable P.A. systems go to high r THERE is now available in either above 's ing facilities for 4 input channels power. The system shown 25 -W. or 60 -W. rating a power capable of delivering 70 to 100 watt ! 2 low - stage which may be added to any (including 2 high -gain and (1621) existing radio net or P.A. amplifier. gain), "neo- dial" controls. variable A of 14 tubes is \fiords proportionate increase of tone control. total output power without the expense of used in the 5 -stage circuit. purchasing an entire new amplifier. Moth units employ 2 type 6L6G beam RADIO CABINET Inexpensive add -on electric phono- power tubes, inverse feedback, built - TOUCH -UP KIT (1622) graph for your home -radio set. (1617) in driver stage, speaker selector switch and facilities for using any NEWEST in cabinet touch -up kits P.M. dynamic or self -excited electro- for use by dealers and Service dynamic speakers. Tube complement: Men is the "right swanky" unit here illustrated. Kit contains quan- power stage- 1 -6N7G, 2- tities of the various cabinet refinish- 4,6G, 1 -5V4G; 60 -W. power stage - ing items used on all types of cabi- 1-6E6, 2 -6L5G, 1 -5V4G, 1 -83. nets as well as all kinds of lacquer finishes in general. The kit is fur- MIDGET TRANSFORMERS nished complete in an attractive GET MODERNISTIC COAT leatherette carrying -case. The dimensions are 6% x 12}', x 11 -5/16 ins. (1619) long, Complete instructions for use (Amplifier Company of America) in the of the 22 different items kit Radio cabinet touch -up kits show in- ACOMPLETE series of compact as well as repair procedures for vari- creasing usefulness. The one shown This add -on power stage conveniently ous types of cabinet -finish troubles Supplies additional output power. audio - frequency transformers, above contains 22 different items the (1618) designed for all circuits operating up are supplied. Service Man needs. Name and address of any manufacturer will be sent on receipt of self-addressed, stamped envelope. Kindly give (number) in above description of device.

32 RADIO -CRAFT for JULY, 1938 www.americanradiohistory.com Highly efficient portable recorder and playoac 1 Unit construction idea simplifies building amateur Wafer -thin crystal Improved ballast resistor. unit permits immediate checking of recordings transmitters; educes possibilities for error. (1623) mike. (1624) tube. (1625) (1626) semi-directional and notably free from feedback. PORTABLE SOUND RECORDER NEW UNIT CONSTRUCTION IDEA This unit has a wide range of applications, en- IN AMATEUR RADIO hanced by the available accessories. The 139 is (1626) singular in that it is equipped with a plug at (Sound Appa-atus Co.) TRANSMITTERS (1623) the microphone, thus making cable replacement RECORDING on the versatile unit here illus- (The Hammerlund Manufacturing Co., Inc.) a simple operation. Chrome finish. Complete with trated, is extremely simple; and presents no MECHANICAL arrangement of amateur plug and ti -ft. cable. Standard 5.'3 -27 fitting. problems even to persons without technical transmitters has always presented quite a This unit features an extended useful range in knowledge or inclination. The record is placed on problem, since not all amateurs have available which the bass is efficiently reproduced. an un- the turntable, the clamping screw at the end of the equipment necessary to make the variously - usual feature in diaphragm -type crystal micro - the flexible shaft is screwed down. After turn - shaped pieces of metal required for modern-type phones. table is brought in motion recording arm is construction. Too, many amateurs are not moved to the edge of the turntable and recording mechanically inclined. The unit, here illustrated, head is placed on disc. Reproduction of the a push -pull R.F. power amplifier designed to use recorded disc is immediately possible. any of the popular triode tubes having ratings of NEW REGULATORS SAVE PILOT Instrument includes a control panel with from 100 to 300 W. output per pair, is the LIGHTS (1625) mixers, master gain control, recording and re- modern and effective solution to these problems. producing switches, monitoring jack, speaker All parts associated with the amplifier proper. (Amperite Company) jack, door control and equalizer; a recording are joined together with brackets of various chassis with motor, recording lamp (to eliminate RADIO SETS in the new "H" series of A.C. - is available in kit form turntable and cutter), provision for continuous shapes. This hardware D.C. replacements. illustrated, are equipped the only tools necessary for assembling and recording, record -cutting mechanism and repro- and with a patented starting resistor which prevents a screwdriver soldering iron. ducer; an S -in. dynamic loudspeaker; crystal wiring are and of lights when the set. is first it is a self -supporting unit which overloading pilot microphone: and 10 -W. class A amplifier. When finished, on. Service Men should be able to go to to a with the mounting turned This machine is built in an attractive leath- can be bolted panel town on this item. At the present time there are screws furnished with the variable condenser; no erette case of 19 x 141/4 x 161á ins. and it is said to be over 300 A.C. -D.C. ballast replacements, equipped with locks and handles. Complete ma- chassis is necessary. and of course any method of simplifying these 30xs are shown in the chine weighs SO Ibs. Operates on 115 V., A.C. Although RCA photo welcomed by both Service Men and jobbers. triodes may be used depending is any of the popular These type KL -25A units will replace all bal- output. A circuit of the upon the desired power lasts, in one make, starting with K. L, M or NEW LINE OF MUTUAL is reproduced. on 4N, in order completed unit pg. numbers 11 and 26, visualize the relation of the components. BK and having between CONDUCTANCE TUBE TESTERS to better and ending in F, G or H. In other words it dimensions are 13 x el4 x S ins. deep. All-over will replace a K -25F. L -15G, etc. Similarly (1627) KL -75H will replace all ballasts starting with AWELL -known instrument manufacturer an- series WAFER -THIN CRYSTAL K. I,. M or BK with numbers 67 to 105 and nounces a new of (patented) dynamic ending in F. G. or H. For example it will replace mutual conductance tube testers with new square MICROPHONE (1624) K -75H, L-100G, etc. Because the regulator is a meters having translucent, illuminated meter (American Microphone Co., Inc.) real ballast, it can take care of a wide variation dials. (The counter -type or model T -53 -C is shown ; a type T -53 -P portable unit is also THE NEW 13-9 crystal microphone here shown in the number of tubes used in a set. It also be only dual- reading units edge-on is a small, lightweight, crystal micro- keeps the tube filaments at ±5r¡ with line available.) Said to the phone, with good response and high output. It is voltages from 100 to 140 V. (Continued on following page)

New, combined automobile and radio control unit. An achieveme -.t i. molded plssi:;. 1`6291 STE TNt ONTROL W. LT OL.CONTROL -TATIIIp N TUNER - ILLU INATING DIAL SEN CONTROL '

This achievement of the molding art marks a new step in the increasing importance of molded plastics and of the liason between automobile manufacturers and radio set makers. The car radio set is becoming an increasingly important, integral part of modern New "splicer " -colored insulating tape -eliminates automobile design. The complete unit is shown in (1628) Newest in mutual conductance tube testers. (162 ) unsightliness of old-style methods. (1629) close -up at upper left,

RADIO -CRAFT for JULY, 1938 33

www.americanradiohistory.com THE LATEST RADIO EQUIPMENT

IC onli nucd from . prereding panel made, with indication of D.M.C. in micromhos of different characteristics, is used at the an- and also as "Good, Bad, Doubtful." Just one tenna -end of the lead -in). setting to make. Easy to operate and understand. For buildings 15 to 25 stories high, one an- No complications and no customer confusion. tenna may be used for operating Other important 15 to 25 radio features are: sufficient plate sets. For buildings 10 stories or to less in height, current accurately check both emission and two downloads may be connected to one mutual conductance; checks gas content; antenna. detects to serve up to 20 outlets. The sale of even a both short and open elements and open sup- single apartment -house pressor -tests antenna system to feed, -grid; short made hot or cold; meter say, 20 outlets leach outlet terminating not affected by amount of plate in its current. individual Multicoupler), is indeed a profitable bit of business. Note that the new Multieoupler unit may be recommended for use where im- SAFETY INSTRUMENT UNIT proved performance is desired on any wave- INCORPORATES RADIO CONTROLS length covered by the designation "au- wave." (1628) NEWEST in automobile plastic moldings is the IMPROVED GANG SWITCHES so- called "safety unit" here illustrated. The (I 632) right -hand end of this molding incorporates radio (Cenfralab) controls as illustrated. To make the molded shell of this new control unit a "cannon" exerts 790,- ACOMPLETE line of selector switches as- 000 lbs. pressure at 350 deg. F. sembled with an isolantite insulation has just been announced. The group designed for the radio amateur operates safely at potentials AT LAST! THE SPLICE GOES up to 1,000 V., D.C. and up to 100 W. The second group, of interest to design engineers, II MODERN ( 1629) is available in all the usual multiple position KNOWN as a "splire" the modernistic wire types. splice insulation here illustrated has come to Zip!, and this new car aerial extends to a height ease of 44 ins.; the way of the technician who strives to do zip!, and it recesses to nearly cow - a CENTER -TAPPED WIRE -WOUND height (arrow, insert). Note control knob below neat wiring job. Adhesive tape seldom presents car's instrument panel (see drawing, above). (1630) anything but an unsightly appearance whereas RESISTORS (1633) the new splices or individual pieces of colored (International Resistance Co.) insulating adhesive, afford not only electrical protection A LINE of new center -tapped wire-wound sufficient for Underwriters' require- resistors ments but also permit matching the appearance rl is available in values between 10 of the and 200 ohms. Carrying capacity is up to 5 W. main conductor (power cord from wall chassis -wound outlet to radio set, etc.). and 2s. W. open -air mounted. Resistor is enclosed in molded bakelite. BUILT -IN RADIO ANTENNA TWO NEW 31/2 -INCH LOUD- AUTOMATICALLY RISES AND SPEAKERS ( 1634) LOWERS (1630) (Utah Radio Products Co.) WHAT is claimed to be a distinctly new de- TWO NEW 31/2-in. speakers have been an- parture in automotive radio aerials is a nounced by a well -known manufacturer. One "Col -Mar" Operative Aerial here illustrated. The unit is a permanent- magnet dynamic (illustrat- use of the word "operative" in the name of the ed), and the other L an electrodynamic type. aerial indicates that the aerial is operated as The manufacturer claims "vast improvement" in needed, being out of sight when not in use. A the performance of these small speakers, one touch on the instrument -panel button causes the improvement being the proportioning of the aerial to rise or to recede Apartment into its case (the generated harmonics in the cone surface to en- house installations employ I "multi - operation is controlled by coupler" for each radio the vacuum created able these small speakers to produce exceptional set. (1631) at the car's intake). It may be stopped at any tone quality. desired position. The announced specifications of the electro- A feature of unusual interest is the very low - dynamic unit are as follows: field coil, 450 ohms; loss short lead -in wire, being only 16 ins, long. voice coil, 3!3 ohms; output, 5 W.; frequency the advantage of which is readily understood by range, 200 to 8,000 cycles. The permanent- magnet those familiar with auto -radio reception. The of the P.M. unit is designed to give a flux density % -in. tube is made of non -corrosive brass alloy, in the air gap that gives this speaker practically topped by a bronze knob, triple- plated with the same performance as the electrodynamic with copper, nickel and chromium; the final chrome a saving of from 3 to 6 W. current consumption. plating being tested under 58 -hour salt -spray test. Antenna extends above car to a length of 44 ins., in one model, and 39 ins., in a second; capacity I4 -WATT PORTABLE SOUND (including lead -in) is approx. 55 mmf. in both SYSTEM (1635) types. (The Webster Company, Chicago) UST announced, is a new 14 -W. portable sound An improved gang switcn. (1632) IMPROVED ALL -WAVE system, using an inverse -feedback circuit. It "MULTICOUPLER" (1631) is claimed that within its rated output, distortion has been kept within 2 per cent. (Amy, Aceves d King, Inc.) This model features a full -length microphone RADIO SERVICE MEN 100 are finding added in- stand with screw -type microphone connections, 1 come in the sale and installation of modern, tone control and 2 permanent -magnet speakers, noise-free antenna systems ; a vitally important all stowed in a single leatherette- covered carrying irjomr.leamm.2 element of such systems is the "coupler" unit case. This model PA -714 amplifier is said to have which serves to match the antenna lead -in to been tested and approved by the Underwriters' the radio receiver. Newest of these couplers is Laboratories. Bakelite -enclosed power resistor. (1633) the "Multicoupler" shown here (a ...

Above -this I4-W, portable P.A. system utilizes inverse feedback. (1635) Left -here illustrated is a P.M. This kit can patch wood, plastic dynamic unit in a new line of and bakelite radio cabinets, (1634) two and 31/2-in. dynamic speakers. white refrigerators. (1636) Special products for technicians. (1637)

34 RADIO -CRAFT for JULY, 1938

www.americanradiohistory.com Service Men may write, requesting answers to specific service questions. Address inquiries to Service Editor. For questions answered by mail, a service fee of 25c per ques- wide interest can be pub- SERVICING tion is made. Only questions of lished. In view of the "rush" character of most service calls an effort is made to maintain 48 -hour service on mail QUESTIONS inquiries. Let us help you solve your service problems. & ANSWERS III 111111 I 11111111 111111 11111111 IIiIIIiIIIIIIIiiIIIIIIiIIIIIIIliIIIIIII IIIIIIIIIIIIIIIIIIIIIII 1111111111111111111111 111111 I III 111111 liii iCi liii III open possible. With the switch in the phono position, ordinarily. has been traced to an -circuited CONNECTION C, RECORD PLAYER the diode load or radio input is grounded, thus .01 -mf. oscillator plate coupling condenser, in Fig. Q.60. Should this condenser Vance, Lebanon, Ky. preventing the possibility of radio interference. as shown (69) Earl prove intact, carry out a resistance analysis of (Q.) We have sold an R98A Victor record In this manner. the receiver volume control the oscillator stage. Resistance readings from Philco model 87-116 receiver and with bass compensation network and tone con- player for a plate. and cathode to chassis should be want to know how to make the hookup for best trol may be used during phono operation. Needle grid the approximately 60,000 ohms, 0.25 -meg., and zero tone and volume. Please state beet method of scratch may be reduced by manipulating ohms, respectively. reducing needle scratch. tone control. (A.) For best results, connect the RCA record Where it is found that insufficient output is player into the volume -control circuit of the obtained by connecting into the volume control in order. S.-W. IMAGE -FREQUENCY Philco model 87 -116 receiver as shown in Fig. circuit, a "phonograph oscillator" is than Q.69. The double -pole double -throw switch may A "phonograph oscillator" is nothing more TROUBLE R.F. oscillator, tuned to some be either the toggle or knife type, and is em- an unmodulated (61) E. J. Symancyk, Westfield, Maas. frequency within the broadcast band, usually ployed to change from radio to phono operation. (Q.) I have a Zenith 12 -tube receiver, chassis the high -frequency end. The receiver likewise The lead to the "high" side of the radio volume at 1202. Within the past few months, I receive the to this frequency. The phono pickup control is removed and brought out to the switch, is adjusted meter stations at 14 mc. and 13 me. In other These attachments are 20 as is a lead from the "high" side of the control. modulates the oscillator. stations are received at 2 points unit connects words, 20 -meter Shielded leads, with shield grounded, are used available. commercially. The phono on 48) which goes (Continued page for this purpose. Leads should be as short as to the oscillator input, the output of to antenna and ground of set. C 56 05C. 34000n PHONO ON 01- 6.i INPUT OSCILLATOR FAILURE -SAFORM ME Ms (60) A. W. Larson. Waterville, Me. -r PHONO (Q.) We have a Zenith model 705 in for repair. RADiÓ- I -1 The trouble lies with the 56 oscillator which 1 - J fails to function. Tubes have been tested as have IP3 SHIELDED been ail resistors and condensers. The condenser WIRE has been replaced. Alignment does not block VOLTAGE I RADIO is heard at the same part of DIVIDER I4 VOLUME help. A whistle ti __ -_ is remedy? TO CONTROL dial. What the GRID 15000n I OF 1ST - 1 DIODE (A.) From your letter, it is to be assumed that PADDER (EACH) I LOAD mentioned with the Zenith 706 re- DET,, the trouble 57 I i SHIELDED traced to the oscillator 0.25-MEG. I-- -4 WIRES ceiver has been definitely stage. 9.60 Fig. Q.59 Failure of the oscillator in this receiver,

RADIO -CRAFT to FREE - A I -year subscription to each person who submits a WITTIQUIZ that in the opinion nc of the Editors is suitable for publication in RADIO -CRAFT. Read the following WITTIQUIZZES; can you spot the correct answers? Now send in YOUR idea of one or moro RADIO good WITTIQUIZZES based on some term used in radio, and win an award. (Contest rules at end of dept.) " WITTIQUIZ O p I I I II II I I II I II I III II I I I I I I I I I I IIIII I I I I I III I II I1I0000001111111111111111111111111111111I III III I I IIIII IIII I IIIp Il l l 100100000001I IIIIII A line voltage regulator. (b) The extra (86) A choke is- (88) A radio speaker is- (a) weight placed in a ship's hold to maintain A patented device, in expensive radio (a) A person that gives radio instructions. (a) A (c) A device used to steady the re- to choke undesirable sopranos. (b) A (b) Anyone who talks over "the radio." (c) stability. sets, used receiv- chassis, preventing vibration. used to filter a direct current. (c) person that's always talking about radio ceiver coil of wire im- A coil of wire used to filter an alternating cur- ers. (d) A device which converts electrical of (92) And that a potentiometer is- rent. (d) A coil offering a high resistance to pulses into audible sound. (e) A member Congress with a knowledge of radio. (a) A meter used in testing for different an alternating current. used by chemists L. BRUCE PAUL FIZelTO potentials. (b) An instrument to determine the potency of certain drugs. (c) (89) A quartz crystal is- A variable resistor. having 3 terminals, and used (86) Hand capacity is- (a) The ice formed by freezing one or more as a voltage divider, or volume control. (a) The biggest handful of bypass condensers quarts of water. (b) A recently-invented device J. VAN HUYRS that can be swiped from your neighbor's radio for foretelling the future by radio- activity. (c) Windsor. Ont., Can. junkbox without being caught. (b) When the An oscillating crystal used in stabilizing the capacity between the hand and some component frequency of a transmitter. (d) An obsolete (93) The emission of a tube consists of- in a detector detunes it. (c) The amount of high tubeless receiving device used in the early days (a) The stream of electrons emerging from voltage that the hand will take without drawing of radio. the cathode. (b) The elimination of static dis- back. (d) The number of radio signals that can FRANK H. TooKER charges which are shunted through a condenser be held in the hand without spilling over (break- to ground. (c) The incoming signal entering the ing into oscillation). (90) Every Service Man knows that a round- grid. PAUL BAUERLS head is- MILTON SCHRAG (a) A bald -headed man who owns a costly radio set. (b) A headphone used by a sound (94) Do you believe that a commutator is- A news -flash announcer? (b) A system (87) Condenser reactance is- technician in a studio. (c) A sound engineer. (a) a proof collector rings on an A.C. generator? (c) A (a) A disease contracted by persons engaged (d) An apparatus attached just below (b) A re- jector for the reproduction of the recorded sound ring of segments which contact the brushes on in the manufacture of condensers. make the current flow in obtained by the use of a con- on the film. (e) A valedictorian in a correspond- a U.C. generator to generation effect A band -switch? circuit. (c) A measure of the ence radio school. one direction? (d) denser in a radio HAROLD Fox opposition offered to the flow of A.C. (d) A JESUS CHICO. heating effect which occurs when a condenser Manila, P.I. (95) A plug must be- is short- circuited. stopping the grid -leak. (b) An J. A. GIBBONS (91) Service Men should know that a ballast (a) Used for Wallasey, England. is- (Continued on pape 66) RADIO -CRAFT for JULY, 1938 35

www.americanradiohistory.com 229 Radio Service Data Sheet

MOTOROLA MODEL 8 -80 (GOLDEN VOICE) CAR -RADIO SET 8 -tube Superhef.; pushbutton tuning; spot tuning; "Acoustinator" control; A.V.C.; Output (max.) 13W.; Battery drain 8.5 amps. (See Data Sheet No. 230 for additional information)

36 RADIO -CRAFT for JULY, 1938 www.americanradiohistory.com Radio Service Data Sheet 230

MOTOROLA MODEL 8 -80 (GOLDEN VOICE) CAR -RADIO SET 8 -tube Superhet.; pushbutton tuning; spot tuning; "Acoustinator" control; A.V.C.; Output (mar.) 13W.; Battery drain 8.5 amps. (See Data Sheet No. 229 for schematic and other diagrams.)

Push -Button Tuner Adjustment highest reading on the output meter. (3.) Adjust the trimmers in the I.F. coil can to To set the stations, as follows: proceed the showing highest reading on the (1.) Turn the set on and let it play for point output meter. (4.) Go over I.F. and diode NOT LESS 10 MINUTES, to assure THAN adjustment several times to secure maximum all electrical circuits reaching a constant accuracy. operating temperature. (2.) Select 6 stations to be "set" and arrange the 6 magnets SETTING THE RANGE to the approximate station frequencies as (1.) Connect signal generator to the con- indicated on the scale, locking them in posi- trol grid of the R.F. tube (78 or 6K7G) tion. DO NOT "SET" WEAK STATIONS. through a 0.1 -mf. condenser, having first (Fig. 1.) (3.) Press the first button. The removed the grip cap from the top of the motor will bring the mechanism to the first tube. Connect a 0.5-meg. resistor from the magnet. Loosen the lock nut. (4.) Tune grid of the tube to the grid cap on the manually to the exact peak of the station. lead just removed from this tube. (See Fig. using the tuning knob in the control head. 3.) (2.) Set signal generator at 1,560 kc. and, with condenser completely out of mesh, (5.) Press the first button half-way in (far gang (Acoustinator, lower -left, is not mounted on set.) enough to energize the magnet, but not far adjust for maximum deflection on the output enough to start the motor or mute the set.) meter. the trimmer in the oscillator coil can All readings except rect. plates are from (6.) Slide the magnet in the direction of labeled 1,400 kc. (3.) Set signal generator at chassis ground to socket terminal indicated. error until a "click" indicates that the latch 535 kc. Turn condenser plates completely Measurements made with 1,000 ohms /volt bar has engaged in the stop. (7.) Tighten in mesh and adjust for maximum deflection meter. Voltage at Battery-6.3 V. Voltage at the lock nut. (8.) Proceed to "set" the other on output meter, the trimmer in the oscil- Receiver -6.0 V. 5 stations. lator coil can marked 600 kc. Current Consumption -8.5 amps. -Output NOTE: The adjustments above set the (max.) 18 W. Spot Tuner Adjustment range so the receiver will track with the 'Note: The numerals heading the columns in the control head. up the calibrations refer to socket terminals (see schematic (1.) Slip the spot tuner housing 5). flexible control shaft far enough to expose R.F. AND ANTENNA ALIGNMENT diagram, Fig. the spot tuner mechanism, which consists (1.) Connect the signal generator to the Automatic Service Notes of a small ball bearing, a brass raceway in antenna lead through a 0.00015 -mf. conden- which it moves. and a slotted retainer clip ser and to chassis ground. Set signal genera- MOTOR FAILS TO START which acts as its guide. (2.) Tune in the tor at 600 kc. and turn condenser gang until (1.) MOTOR CONTACTS IN ACOUSTI- desired station as accurately as possible. A signal is heard. Adjust trimmer on the an- NATOR NOT CLOSING. Open the Acousti- tuning meter is recommended, except for tenna coil can labeled 600 kc. for maximum nator and inspect the motor contacts. If the meter. (2.) Set signal Model 8 -40, which has no Acoustinator deflection of output gap is too great, contact will not be made 1.400 kc. condenser gang receptacle. (3.) With a pair of slip jaw generator at Turn when the button is pressed. Adjust by bend- pliers, one jaw of which rests firmly on the until signal is heard. Adjust for maximum ing carefully. small ball bearing, the other jaw of which deflection of output meter, the trimmer in (2.) POOR CONTACT AT ACOUSTINA- rests on the bottom of the unit, apply enough the antenna coil can marked 1,400 kc. (3.) TOR PLUG. Inspect the contacts between pressure on the ball to force an indentation Adjust for maximum deflection of output the Acoustinator plug and the receptacle can in the brass raceway in which it moves. meter, the trimmer in the R.F. coil on the chassis. (Fig. 2.) Proceed to set other favorite sta- marked 1.400 kc. (4.) Recheck steps 1, 2, (3.) DEFECTIVE REVERSING SWITCH. tions in the same manner. The raceway has and 3, for accuracy. A defective switch would prevent the voltage a double track. Therefore. should you desire from reaching the motor winding. to reset the SPOT TUNER to a new series Use of Oscilloscope in Aligning I.F.'s (4.) OPEN- CIRCUIT IN MOTOR. Check of stations, it can be done by moving the EQUIPMENT REQUIRED: Cathode -ray all connections to motor and check motor ball bearing over to the second track. To do oscilloscope and a frequency -modulated sig- winding for continuity. this. turn the condenser gang to full mesh nal generator. (NOTE: if your signal gen- (5.) MOTOR BRUSHES NOT MAKING (ball bearing at extreme end of raceway) erator is unmodulated, a frequency modulator CONTACT. Check contact between brushes and with a pointed instrument, force the will be required to adapt it for use with and commutator. ball bearing into the adjoining groove. A the oscilloscope-) (6.) LOW BATTERY VOLTAGE. A weak THIRD SETTING CAN BE MADE ONLY or defective battery in the car would not A RACEWAY. PROCEDURE: sufficient voltage to start the motor. BY INSTALLING NEW (1.) Align I.F. and diode trimmers in the deliver Order No. 1X4487. (7.) FLEXIBLE TUNING SHAFT BINDS. part as outlined in preceding regular manner Binding in the flexible tuning shaft places (2.) Connect "wobbulator" to Alignment Procedure paragraphs. an additional load on the motor. If this load control -grid of Osc. -Mod. tube (6A7 or is too great, it will prevent the motor from Plug in the Acoustinator, if the set under- 6A8G) through a 0.1 -mf. condenser, having turning the mechanism. going alignment is thus equipped. Set Acou- first removed the cap from the top of grid (8.) MAGNET FAILS TO RELEASE. If stinator at "Country" and "Voice" positions. the tube. Connect a 0.5 -meg. resistor from the magnet which has previously been ener- Connect the speaker to the chassis and plug the of the tube to the grid cap on the grid gized, fails to release the latch bar for any the "A" lead into its receptacle. Turn the lead just removed from this tube. 3.) (Fig. reason. the motor cannot turn the mechanism. volume control to maximum and leave it in (3.) Connect oscilloscope to the top or high that position throughout the alignment. aide of the diode load resistor. which, in FAILS TO STOP AT MAGNET reducing the signal generator output if this case, is the volume control. (4.) Adjust necessary. (1.) OPEN MAGNET WINDING. Check the "wobbulator" frequency to 262 kc. and for continuity and replace if necessary. IMPORTANT NOTE: observe the picture of the I.F. resonance (2.) MAGNET CONTACT IN ACOUS- The trimmer labeled 600 kc. in the R.F. curve as shown on the oscilloscope "screen." TINATOR NOT CLOSING. Open Acoustina- the field. a top coil can must not be adjusted in Correct alignment will result in flat tor and inspect contacts. Adjust or clean if It is the key point in the entire R.F. align- curve, as shown in Fig. 4A. (5.) Should the necessary. ment and was carefully set in the factory curve appear sharp at the "nose" with a (3.) ROUNDED HEAD ON MAGNET by means of an accurate capacity bridge shelf on either side of the peak, as shown CORE. The head of the magnet should have to its correct capacity (840 mmf.). Before in Fig. 45, adjust the PLATE trimmer of sharp corners. Rounded corners may cause shipment, this trimmer was covered by a the I.F. transformer slightly, until the curve the latch bar to slip going in one direction. strip of black Scotch Tape, which should be approaches the condition shown in Fig. 4A. although it will usually catch in the reverse left in position to eliminate any possibility If the regular I.F. alignment has been direction. of shifting its capacity through error. properly carried out, it will be necessary (4.) LATCH BAR DEFECTIVE. Inspect I.F. ALIGNMENT only in rare instances to adjust other than latch bar to make sure that it has not been (1.) Connect signal generator to control the I.F. PLATE trimmer. damaged. Replace latch bar and gear assem- grid of the Osc: Mod. tube (6A7 or 6A8G) 'OPERATING VOLTAGES bly, if required. through a 0.1-mf. condenser, having first 2 3 4 5 6 7 8 (6.) POOR CONTACT AT ACOUSTINA- removed the grid cap from the top of the VI 265 90 0 X 6.0 4.0 TOR PLUG. A poor contact here means a tube. (See Fig. 3.) Connect a 500,000 ohm V2 6. 255 90 9.4 120 0 4.0 voltage drop which reduces the pulling power resistor from the grid of the tube to the V3 255 90 4.4 X 6.0 4.4 of the magnet. grid cap on the lead just removed from this V4 50 0 .2 X 6.0 7.0 (6.) IMPROPER SPACING OF LATCH tube. Turn condenser gang completely out V5 150 X 0 X 6.0 5.6 BAR. Check the spacing between the latch of mesh. Connect output meter across speaker V6 255 256 0 X 6.0 15.0 bar and the magnet. It should be somewhere voice coil. (2.) Set signal generator at 262 X8 300A.C. X 300A.C. X 6.0 260 between 0.01- and 0.02 -inch. If the spacing kc. and carefully adjust the trimmers in ,.X,. indicates socket terminals used as is greater the pulling power of the magnet the diode coil can to the point showing dumm tie points. is reduced.

RADIO -CRAFT for JULY, 1938 37

www.americanradiohistory.com A WIRED -RADIO "NURSEMAID" (Cuotio ed from poor 31) circuit by means of a low impedance coupling The trimmers have a tuning range of from coil. A harmonic filter is built into the Guardian 250 to 450 kc. If interference from another Ear to prevent radio receiver interference at Radio Nurse is encountered, it may be elim- 600, 900 and 1,200 ke. inated by readjusting either pair of units in Bias on both grids of the 79 tube is obtained the following manner. Shift the frequency of by the use of bias cells. These units have an one Radio Nurse (Bakelite unit) slightly or extremely long life and should not be replaced until the interference drops out. The bakelite unless the plate voltages of the 79 tube measure shell of the Nurse must be removed in order abnormally low. Never test the bias cell with a to reach the trimmer. The Guardian Ear of the voltmeter of any kind. The current drawn by pair is then tuned to resonance as previously the meter will discharge the cell immediately, outlined. and no reading will be obtained although the cell may be in good condition. Only a vacuum - 3 -WIRE SYSTEMS tube voltmeter will show the true condition of In cases where the electric service to home the bias cells. the or apartment is of the 3 -wire, 220 -volt type, The receiver is coupled from the line to a and the transmitter is used on one 110 -volt cir- 6F5G by detector another low impedance link. cuit and the receiver on the other, it is some- The detector is capacity -coupled to a 41 output time., necessary to install a bridging tube. condenser across the outside 220 -volt leads to form a When shipped from the factory, both units are path for the signals. To accomplish this, a Fig. A. The "Guardian Ear" or pick -up unit. adjusted accurately to 800 ke. by means of a special bridging condenser was developed. This variable trimmer in each unit. If for any reason condenser is a special oil- impregnated unit made ing condenser wire is fastened under a fuse on it is suspected that either of the units is not for continuous operation on 250 volts A.C. the opposite side of the 220 -volt circuit in the tuned to resonance, it is only necessary to re- and has a 2.5 ampere fuse sealed inside the same manner. adjust the trimmer on the side of the Guardian condenser case. In some installations, fuses are used on both Ear, until maximum sensitivity is reached. The condenser is connected to the line by the live side of the well Maximum line as as the neutral sensitivity may be found by placing first removing a fuse on one side of the 220 -volt or ground circuit. In such cases is imperative a watch on the it Guardian Ear, and after raising circuit and inserting the metal tab into the that the two fuses to which the condenser is the volume on the Radio Nurse to a point just shell of the fuse socket so that when the fuse connected be in the live leads and not in the below feedback (howl), adjust the Guardian Ear is screwed back into place the metal strip makes ground aide. trimmer for maximum volume of the watch tick. contact with the shell of the fuse. The remain- (Continued on page 53)

tiTRAMITTER 79 A2- 0.47- 4' pADDER (300KC.) + 32V MF( MEG. 127V. +RECEI VER 41 (300 KC.) COIL 2 2 MF +165V. "C. j O1- PADDER 4 ' 02- IL/ 0' MF MPj +175V. T. 033- 100 i100 o 1 MEG. MME MME $ MEG x X ó 0.33- MF o MEG. / i 1.125V. ó BIAS +25V -BIAS CELL CELL 0.1- 0.47- 0.4- (r(.tSF MF. MEG. 0.1- Sv VOLUME MEG. 0.47- \\ h CONTROL MEG. 6BOn 0.33 - - 52MF. 0.1- / GREEN VELLOW MEG. 25V., MF. (5 MOUS BLACK 2,150n 25V. nt) l MEG.1 MF SPEAKER R.FC 5.8V.AL. 84 X I MP X / +232V. IMF t5.8VA.C. mew P f Í 4MF x .-I 300V. 84 2.200 n-oT 2.200 (F man r 165 V.A C. L 18.000n 194V NOTE: . _ 210V. a FO 41,4F. 6 MF. (4MF. 250V., 25n., ONLY 25M V. 20oV. ~ 115V,A.C. T(8MF. 250V.41) to MF. (2 M ZSOV.#) YOOV.!) T 165 VA.C. T, Fig. 2. Diagram of the "Radio Nurse" or reproducing unit shown, in Fig. 8, NOTE: a FOR 25 "ONLY T on p q 53. The volume control knob which extends out of the bottom of the bakite shell of the Nurse is adjusted until the tick of a watch laid on top o the remote "ear" can be heard loudly. The electric light wiring Fig. I. Schematic of automatically circuit the "Guardian Ear" or pick -up unit shown in Fig. A. supplies the required "connection" between the 2 units.

MODIFYING OLDER SETS TO RECEIVE RADIO CREATES AMAZING THE 4 HIGH -FIDELITY STATIONS FASHION PATTERNS (Continued from poor 21) (Continued from page 11) (See Fig. 113.) This will cause a more serious SHIFTING THE I.F. designs which would drive a surrealist artist error in the dial readings than the adjustment Another way more frantic with envy. But space limitations do of the trimmer condensers. However, if the dial to tackle a superheterodyne is by shifting the intermediate frequency. Fig. not permit us to reproduce them. is calibrated in arbitrary numbers such as 0 (See 1C.) Sometimes this will work, but will One of the more complicated designs so favor- to 100, the Service Man can leave a list of the cause a tracking error that may or may not be per- ably impressed the designer of machine -made new dial readings so that the set owner can mem- tapestry that he drew up a sketch of window orise missible. them. Do not take out plates of a condenser curtains using the pattern. A lace factory is to reduce the minimum As a general rule, the high -frequency end of a capacity as it will also receiver also interested in it, with the idea of producing reduce the maximum amount of is the noisiest. It is VERY IMPORTANT capacity and then to get the highest signal- curtains. Thus not only novelty manufacturers will probably reduce the tuning range of the to-noise ratio possible for quiet reception ; especially is find new avenues receiver instead of increasing it. In this case this of expression opened up, but the maximum true where higher- fidelity programs are to be also the producers of more bulky items, as for error would then be at the low - received. Many sets operate satisfactorily frequency end of the dial. without instance these curtains, and floor -coverings, etc.. In adjusting an antenna, or with a poor one on the high - now have at their command a machine that is the trimmer condenser of a powered, lower -frequency stations, but unsatis- superheterodyne receiver, the oscillator trimmer capable of producing patterns in inexhaustible will be the most critical, factorily on the higher- frequency stations. Make variety. the mixer and radio- to up a good frequency stages being comparatively every effort get outdoor antenna Infinite in number and variety are the broad. The for best reception. If a good ground is not obtain- pat- padding condenser can then be readjusted for terns produced by this new RCA cathode -ray proper tracking. If correctly able, sometimes better reception will be had by done, the original not using one all. (See, also, "The kaleidoscope, and plans are already under way dial settings will not be at Problems changed appreciably. in High- Fidelity Design," in December, '34 to inaugurate an "electronic pattern" service If the superheterodyne is not equipped with a Radio -Craft, for additional information on what to the leading dress, textile, plastic, wrapper padding condenser, but depends upon an to do to the set. once high -fidelity programs and jewelry designers of Paris and America. especially -built oscillator condenser, there will be can be tuned -in, to get the most from the This invasion of the field of art by electronics a slight tracking error, but it will not be serious. receiver.-Editor) adds a milestone to radio.

38 RADIO -CRAFT for JULY, 1938

www.americanradiohistory.com RADIO -CRAFT for JULY, 938 37

EUROPE'S UNDECLARED RADIO WARI (Continued from page 9) SUPERIOR PRESENTS that it became very difficult, almost impossible. to hear this station. But it still broadcasts, and is now to be heard on a wavelength of 23.8 THE AMAZING, NEW 1938 1100 SERIES meters. It remains a real mystery. Field! New Refinements, New The Spanish trouble has added greatly to the The Best Buy in the Instrument Many war on the air. First of all, Moscow transmitted Features.... All Proven to Be Sound and Practical! more Spanish talks than formerly. saying to the J Republicans, "We are with you with all our soul." Then General Franco captured several The New Model 1100 -S The New Model 1120 -S broadcasting stations sharing wavelengths with those still in government hands. OSCILLATOR Sebastian used to vie with one D.C. VOLT -OHM MILLIAMMETER Bilbao and San Truly the greate. another, until the capture of Bilbao when from value ever offered the broadcasting station could be heard the entry An All -Wave, di- of the troops. Then General Franco increased rect- reading Oscil- the power of the Salamanca station to unknown lator in Portable kilowatts and transmitted on the same wavelength size. Compares fa- vorably with in- as Madrid. struments selling Another feature of the struggle has been the at three times its entirely illegal use of the amateur wavelengths price! Housed in a on the 40 -meter band for news and propaganda. black crystalline And within the last few months, one or two cabinet with car- stations have begun transmitting on the 20- rying handle. meter band. Both sides do this. They give propaganda in at least 4 languages. and both try to SPECIFICATIONS: jam each other. In addition, it is noticeable that 1. Covers 100 kc. to al the Spanish government transmissions in German fundamentals with suffer more from jamming than any and Italian A sensationally low priced new pocket-size volt- ro paneles band others. Presumably. the German and Italian ohm milliammeter. Features a 3" t'Arsonval switchft` and !re- n those authorities are responsible for this. type 0-1 meter, accurate within 2%; precision Lges ° by dial A strange happening in the Spanish war resistors. No external batteries necessary. isi Neat etched panel. 2. Dial direct reading in frequencies. with bend has been the transmissions of a station calling aluminum switch settings identified both by letters A. B. C. D. El and by frequencies, with the om itself "Radio Verdad," and broadcasting in SPECIFICATIONS spending Identifications dial As 3. F. an outpts obtainable dependentl Spanish. ( Verdad is Spanish for truth.) they 4. Accuracy 1 per cent on I.F. and broadcast bane, 0 -5 volts D.C. 0 -5 ma. D.C. the short waves. use several Italian wavelengths on the medium 0 -50 volts D.C. 0-50 ma. D.C. a. Separate shorts, either the Italians were leakages, g the leaakag of electr`olyti! band, I thought that 0-500 volts D.C. 0.100 ma. D.C. and other condensers. Thus very closing down their stations to allow the Spanish 0 -1000 volts D.C. 0-500 ma. D.C. eistanhier circuit,. be foor continuity. ohms 6. Planetary turn -easy drive, with 4 -1 vernier. station to broadcast its "truth" propaganda. 0 -600 ohms 0-500,000 7. rates on U0.120 volts A.C.C or D.C. More over the O C may be of any commercial frequency. S t or that the Italians were responsible for Model 1100-S supplied with 40, 50. 60 cycles, etc. thing. whole batteries, test leads and in- Model 11204 supplied They give an address in Salamanca to which etruction Size 61/j" x Sit" with tubes. leads, and are asked to write. I wrote, but have x 21Fí"; shipping weight 4 i insruuction, shipping $885 listeners $585 eight se S n had no answer. When listening to Rome at 7 lbs. Our net price z x , Our net price o'clock G1d.T., I heard the station sign off, and then the carrier disappear, before Radio Verdad made its transmission. But Radio Verdad's an- The New Model 1160 -S nouncer has a slight Catalan accent, which shows that he does not come from Salamanca. This made me suspicious. Then a friend used direc- SET TESTER tional antennas on the transmission, and Radio Verdad was proved to be the Italians masquerad- A Complete Laboratory ing as Spaniards. This is not very surprising, since I All in One Unit! perhaps Featuring Our New Type Sloping Panel for have seen it stated that broadcasting in General Precise and Rapid Servicing Franco's territory is almost entirely under Italian Here is a modern tester conforms to all control. Oddly enough, the only Italian I know set that standards of good engineering practice. Utilizes n had a job with the Italian broadcasting company modern, square d'Arsonval type meter and preci- in Rome, and then he went to Salamanca, Gen- sion resistors. Just what every Serviceman need, eral Franco's headquarters. for rapid, accurate measurements. Italian used to be the only major European SPECIFICATIONS language in which the Russians never gave Com- COMPLETE A.C. and D.C. VOLTAGE munist propaganda. I wrote to Moscow and asked and CURRENT RANGES them why ; but, though they answered my letter. D.C. Voltage: 0 -15. 0 -160, 0-750 volts. they refused to answer this question. Jt has been A.C. Voltage: 0 -15, 0- 150. 0 -760 volts. suggested that a clause between the two countries D.C. Current: Ol, 0-15, 0 -160. 0 -760 ma. forbade the broadcasting of propaganda. In addi- A.C. Current: 0 -15, 0 -160, 0.750 ma. had so 2 RESISTANCE RANGES tion, there was a rumor that Mussolini 0-500 ohms 500 -5 megohms successfully jammed all the Russian stations that HIGH and LOW CAPACITY SCALES they ceased their propaganda in Italian. How- .0005 to 1 mfd. and .05 to 200 mfd. ever. lately, Moscow has been giving propaganda 3 DECIBEL RANGES in Italian -just another radio mystery. -10 to +19. -10 to +38. -10 to +53 The Italian broadcasts from Rome and Bari INDUCTANCE: 1 to 700 Henries WATTS: Based on 6 mw. at 0 D.B. in 500 ohm: in Arabic have raised much protest over here .006000 to 600 watts. in England. But in addition to those in Arabic. I. Tests all 4, 6, 6, 7s, 7L, and octal base tubes. there are others in Chinese and other Oriental including diodes. languages. It is these Arabic transmissions that 2. Tests by the well established emission method have compelled the British Broadcasting Cor- for tube quality. directly read on the GOOD '! broadcast in Arabic in order that BAD scale of the meter. poration to 3. Affords separate neon test for leakage and Palestine should have a source of radio news shorts between elements. other than that from Italy. Comes housed in sturdy, black case with 4. All services performed by the use of only fie, And so the B.B.C. feels compelled to broadcast sloping panel. Complete with test leads, controls at maximum, and many tests do not instructions and tabular data require working all the controls. foreign languages : it began with Arabic early tabular charts, in 5. Supplied with instructions and reference table year. I listened to these broad- for every known receiving this When first type tube, including many so that the filament voltage and emission casts, I felt certain that there was a definite transmitting types. SIZE: 85 measuring controls may be properly set for effort being made to jam them. I could hear the 111/4 x 91/4" x 5 ". Shipping the enumerated long list of tubes, which in- chimes of Big Ben perfectly, but the moment wght. 18 lbs. Our net price 7- cludes all tubes commonly encountered in the Arabic announcement was made, it was servicing. overwhelmed by interruption. Whether this in- Model 1160 A -S with Portable Cover, add 95e 6. Work on 90-120 volts A.C. 60 cycle terruption was successful in preventing reception in the East, is another matter. Last night I listened to the British transmissions in Spanish and Portuguese. The half -hour's news bulletins SUPERIOR INSTRUMENT CO. came in uninterrupted. feels that readers be (Radio-Craft its will RC particularly receptive to this article, which con- 136 LIBERTY ST. Dept, -738 NEW YORK, N. Y. tains first -hand information.) Please Say That You Saw It in RADIO -CRAFT

www.americanradiohistory.com 40 RADIO -CRAFT for JULY, 1938

USEFUL CIRCUIT IDEAS (Continued from pago 30) case is made with the 0.4 -meg. variable resistor. gh-e- Ideal radio service Exact setting of the 0.4 -meg. resistor can be car found by comparing with a known accurate voltmeter. Jacks 1 and 3 are for continuity and ohmmeter with 0.4 -meg. resistor as zero ad- FAST-Dependable- Convenient -Economical juster for latter. The ohmmeter may be calibrated with known values as tested with another ohmmeter known to be correct. A 46 V. battery The last word in light, eco- may be used externally with "+" at jack 4 nomical service equipment. and lead on " -" side of battery to test higher values Comes of resistance. Next, jacks 2 and 4 may with large, commodi- be used as a substitute resistance in various ous side car. Gives 120 miles ways, the 0.4 -meg. resistor being calibrated and on a gallon of gasoline, ends read directly on the scale. Jacks 2, 4, 5 and 6 may be used to get different values of resistances parking worries, garage and to use as substitutes. upkeep expense. Draws a D. E. GANDY crowd at every stop -it's the best advertising you can buy. HONORABLE MENTION AN INSTRUMENT CIRCUIT FOR MEASUR- Write for catalog ING A.V.C. VOLTAGES. Fundamental Circuit: (See Fig. 6A.) When opposing voltages are equal there is a zero current and therefore infinite resistance; the voltage as read on V. is then equal to the source being measured. In the diagram (Fig. 6A) T are the terminals for the voltage to be measured; J is the jack for headphones or micro -ammeter and R the battery supplying the bucking voltage. Practical Circuit: (See Fig. 6B.) MOTO -SCOOT MFG. CO. Important: Proper polarity must be observed in connecting the infinite resistance voltmeter 237 S. Western Ave., Chicago, U.S.A. in the circuit under test. WILLARD MOODY

SERVICING PUSHBUTTON TUNING SYSTEMS (Continued from page 19) It will be found that some stations cannot be (5) Excessive side -play in scanning arm blade, tuned exactly to the dial marking, but if they causing the knife edge blade to rock from side are within 10 kc. it will be taken care of by the to side. See Fig. 11 and note that the rocker pin A.F.C. which should always be turned on when flanges are adjustable by means of a screw in the automatic dial is used. back of the scanning arm. Correct adjustment Remove the star tab from the escutcheon hole provides a rocker action, up and down with no directly beneath the screw which has been set side play. up and insert the proper station tab. This opera- (6) Not enough tension on scanning arm. tion is repeated for as many stations as are Loosen collar on shaft at the rear of the sector required. and push scanning arm toward the sector face. Figure 13 shows the appearance of one of then tighten the collar on the shaft. these dial control screws and the dial escutcheon (7) If the Button contacts do not close, or which holds them. The indexing finger on the else fail to make good contact and hence motor control screw sometimes breaks off due to being continues to scan dial Without stopping at desired forced or stuck in the tuning gate, in which case station. Bend or clean the button contacts. a new screw may be installed without dismantling (8) Sector has warped away from its vertical the dial mechanism. The trick in doing this is to position, causing one or more buttons to skip press in on the broken screw while the dial stations. Since the metal is very brittle no at- is not set for the station controlled by the broken tempt should be made to straighten a warped screw. The screw should be turned until the index sector. The best remedy is to replace with a finger falls into the pear -shaped slot and upon new sector. releasing the screwdriver the screw may be (9) Control shaft grounds against the dial pulled out and the new one inserted in reverse and pushbutton escutcheon. If this happens the Ask your jobber order. relay remains energised and the motor will not Other troubles which may be encountered in run. for the this dial system are: Stuck or broken tuning (10) Open or shorted motor condenser causes gate ; no A.F.C. action because of defective switch motor armature to hum but prevents it from NEW CENTRALAB actuated by tuning gate; no signal, or intermit- turning under load. Replace with a new content and distorted signal due to Audio shorting denser of the proper type. Volume Control Guide switch trouble on dial -shaft hub. (11) Open or shorted coil in motor causes G.E. MOTOR -TUNED SYSTEM motor to turn very slowly, if at all. and only in one direction. Replace motor or repair coil. Again . . the servicemen's most The following paragraphs relate to the C.E. popu- The convenience and lar guide . . now available . Model F107 Service Notes on incorrect operation advantages of button bigger and better than ever. and suggested remedies. tuning need not be restricted to today's receivers. only. Button tuning of the trimmer type can Lists 10,000 models! . 240 pages (1) "Touch-Tuning" button leads not making easily be added to sets of the superhet. type of . more than 400 types of radios . good contact to stud screws. Clean contacts and complete line of midget Radiohm Re- re- insert. the past few years. placements . . Also a complete listing (2) Scanning arm blade either covered by As a moneymaking adjunct for the Service of all other Centre lab products: switches. Man, two types of switches are available at sound thin piece of bakelite or else is dirty. Carefully resistors, projection controls, and present and are shown in Figs. 14 and 16. The the new Centralab wire -wound Radiohm. run a file over the top of the blade, making sure not to leave any sharp corners. Also apply circuit- ctosing type shown in Fig. 16 can also a be used in analyzers and test equipment. Figure FREE at your . little vaseline on the beveled surface to prevent jobber 16 the or send 10e to rover handling chattering. shows construction of the "latch" which and mailing to CENTRALAB (3) Scanning arm jumps off because nipple is is common (in one form or another) for prac- too sharp on the adjustable stud screw. Smooth tically all pushbutton switches. MEET CENTRALAB AT THE oaf with fine sandpaper. The circuit transfer type shown in Fig. 14 uses NATIONAL RADIO PARTS (4) Relay armature out of adjustment caus- an ingenious method of progressive switching; TRADE SHOW ing sluggish operation of relay switch. In this that is, a series circuit is maintained up to the where a is whereupon CHICAGO. JUNE 8 -I1 case it will be necessary to adjust the backstop point button pressed in, so that the armature snaps closed when the the series circuit terminates at a lower contact relay coil is energized with 4.6 volts A.C. The of that button. The author has added a Meissner backstop must make a positive contact with the 8-button assembly of the type just described. to back of the armature in the open position. If a high- fidelity tuner (June, 1937, Radio -Craft). the relay will not close at. 4.5 volts and still The troubles which may occur in latch switches maintain proper travel and sequence, weaken the are very few and easily located. MILWAUKEE - WISCONSIN spring on the rear of the armature plate by (This concludes the author's timely, informa- bending the stationary spring support. tive and easily understandable article. Editor) Please Say That You Saw It in RADIO -CRAFT

www.americanradiohistory.com RADIO -CRAFT for JULY, 938 41 HOW TO MAKE A MOTO -SCOOT FOR SERVICE CALLS HIGH -FIDELITY TUNER (Continued from pap' 23) consists of 4,000 turns of No. 32 D.S.C. wire FREE THE wound on a bakelite or hard rubber form of the dimensione given. The wire should be wound evenly but not in layers. NATIONAL UNION The layout of parta can be seen from the photographe (Figs. B and C) and no actual drilling layout is given because of the difficulty of WAY may spotting holes exactly, when substitute parts Here's a grand idea for quick, be employed with a resulting shift of hole loca- low cost transportation for the tions, etc. service engineer. The Moto-Scoot When all parts have been secured to the with side van attached. provides chassis, the wiring can be done, using well - ideal transportation facilities for insulated wire and heavy flexible leads for the test equipment, tools or radio filaments which must be fed from the amplifier chassis. chassis. The wiring should be as short and direct The Moto -Scoot is safe and easy to as possible consistent with a neat and workman- operate and unbelievably economi- like job. The A.F. output leads should be shielded cal to run. You can get about 120 grid miles to the gallon of gasoline. and the lead from the potentiometer to the The unit is supplied complete. of the first tube in the amplifier should consist ready to go with no accessories to of a heavy shielded wire, using the shielded loom buy. It is completely equipped with sold for auto -radio antenna leads. This will keep a powerful lighting system. Get it the capacity between the lead and shield at a FREE for your business. Ask your minimum and prevent bypass (loss) of the distributor for complete details or high -frequency signals. write. With the coils used in this set (it is not ad- USE visable to make the coils at home if consistent flat -top resonant curves are to be expected) a coupling capacity of 0.06 -mfr produces a selectivity of approx. 20 kc. and with the addition of the 0.01 -mfr capacity in parallel with the 0.05 -mf. NATIONAL UNION units, the band -width narrows to approximately 15 kc. The use of 0.02 -mfr in place of the 0.01 - TUBES QUALITY CONDENSERS mf. condensers, the band -width narrows to ap- QUALITY proximately 12 lie.. thus permitting adequate control of selectivity for most situations encountered Thousands topnotchers in Rodio Service are depending in the U.S. of If desired, a switch can be included to cut the on Notional Union Quality. These tubes and condensers 10.000 -cycle filter out of the circuit so that this attenuation of the "highs" may be eliminated have the kind of precision and value that makes good friends when the noise background and monkey-chatter permit. This is not shown in the circuit as the for you too. set was made to be used close to New York where the interference is notably bad. National Union will help you to own "the finest radio service THE AMPLIFIER lob in town." Everything you wont is offered you on a "Free Deal" The actual amplifier with which the tuner is you to get the equipment you need now to do used depends on the individual preference of Plan. It will help the builder; on the volume level required, and better work and faster work and make more money. That's the on the pocketbook. deals . . . . for The circuit used by the writer employs coupling National Union way. Over 100,000 completed which are not commercially avail- transformera more just write . . . . able. However, several very fine input and out- details, put transformers are available and this should not deter any builder from duplicating the am- SEE US AT BOOTHS 205 -207 -Hertz Ave. plifier used in the original model, diagrammed CHICAGO RADIO,PARTS SHOW in Fig. 3. Some readers may prefer the use of the triode output tubes to the beam tubes- but as far as available instruments and the writer's ears are concerned, the beam power NATIONAL UNION RADIO CORPORATION THE ROAD TO 57 State St.. Newark. N.J. RC -738 amplifier gives equally good response and low NATIONAL Please end t e more Information mi: harmonic content with one less stage than the UNION BETTER BUSINESS triode amplifier. (This may be due to the closer Moto- Scoot st match between tube and transformer impedances Full guarantee on 4 N. U. jobber stols Other N.U. "Free" Offers in the beam amplifier.) highest quality ore complete No Name for the rodio tubes. hunting for odd No constructional details are given types amplifiers as this article is limited to the design 2 Cut price business Address the not solicited. and construction of tuner. 5. Timely business 3 Price Protection building aids City 'tale SUITABLE LOUDSPEAKER SYSTEMS mmmmmmm- wowwwwwwwwr However, the subject of speakers and baffles should be mentioned as this is the second "weak 4. EXPER LtanAT NOME E link" in the chain (the detector being the first. RADIO as you will remember). There are several speak- RADIO SPECIALISTS NEEDED HERE IS YOUR OPPORTUNITY ers on the market which will respond up to Your possibilities of making money and getting mind Modern receivers with their complicated circuit sys- about 6,000 cycles, but to the writer's it tems have knocked out the old time cut- and -try ahead are limited only by your ability and skill - takes a really good double speaker unit, using radio fixer. Trained men with up -to -the- minute but you must know more than the other fellow. You woofer and tweeter speakers, to bring out the knowledge are needed fo service these new sets. must be a radio service specialist, as R.T.A. can capabilities of this wide -band tuner. train you. Also, there is little advantage to be gained PRACTICAL TRAINING WHAT R.T.A. STUDENTS SAY in increasing the H.F. response of a set without also increasing the L.F. end. And with this point AT HOME Norwood. Ohio study course is "shop and f have connected with a large firm baffle either Our home practical and in mind, a large area or the use of bench" training combined with a thorough set as Radio Service Manager the infinite baffle, bass reflex or peri- dynamic of practical lessons prepared by an experienced rlste to extend my thanks for your Radio service engineer. Four working outfits help. principle to increase the "lows" cannot be too Joseph Rsnlen, Jr. highly recommended. However, such points must are also furnished. be worked out by the builder in conjunction with MAKE SPARE TIME Yorkville. Ohio From Aug. 1 to Dec. 7, 1936. 7 the amplifier and actual installation. MONEY repaired 163 radios and put up 43 which Is very for This tuner is capable of fine reproduction Our training is complete and practical. We serials good to make money almost from the part time work while studying show you how tsunse. when used with correct amplifier and speaker start. The course ran easily be made to pay our for free (free. Koerner. equipment-and that is the main part of the OF EXTRA COST its own way. Investigate now, write battle, as mentioned in the beginning of this book of details. article. The completed job in its cabinet is To start you making money without delay we equip RADIO TRAINING ASS'N OF AMERICA illustrated in Fig. A. this Circoli yWien and CHICAGO (Continued on page 45) Point Resist Tester. Dept RC -78, 4525 RAVENSWOOD AVE Please Say That You Sato It in RADIO -CRAFT www.americanradiohistory.com 42 RADIO -CRAFT for JULY, 1938

THE RADIO MONTH IN REVIEW FREE (Continued from paye 7) THE WAR WORDS 21.6', from December. Radio factory employees .. tells how to OF averaged $20.58 per week -which is slightly more T HOSE nations which lire not actually engaged than a dollar under the average wage of all in the pastime of hurling lead and gas at manufacturing industries. each other, either at home or in their neighbors' The General Electric Company's annual re- yards, were throwing words at each other's port. released last month, showed sales up 30% SAVE MONEY nationals, according to last month's advises. to $349,740.000 in 1937 ; dividends were $2.21 So for that matter, were the warring nations. ON EVERYTHING YOU BUY! per share, as compared with '36's $1.50 ; taxes up Britain last month inaugurated a "news serv- 54% to $23,266,000; employee earnings up 36% .. NOW READY big new Bargain Bulletin. Describes, ice" in Spanish and Portuguese for listeners in to $145.355.000, and average annual wages $1,933, pictures hundreds of amazing values. Tell us where to Latin -America. C.B.S. announced a short-wave a rise of nearly $200. Expenses also included RUSH your FREE COPY: - service of stock market reports and Press -Radio about two -and -one -half million dollars in pen- news, directed at Europe. Frank E. Mason, sions, etc. About a month after this report, the Ol' can sale many l)ollals n,r i purchases out of 7 this new Bargain Bulletin -tins Radio Sets and Parts. N.B.C. vice -President, was assigned to super- company announced that all full-time employees port log Corals. Watches. flocks. Cameras. Typewriter.. vise spreading "American culture and ideals" earning over $2,000 a year would receive pay Unifies' Specialties. Not elt In. and scores of other art Irin. Thnusanels M smart buyers have disco, Bred this to Europe and South America; news, entertain- cuts ranging from 0.5- to 20%. The plan was sure way In save money on standard, highest quality mar. ment and "other programs" will be featured. adopted to avoid large -scale layoffs. Oland' t. Too gel pl script. courteous service. complet, rellablllly. Get 1.1100p of td;, sasings- -lake. your pick France. at last reports. was busily hunting a Last Minute Flash -G.E.Co.'s orders for first of inr ..Jio. >Luvu to till t r Inr- mist eda. station which purported to be in Paris. and quarter of 1938 were 38"5 below those for a YOUR FREE BARGAIN BULLETIN r IS which took pokes at the Blum government. No like period in 1937. Last month 204.980 stock- word of WAITING Fill In and mail NOW the coupon below this station has been received since Blum holders received 30c a share; year before, 193,364 nI postal or letter. No obligation. Soule hatkgili was supplanted by Daladier; maybe it stopped stockholders received 40e a share. as their Offris s Iegoest while stocks are al transmitting, or perhaps the French just ceased quarterly dividend. !licit brut to care. From Latvia came reports of a short- RADIO CIRCULAR CO., Me. wave station which advocated the overthrow of 915 Broadway Weal. R. C.1. New York. N. Y. Stalin ; and no one knew whether it was in RADIOFFICIAL REGULATIONS Russia or in one of the nearby independent YOUR Reviewer, who is able top off RA4tO'CIRCU LAN Co.. Inc -RC) states -nor, for that matter, wi:o owns it. Japan to a bottle without receiving any sensation. and Se,. rush my F ree Bargain Bullet in. announced plans for the greatest radio coverage who can cross the English Channel with nary ..Lli_.i inI lo m, of the 1940 Olympics in history: the transmitter a qualm, always has a dizzy spell when and antenna of the Denwa Kaisha station in plowing NAME through the quires of paper emanating monthly Ibaragi will be improved and in enlarged time from the F.C.Commission. for the games. A Pan- American short -wave serv- ST. a NO. Robbed of most of genial ice, stressing "good will." was inaugurated over their whereasea, Chairman McNinch announced last month that ...... WIRAL. CITY 4. STATE r he would head committees to investigate "chain An international convention on "broadcast- broadcasting and monopoly in the broadcasting ing in the cause of peace" was held at Geneva industry" and to prepare for and hold hearings last month. Twenty -eight states signed the pact. relative to relaxing the regulation limiting the FORMULAS AND RECIPES Among the absentees were Germany, Japan, power of stations on clear channels. The Com- Italy and the United States. Signatories pledged mittees will recommend action to the F.C.C. themselves to ban broadcasting which might Police stations were For the Practical Man foment revolt in other countries, incite to war, notified that adequate or harm provision must be made for checking and main- to international relations through de- taining frequency. liberate untruths. There appears to be no refer- Ship stations were advised last month that ligure Is the Contents of the Book ence to any harm which might be done to such certain transmitters designed to produce 200- relations by the broadcasting of a few well - watt A -1 would same I. Adhesives: Glues, Cements, Gums, Mucilages. chosen truths. transmission not have the Lubricants. 2. Cleansing: Stain Removers, l'alnt output when A -2 transmission was employed, Removers, Bleaches. Cleaning Fluids. 3. Metal and so must be altered. Craft Coloring. Osydizing, Plating. Itepal ring. Last month F.C.Commissioner made Welding, Polishes, Alloys, Solders, Amalgams. SOMEBODY'S MAKING Craven 4. Paints: Colors, Stains, Varnishes. Enamels. public a criticism of the F.C.C. investigation Luminous faint, Washable Paint; I',, lot. MONEY into Telephone communications. Pointing out liernOsing. Waterproofing. Fireproofing. 5. Glass - that he was not a member at the time. he NCOURA GIN reports drifted in from scat- Working: Cutting, Drilling. Boring, lending. deplored the fact that the press received news Blowing, Etching, Engraving, Frosting, Nllcer- lured radio sources last month. For February, of the report before Congress did. He also Ina etc. 6. Wood- craft: Fillers, Fireproofing, C.B.S. grossed $2,681,735, an increase of 18.454 remarked that it would have helped matters Acid-proofing, Waterproofing; Furniture Polishes, over 1937. N.B.C.'s gross of $3,498,053 was 6.1% Finishes, etc. 7. Inks: Recipes. Eradicators, Ink had the phone company been permitted the right up ; and M.B.S. advanced 12.4% for a Stain Removers; Special Inks: Colored, In- gross of of cross- examination and rebuttal. He suggested $255,532. In March, the was not quite so delible, Sympathetic. Invbible. Hectograph. picture that the report be submitted to the I.C.C. of S. Photography: Developers. Emulsions, Fixers. uniformly beautiful. While had N.B.C. and C.B.S. the Senate and the I. &F.C.C. of the House. This Sensitizing. Toning, Printing. Photographic a record month, slipped The Mutual slightly. was done. Paper, Blueprint Paper. 9. Antidotes for figures, with percentage of change from March, Poisons, Remedies for Burns and Scants. Disin- Commented Walter S. Gifford. President of 1937, are: C.B.S., $3,055.929, up 19.47 ; N.B.C., fectants, First -Aid In Accidents, Emergency A.T. &T., in part last month on the F.C.C.'s $3,806,531, up 5.3% ; M.B.S., $240,637, Remedies, home Remedies. 10. Preparan loti, down "proposed report" on the telephone investiga- Manipulation, Handling, Mixing. 2.7%. These statistics are quoted from Radio tion: Measuring. Weighing. Filtering. PRICE Daily. The listening public, which indirectly pays Tech- "The investigation . . . . was one -sided from Straining Solutions; List of the bills through its purchases of advertised prod- nical Substances; Emulsifying; Use start to finish. We were denied not only the ucts, was said by the World Book Encyclopedia of Hydrometer. Use of Thermometer; 50c right to cross-examine investigation witnesses Tables of and Measures, to be operating 86,800,000 sets, 5.000,000 of which Weights and to be heard in our own behalf. but were Decimal Systems, Useful Tables. POSTPAID are auto -radios. Figures issued by Andre Kos- denied the right to have included in the record telanetz in an were interview 6.000,000 short written material which we had the prepared and of foregoing. (The B.B.C.'s income, by the considered necessary to out way. was approximately point serious and $17,000.000 for the year important errors affecting most of the investi- of 1937, TEC N\IF'd\ about $14,000,000 being license fees paid gators' reports. Commissioner Walker's report by listeners.) Division RC -731 must be appraised in light of these facts. Radio manufacturers, too. made money. Elec- "We have not been given a copy of Commis- 55$ W. WASHINGTON BLVD. CHICAGO. ILL. trical exports were 24% up for 1937, that being sioner Walker's report, said to contain 1.000 the best year since 1930. Radio exports totalled pages, but if the summary of it correctly reflects $32,102,070, an advance of 13.52% over 1936. the report, it presents much that is simply not But the month of February was 32% below true and has been prepared with the same un- February, 1937. though above the preceding fairness that characterized the investigation pro- FREE! month, according to last month's reports. Inci- ceedings." dentally, any radio exporter who does not re- The report, which runs to 22 pages, coat ceive the U. S. Department of Commerce bulle- $1,500,000 being derived from a complete record HAMMARLUND tins, World Radio Markets and Electrical and of 8.441 pages and more than 2,000 exhibits. NEW Radio World Trade News, is missing some great Summed up, it recommends giving the govern- "38" tips on market conditions at the ends of the ment greater power to regulate the operation of RADIO CATALOG earth. telephone companies, with a view toward reduc- Last month the Radio Manufacturers' Associa- ing the cost to consumers. Mr. Craven points latest Hammarlund The catalog with announced a meeting on sales promotion out. however, that investors must be protected, complete data, illustrations, draw- tion be held on 21, and on the 26th to dis- and that the jobs of telephone workers must ings and curves on the entire Ham - to April marlund line. Address Department cuss minimum wages and maximum hours for not be put in jeopardy. RC-7 -38 for your free copy. the industry. The R.M.A. fight to repeal or The same Commissioner also released data on reduce the excise tax failed, but leaders con- his questionnaire, being sent to all stations to HAMMARLUND MFG. CO., INC. soled themselves with the thought that it would secure information as to their earnings and 424 -138 West 33rd Street, New York City probably expire in 1939, anyway. The Associa- investments. The M.B.S. announced its approval tion also released figures on its employment of the F.C.C. investigation into chains, and situation, as of January. There was a decrease of pledged its support, last month. Please Say That You Saw It in RADIO -CRAFT

www.americanradiohistory.com RADIO -CRAFT for JULY, 1938 43 Another ruling of last month extended for 6 months (from March 16) the time in which relay, international, television, highfrequency, facsimile and experimental stations might get their frequency monitors working. The reason: lack of the requisite monitors, which must be accurate to within 2 the tolerance allowed. Coastal stations were chided for transmitting a series of dashes or "V's" to check their frequency. Reason: it sets off automatic alarms. Checking ship logs revealed this. Non -commercial educational broadcasting sta- pAym-- tions were defined last month, and were given a set of extra rules, in addition to those govern- ittovoi ing high -frequency stations. Such non -profit sta- FRFF T tions are permitted to conduct point -to -point work, in order to service specific schools. RPIS 41,000 kc. and Pfi Twenty -five channels between fls 42,000 ke. have been allocated for such service. pwM k*/ Meanwhile, the ratification of the international radio treaty, arranged at Havana last year, is s delayed. The F.C.C. objected to its receiving d CONTINUED UNTIL JUNE 30TH , Senate approval last month; therefore it lies in instru- sleeping peacefully in a State Department pigeon Because of thousands of requests to terms ever offered the vacation before ments industry! hole. If Congress gives itself a continue our "no down payment - Pick ratifying the treaty, radio may wind up in 10 days' free trial offer" we are ex- See your parts jobber today. something of a bobble, with Mexican and Cuban tending the expiration date to June out any Supreme instrument with- stations using waves now enjoyed by U.S. broad- down! If it 30th ! This will give hundreds of more out paying one penny casters. thus causing serious interference. dealers and servicemen an oppor- doesn't measure up to your expec- tations after you've tried it for 10 tunity to re -equip and modernize without MISCELLANY now with new, modern SUPREME days -ship it back to us RADIO the most liberal any obligation on your part! FACSIMILE will be adapted particularly to the instruments -at transmission of news. and relevant to this is Fortune Magazine's survey of how the public NOW! FOR THE FIRST TIME IN A SIGNAL GENERATOR gets its news. The percentages, given last month, are: -newspapers, 45.2%; radio and newspapers, 28.2%; radio. 23.5%; neither, or "don't know." PUSH -BUTTON 3.1%. Meantime, station worries increased last month, with the beginnings of a newspaper Tuning! boycott facing radio columns and program list- ings. Started in Los Angeles, publishers feared Again SUPREME is first with the latest! its spread to other sections of the country. Devel- Model 582 -A Signal Generator offers you A.N.P.A. conven- new, exclusive. rapid, amazingly accu- opments were expected at the rate push -button- tuning for most used tion. IF and RF frequencies PLUS complete Aurora Borealis moved in on the northeast not only frequency coverage on manually tuned part of the U.S. last month. Her antics dial. Use the push -buttons with easy -to- marred broadcasts. but also hampered telephone read figures for almost all your alignment communications. problems -catch the "in- betweens' Last month British manufacturers commenced and "high fregs" with the manual dr- a campaign on self- contained crystal sets, of a cu!t which has hair -line, shadow -indi- type known as A.R.P., which signifies "Air cating, spotlight tuning on giant dial. Raid Portable." The idea is that if Civilization In addition you get the following ex- comes to Britain, its bombs may wreck power clusive features: (I) Wide Frequency plants, but subjects will still be able to hear Coverage (2) Air Tuned Trimmers and government broadcasts telling them the safest Special Iron -Core Inductors for more places to crawl in and hide, etc. Accurate Calibrations (3) Four types of A radio -equipped balloon. sent up by the U.S. Output (4) Automatic Electronic Fre- Weather Bureau, set a new altitude record of quency Modulation (5) Razor Edged 17.3 miles last month. Would that the stock Tuning on Giant Dial (6) Specially De- market would follow! MODEL 582 -A- PUSH -BUTTON SIGNAL GENERATOR signed Attenuator Circuits, etc. NO DOWN PAYMENT AND $6.14 PER MONTH FOR A new distortion reducer, tested out at WEAF See the new Model 582 -A at your parts 12 MONTHS OR CASH PRICE -$6695 and WJZ last month, cut transmitter distortion Jobber of write for literature. to 1 /30 its former level! Plans were announced MODEL 582 -SIGNAL GENERATOR (without push- Visit the Supreme booth at the Radio Parrs .Show. Breaths 212 and 214 Hertz Are., Stnens to Install it at all N.B.C. stations. It employs buttons) NO DOWN PAYMENT AND $5.50 PER MONTH tone!. June h. Q. la and 11, chit neo. the reverse -feedback principle, to cancel out FOR 12 MONTHS OR CASH PRICE -$55995 transmitter harmonics. Czech authorities last month sentenced to death a man with a short-wave transceiver. He was acting as a spy for an unnamed "neighbor- ing state." SUPREME INSTRUMENTS CORP. Sixty yachts and cruisers along the Atlantic GREENWOOD, MISSISSIPPI, U. S. A. coast were equipped with transceivers which NEW YORK, N.Y.. CABLE ADDRESS: LOPREH, N.Y. enabled them to be radio-linked to shore tele- I ; D PT. ASSOCIATED EXPORTERS CO ,145 W. 45th ST., phone lines last month. Cost of equipment varies from $500 to $3,000, without "scrambler" that insures secrecy of communications. Most yachts- Action! Thrills! Sights! Fun! - men don't want it. anyway. Last month London papers printed reports (but no details) of a. marvelous radio ray, said In Every CANDID CAMERA Shot! to be capable of detecting "parked" submarines as much as 15 miles away. There is no record of The country's new craze-CANDID CAMERA any tests being made in the Mediterranean. Shooting. Everyone from north to south -east to west is using a minicam. Anywhere you go-day KYW's $600,000 station was scheduled to open or night -under any conditions. there're thrills on May 16. Features are: 7 stories, air condi- taking CANDID CAMERA pictures. In a flash tioning. 6 floors entirely devoted to radio (2 of you catch your subject -a popular golfer, a screen or radio star, a ball player. your children, an action them to television) ; mammoth studio in base - scene- ment-5 other studios, visitors' galleries; 71R- anything you want. is be world's tallest. foot triangular antenna to This miniram. Popularly priced at $3.98. Is comparable to others netting Power will be 10 kw. with application in for at a much higher cost. It takes 1g pictures. either Instantaneous or time and 60 kw. exposures. Equipped with Vollensak 50 mm. strong lens, speed shutter Shipped P O S T. accurate "spy clew-finder. Fixed guarantees sharp PAID anywhere in I %x% Incs. Enlarges with clarity up to Wince. ilasspecilaa com- withth guar- $398 partment to carry xtra aim roll and tripod socket for mounting. Uses eco- antee of safe de- nomical Kodak 127 e or Agfa AS film In color or black and white. Rousing livery RADIODDITIES built of unbreakable Bakelite- Composition. Camera weighs only 9 ounces. a lead -in and measures 5" long x 3" high x 1%s' wide. Easy to operate and extremely in- LIGHTNING sneaked down expensive climbed into bed with a Wisconsin youth last to use. month. He was not hurt by the resulting blaze. The Marx Brothers (Groucho & Chico) last HUDSON SPECIALTIES COMPANY 40R West Broadway New York, N. Y. (Continued on following page)

Please Say That You Saw It in RADIO -CRAFT www.americanradiohistory.com 44 RADIO -CRAFT for JULY, 1938

THE RADIO MONTH IN REVIEW (Continued from preceding pagri SEEKING RICHES month lost their appeal ,m a radio program aminers graded what they heard, then listened plagiarism conviction. The fine remains at $1,000. to records. Records revealed more faults than French prisons adopted a radio mattress- tester examiners had heard on their first listening. Dis- last month. It finds knives, guns, saws, files, etc., gruntled candidates demanded re- exams. Alibi: FROM THE EARTH when such gadgets are concealed in convicts' "mike fright." beds. Every year since the advent of radio, some To keep skiers from becoming lost, a beacon newspaper prints a story about the use of radio BY RADIO system was established in a Swiss resort last in the barn to increase milk production. Last month. It sends out a beam. which the radio - month the N.Y. Daily Mirror was no exception. equipped slalomera may follow back to safety. In Hawaii last month. Japanese and other STEADILY the technique is developing This may mean unemployment for the St. Ber- non -government craft were barred Pearl for the location of precious ore bodies nard dogs, even though no one has invented from and other mineral deposits in the earth a Harbor during naval maneuvers. War games radio wave which is able to carry a cask by using radio. A very comprehensive arti- of took in the civilian population. who were asked cle has been prepared, revealing circuits and brandy. to listen -in on a special military wavelength methods, all based on verified experiments, The Batchelors Pea Cannery, Sheffield, Eng- "which might be used in case of an emergency giving full insight into this fascinating and land, installed radio in room its sorting last or catastrophe." They were urged to use auto - promising field. By using methods now fully month. It makes the hundred girls work faster. disclosed, gold coins, buried by prearrange- radio and other battery sets, "as if power comment, were recovered, to the consternation Paul Wilson, Illinois farmer, no longer has to panies had been destroyed." call his hogs to dinner. Last month they learned of amazed onlookers. Radio may speed to come when he tunes in a hill -billy up communications, but it program slows up All the world over the eager search for on his barn radio. So now you know who likes homing pigeons. 'tis said. Pigeons re- the riches reposing In the recesses of the leased near W9XF did not behave normally; took earth goes on. Success attends hill -billy music. (P.S. His cows and horses come, those efforts too.) 10 minutes longer to fly 30 miles. Commentators that scientifically determine the non - say this study of homogeneous character of the earth. Inter- Money- making through radio! A woman living effect of radio waves may be pretation of these findings determines the next to the M -G -M studio received day extremely important. It doubtless will be-to the $25 per pigeons whose straight path to precious deposits. not to run her radio last month. The sound time is so wasted. interfered A super- station being erected outside of Paris. Acquaint yourself with the full facts about with recording. Ancient alchemists sought means to transmute France, was reported as coming along nicely last the earth as a treasure chest, and the ex- month, with ploration by radio devices by those seeking base metals into gold. Scientists at the University the antenna nearly completed. The riches. Be among those fully conversant of Rochester. however, put gold into their 51- station will probably go on the air in June. with the requirements for successful ap- million volt atom smasher last month and turned Last month Vienna police took on the appear- seeking your- paratus. Join in the treasure- the switch. The gold became mercury. As the ance of camera fans. Selected officers were pro- self. The details are revealed in the full Two Black Crows used to say, "You can't make vided with small portable transmitters, to be article that treats of worn slung over their shoulders. Batteries were this historic develop- any money like dat I" ment of methods of When you tune -in an all -request phonograph carried in their pockets. Yet anschlusa took wresting the secrets program at midnight, there's a good chance you place, just the same. from the earth, from are listening to some secret code for the rackets. In Egypt last month, the King's bounty the first divining rod according to reports of an F.B.I. investigation brought happiness to thousands of his poor but the latest high - to 255/` last month. The racket boys were honest subjects. He commanded that 3,000 radio powered beat oscilla- coding their tor. Remit with messages by combinations of song titles, re- sets be distributed among impoverished peasants order. POSTPAID questers' names and addresses. Many stations in the Nile Valley. Only fly in the ointment was now omit reading of telegrams, this having been that he also decreed an increase in educational a popular form of coding. broadcasts. RELIABLE RADIO COMPANY British programs, being government -regulated, Irish Tenor Morton Downey, returned from carry no advertising. London's Reynolds' News Europe last month, praises American broadcasts. 143 West 45th Street, New York, N. Y. suggested last month that British advertisers He remarks that European broadcasts are propaganda- buy time on American short waves. Those from packed -are permitted to run short or long of Schenectady and Pittsburgh, was said, are their allotted time -that there are long it them. heard in England regularly, and with good pauses between Yet there are times when volume. your Reviewer would substitute an itty -bitty pause for an over -long commercial. English spellers, defeated by an American CAUGHT ON THE FLY group in a trans -Atlantic spelling bee early this year, came back last month to avenge their New York's mayor, F. H. LaGuardia, last defeat. The score, 27 -37. Screwdriver month expressed his regrets at his inability to Amateurs may recall Eric Palmer, operator of attend the Police Department's Communion W2GRB, and author of "Riding the Greatest breakfast. Airwaves." At home, he listened -in on his radio. Mr. Palmer, now a member of the WQXR engi- p Radio Man Former Judge Bleakely, speaking at the break- neering staff, married Miss Lillian Kaprat last fast. criticized the mayor for party irregularity. month. Mayor U d LaGuardia leaped into his car, sped to When a Navy bombing plane was lost last Ever the breakfast, and broadcast his reply. month, among its crew were George T. William- The municipal station's most popular program son. radioman. 1st -class, and C. R. Oulundsen, is the weekly broadcast of the deliberations of radioman, 3rd -class. in Servicing the City Council, according to a statement issued The police of Hove, England, were given radio last month by S. N. Siegel, director of WNYC. equipment last month, so you'd better stay away a Labor The station receives about 1,000 letters per pro- from there if your conscience hurta. or in gram. "Some of the letters are derisive," Dr. RCA stockholders last month passed a motion Siegel admits. "The meetings are called circuses." accepting RCA President David Sarnoff's report this FLEXI- (Editor's Note: -Our own little group calls 'em with thanks. Their only other motion called for USE "The Hyena House. ") a radiogram carrying the and felici- SCREWDRIVER greetings -the screwdriver that Radio tations of the stockholders to Gen. James G. Hy goes around a corner -in your boosts for the New York World's Fair radio service work or laboratory. were started over a local station last month. Harbord, Chairman of the Board of RCA. who It reaches was many awkward places where a screw cannot Plans were announced for the inauguration of then in Australia representing the company be reached by a straight or offset driver. network publicity. as well. at a World Radio Conference. Guess what sys- Has a thousand and one uses -ideal for repairing tem was used to send the message. You're radios. right! refrigerators, automobiles, oil burners. The Golden Gate Exposition (1939 World's The spectators of the Oxford -Cambridge Boat iarhinery, shop equipment, electrical appliances. Fair of the West) likewise made advances last e um cleaners, Race last month were kept appraised of the marine equipment. household month. The Exposition will feature television, jobs, etc. The FLEXIBLE SHAFT SCREW- boats' positions by means of 81 giant loud- DRIVER has a shaft of laminated steel electronic music, demonstrations of "atom wire speakers. -tempered steel blade-chromium- smashing" and so forth. plated attings- fluted, hard- Acoustics will be demonstrated in a room being w den handle. length over- S 122 N.B.C., month by the ail 8'. PRICE, POSTPAID before last, devoted a complete built University of California for the 1939 News Service release to taking bows for its World's Fair -the one in California, not the one GRENPARK COMPANY 1229 Park Row Bldg. New York, N. C. Toscanini series. Release showed the mild maestro in New York. According to reports received last N 7 and the orchestra ; quoted tributes from press month, the room will illustrate why singing in GRENPARK COMPANY RC -7.39 and public. the bathtub has become one of the nation's lead- 1229 PARK ROW BLDG., New York. N. Y. Pitcairn Island, isolated since 1790, hit the ing indoor sports. news Gentlemen: Enclosed you will find my remittance last month. In 1920, one of the Islanders In Canada last month, radio receiver licenses of $1.00 (One Dollar) for which please send me, erected a station. Last month, Coto -Coil engi- were upped 4 bita to $2.50 despite the wails of POSTPAID one FLEXIBLE SHAFT SCREW- neers increased 50 650 watts. listeners. A organization made a survey DRIVER. its power from to Toronto Station owner began broadcasting praises of of 24,000 listeners, of whom only 38 considered engineers and cluttering up wavelengths. Britain the increase justified. Others protested that they Name issued orders restricting Island's communications listened to U.S. stations most of the time any- to passing ships, its radio power to 00 watts. way, and did not see why they should be called Red -faced, N.B.C. canceled arrangements for upon to contribute more heavily to the Canadian Address Island broadcasts. system. Extra loud howls came from owners of New York candidates for teachers' positions more than one set-who must pay $2.50 on each. City State last month faced a microphone and recorder for Battery set owners were less bothered; their fee J oral speech tests, while examiners listened. Ex- remains at the $2,00 mark. Please Say That You Saw It in RADIO -CRAFT www.americanradiohistory.com RADIO -CRAFT for JULY. 1938 45

with a r TECO TEST EQUIPMENT Sold GUARANTEE & 10 DAYS FREE TRIAL!!! other Buy direct from the factory on 10 Dar Trial. If the Instrument you buy does not meet your needs, return it for full rr;dit on any TECO equipment. Buy TECO and SAVE the difference! -,//

TECO POCK -O -METER AC and DC A new pocket size volt- ohm -milliammeter that includes AC measurements and is the lowest priced, full- service instrument ever offered! Has 3" d'Arsonval movement 0 -1 milliammeter. Comes with etched panel. SPECIFICATIONS 5 DC ranges: 0/1.5/16/25/76/500 volts. 5 AC ranges: 0/15/40/75/200/1200 volts. 4 DC current ranges: 0/1/10/100/600 ma. 2 resistance ranges: 0 /500 /500.000 ohms I low ohms read to 1 ohm) Pock-O -Meter supplied complete with batteries, test leads, and instructions. Size 7s 614 x 31,4 x 21íj' ; shpg. wit. Y 5 Tbs. Our net price

NEW TECO TUBE TESTER A go naine achievement! Model T -10 For accurate and rapid work. Has d'Arsonval moving coil meter. Tests all types of tubes. For use on 110 V., NEW TECO MULTIMETER Here's the unit yyou need for rspId. 5. and MODEL T- 15 te measurements. A 1000 Features ease tutee. Testa by the Instrument featuring 5Cal i,, method for tube quality, direct- ')10.1 M Illamm treAcuracy AttractiveAt etched metal panel. For use on 110 V. 1 Bad scale of the meter. lt read -.1 60 cycle AC. 4 RESISTANCE RANGES. 0.500 ohms, leakage shorts m HIGH AND 1.0W CAPACITY 5 500.5 gohms.. betweenween cl. wi:.. ) All s sen ices with SCALES. 0005.1 f. and 05 -200 inf. al maximum -many teste not requiring all COMPLETE AC d DC VOLTAGE and CURRENT controls RANGES. DC Voltage: 0 -15 0.150. 0.750 volts: attractive panel DC h reno,at 1d ,. AC Voltage: 0.15. 0 -150. 0.750 lts: Curent: In rugged leaa t etrte arrying rase with 0.1, 0 -15. 0.150. 0.750 AC Current: 045. hinged corer and handle. 60 cycle 0.150. O.i Ú ma. THREE DECIBEL RANGES. AC operation. Supplied with in- as Millimeter e, e complete table corer- n e h teat atruetions and reference S andd Ìfeue a Ú lx9tunjIx Mg all tubes which you will rant- III l. tl Ihr. aaaa moult' encounter in servicing. 812e Our net price 111i 5 9% a 5K ". Net frire ' Free New eataioJ Just Off the Press Shows Entire 'Line -Send for Yours to TEST EQUIPMENT COMPANY ,6 am..,.. 139 CEDAR STREET RC-7 NEW YORK, N. Y.

KILLED BY RADIO HOW TO MAKE A HIGH -FIDELITY TUNER A warning about using electrical apparatus in (Continued from page 41) the vicinity of water was issued yesterday by LIST OF PARTS Three Continental Carbon resistors. 25.000 ohms. the Stockport coroner. 2W; Recording a verdict of death by misadventure, One set of coils, type 472A antenna, 472RF, Two Continental Carbon resistors, 3,500 ohms. Catherine Victoria Lightfoot. aged 36, of Bram- (2) 472 BP band pass, (2) EL56 negative 2W: who was found dead in her bath with a hall, mutuals. and 472ÚT, untuned, LI to L7 incl.; One Continental Carbon resistor, 300 ohms, 2W : submerged wireless ( "radio' -Rd.) set partially One 4 -gang 350 mmf. variable condenser, Cl to One Continental Carbon resistor. 600 ohms, 2W; in the water, the coroner said he wanted to warn C4; Two Continental Carbon resistors, 0.5 -meg., 2W; the dangers with the public about little -known One 2 section 3 position switch (open -circuit One Continental Carbon resistor, 1 meg., 2W; which they might be confronted when handling type). Swl, Sw2; One Continental Carbon resistor. 75.000 ohms, electrical apparatus. One replacement 10 kc. filter type 446 -2H with 2W; It was apparent, he added, that the woman C102 85 mmf. condenser, L8; One Continental Carbon resistor, 4.000 ohms, had received an electric shock through handling One Centralab 0.5 -meg. volume control (A.F. 2W; the wireless set while she was in the bath. grid taper), with switch VC; *Three octal wafer sockets; Medical evidence was that death wns due to One 420 mhy. coil, home wound. L9; One 6 -prong wafer socket; of a high voltage. shock from electricity Three Cornell -Dubilier mica condensers, 0.05 -mf.; One dial (type to suit installation) ; (The above item, reprinted from a recent issue One Cornell- Dubilier mica condenser, 0.06 -mf.; One mounting and escutcheon plate for tuning- of the Sunday Referee (London, Eng.). is offered Two Cornell -Dubilier mica condensers, 0.02 -mf. eye tube; with the idea that "an ounce of prevention" Two Cornell -Dubilier mica condensers, 0.01 -mf.; Two 2- contact terminal strips: . etc.) One Cornea- Dubilier mica condenser, 0.002-mf.; Three screen -grid clips; One Cornell -Dubilier mica condenser, 50 mmf.; One glass tube shield; FLASH! -NEW TELEVISION RE- Seven Cornell -Dubilier paper condensers, 0.01 -mf. Two RCA type 6K7 metal tubes; 400 V. D.C.; One RCA metal -glass type 6C8G tube; CEIVER ANNOUNCED! One Cornell -Dubilier paper condenser, 1 mf., One RCA 6C5 tuning -eye tube; As we go to press we learn that a manu- 400 V. D.C.; One 8 x 8 x 3 in. deep chassis; facturer has announced the immediate avail- Three Continental Carbon resistors, 0.1 -meg., Miscellaneous grommets, wire, screws, etc. ability of a 441 -line cathode -ray type television 2W : *Moat Radio mail order houses can supply this receiver. Read August Radio -Craft for more One Continental Carbon resistor. 20,000 ohms, item if properly identified as to title of article, details! 2W; issue (month) of Radio-Craft and year. Please Say That You Saw It in RADIO -CRAFT

www.americanradiohistory.com 4o RADIO -CRAFT for JULY, 1938 ` - only SERVICING UNIVERSAL A.C. -D.C. RECEIVERS (Continued front page 15) 1.1"to.F.II?' - 2 tubes supply sufficient power for loudspeaker Having located the leads and determined the field coil excitation, and hence a loud- ro `r °1A, dynamic functions of the various sections of the electro- speaker will usually be found. A single 12Z3 tube lytic filter condenser block, you are ready to for this new l cannot, however, supply enough current for both place on your sketch the approximate capacity "Push the loudspeaker field coil and the receiver circuits values for each section. Use the following general

' Button" Tube and last a normal length of time. rules as your guide: .UniversalChecker Another power pack circuit using a 25Z5 rec- Input Filter Condenser -any value between tifier tube is shown in Fig. 5. Here the filter 10 mf. and 20 mf., rated at 200 volts D.C. work- aL0a0L0C0:0Z0`a0'0 choke is placed in the negative plate supply lead, ing voltage: Output Filter Condenser -any value and the voltage drop across the choke is used as between 6 mf. 16 o and mf. rated at 200 volts D.C. C0á0a0í0i.Cj0:0.Ot0a9- See it C bias for the control grid of the power tube. working voltage; Loudspeaker Field Coil Filter When the okRá9054í0SL0í019 at the voltage drop across this choke is not Condenser -between 4 mt. and 8 mf., rated at `. correct for biasing purposes, a resistor is in- 200 volts D.C. working voltage; Cathode Bypass SHOW serted between points x and z in Fig. 5. and the Condensers -5 mf., rated at 25 or 35 volts D.C. control -grid return lead of the power tube is working voltage. Direct Push Button Test run to point x, as indicated by the dotted line, While condensers smaller than the minimum New Easy Reading Scale instead of point y. The ohms value of the inserted values given should not be used. the maximum resistor is so chosen Tests all Standard Tubes that the voltage drop across values may be exceeded without impairing the the resistor equals the correct bias voltage for operating qualities New Precision Design of the receiver. The voltage the tube. Notice that the cathode of the power ratings can likewise be higher than the minimum Looks like a Million tube is grounded, eliminating the need for a values given. Outstanding in performance. precision and design. cathode bypass condenser and resistor. A de- Your electrolytic condenser block sketch now Universal for all tubes with the convenience of direct "push button" readings. coupling resistor and condenser are required in gives you the necessary data for ordering a re- the control -grid circuit of this tube, however. placement unit. If a unit having the desired in- MILLION RADIO and TELEVISION LAB. A rather unique method sometimes used to ternal connections and desired capacities is not 559 NO. UNION ST.. CHICAGO. ILL. secure a positive screen -grid voltage for the de- available, the next best thing is to order a con- tector tube is shown in Fig. 6. Observe that here denser block having the desired capacities and the detector screen -grid is connected directly to separate leads for each section. If even this is the cathode of the power tube, which is suffi- not available, make up your condenser block ciently positive with respect to the detector tube from two or more separate electrolytic condenser cathode for this purpose. unite having the desired capacity and voltage Listen Comfortably ratings. When ordering separate units in this WITH FILTER CONDENSERS way, be sure to check the available space and Filter Condenser Connections. When the filter choose units which are small enough to fit this choke is in the positive aide of the power pack space. BRUSH circuit, all electrolytic condensers will have a common negative lead. When the filter choke is JUSTIFIED COMPLAINTS in the negative side of the circuit, however, the Is the Customer's Complaint Justified! The "Hushatone" negative side of the input filter condenser does operating characteristics of a universal A.C.- r pillow speaker) not connect to ground (chassis) and consequently D.C. or "cigar box" receiver of the T.R.F. Put this radio accessory under your pillow requires a separate lead. In this case the 2 filter variety must be carefully considered before at- and listen to your favorite programs. condensers may have a common positive lead, tempting service work, in order to make sure that Write for details. as is the case in Fig. 5. the customer's complaint is justified. These little Failure of filter condensera is quite a common receivers are designed primarily for reception of THE BRUSH DEVELOPMENT CO. occurrence in universal A.C.-D.C. receiver.. powerful local stations which are spaced well Oftentimes will be 3312 Perkins Ave., Cleveland, Ohio there no markings whatsoever apart in the broadcast band. The receivers have on the old condenser block to serve as a guide in little selectivity, so that local stations which are ordering a new unit; in a case like this, the fol- separated by less than 100 kc. may be expected lowing method of reasoning will allow you to to interfere with each other. The receivers like- order a satisfactory replacement. wise have poor sensitivity. and the reception of A Neu' Development in Acoustics Make a sketch of the old condenser block. distant or even semi- distant stations will there- showing all leads which come out from it. Now fore be unreliable. Where the complaint of the BI - PHONIC REPRODUCERS trace each condenser lead and determine where customer simply involves one of these factors, no BI- PHONIC housing - really new it goes in the circuit. By this time you will be service problem exists. Likewise, good fidelity development In acoustics -- instead able to recognize the type of power pack circuit and freedom from blasting at full volume should of damping -out the rear rrslanisr actually utlllres the lodspeaker's used. Label each lead on your sketch according not be expected from these receivers, particularly backware. Frequency response at to the point to which it connects, and indicate if they employ a magnetic -type loudspeaker. The both low and high ends of the its polarity. Once you recognize the type of customer making complaints which involve these audio- frequency spectrum 1s greatly Increased. Volume and circuit used, you will have no difficulty in deter- factors is asking too much of his receiver and definition are tremendously in- mining the polarity of any with respect requires a better receiver to meet his nceda. creased. point A complete description of BI- to the "B -" lead and in drawing the internal Common Troubles. The simplicity of the cir- PHONIC REPRODUCERS -and connections for the condenser sections. Condenser cuits used in universal T.R.F. receivers greatly their advantages sent on request. block sketches for the power pack circuits given limits the variety of troubles which may develop. BI. PHONIC REPRODUCERS previously in this article are shown in Fig. 7. The complaints which will most often be encoun- ar e available from $25.00 up. Here are a few tips towards identifying the tered are: Set is dead; local signals are weak; BI - PHONIC REPRODUCER various leads. If the filter choke is in the positive hum is excessive; set distorts; oscillation (squeal- LABORATORIES side of the power pack circuit, as evidenced by a ing) exists; set operates intermittently. 45 Ashland Ave.. direct connection from one of the choke ter- Servicing "Dead" Receivers. When the receiver Baluwin. L. I.. N. Y. minals tu the cathode or cathodes of the rectifier is "dead," determine first of all if the tubes light tube, then all of the filter condensers in the or warm up. An open -circuit somewhere in the block will have a common negative lead. You can series filament circuit is indicated if they do not. identify this common lead by the fact that it Take out each tube in turn and check its filament connects to the receiver side of the ON -OFF prongs with an ohmmeter for continuity or test power switch either through the chassis or the tube in a conventional tube tester. If tubes through a common lead. Once this is done, you are OK, check the filament voltage -dropping can draw in the internal connections of the resistor with an ohmmeter. If a ballast tube is condenser block just as has been done in Fig. 7. used for this purpose, inspect its socket connec- If the choke is in the negative side of the tions in order to determine between which prongs This is the latest development power pack circuit, as evidenced by the rectifier there should be continuity. If a line cord resistor tube cathode tracing directly to the screen grid is used, check with an ohmmeter between the in Dry Electrolytics . and of the power tube without encountering any line cord resistor lead and each prong on the all the radio world is in favor of current -limiting or choking devices, you can lo- wall socket plug in turn (the plug being re- it! Ask for cata!og. cate the negative lead for the input filter con- moved from its outlet) ; with the power switch denser by the fact that it will be the only filter open. or one tube removed, there should be con- Solar Mfg. Corp., 599-601 B'way, N.Y.C. condenser lead connected to the switch side of tinuity between one of the prongs on the wall the filter choke. Where the loudspeaker field coil plug and the receiver end of the line cord re- gets its current from a separate section of the sistor if this resistor is OK. If there is a shunt If vos want CO know em- 25Z5 rectifier tube, there will be a condenser resistor across the pilot lamp or lamps, check plorment opportuniti a across loudspeaker field coil with its this with the ohmmeter for continuity. and ,equiremenw m naia the negative Check and related miseries, get lead also connected to the switch. In most cases pilot lamps also for continuity. National% book of fato a single common negative lead is used for both If the set is dead but all tubes light up and feed jet YOUR condensers. The positive leads for these contest OK, use the D.C. voltmeter section of your PRET COPY TODAY densers are easily identified; the positive lead of multimeter to measure the voltage between the RC -r ano t. risa,.. the loudspeaker filter condenser will go to that common rectifier -tube cathode connection and the 25Z5 cathode to which the speaker field is also tuning condenser frame (this always being at connected, while the positive lead of the input "B -" potential and convenient to reach with a filter condenser will go to the other cathode of test probe). With the set plugged into an A.C. the rectifier tube. outlet, you should measure between 90 and 120 Please Say That You Saw It in RADIO -CRAFT

www.americanradiohistory.com RADIO -CRAFT for JULY, I938 47

Volts, while with the set plugged into a D.C. moving the control -grid leads around enough to outlet, this voltage may be as low as 85 volts. secure a small amount of regeneration. If no voltage is measured here on D.C., try It is a good idea to check the line voltage in reversing the position of the line plug ; proper the customer's home when weak reception is the polarity must always be observed on D.C. complaint ; if this voltage is below normal, report A low rectifier -tube output voltage on A.C. the matter to the local power company. Ordi- operation is an indication of defective filter con- narily there is nothing you can do to a receiver densers. Check each condenser or condenser sec- of this type to offset low line voltage. Excessively tion in turn, by disconnecting one of its leads high line voltage is not serious in these small and then checking the condenser for leakage with receivers, for the tube filaments and the pilot an ohmmeter. If leakage resistance is lower than lamps are designed to stand up under all normal ECIAE the normal value for a condenser of similar size, fluctuations in line voltage. With D.C. power the condenser is defective and requires replace- lines particularly. the line voltage on peak loads ment. Even if leakage resistance is normal may drop to a point where no reception is (check the leakage resistance of a new condenser obtained, and again the trouble is not the fault of about the same size for comparison if you of the receiver. are uncertain), the condenser may still have Servicing Receivers for Ham. A certain amount deteriorated through drying out of the electrolyte, of hum is to be expected in any receiver operat- with a resultant lowering of its capacity. Try a ing from an A.C. line. Many Service Men forget new filter condenser at each position in turn. this fundamental fact and spend hours trying to while the old unit is disconnected. Separate eliminate perfectly normal hum which they ob- 8 -mf., 475 -volt test condensers should be kept on serve after correcting the original defect in the hand for tests like this on any receiver. If the receiver. Hum should never be so loud. however. a FREE three -month subscription to rectifier-tube output voltage comes up to normal that it becomes annoying when listening to the Sylvania News when a new condenser is inserted, this is a sign program from a local station. Excessive hum is that the old condenser was defective. often caused by a reduction in capacity of filter some when one section of the old electro- condensers, by a heater -to- cathode short in Even only of filter con- lytic filter condenser is bad, a new block should tube. by an improper connection a denser, or by an open control -grid return. be installed, for there is a good possibility that the the other sections of the block will soon fail in Curing Distortion. Improper centering of When loudspeaker voice coil is a common cause of dis- a similar manner if left in the receiver. apply here using a test electrolytic condenser in this manner, tortion ; the usual corrective methods very care- just as in larger receivers. Always try a new out- you must, of course, observe polarity for fully. for connecting an electrolytic condenser put tube when distortion is the complaint, will the great amount of heat dissipated by the heater to a voltage source with improper polarity in the in most cases ruin it. in this tube often affects other electrodes tube voltage of the tube. If the rectifier output between the detec- "dead" receiver is normal, check the D.C. voltages A leaky coupling condenser between the "B point in the circuit and each tor and the grid of the output tube is another -" likely cause of distortion. If you can measure a plate and screen -grid prong of each tube. Repeat output this test for the corresponding tube socket lug: D.C. voltage across the grid resistor of the of readings for any one tube tube when the positive voltmeter probe is con- failure the two of resistor, a leaky electrode to correspond indicates a break be- nected to the grid end this the tube socket prong con- coupling condenser is indicated : replace with.a tween the lug and if you can- nection, making the installation of a new socket 0.05 -mf., 600 -volt cartridge condenser not determine the value of the original part. necessary. bias re- Improper voltages on any tube electrode will Check the ohms values of the cathode trouble. as in the sistors, and check cathode bypass condensers for point to the source of just described, for case of an ordinary A.C. receiver. The circuit leakage in the manner already will give you an idea as these are also possible causes of distortion. diagrams in this article the volume con- to what voltages to expect; obviously the detector Distortion often occurs when voltage trol is turned up too high when tuned to a strong tube plate voltage and the control -grid due to will low due to the local station; this is a normal condition on the power tube be quite or of the loud- 55,000 live -wire radio men read each issue of high values of resistance in these circuits. overloading of the receiver stages speaker. and the remedy obviously is for the cus- Sylvania News* and letters keep pouring Simple continuity checks of various receiver ... tomer to keep the volume level below the point in telling us how helpful it is. circuits often prove the speediest way of locating at which distortion begins. trouble in a "dead" receiver. There should be Curing Oscillation. A certain amount of oscilla- Join the ranks of the well- informed -get your continuity between the rectifier-tube cathode and tion is to be expected in these midget receivers free subscription to Sylvania News. In every screen- grids. of all other the plates, as well as when the volume control is advanced t'o its maxi- issue you'll find-not only the latest news of tubes in the receiver, with the exact ohmmeter of these sets de- mum setting, for the designers the trade -but also a wealth of technical and reading depending upon the sizes of the resistors pend to a certain extent upon regeneration for in the various circuits. There should be con- high gain. Oscillation nt low volume control set- servicing hints ... practical merchandising tinuity from the receiver side of the ON -OFF tings can be due to open bypass or filter con- ideas tips on how to improve your well as the ... power switch to the control -grids, as densers, as well as to failure to use tube shields business.' cathodes, of all tubes in signal circuits. provided. Shielding of if they were originally three.. Rotor and stator plates of tuning condensers the control -grid leads of the R.F. and detector Mail the coupon below, and your are sometimes shorted together; inspection will tubes. if these leads are over -exposed, or chang- month subscription will start with the very often reveal such a short, but if doubt exists. ing the positions of these leads are likely cures. next issue. disconnect the coil lead from the stator of each Connecting the aerial to an external ground is section and check each section individually with sometimes effective in eliminating oscillations. The official "house magazine" of Hygrade an ohmmeter. There should be no continuity Cramming the aerial into a small space will Sylvania Corporation. Also makers of the between rotor and stator plates of a section. often cause circuit oscillation ; keep this wire famous Hygrade Lamp Bulbs. To check the bias resistors in the cathode stretched out to its extreme length. As a last leads of the detector tube and the power tube, resort, when oscillation cannot be cured in any See us at 204 -06 Ampere Avenue, the electrolytic cathode bypass way, detune the trimmer condensers until Nati Radio Trade Show. first disconnect other Chicago. condensers and then check the resistor with an it ceases. Hotel Stevens, ohmmeter. These condensers often have sufficient Intermittent Reception. Any of the usual causes leakage to mask the effect of an open resistor. of intermittent reception in radio receivers are While making this test. check the leakage re- to be expected in these midgets. but my experi- sistance of the bypass condenser with the ohm- ence has shown that in most cases either a SYLVANIA meter. defective type 43 output tube or a defective Circuit disturbance tests on these receivers are coupling condenser between this tube and the Set- Tested Radio Tubes limited to touching the control -grid caps with detector stage will cause intermittent trouble. the finger or removing the caps, for pulling out Try a new output tube first of all, then try a a tube opens all filament circuits and masks the new coupling condenser. If the trouble persists. HYGRADE SYLVANIA CORPORATION effect of the test. The above tests should result wiggle each of the tubular condensers in the Emporium, Pa. RC -78 the trouble in any "dead" universal - with your hand in an attempt in location of receiver in turn Please send me Sylvania News for type receiver which uses a conventional T.R.F. to make the trouble appear. If this is not suc- the next three months free. circuit. cessful, resolder all connections in the receiver. If the volume control is noisy in its action, install Name ADDITIONAL DATA a new control. Check the aerial with an ohm- it. slowly back and forth Servicing Weak Receivers. Essentially the same meter while bending Address tests are made on a weak receiver as on a dead through its entire length. for this will some- reveal a break. receiver. In addition. the dynamic loudspeaker times State field coil and its supply should be checked by General Suggestions. Unless you are thoroughly City applying a screwdriver to a pole piece: absence familiar with the socket connections of the tubes Dealer Service Man of pull indicates a defective field coil or no supply used in these midget receivers, always have tube Amateur Experimenter voltage to it. The continuity of the aerial should base layouts at hand for ready reference. These be checked with an ohmmeter, and the trimmer layouts are particularly helpful when making Name of Jobber condensers should be readjusted for maximum point -to-point voltage or resistance tests and J output. Weak reception can often be cured by when locating various parta in the receiver. Please Say That You Saw It in RADIO -CRAFT

www.americanradiohistory.com 48 RADIO -CRAFT for JULY, 1938 THE LATEST RADIO EQUIPMENT A SURE - PROFIT FIELD (Continued from page 34) for Alert Radio Men ! CABINET PATCH KIT (1636) A resilient split collar of brass assures a firm HERE'S connection. The ferruled nut on the suppressor HOME RADIO DIATHERMY a very handy complete kit of shellac is equivalent patch sticks will to that on the spark plug, but is that fill almost every de- removable to accommodate a Ilundreds of Ra- mand. With this you spade connection. kit can patch wood as well The is dio Servicemen as the new plastic other unit (B) a 10,000-ohm distributor and bakelite radio cabinets, suppressor with a special are now repre- and white refrigerators. Simply heat spring insert which senting our the spatula assures firm contact with the spring clip on the on the alcohol lamp, and melt the shellac sticks ignition wire. Home Short into the nicks or scratches, The resistor element is molded in and smooth off with the bakelite shell of the suppressor. wave diathermy fine steel wool or hot spatula. Apply a little polish line and acting and the job is done! as our agents in all parts of the PLUG -IN METER RECTIFIERS (1639) country. We of- SPECIAL PRODUCTS FOR TECH- (The Triplett Electrical Instrument Co.) f e r exclusive NICIANS (1637) ALL TESTERS that use one instrument to territory with UNIQUE properties of several chemical measure both D.C. and A.C. require a recti- absolute protec- THEproducts developed for use in the laboratories fier to change A.C. to D.C. The usual practice tion for a 11 and factories of a well-known company are so has been to build in copper-oxide rectifiers. Line agents accepted interesting that they are being made available surges, accidental misuse, etc., frequently cause by us. Our Short for general laboratory and other applications. As burnout of the copper-oxide rectifier and this wave diathermy line is standard and has illustrated these materials include the following: has heretofore required not only the problem of been definitely accepted as by "fool- proof" A metal etch solution, D, which provides opening up, getting at and replacing the copper - all who have made the most rigid tests means for printing permanent markings on oxide unit, but also recalibrating. possible on Diathermy equipment. brass, copper and silver, as well as for marking This new plug -in rectifier makes this problem Our agents have averaged better than $40.00 a tube bases, etc. A safety etch paste, for frosting as simple as renewing a burned-out fuse. The week part -time. Full -time agents can do easily glass surfaces in 5 rectifier is mounted in a small plug with regular better. We show you how! Write for lull partic- or 6 minutes (glass to be etched is first paraflined or lacquered and then tube -base prongs. In the shell with the rectifier ulars and details on making a real good income. are the necessary calibrating resistors, making cleaned off in the design to be frosted) ; an acid frost material, J, which affords convenient, rapid possible the interchangeable feature of the plug - SCIENTIFIC DIATHERMY in CORP. etching or frosting of glassware in from 10 to unit. 200 WEST 34th STREET NEW YORK, N.Y 15 seconds (may be used to produce a satin finish on glassware) ; glass etch material, I, that pro- N-10 NEUTRAL)ZlNO duces permanent CONDENSERS white markings or monograms V ANV DESIRED on glass; may be applied by rubber stamp and TYRE De TUBE flow! %E Pn dries rapidly when heated. A vacuum cement, A, which seals vacuum - furnace made joints vacuum -tight ; also may be used to seal joints between metal and glass surfaces; AMAZINGLY does not become brittle with age, and adheres to, almost any surface. Q` SIMPLE! A fluorescent chalk, H, that glows in pitch - black Only 4 standard types darkness when illuminated by ultra -violet of rays, appears Amperite AC Regulators white in daylight ; used on a black- -DC board it may be made will replace to fluoresce by using a 90 °0 (over 100 types) of sunlamp or a black -light bulb. AC -DC Ballast Tubes now in use! A stopcock grease, C, No. 6, for lubricating WRITE FOR CHART AR. glass stopcocks which may be subjected to high temperatures New Low Price while at the same time maintaining $1.00 List a vacuum -tight joint; stopcock grease, C, No. 7, Schematic circui of the Hammarlund unit -type ama is particularly adapted for use on stopcocks slur rad o transmitter illustrated photographically which are connected in high -vacuum and on pg. AUTOMATIC exhaust described 33. This factory pre- design systems; No. 8 is used in obtaining vacuum -tight of the assembly helps insure best results. (1623) AMPERI TE REGULATORS joints and also in providing lubrication when rubber hose connections are made with the metal tips of vacuum exhaust pumps; No. 10 is recommended for general laboratory use at atmospheric Make SILENT Motion Pictures pressure. New spark plug m!!!!Itel Glass marking ink (black), G. which may be resistors include into HOME TALKIES with used with a steel pen for applying letters to a 5,000 -ohm unit, Latest various glass surfaces; glass marking ink A, and a 10,000 - FILMOGRAPH ohm suppressor, URPOSE ( white), B, also may be used with a steel pen Electra- Mechanical device for recording and for lettering glass; silver monogram ink, E, may e, both of car- reproducing Sound On Film as featured in be applied bon type. ( 1638) FgZSEN 0115 MAY issue of RADIO-CRAFT. Records and to glass surfaces by means of a reproduces instantaneously without process- rubber stamp; black monogram ink, F, which ing VOICE, MUSIC, RADIO PROGRAMS, dries in about 2 minutes, also may be applied to -B- ETC. Sound tracks are mechanically im- glass or metal surfaces by means of a stamp. pressed on the film and WILL NOT show on screen when projected. 80 minutes of recording coat 75 cents, including film. TWO NEW SPARK SUPPRESSORS Guaranteed for 1 year. Patented. Descriptive matter on request. (1638) Sole Manufacturers and Distributors (Continental Carbon, Inc.) TO ACCOMMODATE B8á7 modern spark plug and MILES REPRODUCER CO., Inc. 8ss1larM distributor wire designs, 2 new designs in Cable Address: MILESMAN, N. V. molded -bakelite, carbon -type spark suppressors have been announced. One unit (A. in photo) is a 5,000-ohm suppressor which snaps directly onto the ferruled brass stud of the spark MODERNIZE YOUR OBSOLETE plug. TUBE CHECKER OR SET ANALYZER with "PRECISION" SERVICING w -I to for details. Mention make and model number of your old instrument. QUESTIONS & ANSWERS PRECISION APPARATUS CORP. (Continued front pope 35) 182I EAST NEW YORK AVE.. BROOKLYN. N Y. on the dial. How can this be corrected? (A.) Reception of 20 -meter broadcast at both 14 mc. and 13.1 mc. is entirely in order. This Servicing is Made Easier with second setting is due to image- frequency "interference." Response at 14 mc., however, RADIO CHASSIS CRADLE! should be far greater than that at 13.1 me. In order to service shops need the RADIO GIMBLE (chassis c dlel for correct this difficulty, band D must be re- aligned. efficient servicing, testing The correct method of aligning this band and pairingatlttof receivers con- to cradle sists of "rocking" the tuning gang condenser hick ant be ad. lusted to any angle. Accom- with indicator set at 18 mc. and the signal lutes chassis up ta 13 x Excellent for generator tuned to this frequency, while adjust- displaying receivers. Write for 2illustrated New plug -in meter rectifier eliminates the pre ing the trimmer for this band for maximum iously required recalibrating of resistors in the WM. A. THOMAS CO., 321 Caroline St., Neenah, Wise. output. event of a burned -out copper -oxide unit. (1639) Please Say That You Saw It in RADIO -CRAFT

www.americanradiohistory.com RADIO -CRAFT for JULY, 1938 49

INTRODUCING -A 5 -METER CONVERTER (Continued from paye 31) (2) Experimental programs of several types. in the converter delivers an I.F. of just over including special high- fidelity broadcasting on 1,500 kilocycles, which is fed directly to the about 7 meters; and the audio channels of the antenna of the broadcast receiver on which the ultra -highfrequency television Mations, may be dial is set to the above frequency. The con- heard. verter has an on-off switch and a switch to (3) It L also possible to "keep tabs" on convert the antenna directly to the broadcast programs the ordinary run of sete cannot tune receiver when the converter is not in use. This in. Ultra- shortwave broadcast programs may be means that once hooked up the converter need heard, with high- fidelity characteristics, when never be touched. regular broadcast reception is at a standstill due to static. PLACING THE CONVERTER IN OPERATION The Kadette No. 210 converter is designed to convert any broadcast receiver-superhetero- This converter is designed to be used in con- dyne or tuned- radio -frequency -for reception of junction with any receiver, either superhetero- frequencies from 30 to 45 megacycles. The pri- dyne or tuned- radio -frequency type, which mary interest in this range lies in the broadcast tunes -in the standard broadcast band and fre- band at 40 to 41 megacycles. Many of the quencies up to 1,520 kilocycles. regular stations in large cities are installing Place the converter, preferably on a table, as transmitters to operate in this newly assigned close as possible to the receiver. If placed direct- band. They feature programs of special interest ly on receiver, microphonic noises may result. with emphasis on educational programs, sport- To connect the converter to your receiver, first ing events and special "from the scene" broad- disconnect the antenna from the receiver. (If a casts. Many of the stations are entirely on a ground is used leave it connected to the receiver non -commercial basis with no advertising al- as it is.) Then connect the white wire, of the lowed on their programs. twisted pair of wires at the back of the con- These stations are practicable only in large verter, to the antenna post of the receiver and cities, as transmitters on these ultra- highfre- the black wire of the pair to the ground post quenciee, regardless of power, cannot cover a of the receiver. Finally connect the antenna to radius of much over 50 miles with the ground the green and white wire on the converter. Any wave. The skip distance is so great that the sky antenna which gives good results with your wave will only be heard across the continent or present receiver will be satisfactory for both in Europe. This means complete absence of receiver and converter. interference between stations even though they With the power cord of the converter plugged operate on the same frequency and are only a into a source of proper voltage supply, using a TEN few hundred miles apart. Atmospheric inter- double outlet if necessary so that both converter ference is much less noticeable on these fre- and receiver are plugged in. the connections quencies. When there is more than one station made as described above, and your receiver in a city, they are required to operate on chan- turned on. turn the left-hand knob on the con- REASONS nels 40 kilocycles apart. This gives an oppor- verter clockwise. This switch turns on the power tunity for true high-fidelity broadcasts which supply in the converter. Turn the right hand are Impossible on the regular broadcast band knob counter -clockwise to the position marked for specifying with only 10- kilocycle separation. "S.W." This connects your antenna into the In addition to this broadcast band, the con- converter and your receiver to the converter. verter tunee many special government services NOTE -When this switch is turned to the and the 2 -way police systems throughout the clockwise (B.C.) position, your antenna is di- UTAH! country. rectly connected to your regular receiver and The converter is easily installed and contains the converter disconnected so the receiver may Here are ten good reasons why Utah its own A.C. -D.C. power supply- A mixer circuit be used for its regular tuning bands without Vibrators give better performance and changing any wires when the converter is not last longer! Add to them the fact that in use. When the converter is not in use, the Utah Vibrators cost na more and you'll power switch should also be turned off. know why an increasing number of Utah Vibrators are bought each year! With the converter and receiver on and the Ask your jobber for Utah for all auto switch in the "S.W." position. tune the receiver and farm radio sets! to about 1,520 kilocycles on the broadcast band. A hissing noise will be heard at this point and Utah has pioneered practically every the receiver dial should be tuned to where this 1 major Improvement In vibrator con- is loudest. Now tune the center knob of the struction I converter for stations. Rotate the knob very e2 Sulphur -free molded rubber liner elimi

slowly as stations on the ultra -highfrequencies tulles cbetnical corrosion eat metal parts-- - tune very sharply. The converter should be particularly contact points. tuned exactly "on" the station for beat results. Rubber liner consists of two parts beveled For a very fine tuning adjustment, the dial on 3 to make a closer at and suppress noise. your receiver may be shifted slightly. The dial is arbitrarily calibrated so that the figures do 4 Laufer liner molded to fit In order to hold mechanism in position In center of vibra- not correspond to actual frequencies of the tor shield. supporting leads and pre- stations. Volume can be controlled with the senting undue vibration. volume control on your receiver. Exclusive fiat frame provides simpler con- Figure 8. This is the compact chassis of the 5 -meter Names of manufacturers will be supplied upon 5 struction and more permanently rigid converter. It supplies its own operating power. neript of a stamped and self- addressed envelope. mounting for contact arms. Short leads are clamped and held steady 6 against vibrator frame eliminating vibration and preventing breakage of leads. Reduces radio Interference usually result- THE FIRST IO STEPS IN RADIO SERVICING ing from lung leads. How do you go about servicing a set? One specified values in circuit diagram or tube Tapered reed prevents undue strain and 7 equalizes bending presiding longer reed well-known radio engineer submits the following data book. If voltages on individual tube, life. as the first 10 steps. are high or low, test components in the feed circuit. Special design provides right degree of (1) See that power supply to receiver is satis- 8 wiping action to keep pure tungsten contact points clean. but not enough to cause factory. Check loudspeaker leads, antenna (7) Make certain that the audio circuit is excessive sear. and ground connections. functioning satisfactorily, then proceed to work from the detector to the antenna, one 9 Highest grade mica insulators. (2) Operate the set if possible. If trouble is tube at a time, until the fault is located. not obvious, remove tubes and check them. i O Stack is held to frame ith TWO .crews (8) If no apparent troubles can be found, ex- staking a mounting with leas likelihood Touch the of misalignment. (8) grid cap of I.F. tube or tubes amine carefully all wiring, grounds, switch with metal object, such as a screwdriver, contacts, socket contacta and controls. and listen for click in speaker. Visit the Utah Booths 113 -15 Marconi (9) Use meters and check values of all com- Blvd., Chicago Radirr Parts Show, June (4) Check speaker transformer, voice coil and 8 to 11! field, and make certain they are satis- ponents in inoperative section. factory. (10) Check, clean and adjust all wave -change TAH RADIO PRODUCTS CO. (5) Remove chassis and check power supply switches, and if necessary, clean dirty tie CHICAGO, U. S. A. completely. points which would otherwise cause low insulation resistance to ground. Clean in- CABLE ADDRESS - " UTARADIO" - CHICAGO (6) If power supply is OK, next measure all sulation on gang condensers and resolder BUENOS AIRES -UCOA RADIO PRODUCTS CO. filament voltages, plate and screen -grid all weak connections in set. Replace noisy voltages, and bias voltages-compare with controls. Adjust alignment of receiver. A6 TEARS OF LEADERSHIP' Please Say That You Saw It in RAplo -CRAFT

www.americanradiohistory.com 50 RADIO -CRAFT for JULY. 1936

"BI- FONICII SOUND MAGNIFIER fCowlti,luc.l from pape 25) ACTION AT HIGH FREQUENCIES author), the back-wave is inverted and used at ú i eur,tuag icy all frequencies. Figure 2 shows graphically how the very high - author has of these reproducers frequency waves are reflected in whole off the The several in New and vicinity, and half -round blocks. Some of the waves are operation in York City the results were noted: EXTRA PROFITS reflected back through the cone and others re- following sense of music coming from a cabinet or flected to another curved surface. To avoid con- All diaphragm was lacking. PrRO PANTAGRAPH fusion only 2 of these waves are propagations were shown; actually, there are many hundreds. Bass notes present in correct proportion at all volume levels. At the very high frequencies, 2,000 to 10,000 Bass notes were not boomy but were solid cycles the back -wave of the cone hits the set of and gave the foundation body so necessary to curved surfaces directly in back of the cone. music balance. Because of these surfaces being curved some of For a given acoustic output about one -half the waves are projected through the cone; others the power was required that would be necessary With this PYRO are projected against the walls of the enclosure rAN TAGlt PII with an infinite baffle. turn leisure line where they are further broken and weakened, thus In actual testa a 12 -inch permanent -magnet f n to profitable a period of reverberation within the re- creating mounted in Bi Reproducer hours. Make producer. The glaze or varnish on the curved cone a -Fonic hous- money a novel. ing out -performed an 18 -inch electromagnetic - easy y- "Burn surfaces determines the rate of this reverberation. Your rWay to Ex- field dynamic cone mounted in an "infinite tra Dollars with baffle." (See "Facts About the Infinite Baffle," Pyro P a n t a ACTION AT MEDIUM FREQUENCIES 'rash." Radio -Craft. May. '35 ; and, "How to Make An Figure 3 shows graphically how the frequen- Infinite -Battle, or High- Fidelity Speaker System;" Shipping weight.3113N VOGU cies are large enough to cover more than 1 ball- in the May, '37, issue. for additional, useful This tly..onlly designed round reflecting surface and are therefore broken information on this general topic. Editor) burning desiglnstulrpermanently . into many parts. Some of the broken wave - Cork. Gourds, Bakelite. Simply plug the Pyro- ielectric pencil in any 110 -volt AC or DC outlet and reflections are reflected such angle as to t Is ready to be used. Plug and cord furnished at an CONSTRUCTION NOTES part of equipment. be projected through the cone. Note -The author warns anyone contemplat- Pantograph the At the medium frequencies (200 to 2,000 outfit. a ray odesign may reproduced eitheriither in ing construction of one of these reproducers that original. reduced or eailarged form. cycles) the and area of the curved sur- length the relation of the various dimensions and the consists of: one Pyroelectric Pencil faces are such that these waves are broken by three hardwood brittle flexibility of the various surfaces have a tre- oPantograph:\ rni; rush tracing tipoand t the alternate vertical and horizontal strips on the instruction Sheet. mendous (Personal experience indicates that the Page back surface. The broken wave parta are Pro- Outfit will be forwarded by Express Collect adjective is well -chosen ; in fact, we're tempted if jected against the side walls where their strength not sufficient postage included with your order. to prefix "tremendous" with "very"I -Editor) is further divided. At these frequencies the effect upon the operation of the re- is less than half that of proper period of reverberation producer. WELLWORTH TRADING CO. the extreme "highs." This avoids any cabinet NO W. Washington Blvd., RC.7:8 Chicago, III. resonance ( which generally lies within this band A "standard" Bi -Fonic Reproducer (suitable of frequencies). for mounting cones from 8 to 12 inches in diameter) is shown in Fig. A. It stands 86 inches ACTION AT LOW FREQUENCIES high, is 20 inches wide and 13 inches deep. It is constructed of % -inch pine plywood and Figure 4 shows the shell of the reproducer masonite. The half -round pieces are of spruce FREE TRIAL OFFER minus the reflecting half-round surfaces, since or cedar, and treated with several coats of Bake- they are not in use at the low frequencies. lite varnish. The back is varnished and then NEW REMINGTON NOISELESS PORTABLE! This figure shows how the wave is reflected coated with wax. The other surfaces are painted AS LITTLE AS from the large reflecting surfaces at the end of to prevent the absorption of moisture. All joints each of the tubes. And how they are finally mast be air tight and solidly made or they will projected into free air. The dotted lines represent break open and rattle. the pressure or compression area of the wave- By way of demonstrating. comparatively, to forms at any one instant. It is this pressure music critics just what the Bi -Fonic Repro- area which always stays on the same side of ducer could accomplish, a switching system was the envelope; but the wave envelope changes devised whereby a midget set's loudspeaker could Famous Remington its form. be disconnected and an equivalent -size unit, in a Nnleele Portable that Note -The tubes are left out of the first a Bi -Fonic housing. driven by the output of the si i r Pay as little loe a as day. preceding 2 figures (Figs. 2 and 3) because, Guaranteed by the factory. Standard keyboard. same set. Immediately upon switching to the pictured. tubes no Automatic ribbon reverse. Variable line spacer at the frequencies the play Bi -Fonic set -tip the "highs" became more bril- and all the conveniences of the finest portable ever part in the operation of the reproducer. liant and louder. and the very-low notes became built. PLUS the NOISELESS feature. Act now. Send coupon TODAY for details. The low frequencies cannot be reflected by the cleanly and individually distinguishable; and surface in back of the cone because of the air timbre became a noticeable characteristic- (In You don't RISK a Penny pressure built up between the cone and the back order to deliver to the Bi -Fonic unit the very- We Bend you Itemington Noiseless Portable for surface at these frequencies. Therefore, they ap- low notes it was capable of reproducing. it was 10 days' free trial. If not satisfied. send it back. at the of least resistance slot or We pay all shipping charges. pear point -the necessary to change the value of the coupling "tube" between the back and the bottom surface. condenser, in the control -grid circuit of the out- Typing Coursa and Carrying Cow In this way the cone is automatically coupled to put stage of the midget set being used for You will receive FREE complete simplified home the mass of air contained in the 3 tubes at the the demonstration, from 0.006 -mf. to 0.05 -mf.) course In Touch Typing. low -frequency wave handsome sturdy carrying low frequencies. The pro- This, of course, is in accordance with the case is included. No obligation. Mail coupon for jected into the first tube strikes the masonite results, which engineers will appreciate at a fun deuils -NOW. Because of the pressure ex- bottom of the tube. glance. indicated by graphs A and B of Fig. 5. between the cone and tube the wave Remington Rand, Inc., Dept. 189-7. isting the These curves were made at a commercial labora- and 405 Washington St.. Ituffalo, N.V. again takes the path of least resistance tory and clearly show the advantage (curve A) Tell me. without obligation, how to the mouth of the second tube. However, in get Free Trial enters of a high- grade, 6 -in. (3 -1b.) permanent- magnet of a new Remington Noiseless Portable. including Car- being reflected from the masonite surface com- rying Case and Free Typing dynamic reproducer mounted in a Bi-Fonic Course for as little as to these tubes. is 10c a day. Send Catalogue. mon the phase of the wave in- housing, as compared to the same unit in an verted so the wave travels up tube No. IN- Name f infinite -baffle housing of proper design. PHASE with the front -wave component. Addreu Curve B of Fig. 5, however, is the one which The same sequence takes place between tube City State will make the professional sound man look twice. No. 2 and tube 3, causing the wave to be No. It is "something to write home about," isn't it. projected down tube No. 3 OUT -OF-PHASE to find a gain of anywhere from 8 to 10 decibels. with the front -wave of the same component. straight across the board. from 40 cycles (the inclined reflecting surface at the PRACTICAL Striking the low -frequency cut-off point of the particular end 3 the wave is into of tube No. projected loudspeaker used) to 9,000 cycles (the high - free air IN -PHASE with the front -wave. This frequency cut-off point of the speaker), over has the effect of creating the equivalent of a rever- that obtained with a -designed infinite- beration period at the low frequencies. The properly ADIO baffle? The same 12 -in., high -quality permanent - - length of the tubes and size of reflecting half reproducer was used in both ENGINEERING chosen magnet dynamic round surfaces are so that frequencies instances. Don't "sit-down" on the lobl Get SEND FOR high enough to cause half-wave cancellation are busy and prepare yourself for the not projected into the tubes. bigger jobs in tore for technically FREE SUGGESTIONS TO RADIO AND SOUND trained me CREI ffen home - of the tubes the training n both Radio En- BOOKLET At the resonant frequency gineeringStudy and d Public is out the tubes. MEN Service brings resonating wave cancelled within you our 46-page book ofd This is due to the phase inversion taking place The writer, for 4% years a studio-control mg boue future staff of one of the io -and bow we you within the tubes. engineer on the New York tampers tor it. Please networks, has long been associated with the her intersd in As a result of these functions the cone is Radio Engineering or Service. undamped at the high frequencies and at the very sound field; and was for 6 years a radio Service CAPITOL RADIO low frequencies the cone automatically sets a Man. As a result of this association he ventures much larger body of air into motion. giving to suggest to radio and P.A. men a few outlets ENGINEERING INSTITUTE proper air displacement to the low notes. Also. for loudspeaker housings of this type which the Dept. RC-7 14th 6. Park Road, N.W. WASHINGTON. D. C. and for the first time (to the knowledge of the technician will find profitable. Please Say That You Saw It in RADIO -CRAFT

www.americanradiohistory.com RADIO -CRAFT for JULY, 1938 51

For instance, a very fine installation can be but where music is to be reproduced and wide - made, where the customer already has a fairly angle radiation is desired, it is unbeatable, either good radio set, by removing the loudspeaker from indoors or outdoors. It is exceptionally suitable For Both A. C. his present set and installing it in a Bi -Fonic as a broadcast -studio monitor speaker. Here are Reproducer housing. This "trick" has the effect a few ideas, for your consideration; concerning of making the set apparently more sensitive to the application of "Bi- Fonics": and D. C. Testing weak signals, and at the same time almost Churches, Ledges, Clubs, Theater Sound Sys- doubles the effective power of the set; these tems, Doctors' and Dentists' Offices ( waiting Use things, aside from the increase in bass response rooms), Schools (auditoriums), Parks (summer- and the consequent added depth of tone. (Invite time municipal park concerts), Restaurants. MODEL. 666 prospective customers in to hear a set-up of this Because of the increase in the efficiency (more type in your display room or shop, if neces- efficient loading) of a cone mounted in a Bi- sary.) Funic Reproducer housing, about ,., the power Another good sales- getter, and one which we is needed to produce the same loudness as a cone have hinted at in the foregoing description, is in an infinite -baffle. As a result, you can use to take a medium -size mantel set (such as lower power for the same degree of intensity. illustrated in Fig. A), and connect the voice and In most cases, use class A amplification coil leads of its loudspeaker into the voice coil (with its inherent lower degree of total har- of a P.M. speaker installed in a Bi -Fonie housing. monic distortion) instead of A- prime or B. With this idea you can make very satisfactory In conclusion the author desires to emphasize remote -control jobs. the following points: Public Address specialists will be interested to (1) The back -wave is utilized at all frequencies; note that the Bi -Fonic Reproducer's field of (2) There is no noticeable resonant point; application is practically unlimited: the unit's (3) Bass cut-off is limited only to the cut-off response is uni- directional over an angle of about characteristics of the speaker unit: 120 deg., and is most effective in the very low (4) In addition to greater air displacement at and very high frequency range (and hence is not the lower frequencies, cone efficiency is suitable to apply in those cases where a high raised over 3 db. in the middle register, over directional quality is wanted and only the speak- 6 db. in the extreme high register, and from ing voice is to be used, as a horn or projector). 5 to 10 db. in the bass register!

MATCHING LOUDSPEAKERS TO TAPPED TRANSFORMERS ((:os t In uri from page 27) 5"00 Since the impedance of the primary, as And check: Dealer Price $1 measured, is 20,000 ohms, the actual Z the tube Zra equals 4/2.42 x 5,000, or 8,200. plate will encounter is the result of these two Zrb equals 8/9.02 x 5,000, or 13,250. in parallel or 4,770, which is a mighty fine load Zrc equals 2,000/37.9 x 5,000, or 264,200. Volt- Ohm for an average power tube. Putting these in parallel, because that's how Pochet But how about the secondary? We've just fin- they look to the tube output, we obtain 4,980, ished telling you that there is no power drawn which is close enough. /fiiI/iammetet from a pure inductance, and that the impedance It is worthy of notice that the impedance that mismatch as indicated by the ohm value means a load reflects into the primary is a function Has 3" Sq. Triplett Improved Rectifier nothing in this case. In a tube, yes, lip is honest - of the ratio it bears to the impedance of the to- goodness resistance in ohms, and you must secondary tap from which it is supplied. Thus, Type Instrument. 10- 50 match to it ; across an inductive secondary, no. in the extremes, if the load is infinite, the re- AC -DC Voltage Scales Read: -250- How about fidelity? Who ever said that if you flected Z is infinite, because infinity divided 500 -1000 at 1000 Ohms per Volt. have an inductance across which appears some by any number, except infinity (which is not D.C. Milliampere Scale Reads: 1 -10 -50 -250. power which is to be used by a load, across a number at all, but a concept) is infinity. If Ohms Scales Read: Low % -300; High it, the load must be twice anything for maximum the load has 0 ohms impedance, theoretically on 250,000. fidelity? That, my friends, is true for a tube, short-circuit, the reflected impedance is also Size -3 -c' x 5 -?8 x 2 -1A ". in the primary only, and indeed here we have 0 ohms, or the theoretical short-circuit, because Black Molded Case and Panel. taken it into consideration, but found we'd 0 divided by any number, although mathemati- rather have power output than fidelity. But, fre- cally speaking imaginary, is in actual practice. Low Loss Selector Switch. quency response in the secondary, as far as 0. If you have a month's apare time, look into Complete with Alligator Clips, Battery and "highs" are concerned, depends on the in- the mathematics of this. Test Leads. ductance and distributed capacity of the sec- on load. In a designed DEALER PRICE . . . . $15.00 ondary, not the properly- SERIES VS. PARALLEL CONNECTION transformer, these are well designed, and the A complete instrument for all servicing and will come quite well. As for One more point deserves mention. Why not ',highs" through other needs. Can be used for a 1 A.C. -D.C. "lows," that depends on the way the primary put the two speakers in this problem, or the speakers in the first illustration, in series, in- voltage, current and resistance analyses. looks to the lip, not on the load on the secondary by and its relation to Za. These mistaken notions stead of parallel? Quite feasible. Thus in the Resistance range can be increased are prevalent, but very unfortunate. There are problem cited. the diagram would look as adding external batteries. a few other considerations which determine the follows: (See Fig. 1D.) Attractive, Heavy Black Leather Carrying frequency response obtainable in this arrange- Only the upper tap is altered, the others Case with Finished Edges and Strap, ment, such as saturation, efficiency of trans- remain just as they were. Now the load Z Model 669, supplied extra. formation, etc., but the load on the secondary is 16 ohms. still 8 watts, and, applying our affects it only as far as its reflected impedance rules, Za equals 9.68 ohms. Since 16 is DEALER PRICE . . . . $3.67 goes, and thus we see the importance of this to 9.68 exactly as 4 is to 2.42, the reflected reflected impedance in spite of the very little Z is the same, and, apparently, the problem WRITE FOR CATALOG attention given it. is unaltered. SEE THE NEW TRIPLETT 19381539 LINE AT THE CHICAGO JUNE RADIO PARTS SHOW But. suppose now one of these two speakers BOOTHS 2I3.I., -Hrnry Awn. is removed, either because unnecessary, or, due MULTI -SECONDARY TRANSFORMERS to failure in operation. In the series arrange- And by the way, don't think that the methods ment, this opens the load on Za, and the whole ' outlined are applicable to tapped secondaries kaboodle is thrown out of balance, How much? only. They work equally well with multi- Well, if it fails in operation. the remaining re- Q' 7)Le1 secondary transformers. For instance, suppose flected impedance is now 11,200. hence the tube we want a set -up using two dynamics, 9 ohms, output is materially decreased, and other speak- Aaecivah 4 watts ; one at 8 ohms, 5 watts, and to bolster ers will suffer. If it is removed, and the one up the "highs" as much as possible, we will use is connected across the whole winding, it will be ECTFtICAL INSTRUME a magnetic speaker of 2,000 ohms impedance on overloaded slightly, to begin with, and the re- L another winding. This arrangement is shown flected Z will be 3,120, slightly overloading the The Triplett Electrical Instrument Co. below: (See Fig. 1C.) The impedance we want tube and really disrupting the balance of the 167 Harmon Drive, Bluffton, Ohio reflected must be 5,000 ohms. whole arrangement. -Please send me more information on Z-1 equals two 8 -ohms impedances in parallel, In the parallel arrangement, if one fails or Model 666:- --I am also interested in. or 4 ohms, 8 watts; is removed, the total reflected impedance will be Z -2, 8 ohms, 5 watts: 6,700, which will not upset the arrangement Z -9, 2,000 ohms, 11 -watt. enough to cause worry. Moreover, the remaining Name What are to be impedances of the secondary speaker will not be overloaded. In practice, there taps Za, b, c? is little advantage in connecting them in series, Using method 1, because this is the author's and the parallel connection is most commonly Address pet: used. Za equals 8/13.26 x 4 or 2.418 ohms. It is hoped that the above discussion, in which Zb equals 5/19.25 x 8, or 3.02 ohms. test cases were used as examples, will be useful City Z3 equals .25/13.25 x 2.000, or 37.8 ohms. as a practical reference on the subject. ti Please Say That You Saw It in RADIO -CRAFT

www.americanradiohistory.com 52 RADIO -CRAFT for JULY, 1930 UNIFIED P.A. EQUIPMENT (Continued from page 2s) all normal work, equipment properly chosen I microphone power supply unit will perform correctly the first time tried. Com- 1 speaker field power supply unit mon apparatus is built with sufficient versa- I speaker line matching transformer tility to meet normal variations in requirements, or a total of 7 additional pieces of apparatus, and specialized models are available at reason- to be wired together on the job and to clutter able cost because even special jobs are now the customer's premises. Send for tin. FREE catalog relatively common. today. Page after page Eye appeal is one vital business of Further, much time was wasted in the factor in money saving values in Lafa- past, modern P.A. work, now that P.A. is a when P.A. systems had to really yette Radios be bought as so business and "Ham" equip- /////,, the customer's premises - many individual components. in the are no ment- Public Address -parts mere low - longer treated as a laboratory, to be supplied and tubes. pay work of connecting up cables, attaching with assorted chunks of black apparatus. plugs and similar unprofitable activities. Such Streamlining, chrome, aluminum or cadmium NEW CAMERA SECTION practices are now unbusinesslike. The P.A. man trimmings, illuminated controls and attractive Features o complete line of economizes his high -pay time in surveying jobs, cameras and photographic contacting his customers. color combinations are some of the features and other business manufacturers now offer the P.A. merchant, supplies. Make this your buying activities. and leaves attaching plugs and and the which he in turn passes on to guide. Send Ior your FREE like to the factory production line, his customers. where they They are factors that he uses in meeting copy of Catalog No. 71 -3G8. belong. competition. and their cost is insignificant while their value is very large. The renter or user is PRIMITIVE AND MODERN METHODS WROLESRLE RflDIO SERVICE CD impressed with the fact that he is receiving a finished 103 Sixth Avenue New York, N. Y. The full extent of the difference between what product -an article of merchandise -a may be called the "primitive" and the "ad- machine that can logically be prettied up because it has its pioneering is $-VOLT UNIVERSAL POWER vanced" methods of handling technical and passed days and a stand- PACK business problems in P.A. can best be appre- ardized, definitely useful article. The cost is At Loss Than Prieto .-Prong Synchronous Vibrator Alone! ciated by considering two practical P.A. jobs, trifling because all such costs are trifling when LISTS $15.08 Operates 2 volt set from 8 volt etorass both a market is large enough to - battery, also operates fi Volt house treated first according to the old and then permit production sets. auto ut,. S.W. transmitters and according to current methods. Two jobs must line manufacture. receivers. Output. 180 Volts at 50 be taken into account instead of one, since the M.A. On 4 Volt cell supplies 120 versatility Volta at 30 KA. Housed in case of modern apparatus is one of its PRESENT -DAY PROCEDURE prime advantages. rs4Wz8%'. ship- ONLY Business ping Wt. e lbs. N[T°-' -like procedure is another way in Consider that the first requires only a micro- which the present ARROW SALES COMPANY -day P.A. merchant meets com- phone and. say. 10 or 12 watts power, with 2 petition, not merely 27 S. Jefferson St. Ch lease. III. through its economy but loudspeakers ; the second. 2 microphones (1 re- because of the favorable impression such pro- WHEN YOU motely, located), a phonograph pickup. 30 watts cedure leaves in the mind of the potential buyer. power and 4 speakers. In sizing up a given P.A. job, the first factor THINK Under the old dispensation the P.A. man re- to be considered is almost always the power out- eaurto moves the system from rental job No. 1 and put required. The cost and type of amplifier to be to Kee rl0ue considers what parts of it he can salvage for used is thus established. Given a normal prob- FREE 1938 OF P. A. CATALOG rental No. 2. Assuming that the amplifier had lem and a modern system. the same data also el banne, D.. tes b, A C Start, enough reserve power, he might use all of it. He ends all speaker questions. since a modern sys- would then need, in addition, a -amplifier for tem of the given power rating will curry with AMPLIFIER CO. OF AMERICA pre the second microphone. a mixer the three it the correct number of 37.47 west 205h St., New, York. N. Y. for speakers, correctly sound sources. and a matching transformer or matched and properly baffled, for any ordinary transformers for the 2 speakers already used, to indoor or outdoor application requiring that enable them to work with 2 additional speakers amount of power. Only in special cases will it be RADIO ENGINEERING from the same output impedance. Having necessary to return to the older method of deter- RCA Institutes offer an intensive course of equipped himself with these assorted parts he mining individual speaker requirements high standard embracin all phases of Radio in the and Television. Practical training with modern might spend from 2 to 10 hours wiring them field. and of calculating speaker impedance and equipment at New York and Chicago schools. up to the appropriate cables, testing them out, field power matching problems. %Leo apeclaltud courses and Home Study Couru under No obligation' pian. Catalog grounding them here and there to cut down hum. Selection of the microphone is. however. some- Post. RT -311. taking some of the grounds off again and con- what more complicated because of the still wide RCA INSTITUTES, mo. necting them in different locations to avoid elec- variety of microphone needs. and for that reason A Radio Corporation of America Servie. trical feedback, and generally, impressing his P.A. systems are often sold today with choice 7$ Varlet St.. Mar York 1164 Mnroa.dlu Mart. Chicago customer with the idea that P.A. is a very nice of microphones. The Lafayette system referred plaything, and may become practical some day. to above is available with crystal, velocity or Today, removing his equipment from job dynamic microphones. directional or non- direc- NAVE YOU SOMETHING TO "SWAP" No. 1 (and again assuming that the amplifier tional. The directional microphone is of course where or is there some article that some one has sufficient reserve output. which is now very desirable acoustic feedback may prove else has, and you would like to get? inexpensive) he merely plugs in his additional difficult and where other considerations of the Read the RADIO -CRAFT "SWAP microphone and phonograph. His amplifier will service to be performed permit its use. Another have enough gain: no preamplifiers point worth remembering SECTION" which appears on page 62 needed; in the case of micro- of this issue. IT IS OF GREAT IN- and the mixer will be built -in. He will plug -in phones is that where the performer is featured. TEREST TO YOU. (or possibly, in this case, connect by cable) 2 he (and especially she) prefers a small instru- additional loudspeakers. To match impedances ment. which will not hide his or her face from he consults his manufacturer's instruction sheet the audience. But there is no microphone match- and changes a tap or pin -jack connection in ing problem; all the many types of microphones Complete Electric Plan +s the amplifier. thus obtaining a new output im- that are offered optionally with a modern sys- pedance to match the new load combination. tem simply plug in. Oasts A. C. plane. Israeli alms cornt ato cit. Imes. 110 W For Grounding for hum or 'all. eyrie lanais. amp., electrical feedback was It will be seen that the field engineering prob- construction lona. Opa . .I... warve taken care of in the factory. Time spent is a all &opiu ..... Sew modela. 650 to Sal lema of ordinary P.A. work have been simplified C. the assts. 6, 12.33 sed 110 volt D Models 837.30 half -hour at most; if his equipment is to the point where setting equipment for dem- ,...1 .n ti.. ,o. n k. C. . D. C. ands. really modern, probably less than 10 minutes. Shipped =ample . ready serum. onstration presents no difficulty and little delay. Write lee details. providing only that the power output has been D. W. ONAN SONS PRESENT EQUIPMENT COMPACT AND estimated correctly for the requirements. 157 Rnyaeton Awe .. Minneapolis. Mlsi..oea and ATTRACTIVE that modern coordinated equipment is used. The illustration shows modern equipment. in this case. a Lafayette coordinated sound sys- ADVANCED CIRCUIT ADVANTAGES RADIO MATHEMATICS tem, which combines within itself all the func- A large part of this seeming simplicity is in Practical Book for Nome Study tions of the mass of earlier appliances included fact based on highly complex engineering. Complete training in useful radio mathematic.. Ex- in the contrasting picture of primitive appara- through which technical problems that formerly plains and interconnects simplified arithmetic and the with tus. The present day equipment performs obtruded themselves in the field. and disgusted algebra real everyday radio problems. Covers functions of in detail every phase of radio work. Size: 8 t f the customers, are now taken care of in the 11 in. Special price, only 50c. postfree. Preamplification for two channels factory design. A highly important factor in S 4- channel mixer SUPREME PUBLICATIONS 3729Ccae. WáI"ht' this connection is acoustic distortion. which often Power supply to photoelectric cell, microphone required elaborate experiment with speaker posi- or other input source tions. Nothing that can be done with a sound Power supply for loudspeaker fields system will change the acoustics characteristics Booster amplifier, for 132 db. gain of an enclosure, but it is very possible to use Speaker line multiple impedance matching individual bass and treble tone controls to corn- transformer. pensate for defects in a building and so to pro- The same functions in earlier days (uncertain- duce pleasing sound where straight -line amplifi- ly performed because of external wiring. doubt- cation over all frequencies might sound un- ful shielding. and so on) would have required: natural. As long as the straight- line- amplifica- 2 preamplifiers tion characteristic is present and can be used, I mixer when conditions favor it. the listener is the 1 booster amplifier gainer by the further existence of H.F. and Please Say That You Saw It in RADIO-CRAFT

www.americanradiohistory.com RADIO -CRAFT for JULY. 1938 53

L.F. controls that combine with acoustical re- field free to concentrate on his logical problem sponse to produce a straight-line result at the 01 merchandising a sniffed, *Oohed and polished listener's ear. article of customer appeal. Reverse feedback is still another modern fea- The illustration shows the functioning of one ture. saving the P.A. man the necessity for of the modern, business -like systems. Four - apologizing for distortion inherent in his am- position mixer, preamplifier. individual high - m plifier, if the customer should ask to "Hear how frequency and low -frequency compensating con- SPRAYBERRY'S it sounds if you make it a little louder." trols, field power supply, microphone or photo- Having sold his customer, the P.A. merchant cell excitation supply and speaker line matching PERSONAL HOME TRAINING PLAN delivers a complete article, with (as before transformer are all built into the amplifier itself. mentioned) plugs attached to cables, cables at- Connections to the speakers and the microphone Actually Sets tached to microphones and speakers, and so on- or other sources of sound is by plug- and -jack You Up For a in fact, with everything ready to use in 5 min- method. Reverse feedback eliminates harmonic utes, except that because of shipping problems distortion at high volume levels. Convenience in PROFITABLE BUSINESS the baffles must be mounted in the field. the field is promoted by the fact that the sys- Those Public Address merchants who Ile your own Doss! Get Into keep tem leaves the factory as a single unit, tested th fast moving Radio i themselves fully in step with such advanced as a unified assemblage with all parts connected ry. Ifsm , are antra bitXttious fellow , :], procedure are the ones that find P.A. a busi- and working together. Modern styling. enhanced you for n good pacing full part time Job ness and a profitable one; but unfortunately by the fully ventilated cover case that hides all with ` of ahead. My training Ii. distinctly there is still a little work, here and there, that working parts, by the convenient handles at new mid different. is being done according to the very earliest prac- both top and sides, the self- glowing nco -dials Television Covered - . - tice, and some at all stages in between. There of the controls and similar details, makes for a Earn While You Learn are still today some "complete" systems, adver- professional, finished appearance that removes sold as which are without from not only covers Wnr.Ughiy all phases tised and complete, the buyer's mind the idea of laboratories aú Ì b'e heroil ngd you baffles. Step -by -step, however. the industry has and experiments, and substitutes the idea of start In business. I how you Ii how get profitable Were time Radio ice work. Moreover, I show you progressed along the logical lint of concentrating merchandise of value. how to do these jobs. You gain practical add experience all problems of selecting parts, and of matching This article has been prepared easy cash to bank account while learning. from data BIG PROFESSIONAL OUTFIT GIVEN! and inter -wiring them, in the hands of the supplied by courtesy of Wholesale Radio Service Consists of All -Ware, All- Purpose Analyser, Rider Man- factory engineer, leaving the P.A. man in. the Company. uals 17,078 pages), Tool Kit. Electric Eye Outfit. Ex- perimental Apparatus. THE SPRAYBERRY COURSE. IS SOLD UNDER AN IRON -CLAD MONEY -PACK AGREEMENT. L5ng1 have "Since enrolling I cleared a net profit more 515011 in re time ` lone . .n, and I an, not half through the Coursec yet. Honestly. 1 cannot undrrstaud how you ene h dope for littlen y.' SPECIAL SERVICEMAN'S COURSE A WIRED -RADIO "NURSEMAID" Advanced Training for those already In Radio- teaches the easiest way to do the (Continued from page 38) hardest John. Complete details of this ad- featuvanced course and funiamontal co res. fully described in y 48 If it is found difficult to trace the wiring of sitivity unless such isolation has been made, page FREE. hook. Send for our cony today. the fuse box, simply try the condenser under and the units separated far enough, and well various pairs of fuses until you find a combina- isolated by separate closed rooms to avoid howl tion that couples the 220 V. circuit. with the volume set maximum. properly control at SPRAYSVARY ACADEMY OF RADIO or until a combination is obtained which pro- F. L. Sprayberry, Pres. Interference from A.C.-D.C. receivers. Due to 120-0 University Plue. N.W. duces satisfactory operation of the Radio Nurse. the type of circuit, and rectification system Washington, D. C. This condenser is fully protected by its internal Please semi me FREE copy of employed in A.C.-D.C. receivers, they may cause ^More Money In Radio." fuse, and even if improperly installed will cause loud interference in the form of a hum to be no difficulty whatsoever from short- circuits, etc. heard in the Radio Nurse. This can be overcome by connecting a filter at the socket to Nam. Age IMPORTANT INFORMATION which the A.C.-D.C. receiver is attached. A Address If the Radio Nurse Lacks Sensitivity: The soldering iron or curling iron may also cause this interference which Radio Nurse is designed to operate under normal in case the same filter ii.i , 1., . home conditions. When it is operated in a com- units may be applied to the interfering device. IN======.======mercial establishment, lack of sensitivity may Names of manufacturers will be supplied result due to heavy light loads, heavy power upon receipt of a stamped and self-addressed loads, high line capacities, split wiring circuits envelope. and heavily bypassed or filtered wiring commonly used to reduce line disturbances in radio receivers. The Radio Nurse being a radio- Answers frequency-operated device depends on freedom IN PUBLIC ADDRESS of loads or capacity on the line which factors HUM YOUR partially or completely bypass the signal. To INSTALLATIONS overcome this condition and obtain proper efficiency from the Radio Nurse in commercial With the introduction of the bass reflex speaker Questions installations, the various factors must be elim- and its consequent improved low -frequency repro- inated. If, however, this is not possible, then an duction, the question of hum in Public Address isolated power line must be used. Isolation can installations is becoming of greater importance. be accomplished by placing an R.F. choke in The manufacturer of sound equipment in this each 110 -volt lead of the wall outlet, and running respect needs very keenly the assistance of the the 110 -volt leads from the chokes to both the installation organization to the end that the in- DREW'S Guardian Ear and the Radio Nurse direct. Do stallation should be properly made. not determine that the Radio Nurse lacks sen- It is very important with the low -level microphones that are now being used. that the con- HOW TO PASS tinuity of the shielding be perfect. In other words. even a break as small as 1 inch in the Radio microphone wire shielding will introduce a seri- License Examinations ous amount of induction pick -up in the system. By CHARLES E. DREW, I.R.E., A.I.E.E. The amplifier should be grounded to eliminate This the floating chassis condition. The selection of book is more than just a new the edition of a famous work. It has been proper type of tubes is also important. It completely rewritten, and will serve as is an unfortunate matter that many of the radio an tubes available on the market today, while ideal- excellent guide to all radiomen. Im- ly suited for use in radio equipment. are of too portant phases of the subject are given noisy a character for general Public Address thorough treatment, so that the man work. who understands the content of this The construction of the tube heater struc- book will be well qualified to pass the ture has much to do with the amount of hum examination for his commercial license. that will be generated by the amplifier. It is a fortunate fact that the manufacturers of tubes Published March 1938 $2.00 are appreciating more and more the importance of humless tubes for public address work and ON APPROVAL COUPON to this end a number of manufacturers have John Wiley & Sons, Inc. worked very closely with Webster -Chicago to 440 Fourth Avenue, New York, N.Y. supply tubes particularly adapted to audio ap- Kindly send me a copy of Drew's HOW plications. It is to be hoped that in the future TO PASS, on ten days' approval. If I de- tubes will be available with some type of cide to keep it, I will remit 92.00: other- designation marked thereon indicating that they wise I will return the book postpaid. have been picked or selected for high -gain audio Name work. On some of the smaller light plants, where Address the waveform is not particularly good and the City and State power supply contains harmonics of the order of the 17th, 19th, etc., inductive sing Employed by Fig. B. Interior view of the "Radio Nurse" or becomes a Iti 7-3t loudspeaker unit. This is an upside -down position, problem that requires close attention to input since the volume control operates from below. shielding and grounding. Please Say That You Saw It in RADi0 -CRAFT www.americanradiohistory.com 54 RADIO -CRAFT for JULY, 1938 WAX AND OIL CONDENSERS IN RADIO SERVICE WORK Formerly (Continued from page 21 Sold or voltage is applied before the heaters have come mate invasion of moisture results in direct 81f5.00 up to fall values of current and voltage. failure.

VARIABLE CAPACITY AND VOLTAGE SERVICING MULTI-BAND SETS ¡peed induc- CONSIDERATIONS In the servicing of multi -band receivers today, tion type self -starting. 110 volt, 25 to GO ryrl.. .t.e'. nilh speed control. Plug and cord. Speed range from 5 to 200 In the replacing of wax- or oil -impregnated the Service Man will notice that the original R.P.M. Can be installed in place of old- faehloned. hand - paper "capacitors " -as they are known today manufacturer has had to resort to a few new winding speed motor. Also ideal for display turn table. Among those he saw was the difficulty and hundred other uses. These General Electric Motors to the trade -the Service Man is concerned with tricks. are brand new, In original factory cartons. S e9ó capacity, working voltage. test voltage, capacity in properly bypassing the radio- frequency cur- O. E. Electric Phonograph motor as de- A sections, rent at widely different frequencies. In many scribed tolerance, inductive or non -inductive Shipping Weight -12 lbs. power factor, size and price. Many manufac- cases, special condenser construction was re- turers do not pay close enough attention to quired. such as in the shape of the unit, the WESTINGHOUSE capacity tolerance, and snack units anywhere casing or mounting. and the length, width and from 25 to 3O j from their actual rapacity values. size of the leads. UNIVERSAL MOTOR The actual capacity marking should be care- Usually in replacing such a unit which has fully checked by the Service Man before final failed, it is necessary to use an exact duplicate 110 Volt. is made set. After locating replacement in every respect, in order to AC sad DC replacement in the type $Á.55 and repairing the trouble. the Service Man can have the set function properly over all the bands. Shipping check against the rating of the new condenser. Otherwise the units may be satisfactory on 3 Weight if the condenser is one where the capacity value or 4 bands, and be entirely unsatisfactory on .1 lbs. is at all critical. This applies especially to the the 5th, or ultra -highfrequency band. due to the Specifications: 1/30 R.P. operates on either smaller -type condensers which are used in oscil- lead length being large enough to resonate with A.C. or D.C., 110 volt'. lator circuits. If the capacities are not of the the condenser. setting up a resonant circuit not 5000 R.P.M. Rheostat proper value, the oscillator will not properly band. can be used to vary speed. desired on that particular Height Length operate as originally intended by the set When replacing condensers in multi -band re- W, ,Widh , ono manufacturer. ceivers, it is absolutely necessary that the leads inch tang. Can be used to drive Sewing Machines. Mod- be connected to the same point where the el.. Buffing Lathe, Polishing FOR "WAX" OR "OIL" original condenser came off. It is absolutely Head, Drill.. Grindstones. CHECKING etc., etc. When selecting the proper working voltage necessary that the lead length be as short as possible. and that the replacement condenser be MOTOR only $2-$$ at which the units are to be operated. the Serv- placed as near to the original relative position as S3.55 ice Man should take into consideration the likely MOTOR with Arbor and 'A' Chuck possibility of transients causing high peak possible. Add 25e for epochal pack /fie/ and rnallsnq voltages due to line surges and other faults be- At the ultra-highfrequencies, one can readily anywhere In U. S. A. yond the control of the usual operation of radio see where an addition of or 11, -inch will the Express Collect receiving equipment. make an entirely different picture in circuit We will forward Shipments by operate under if sufficient postage is not included. In the manufacture of wax- and oil-impreg- and the receiver will not properly those nated condensers, each unit is originally flash - conditions. It is also necessary to notice when servicing WELLWORTH TRADING COMPANY tested from 3 to 5 seconds at twice the work- for that the con- ing voltage. A representative unit of each group ultra- highfrequency equipment 561 W. Wuhiagton Blvd., Dept. RC -73$, Chicago, Ill. are the non -inductive units. manufactured is placed on life test at 3 times densers has been data the rated voltage with a 10% superimposed A.C. This article prepared from voltage. These conservative ratings of con- supplied by courtesy of Cornett- Dubitier Electric WAYS densers by reputable manufacturers assure Corporation. 300 Men freedom from future breakdown Service TO MAKE MONEY provided they are used when replacements are made in a radio receiver. NEW RADIO SERVICE "CAR" The choice of inductive or non -inductive sec- SPECIAL (Continued from page 18) INTRODUCTORY 68 PAGES tions for replacement work can easily and quickly be chosen by careful observation of the unit OFFER The unit starts instantly, is easy to operate, which has failed in service. A non -inductive sec- easy to balance and simple to steer and control. Good Only For tion is usually wound with an extending margin The Motor Scooter is completely equipped with A Short Time of foil on either side of the paper or dielectric. a powerful lighting system, good brakes and the The inductive type of winding appears with necessary accessories for average safety and con- paper extending beyond the foil, with tabs as venience. 1O¢ connectors. Motor Scooter models in a number of styles and power are available through nearby branches PER COPY FACTOR of the manufacturer or may be obtained as a MAIL ORDER PLANS POWER The power factor of a wax- or oil- impregnated premium through the purchase of radio tubes TESTED MONEY MAKERS condenser is often of vital importance. It is a and condensers on the terms of an offer made A Bread by the National Union Radio Corporation, to BUSINESS SECRETS measure of power loss in a condenser when New Book placed on A.C. or radio frequency, and is ever whose cooperation Radio-Craft is indebted for SUCCESS SCHEMES 1938 Copyright present to a greater or lesser degree. The effect the specially-posed, exclusive photographs here of poor power factor in a condenser may be reproduced. fUdlll i11 \\\ In "CASH IN" likened to that produced by building in a series you will find all resistor with an otherwise perfect condenser. the red money - Poor factor in a condenser may be 25 makers dozens power SOLD ON A coin - caused by a number of reasons. For example, a MONEYBACK of profitable tested GUARANTEE! mail order plans, poor or low grade of paper, poor or low grades confidential business of wax and oil, improper impregnation, high - secrets, dozens of practical tested for- resistance leads or tabs caused by tarnish or the mulas. successful, and honest tested schemes use of solder, poor sealing. and many other small -many actual experiences of men who have sundry reasons which close production control started on the proverbial shoestring-with less than $10 capital. can eliminate. "CARD 1N" contain* 68 pages of tested ideas enter- Condensers today are available in many styles. ing et ery type M full -or spare-time enterprise -it is shapes and containers. The particular type is a really a "masterpiece'' in business ventures -OVElt 40,000 WORDS IN THE TEXT. consideration usually dictated by the space and Special Introdacfory offer- mounting room available in the radio receiver. la CENTS per copy. (Regular price 25e.) Sent In replacing condensers, a Servioe Man some- POSTPAID anywhere in U. S. upon receipt of fen times the condenser close to a resistor or cents in stamps or cols. places a vacuum tube. The results are noticeable in a NATIONAL PLANS INSTITUTE short time. The heat of the resistor or vacuum NEW YORK, N. Y. 246R FIFTH AVENUE tube is absorbed by the condenser, melting the wax filler. The condenser is then forced to "breathe" by expansion and contraction as the set is turned on and off. As the seal of the condenser is ruined, moisture enters the unit and in short "B -A" serves the trade with every need order the unit is made ineffective. Condensers In radio-complete 160 -page catalog of should never be placed in close proximity to nationally known radio receivers. public address, parts. supplies and equipment. resistors. tubes or any other heating elements. Orders shipped same day received. Many manufacturers in designing equipment Mr. Service Man: The scooter model shown above make the mistake of laying out the chassis with is a 3- wheeler, having a convenient sida trunk (faking the place of the usual side car in the the tubes below the condenser. where convection motor cycle) in which can be carried all the neces- currents of heat pass around the condenser, sary service instruments, tools and manuals for BURSTEIN-APPLEBEE CO. 1=:: '=.tMr,: causing it to heat up. Melted wax, and the ulti- any service call. Please Say That You Saw It in RADIO -CRAFT

www.americanradiohistory.com RADIO -CRAFT for JULY, 1938 55 OPERATING NOTES AERIAL INSTALLATION (Continued from pape 29) PROYES EXTRA INCOME the ganged tuning condenser should be removed, be found due to a short- circuited oscillator sec- and contact and shaft polished with fine sand- tion of the tuning gang, which is occasioned by FOR RADIO SERVICE MEN paper. This will insure freedom from birdies the shorting of the heavy flexible copper banding that are hard to locate. lead, between gang condenser and chassis, to the Tighten all tube socket contacts. It will be bussbar stator lead of the oscillator section. This o1111u necessary to remove the filter block to reach pigtail is unnecessarily long and since the tun- the sockets of the types 80 and 47 tubes. ing gang is floated, trouble at this point is un- TURN idle hours into Always check the tone condenser before avoidable. profit! Every customer a replacing the tone control. A leaky condenser The symptom of choked, irregular and distorted prospect for a better aerial here will ruin an expensive control. reproduction has been traced to a short-circuited and you can easily sell or leaky 6B7 cathode bypass condenser. This is them on the idea. Sparten 913. There are many of these old sets a 4 mf. electrolytic unit mounted on the terminal still afloat. One of these with an added amplifier strip located near the rear wall of the chassis using a 485 gave intermittent reception. With under the 6B7 socket. The degree of distortion the aid of a new socket analyzer the trouble will depend upon the leakage of the electrolytic was found in the primary of the audio trans- condenser. The correct resistance to be obtained former of the added stage. This was replaced with an ohmmeter from the cathode of the 6B7 by capacity coupling. See Fig. 3. socket to chassis is approximately 4,000 ohms. To remove oscillation in this model bypass As with the models 121, 122, reception of al- the plates in the R.F. box. The power -pack and most all strong stations at two resonance peaks the balancer in the 182B filament circuit are about 20 kc. apart, with distorted, muffled re- additional weak points. production between these two points, is due to This set may be rotubed with types 27 and 71 a short -circuited or leaky 0.05 -mf. secondary- tubes. If oscillation is encountered bypass the return bypass condenser of the I.F. stage. This plates as above. condition will be noted only when the volume Install the new "MULTI - control is advanced to a higher level than COUPLER" ANTENNA SYS- Chevrolet 500.565. Vibrator noise drowned-out usually maintained. TEM, the latest all -wave noise - the locale on this set. The vibrator pack was BERTRAal M. FREED reducing antenna system removed and a "B" eliminator substituted. The employing many vitally im- set worked fine. It was found that the filter con- portant improvements. Master were removed. densers had dried out. They IN antenna systems are equally See Fig. 4. NEW CIRCUITS adaptable to private homes as As this was a hurry -up job an 8 -mf, midget MODERN RADIO RECEIVERS they are to large apartment electrolytic was wired across the input. The buildings. (Continued from page 20) vibrator noise almost vanished. Installation season starts Small A.C.-D.C. midgets. Oscillation is a com- (4) DOUBLE -ACTING TONE CONTROL NOW! We furnish standard mon complaint. It can be cured by shielding Sparton Models 1268 and 1288P. In one unit. installation specifications both detector and R.F. tubes. The detector grid a tone control supplies bias for the driver and FREE, and help you solve spe- lead may be too close to the 43. is active on both low and high frequencies in cial antenna problems. electrolytics as 4 stages. For complete details. write today. Hum may be due to dried Adelress Dent. C. above. Cut loose the "B" -plus lead at the recti- As illustrated in Fig. 1D, from the viewpoint fier cathode or cathodes. Run this to "B" -plus of the output stage the tone control 1-megohm AMY, ACEVES & KING, INC. to set chassis. Don't of eliminator. Connect "B -" potentiometer and the 0.01 -mf. condenser with 11 West 42nd Street, New York, N. Y. ground either chassis. If you are on a concrete the 0.1 -mf. condenser act to bypass the high not shafts. Antenna Systems-LicensorSystems LSpn.or tr floor don't touch any bare frequencies increasingly as the slider is moved leadi Set de antenna aau.e- R. Dgex, Ja. toward the right end. However, as it is moved o art toward the left end, to compensate for the (Air Chief) Stewart-Warner R -172A, Firestone apparent increase in volume, the intensity of Judged by the number in use R -166A Chassis. Weak or no reception on the the entire signal is reduced. The choke coil band. -wave reception OK. A broadcast Short prevents high frequencies from being shorted out S TODAY'S short at the broadcast antenna shunt trimmer of the grid circuit while most of the grid im- MOST on top of the center section of the 3 -gang tun- pedance is shunted out by means of the 0.1 -mf. ing condenser has caused this trouble in a condenser. POPULAR number of cases. A soldering lug on the con- The D.C. bias for the 6JSG driver is supplied denser framework is too close to the trimmer from the end of the field coil through a 270,000 - Tube and should be bent up to clear. This defect is ohm resistor. hard to locate and requires very close inspection. Tester On one Stewart -Warner this lug was just close (5) AUTOMATIC TONE CONTROL enough to cause intermittent reception. It is advisable to check up on all models using this Silvertone Model 6101: Factory No. 101.496. Model 4,+(I same tuning unit. Vacuum-tube tone control automatically reduces Dealer Price high -frequency response as volume is reduced. Victor R -32, RE-45, R -52. Quite often the 110 - The automatic tone control circuit is shown - e found burned-out in these re- in Fig. 1E. From the ordinary diode 2nd I ONLY $ 1 volt pilot bulb is volume Adju tenmt 9.80 ceivers. If other repairs are to be made at detector output control, the signal is conveyed to the of a 6U7G with Leakage and Snort the same time it is a good idea to rewire for grid pentode its Test screen-grid and suppressor-grid connected, and Positively Checks a 2.5 -volt pilot bulb as these are always on hand Uses Triplett Radio Receiving Tubes and give sufficient light. The tote] cost of supplied with a positive screen -grid voltage (GOOD -BAD) a load, Instrument According to Latest a new socket and bulb is no more than the through 50,000ohm resistance The plate is connected through a 0.5 -meg. resistor to the Recommendations of 110 -volt bulb and future replacements will be Tube Engineers. Five flush type sockets pro- that much easier. Connections are made to the A.V.C. supply lead. In addition. a manual tone in is connected from common - vide for all tubes. Complete attractive, type 45 amplifier filament supply. control the screen suppressor connection to ground. sturdy, quartered -oak case. Sloping etched Using this grid connection as an panel of silver and black. Suitable for port- Zenith 50 and 60 Series. When any one of anode, the use. signal introduced into the 6R7G grid depends on able or counter these receivers is very weak and an attempt Model 431 same as 430 except has Readrite to balance the trimmer condensers at any par- the ability of the 6U7G to amplify or at least transfer the signal to the 6R7G At low (GOOD BAD) meter Deal- $15.90 ticular frequency makes it still weaker over the grid. er Price rest of the tuning range, remove the tuning con- signal strengths the 6U7G plate is practically at ground potential and the tube operates to A MODIFIED EMISSION TYPE denser shield, loosen the screws holding the stator TESTER...APPROVED CIRCUIT plates and center each section separately while shunt out practically all high frequencies. As fully meshed. Check the spacing again with the the signal increases. the plate is driven nega- , stators turned halfway out. It may be necessary tive improving the characteristics of the tube to to bend a plate here and there to obtain satis- amplify high frequencies which are carried to factory clearance. Replace the shield and re- the 6R7G control -grid. As the high frequencies volume, there is somewhat balance. If the spacing is carefully done the are decreased with An annoying hum less tendency toward background noise on low results are almost astonishing. signals. 7 at low volume levels in these sets may be sup- READRITE METER WORKS pressed by adding a 1.0 -mf. condenser from the 716 College Aue., Bluffton, Ohlo detector cathode to ground. -Please send me more Information on Model 430. HOME -MADE PORTABLE --Model 431. RCA Victor 128, 224. The peculiar condition may be encountered on these models where the RADIO SET receiver is totally inoperative except at one "Going places" this summer? Take along Name point on the broadcast band. A powerful station a 4 -tube portable radio set -use it at camp. at 660 kc. is heard weakly at this setting, with on the lake, etc. Complete construction detail+ another station whose regular assigned frequency in August Radio-Craft, on the newsstan& Is 710 kc. heard as a background. The trouble. July 1. State unquestionably one in the oscillator circuit, will Please Sap That You Saw It in. RADio -CRAFT www.americanradiohistory.com 56 RADIO -CRAFT for JULY, 1938 FOUR NSW 1O' RADIO BOOKS!

FANS EVERYWHERE -these little ten cent text books give you an excellent foundation for the RADIOstudy of radio. They are clearly written, profusely illustrated and contain over 15,000 words in each book. You'll be amazed at the wealth of information these volumes have. They are handy for review or reference books. NO. 5- BEGINNERS' RADIO NO. 6 -HOW TO HAVE FUN WITH NO. 7 -HOW TO READ RADIO NO. 8 -RADIO FOR BEGINNERS bO NARY RADIO DIAGRAMS Hugo Gernsback, the internationally Are you puzzledIuzsle language' Can Stunts for parties. l,,racthwl Joker, seien All of the symbols commonly used in famous radiomagasines. pioneer. author and editor, you define frequent'? Kilocycle? Tetrode' title experiments and other amusements diagrams presented in this whose SHORT WAt grid? Baffle. If cannot define which cann be done with your radio t ok, together with pictures boradioof the TELEVISION and ItADm -CRAFT these radioy are explained in this fascinativol. apparatus they represent and explana I. millions, scores another triumph of ther, nmmore re technical, terms tells how to nuke newspaper lions giving an easy method memorize wreadith titis new book. I.eginner who used In all radio rmagazines and In- talk-how to produce silent mu lc for This reads it ill get a thorough ground atnactlon books, you need this book in dances-how to make visible music-how the 'ell radio w ertand Elbern,member work in radio theory. clearly explained W Make a Rent radió unit. usable by of mtyothe editorial staff of RADIO.CRAFT in simple language. and through the your library. It's as modern as to. deafened-how toys which also contains two dozen pic- use of y lilustrations. Analogies are morrow-right up to the minute. It tells dancevtop11 music-sixteen clever tumagasine,re wiring diagrams nd two dozen Oiled to make the mysteries of radio an you In simple language Just what the u ing stunts in all. Any of can schematic diagrams of ample radio sets also f ca is Instructions building words that puzzle you really mean. You done by the novice, and most that you build. Every diagram diagrams andnd ome,letely Iained in language sets. fully understand the articles you them require no more equipment thin hick reacannot what is ally understood by he radio be- If to "W owl howoirai,- d unless you know radio terms Irefound in he average home. End. lo tier, and receivers work, how rai mean. This is the look that explains the leas hours of added entertainment will Len interested In learning the derivation waves traverse space. and other intere, meanings to you afford to be be yours if you follow the Instructions of diagrams, and the many other inter- about this without It You one day longer? given in this lavishly Illustrated took. esting facts which this book contains. this is theet Ìcommunicaion, for Folle other volumes In this ten -cent radio book series -each on a popular subject- Other Titles In This 10c Book Series! are al reliable. The lilies are: No. I -HOW TO BUILD 4 DOERLE SHORT -WAVE SETS No. 3- ALTERNATING CURRENT FOR BEGINNERS No. 2 -HOW TO MAKE THE MOST POPULAR ALL -WAVE I- AND 2.TUBE RECEIVERS. No. 4 -ALL ABOUT AERIALS BOOKS ARE ALL UNIFORM RADIO PUBLICATIONS. Dept. RC -738 ICI HUDSON STREET. NEW YORK. N. Y. Every book In the GEItNSBACK EDUCATIONAL LIBRARY has pages -with illustrations tarring from 30 to 66 in number. Each tin, Gentlemen: )'lease send immediately. POSTPAID, the book numbers circled below. I am book bus' enclosing rents -each book being lite. tribune contains over 13.000 Lords. Positively radio's greatest If you do not think these (torts worth the Oflee asked, return them 1 2 3 4 6 7 8 hours and money will be instantly refunded. O Rend FREE listing of 48 new 10e publications. 24 your Name Address RADIO PUBLICATIONS City State Remit by check or money order -register letter If you send cash or unused U. S. poataga 101 Hudson Street New York, N. Y. stamps. ti MAIL COUPON TODAY! J L.Es Correspondence Courses In RADIO WITTIQUIZ RAD10,0ELECTRICAL ENGINEERING (Continued from page 35) g°d: ELECTRICAL ENGINEERING Ott Vet! epithet for the horse you bet on. (c) Used in vial field. Prepare yourself, at Low Coat. for seco fu- can eratana aickl conjunction with a jack to connect external ou RADIOOEÑBINEÉRlIiNG 1Ìcy debele. öñolo EieíKrdlen' wñr4. equipment or parts in a circuit. CONTEST RULES Trains you to be uper -servil n real vacuo tube A. WILSON technician. Eger kits furnished. Diploma on completion. Tuition. either course. Deferred payment den. Toronto, Ont., Can. (I) An award of a 1 -year subscription to school student to each person magazines.ecompee etcatalogs, 40 Radio -Craft will be given FR E who submits one or more WITTIQUIZZES 131-$. NEBO. ENOINEENINO SCHOOL, gas LINCOLN, that the Editors consider suitable for pub- (96) A Western Union joint is- lication in Radio -Craft. MARKS (a) The place where you go to send tele- (2) WITTIQUIZZES should preferably PATE NT S -TRADE grams. (b) A new and improved type of uni- All cases personal attention by be typed ; use only one side of paper. submitted given versal joint. 1c) The bad knee telegraph mes- members of the firm. (3) Submit as many WITTIQUIZZFS Form "Etddenee of Conception" and sengers get from riding their bicycles. Id) A efructions simple, approved method of joining the end+ as you care to -the more you submit the of winning each "How to Establish Yonr Riphti"-Free of two wires so as to be mechanically strong more chance you have -but LANCASTER. ALLWINE & ROMMEL and to preserve conductivity. should be good. PATENT LAW OFFICES (4) Each WITTIQUIZ must incorporate 436 Bowen Bldg. Washington, D. C. humorous elements, and must be based on (97) A Around wire is- some term used in radio, public address or (a) A conduit run under the ground. (b) A electronics. Each WITTIQUIZ may have 4 wire used to connect an electrical device to a "answers." only 1 of which of course will ground plate or water pipe. (e) A wire that is be correct; and, only 1 of which is non- MANY NEW RADIO BOOKS drawn rough, and ground down to correct size. radio. have been added to the ever - E. W. WITTE (5) All answers must be grouped. by popular RADIO -CRAFT LIBRARY question number and correct-answer letter, on a separate sheet of paper. to a shield SERIES. Please turn page 58 (98) Everyone knows that is- (6) All contributions become the prop- soldiers used to carry. read the announcement on all (a) Something Roman erty of Radio -Craft. No contributions can and keep tinkerers mice) (b) Something to (and be returned. the books in this series. away from vital radio parts. (c) A piece of - metal placed between 2 or more radio com- (7) This contest is not open to Radio ponents to prevent interference or coupling Craft employees or their relatives. between them. (8) The contest for a given month closes NEAL S. GI7tRISit on the 15th of the 3rd month preceding How wwW you like to save up to 50% on magazine -issue date. (For instance, contri- Nationally advertised Radios. such as Strom. on the berg Carlson Ph l o. RCA. Zenith. G E butions to Sept. 1938, Radio -Craft, etc etc lot home farm and auto. over newsstands about August 1, must be re- 403 models to choose horn Also hundreds of ANSWERS ceived at editorial offices not electric aipphance r for the home Wnte Radio-Craft today In the our í193n got catalog FREE. (85d) (06b) (87e) (Rod) (89e) later than June 15. 1938.) (90d) (91a) (92c) (93a) (94c) MODEIL'f Dept 57 Bretton St., N.Y.C. (95c) (96d) (97b) (98e) Please Say That You Saw It in RADIO -CRAFT www.americanradiohistory.com RADIO -CRAFT for JULY, 1938 57

TELEVISION WITHOUT SCANNING? (Continued from page 12) EVERYTHING IN RADIO the minority of people rather than the majority. amplifier" of our radio receiver for a distant If we extend this reasoning into engineering, we station. AT LOWEST PR /CES might then say. In a new science, there is the possibility that the majority of engineers are PROBLEM: THE "LIGHT AMPLIFIER" doing the wrong thing." It is readily apparent that this entire plan Let us therefore, join the minority and detach depends upon a successful light amplifier which ourselves and come out from under the influence will amplify the size and brilliancy of the picture 56 of popular theory and practice and take a new without distorting it. A cascade system of modern NEW channel of thought; let us dare to look at electron image tubes appears to answer this re- SETS El Dorado. Can we think of a television system quirement very nicely. without scanning? I can think of a rery good By reference to Fig. 3, we see a form of and very logical way in which television may be electron image tube; as described in a past issue accomplished with optical and electronic means of Radio -Craft, a sensitive photoelectric coating without scanning! is deposited upon one end like a camera plate When I first considered these possibilities, they film. The lens focuses an image of a performer upon photoelectric surface. Electrons leave were in the form of amusing thoughts, but as this Dealers! Service Men! Sound time has passed, I have been inclined to look at this surface in proportion to the strength of Men ! Amateurs! Set Build- these possibilities more and more seriously. I the light falling thereon, that is, many electrons ers! ALLI ED'S big. new Spring- and -Summer Cata- have been further stimulated to point out to leave from the points where there is consid- log hi ligo you everything the uninformed that television must not be erable light and no electrons leave from the black in Itudio --at sensationally counted as an addition to a radio set where parts of the where there is no light. lev prices! Over 12,000 picture parts; revolutionary n e w one will see the comparatively uninteresting These electrons are accelerated in straight lines P.A. Systems for every images of people reading script before a micro- through the rings charged to a positive poten- purpose -10 to 80 watts portable mobile, perma-- phone in a broadcasting station, but rather an tial in front of the photoelectric coating which nent; all types of latest entirely new and separate service. It will be is charged negatively. Since these electrons travel test equipment : new tms- unimportant to the user of television how the through the opening like light through a pinhole tour Gear; Kits; books. tools. etc. -and 56 new, pictures get onto the screen in his home. He camera, or through a lens, they are focused upon supervalue KNIGHT Radios will be satisfied to have it arrive via wire, radio, the fluorescent screen at the other end of the with Push- Button Timing, etc.. at amazing low prices. Radio men everywhere say: or pipe as long as it is clear and not too tube where we obtain a reproduction of the ALLIED'S catalog saves you time and money!" Send expensive nor cumbersome. image focused upon the photoelectric material coupon now for Spring- and -Summer Issue -it's FREE! Therefore, let us look into a system which is at the other end. FREE! RADIO BUILDER LISTS extremely simple in principle, comparatively Since the brilliancy of the image is propor- We supply Free Parts Lists of inexpensive, and much higher in fidelity than tional to the potentials applied between the matched kits for building any dr- suit described in this or any other the present scanning type of television. cathode and rings as well as the number of elec- magazine. Just specify where seen. trons released, it is only necessary to apply A "SCANNER-LESS" SYSTEM OF higher potentials to increase the brilliancy up to TELEVISION certain limits. Therefore, a feeble image -small, and dimly illuminated on the photoelectric end Let us assume that we go to the top of a - a large becomes a strong, bright image on the fluorescent ALLIED RADIO CORP. tower in the center of a city and set up end of the tube. This image is comparatively un- 833 Jackson Blvd. with wide- Chicago, Ill. DepL2 -G -38 modern motion picture projector a distorted and is limited in quality only by the angle projection lens. Further assume that we Bend me your new Spring- and -Summer cata- texture of the photoelectric deposit and the log -FREE may use a powerful source of infra -red radia- fluorescent screen. tion rather than an arc light on cloudy or rainy If, after one stage of amplification through a Name days for illuminating the film. We project the tube of this kind, the image is still too small image directly out into space from the projector and too weak in brilliancy, we can add another an though screen were ; while at just a present we do a. or am- objective lens. tube just like in radio receiver MIMI NMI WEE MIMI the same time using no screen or plifier when the sound is too weak. We then place Again assume we use several of these that the photoelectric material in one tube right up projectors and point them in all different direc- next to the fluorescent screen of the other and tions so that we cover a complete circle. Let us amplify the picture brilliancy. We can repeal imagine that such a tower will look like the this operation again and again just as we add one artist's conception shown in Fig. A. tube after another in radio practice until we If these projectors were set into operation and reach the limit of amplification. anyone went to the roof of his house and looked through a pair of binoculars, he would see a clear A complete illustration of a machine for pick- and distinct view of the motion pictures just as ing up this extremely weak image and project- though a screen were present. If he used a large ing it upon a screen in your living room is spyglass or telescope, he might actually project shown in Fig. B. Such a device only requires a a very small picture on a screen from the eye source of voltage from a rectifier, and negligible piece. The image becomes dimmer and smaller as power as compared with a radio receiver; and one moves farther away from the original pro- there is nothing about the light amplifier tube to jector, and finally, becomes invisible. If a man wear out for many years There is no scanning; constructed a periscope in combination with his there are no controls for synchronizing or tun- telescope, he could then stay inside of the house ing; there is only the necessity for one control without going to the roof and see the motion and this is a mechanical iris like the diaphragm on a camera which can be automatic or manual Tiny, pictures. This might be called a form of "peep - but... hole" television. The optics of such a system like the volume control on your radio receiver. are shown in Fig. 1. Like all telescopic images, There is no electrical interference, and briefly, no * It's a genuine hermetically -sealed metal - they would be small and lack brilliancy. fuss and commotion. can electrolytic with insulating jacket. We can see at a glance that all we need is We are so seriously interested in the pos- the counterpart in optics of the amplifying radio sibilities of this equipment that we are giving 4, 8, 12, 16, 24, 30 and 40 mfd. 150, tube and loudspeaker in radio broadcasting sys- it considerable attention in our laboratory. We 250, 350 and 450 v. d.c. working. tema. See Fig. 2. If we can amplify the bril- have every reason to believe that other labora- liancy of the light and project a small picture tories actively engaged in television development Insulating jacket edges spun over can same thing. * received upon a large screen. we have a rather are doing the ends. Leads can't short on can. Red and satisfactory television system without much fuss black end disks indicate polarity. Pro- is ANSWERING QUESTIONS and commotion, providing the light amplifier vided with vents. not too complicated. Certainly the cost of the There is one point that I am sure you are the projector in the wondering about, which I almost neglected to periscope, the tubing and Logical choice where space- and cost - tower is insignificant compared to a television explain. The natural question at this moment is. * transmitter and receiver. If the light amplifier "How could we pick up sporting events or any saving are absolutely necessary. is cheap, then the whole system is cheap. action and transmit them immediately with- Furthermore, the definition of the picture is out reducing the action upon film first for pro- Ask Your .lobber . . . as good as that of the motion picture and there jection through the tower lantern?" The answer is nothing left to be desired with the exception is best illustrated by saying. "How do you pick show you these latest space -saving elee- of overcoming the obstacles of dust, smoke and up a signal from a speaker's voice in a micro- *He'lltrolytles. Ask for literature -from him or from fog which would obscure the picture if one is phone and build it up to a large enough energy us direct. very far away from the projector. If, however. to broadcast it everywhere from a powerful the light amplifier could work on long, infra -red radio station?" The answer to this is, "We am- rays -which pass easily through smoke and fog plify it." Obviously then, we use the same kind -and convert this infra -red radiation into visible of amplifying projectors to pick up the original radiation directly just like a radio receiver con- event. We amplify the light and we project it. verts highfrequency carrier signals into audible Certainly, we use bigger tubes and bigger peri- voice signals, then we could see the images at scopes and telescopes, but we can pick up any all times of day or night regardless of weather action and rebroadcast it. We use infra -red rays CORPORATION conditions by just raising the "gain" (amplifica- or light as a carrier. 70 'Nn.hm: pan St. Brooklyn, H. Y. tion) on our "light amplifier" just as, similarly, Now you may say, "This system is limited by we Increase the volume control on the "audio (Continued on following page) Please Say That You Saw It in RADIO -CRAFT www.americanradiohistory.com 58 RADIO -CRAFT for JULY, 1938 TELEVISION WITHOUT SCANNING? (Continued from preceding page) the horizon. Any building will shadow reception and we shall have to extend our periscopes up high enough to see over them." To this, my answer is, "These same limitations apply to ultra -shortwave television using scanning. If one objects to the tubing on our periscopes. how about the coaxial cable for ultra -shortwave television? The tubing for the periscope is actually cheaper and easier to install and service." If one says, "How about the lens on the roof 1" We answer. "It is cheaper than the dipole antenna required for good television reception." Then if one asks. "How about the light amplifier tubes?" We can say. "They should certainly be less expensive than a modern television receiver." CONCLUSION In conclusion, even though the modern scanning television system be highly practical and useful, we have herein another way of doing the same thing in an equally effective manner by using electronic and optical means, and it is HEW Jíttes awaseI&m tle further possible that we may come to have two great entertainment utilities tomorrow instead of one, just as we have gas and electric companies now giving the same general kind of service in C a different way. We may have the radio system RADIO R A f TIIBIARYSEA'/ES for certain locations where periscopes will not be so easily installed, and we may have peri- PRESENTED on this page are all the books in the RADIO -CRAFT LIBRARY SERIES- scopes where the radio systems may not be so the most complete and authentic set of volumes treating individually important divisions of radio, easily used. In fact, we may hear the announcers refrigeration and air conditioning. Each Look has been written for the purpose of giving you the of tomorrow saying, "This is John Brown of the to specialize opportunity in one or more of the popular branches of the subjects mentioned. The All at Once Company signing off," or, "This is material in these books is very helpful . you'll find them valuable in your work. The authors of these books are well- known-they are authorities on the subjects on which they Jones of the Spot -by -Spot network." bave written. This is the first time that you are enabled to build a library of uniform technical books Are we serious? Do we expect to announce by such popular writers. such a thing in the near future and make a demonstration of it? Time will tell, and I am Here Are the Titles willing to wager that upan reading this article. Book No. 2 Book No. 12 Book No. 17 several Eastern Laboratories I am thinking MODERN VACUUM TUBES PUBLIC ADDRESS INSTAL- SERVICING WITH SET about will put on ,;a.ed to beat us to it. And How They Work LATION AND SERVICE ANALYZERS with Complete Technical Data Modern Methods of Servicing and A Study of the Theory and on All Standard and Many Spe- Installing Public Address Proper Applications of Modern cial Tubes Equipment Set Analyzers and Associated SERVICE MEN!- REPAIR YOUR By ROBERT HERTZBERG By JOSEPH T. BERNSLEY Apparatus By H. G. McENTEE CUSTOMERS' SETS Book No. 18 Book No. 3 THE SUPERHETERODYNE ABC OF AIR CONDITIONING Book No. 18 "BETTER THAN NEW "! BOOK An Accurate Simplified, Techni- POINT -TO -POINT (Continued from page 17) cal Review of the Fundamentals RESISTANCE ANALYSIS All About Superheterodynes of This Latest Branch of Engin- back a chassis that tunes -in notes on resonance, How They Work. How to Build eering. Including Servicing Data Theory - And Application of and highfrequency on the sidebands, give him and How to Service Them This Modern Test Procedure in on Present-day Units the whole musical scale at once, that is what you By CLYDE FITCH By PAUL D. HARRIGAN Every-day Radio Service Problems are being paid for. If the customer wants a radio set Book No. 6 Book No. 14 By BERTRAM M. FREED for distance work, sell him a professional communications job. BRINGING ELECTRIC SETS POCKET RADIO GUIDE UP -TO -DATE Book No. 20 When spreading the I.F. curves you will proba- Handy Reference Book for Ra- bly lose some but dio Men Construction THE CATHODE -RAY gain, this decrease of sensi- Wibh Pentodes, Multi -Mus, Dy- -Set Ar- is more namic Speakers- Complete In- ticles -Audio Amplifier Circuits OSCILLOSCOPE tivity than offset by the improved tone formation on How to Modernize -Useful Radio Formulas and Theory and Practical quality of the set. Remember, the primary A.C., D.C., and Battery- Data -Handy Short Cuts -Index Applications purpose of an oscilloscope in service work is to Operated Receivers to Important Articles Printed By CHARLES SICURANZA give you a visual indication of the selectivity By CLIFFORD E. DENTON in Radio -Craft Magazine of the radio set under teat. Just the By N. H. LESSEM peaking Book No. 21 I.F. stages for maximum gain can be done just Book No. 9 BREAKING INTO RADIO as efficiently with an ordinary output meter. Book No. 15 SERVICING AUTOMOBILE RADIO AND ABC OF REFRIGERATION Next we adjust the wavetrap for minimum SERVICING Simple Instructions and Pro- peak. and then align the R.F. and oscillator A Compendium of the Principles A Complete Treatise on Sub- cedure for Starting a Profitable circuits. If necessary, bend the oscillator con- the of Refrigerating for Service Men Radio Business of Your Own ject Covering All Phases from with a Detailed Listing of De- denser plates to insure proper tracking of the Installing to Servicing and By ROBERT EICHBERG fects and How to Overcome pointer to the dial calibration ; once again ft Maintenance will be By LOUIS MARTIN Them, with Hints on Setting Up probably necessary to sacrifice some a Service Shop ALL BOOKS UNIFORM sensitivity in order to keep the dial pointer on By TRAFTON MASON calibration -frequency Book No. lo The books in the RADIO - at the low portion of the dial, but it will please the customer to know that HOME RECORDING AND Book No. 16 CRAFT LIBRARY SERIES . he can now tune stations where ALL ABOUT are all uniform size -in exactly the IT PRACTICAL RADIO CIRCUITS 6 x 9 inches. Each volume newspapers say they are. Now take an overall A Complete Treatise on Instan- A Comprehensive Guide to All contains an average of 60 selectivity check of the chassis by supplying a taneous Recordings, Microphones. Types of Radio Circuits for the to 150 illustrations. The 1,400 signal to the antenna Recorders, Amplifiers. Commer- Service Man. Constructor and books are printed on an ex- kc. terminal, and cial Machines, Servicing. etc. Experimenter cellent grade of book paper. make any slight adjustments necessary to th By GEORGE J. SALIBA By DAVID BELLARE I.F. trimmers to give a nicely balanced wave form. RADCRAFT PUBLICATIONS, INC. 99 HUDSON ST. NEW YORK, N.Y Now the job is practically finished, connect the oscilloscope to the voice coil of the speaker, and CLIP COUPON - AND MAIL TODAY! supply a 400 -cycle audio note to the output of 'u the 2nd -detector, check the resultant image for essentially pure waveform at moderate volume; RADCRAFT PUBLICATIONS, INC., Dept. R6-738, 99 Hudson St., New York, N. Y. if bad distortion is noticed, check the audio re- I bave circled below the numbers of books in the RADIO -CRAFT LIBRARY SERIES, which sistors. coupling, and bypass condensers and you are to send me POSTAGE PREPAID. My remittance of $ is enclosed at the cost of fifty cents for each book. transformers until the faulty part is located. Shut The amount of my remittance is (Stamps, checks or money orders accepted.) off the oscilloscope and run the audio generator Circle numbers wanted: 2 3 6 9 10 12 13 14 15 16 17 18 20 21 through its entire range to check the speaker for cone rattles. Now connect the radio receiver Name Address to an antenna equivalent to the one used by the customer and let the set run for a half - City State hour on a local station as a check on fading. Send remittance by check, stamps or money order; register letter if you send cash or stamps while you prepare the next chassis for the L a oscilloscope. Please Say That You Saw It in RADIO -CRAFT

www.americanradiohistory.com RADIO -CRAFT for JULY, 1938 59 AMERICA'S RADIO COLOSSUS (Continued from page 13)

Its stockholdings in the Canadian Marconi Com- White and the Seven Dwarfs," you have seen pany were sold for $1,725,000 in cash. The profit one of the more important pictures which are from this transaction will be credited in this completely RCA -equipped (so far as sound is year's account to Earned Surplus. concerned). Of the company's total assets approximately Other products include transmitting appara- 94 per cent is now represented by investments in tus for broadcasting stations, sound systems for and the United States, only 6 per cent remaining in schools and auditoriums, aircraft airport I.' you evilfa other countries. These latter investments, nearly radio equipment, police radio systems, equipment master Jthe whole scence Radio. Elec. all of which are wholly-owned subsidiaries, are for amateur use, and tubes of all kinds and trii( and Television -'IV largely confined to South and Central America. for all purposes. reading G iiirardl's Diohome -study RA. This does not mean that they are withdrawing PHYSICS rotlass:. foreign they have patent li- its many exclusive fea- from the field, for RESEARCH tures cense and engineering service agreements with to-understand l lemas, All these products are the fruit of research account for us I'S leading companies in the principal foreign coun- more radio schools a tries, resulting in payment to it of substantial which is constantly going on in their elabor- students than any other most im- radio honk In theworld. royalty and servire fees. The RCA Manufacturing ately- equipped laboratories. The two portant products of ,odio research new in ad- HERE'S WHAT Company also does an extensive export busi- Only YOU GET: ness in many parts of the world with radio re- vanced stages are Television and Facsimile. 1 Sound-Electrical ctric,; ceiving sets, tubes, broadcast transmitters, Various broadcasting stations have already Currents Electro- magnelistm - Transformers-1. dueiance-- Condensers- Mennuring Instruments- sound motion picture equipment and related commenced experimental transmission by fac- Rad Meet lvltY -Broadcasting - Receiving - yacuu,;, Tul,e,. --Amyl If icatlon- sutmrheta -Cu r lw- Speakers -- products. simile of news bulletins and pictorial material Receivers f all types-Short-Wave-Auto-Radio- to a limited number of receivers in their local Aircraft Radio-Public Address-Photoelartrle Cell- Among its liabilities is $10,400,000 of notes -cathode-Ray Tubes -Te le v Islon- TestIng aml of this areas. The fundamental technical problems of Motion payable to banks. Ten million dollars ids-5500 Review fo eu.studVe -o;.l amount was borrowed from banks in 1986 to facsimile have been solved and RCA is now DOZENS of otter subjects! 7r,3. building facsimile transmitters and several hun- TRY RI finance the retirement of the company's tanrardl'a I Big Rook will get you started i "A" Preferred stock. Twenty -four million dol- dred receivers which have been ordered by inde- Radio l/leklyy, imply. easily! Cral, this n ,r broadcasting stations. 501005 bargain now-order your copy this eas lars of this amount was paid off in notes to pendent sou writew our to address this ad- ,end it In with $4 today $4.50 forci Eve, banks, reducing the remaining liability to While the technical and economic problems d of rret, $8,000,000 and saving thereby $56,000 a year of television are far more complicated, definite o°Obligation. write at ofee!ic°. RADIO J TECHNICAL PUBLISHING CO. in interest chargea. progress is being made toward their solution. 45 Astor Place, New York Dept. RC7$ Television pictures are larger, sharper and more brilliant than a year ago due to marked im- TAXES provements in both transmitting and receiving This huge corporation does not thrive with- apparatus. The industry must now decide upon TO LEARN RABID! out paying for its business privileges; and it the acceptance of definite technical standards pays well. RCA last year paid in taxes a total before any public television service can be made of $4.297,500. The total of all taxes for the practicable, year 1987 equalled 42 cents a share on the stock of the company -almost exactly Common COMMUNICATIONS Your Service Work the figure earned on these shares. The govern- with GADGETS ment received more than twice the amount in The direct contact which RCA Communica- GHIRARDI'S taxes that the stockholders of Common stock tions facilities afford with 43 foreign countries Ill flash Shootenspot received dividends for the year. The radio is an important factor in our international re- over ROO different set tFa- from la l eds -Ey. et TESTS industry is not a large tax -payer but has lationships. In time of war these facilities would EDyES. only HOMEME d AUTO aloe. a- become a substantial member of the American be indispensable as an important arm of our Trial. Circular-no peace they are obllQ write RADIO Ss business community employing many thousands national defense and in times of TECHNICALi! PURL. CO.. k of worker. and bears its huge share of civic of vital importance in helping to guarantee not Astor Pl, t -5. and social responsibility. only the unhampered communication between our government and foreign countries but aise to keep these same avenues of communication MANUFACTURING open for our newspapers, financial institutions, At the present time the company is operating business enterprises and our people in general. at a profit in all of its divisions. The steep de- Further, the daily short -wave programs of the cline during recent months of the nation's National Broadcasting Companies to foreign volume of business and profits has affected its countries, operating continuously 1$ hours e income and profit figures. Nevertheless it is day. broadcast in 6 different languages, serve estimated that the net profit for the first -quarter as an ambassador of good -will every day in of this year will be more than adequate to the year. Through both its national and inter- cover the Preferred dividend requirements, leav- national services day by day assistance is ren- ing a small balance applicable to the Common dered to many branches of the government in- stock. cluding the Departments of State, War, Navy, Its manufacturing divisions have developed Interior, Commerce and Agriculture. These and a widely diversified line of modern facts, however, tell only a small part of the Use "Ri- paasit for produced quiet radio reception. products. Radio receiving sets, although an im- story of how this tremendous radio organiza- Interference from elec- portant item, are only a partial source of its tion serves the "public interest, convenience and tric shavers, sewing sales. Records, phonographs, combinations, and necessity." machines, refrigerators. ti record players represent an important and Radio is the greatest gift of education, cul- and countless electrical appliances is stopped by profitable line which has grown rapidly in re- ture and entertainment ever presented to more to reproducing im- Bi- pasait, the bakelite cent years due recording and than 100,000,000 people. Radio has broken down Filternoys suppressor provements based on radio inventions. age -long barriers of distance and isolation and made by CONTINEN- RCA Photophone equipment for motion pic- to this tremendous radio organization, the TAL CARBON. Inc. For ture studios and theatres is now strongly en- Radio Corporation of America, rightfully goes use on grounded a -e cir- trenched in this field. If you have seen "Snow a huge share of the credit. cuits. Code F18. each 35e F Quiet severe interference with Filternoys FO1DH, dual choke, triple capacity filter "WHEN YOU CAN MEASURE" with the ground lead that radio interference to this General Electric has just sensitive, accurate measuring devices engineers diverts Under title Co. the earth. Recommended for released a 32 -page brochure which radio men may have perfected. washing machines, h a i r obtain upon application on their business letter- Since measurement, in its final form, depends driers, dental motors, food head. upon comparison with some carefully- chosen mixers. electric shavers, cash Telling in brief the contributions of G.E. en- standard, a section of the booklet is given over registers, etc. Five ampere gineers and scientists to the important art of to a description of the Company's standards of current carrying capacity l Measurement, this attractive, beautifully- printed Voltage, Resistance, Time and Temperature. For any a -c or t1 -c power publication describes in pictures and words the mains up to 120 volts. Enjoy story of how instruments are designed, construct- radio at its best, without ed and tested by this group. interference. Code FOIDH, "CONTINUOUS -FILM each $1.00 Code FOIDH Every development in electricity has grown out of experiments in which instruments played a TELEVISION" major part. The incandescent lamp, the electric Under this title readers of August Radio - 11-CO1v7rXE11lTAL CARBON lncl motor, electric household appliances, radio sets ('raft (newsstand, July 1) will find a descrip- and apparatus of all kinds -none of these com- tion of P. T. Farnsworth's latest contribution 13914 LORAIN AVE., Cleveland, Ohio would have been pos- Also, Toronto. Canada monplaces of modern living to the art of television. Makers of Carbon Resistor, Paper Condensers, and sible without the imposing array of ingenious, Noise Suppression Filters Please Say That You Saw It in RADIO -CRAFT www.americanradiohistory.com 60 RADIO -CRAFT for JU LY. 1938 MAN STILL CHAMPION OF THE AIR A FREE BOOK Dr. Irving Langmuir Explodes the Story of the Fly that It Faster than Sound FOR EVERYONE IN RADIO DIGRESSING for the moment from the usual types of scientific investigations which ordi- RADIO- CRAFT -complete in everything radio men need, narily occupy his time, an industrial research gained popularity and leadership in a few years. scientist has exploded -with proofs aplenty in Never once has RADIO -CRAFT shortened its stride of different ways-a fantastic yarn about an insect editorial progress. Broader in news scope -excellence in that flies so fast it before you hear illustrations- continued improvement in editorial tech- arrives it nique-accuracy in wiring diagrams and schematics - leave -a fly with a speed of 818 miles an hour these are the basic ideals upon which RADIO-CRAFT (sound travels only 740 miles an hour). success has been achieved. The scientist is Dr. Irving Langmuir, as- The publishers of RADIO -CRAFT make you a sociate director of General Electric's research very liberal offer -they want you to read every laboratory and Nobel prize winner; the fly whose monthly issue -they want you to get the bene- reputation he has smashed is the deer bot -fly, fits as do thousands of other readers -they which repeatedly in recent years -and more and have arranged a special oiler with an attractive premium -and they have made a more as time has progressed-has been held up special price for you. as something which has far outstripped man's To readers of this announce- puny efforts to become flight -speed champion of ment the SPECIAL OFFER the living world. Man's planes hurl themselves IS . A SEVEN MONTHS' SUBSCRIPTION through the heavens at a mere rate of hardly TO RADIO -CRAFT and more than 400 m.p.h. a FREE COPY of the 1938 RADIO REFER- Particularly in recent months have there been ENCE ANNUAL. If you cartoons and news items referring to the speedy are a regular subscriber deer bot -fly or again simply to the deer flu. at the present time. you Now Dr. Langmuir, writing the March 11 may take advantage Of in this opportunity lust issue of Science, has shown: the same. The publishers will be glad I1) The non -streamlined -and really flat-head- to extend your pres- ed -fly at ouch a speed would encounter a ent subscription an additional Seven Months, wind pressure against the head of about S and at the same time. send pounds- per-square -inch, probably enough to crush you a FREE copy of this new book. the fly. R= pd2v2f is his proof. Use the coupon below for entering (2) Power consumption for maintaining a your subscription to RADIO -CRAFT. velocity of 819 miles -per -hour would be about (t9 INCHES Here le the Oontente of the one -half horsepower which, for a fly, would be a 1938 RADIO REFERENCE ANNUAL good deal. (3) If the fly equals man in efficiency -and it SETYILDINOarThis design and construction on P. A. Tuner: section of the ID3S RA- Handy Amplifier: and an Infinite Baffle doesn't seem as though the fly can be more DIO REFERENCE ANNUAL contains a desert, Loud Speaker. ef- than of a number of important. as well ficient than man who himself has a high thermo- interesting receivers. They are as Á TEST Egli Simplified Converter: A Farm Re Radio Service Men who prefer to build dynamic efficiency -the fly must consume 1.6 Iver: An Executive's A.C. -D.C. Desk Set; their own equipment will find 11 the con- Handy Book -End Novel Receiver. Other traction details necessary for building the times his own weight of food each second to hera described a Crystal Set, Portable following: Condenser Analyser. Midget deliver the 370 watts, Receiver, d several then. Fach Oscilloscope with 1- and 2' tubes; Service or nearly half- horsepower receiver is described ccu taffyy complete Audio Oscillator. of energy, such speed requires. wiWeeth constructional data and Its'[ required. of parts (4) A piece of solder of roughly the dimen- A variety of topics havelCl een selected for a[RVICINo their Interest and Importance. These sub- sions of the fly can be seen only as a blur if, in This chapter ie devoted to Radio service to cover-Home Broadcaster; Remote Set Instrument. in general. Special emphasis is T ingvCarrier -TOype Interphone Systems a brightly -lighted, white-ceilinged room it is at- given to number of the more essential In. and number of others. -they : Service a Oscillators. tached to a silk thread and swung so that its Strumentsliver Circuit., V.T. Voltmeters and an In- MIaC[LLAN[OY! speed is terference Flim inator, A comprehensive Index of important ar- 13 miles- per -hour; that at 26 miles -per- PUaLICthose ticles wic appeared In RADIO -CRAFT du,, hour it is barely visible; that at 43 miles -per- For who ing 1037. This section also includes data find public address their on recently developed tubes and many other hour it appears only as a faint line and that chief I:.h test. here you will find complete hints and suggestion'. its direction of flight cannot be told; and that 64 pages :: Over 90 Illustrations at 64 miles -per -hour the solder "fly" ie invisible. (The higher speed attributed to the fly was based on a published report of an entomologist that he had seen the insects fly past him so fast they could be seen only as a blur, and that he RADIO -CRAFT estimated their speed as 400 yards a second, or 818 miles-per -hour.) 99 Hudson Street, (5) Laboratory light intensity measurements and calculations also prove that an object the NEW YORK, N. Y. size of the deer fly is invisible at speeds of 64 miles-per -hour and above. (6) A fly striking a person at such a speed 7 would exert a force of 310 pounds, or about 4 tons-per-square-inch, and would penetrate deeply RADIO -CRAP i . 99 Hudson Street, New York. N. Y. RC-738 into human flesh -and the first such instance is Gentlemen: i. r 1 you will find y remittance of One Dollar 1E1.00) for which enter my subscription to yet to be reported; and finally- RADIO -CRAFT )i...:.v.ine for Ses en Months. Send me. ABSOLUTELY FREE, and POSTPAID, my copy of tue 1938 RADIO REFERENCE ANNEAL. (7) Dr. Langmuir concludes a speed of 25 miles -per -hour is a reasonable one for the deer New Subscriber Extend present subscription fly, while 800 miles- per -hour is utterly impossible. Aviators, then, do not have to hang their heads Name Address in shame because they can hardly surpass 400 miles- per -hour with today's airplanes. Nor will City State they ever have to move over in their courses (Send remittance by check or money order. Register letter If you send cash or unused U. 8. l'mtage Stamps ) to give the right -of -way to deer fly speedsters. J Incidentally. Dr. Langmuir is a licensed air- CLASSIFIED ADVERTISEMENTS plane pilot. In September, 1936, in the Journal To Readers of RADIO -CRAFT of the Aeronautical Sciences, he also digressed Advertisements in this section are inserted at the from such subjects as monomolecular layers, dis- cut of fifteen cents per word for each insertion FREE POSTCARDS MAY BE HAD UPON - sociation, and such G -E research laboratory sub- name. Initials and address each count as one word. WRITING TO THE PUBLISHERS Cash should accompany all classified adveruse- jects to tell, in an article cosigned with Alexan- by ments unless placed a recognized advertising These post cards make it easy to answer der Forbes of the Harvard Medical School, about agency. Not lesa than ten words are accepted. advertisements which appear Advertising for the August. 1938, issue should he in RADIO - "Airplane Tracks in the Surface of Stratus received not later than Tuesday, June 7, 1938. CRAFT, without cutting valuable data which you may wish to save. Clouds." In Many times that article he told how he had closely manufacturers request you observed such clouds, had RADIO to "clip the coupon" when answering their cut through them with ads. Often this means destroying part of his airplane, and had swung around and exam- YOU RADIO MEN WHO WANT TO READ RADIO'S an article on the reverse page you may need ined the clouds and the changes wrought by the Lives[ Magazine every month and learn about every new later for reference. your - development which takes place -In servicing, in new Save RADIO whirling propellers and the cuttings of the tubes. In foreign developments. In facsimile, in tele- CRAFT issues complete. If you should ever wings. He had photographs of his observation,. vision, in test equipment. read the announcement which want to sell bound volumes, or certain Still other instances of non- molecular reports appears above on this page. Learn how you can subscribe copies of RADIO-CRAFT, the resale value of be mentioned. to RADIO-CRAFT anti get an Invaluable free premium. of uncut issues is very much higher than this scientist could For instance, in Science for February 11, 193s, Dr. Langmuir SONG POEMS WANTED that of mutilated ones. So send for a supply of these free poet cards and use them in wrote on "Surface Motion of Water Induced by WANTED ORIGINAL POEMS, SONGS. FOR IMME - answering all RADIO -CRAFT advertisers. Wind," basing his report on observations made diste consideration. Send poems to Colonial Music Pub - Ushers, Ltd., Dept. 1'69, Toronto, Canada. from a trans- Atlantic liner! Please Say That You Saw It in RADIO -CRAFT

www.americanradiohistory.com RADIO-CRAFT f o r JULY, 1 9 3 8 61 LOOKING AHEAD TO TELEVISION OCCUPATIONS Modern science and invention constantly are creating new occupational opportunities in a rapidly moving world. In the accompanying article a prominent New York City consulting industrial engineer gives a fascinating overview of what may be expected occupationally with the coming development of television. The LOOK ALL YOU LIKE information is most valuable to counselors of youth who might well heed the warning to proceed with caution! COMPARE ALL YOU LIKE there is no tube tester value on the market like the NEW DR. ALFRED N. GOLDSMITH 111111111111111111111! IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII1111111111111111111 ASTUDY of occupational possibilities in the capable of doing research, development, and de- DYNOPTIMUM TEST field of television before that interesting sign work in that complicated field. These men Dependable Checker Tube s 95 art has made its commercial début is pos- must be technically trained and well -qualified Model 30 7 sibly premature and certainly hazardous. It along conventional radio lines in order to meet ... and all it costs is 1ô savors slightly of planning the Panama Canal the more difficult problems of television. These All these features in one low- priced In- shortly before the discovery of America. At best, radio engineers are, in fact, electrical engineers strument! any vocational analysis of the television of the with specialized training in the particular field Testa all types of tubes Including 024 and future must be read with several provisos in of communications. In the factory there are also other cold cathode reetaiers. Tests all who ballast tubes. 111gh sensitivity neon shen mind. needed tube engineers will handle the similar and leakage test for each Individual element In the first place, a normal engineering de- problems of vacuum -tube and cathode- ray -tube Latest improved circuit test tubes at II\Lt velopment of television is assumed. That is, it production which are an integral of the specified voltages and loads as approved by part all tube manufacturen. Individual trot. is taken for granted that technical knowledge television transmitters and receivers. Some of of each section of full wave rectifier, do of television will increase apace, enabling the these men may be university-trained physicists diodes and all multi- purpose tubes. square D'Arsonval meter. accurate practical solution of the remaining engineering who are prepared to enter the equally complex 2%; direct reading. multi- colored dial. problems of television within a reasonable time. but more commercial fields of tube research and Accurate line voltage Indication and conu,d If any apparently insuperable obstacles should design. The usual factory personnel will be re- Simplest to operate; unsurpassed work prevent the engineers from designing equipment quired for television equipment construction, in- manshipr altraetlse design. Alert available In combination meeting the reasonable needs and desires of the cluding test men, supervisors, production and counter-portable model $18.95 future television equipment purchasers, this manufacturing engineers, and the like. See your Jobber. Write to Dept. C for estalos. might upset all calculations. We are all familiar The qualifications here are similar to those for with arta where normal progress has been positions of the same type in other fields except retarded by dangers or limitations which the that the manufacturing and test problems are engineers have not as yet been able to overcome. probably more difficult and more rapidly chang- RADIO CITY CO. There is a slight but nevertheless existent chance ing than in most other fields, thus demanding that such obstacles might put off the commercial a flexible, responsive. and original mind as well 85 PARK PLACE I 1 r I NEW YORK CITY advent and general acceptance of television for as great native energy and determination. some time. In the second place, a normal economic de- TRANSMITTING STATION JOBS velopment of television must be regarded as Once the television transmitter has been built probable in any analysis of its occupational pos- and shipped. it must be installed in the tele- sibilities. Television transmitting and receiving vision transmitting station and thereafter main- equipment is elaborate and relatively costly. tained. At this point, an entirely new series of BE SURE TO READ Television program construction will be more openings will exist. Television station engineers complex and expensive than radio program con- will include fieldeurvey engineers who will de- struction of today. The television art is a com- termine the best location for the station and it, paratively luxurious one. Manifestly, such an art antenna system and who will study the strength can hardly be introduced rapidly on a large and acceptability of the signals throughout the THE scale in times of marked economic depression service range of the station. These men will alao nor can it be expected to win public favor under furnish the data which will satisfy the govern- such circumstances. mental authorities that the station is covering its The television programs will be paid for, under territory with an adequate service in the physi- our present system of broadcasting operation, by cal sense. The equipment must be maintained advertising sponsors in the main. The sponsors in good condition at all times, and emergencies will in this way purchase a portion of the pur- must be met, and this is the job of the main- chasing power and general good will of the look- tenance staff of the station. Men of great re- ANNOUNCEMENT ing and listening public. But the size of the liability and prompt resourcefulness are required audience, its purchasing power, and its mood for this type of work. will all influence the extent to which the adver- The television- station studios will require a tiser can justifiably support television broadcast- staff of their own of considerable size and of ing. Accordingly, there is an action and reaction wide diversity of tasks. Considering the technical WHICH APPEARS ON between economic conditions and television suc- men only for the moment, there will be lighting cess. If times are bad. the programs must be experts who will arrange and control the power- restricted which, in turn. affects the public re- ful illumination which floods the sets (scenery) sponse that justifies the broadcasting of the pro- in the studio, and the actors. These men must be grams. Only in reasonably good times can this skilled electricians capable of handling, shifting. PAGE 4 circle of effects be broken advantageously. Ac- and controlling illumination in any desired cordingly, those contemplating television as a fashion. There will be the microphone or sound career will watch closely for times of general men in the studio who will place and control the economic recovery since it is in such times that microphone supports or booms which hold the arts like television can be expected to flourish microphone close enough to the actors to pick up OF THIS ISSUE and to afford opportunities for a multitude of speech or music, while still keeping the micro- new workers. phone outside of the view of the camera. Here Assuming that television comes into its own men with steady hands, quick responses, and a in the next 5 or 10 years, probably the best way cool way of working effectively will be required to outline the various occupational opportunities (particularly in the stress of high -speed opera- which it will offer, and the requirements of each tions during the studio performance). In the position, will be to describe the activities of the control rooms of the studio, there will be sound - You need our 1938 Catalog field in some detail (with the various prospective control men and picture- control men who will openings italicized). handle respectively the quality of the sound and It illustrates and describes our cony!, r, the picture which is being transmitted. These un of OPPORTUNITIES IN MANUFACTURING men will be technically trained, probably as RACKS PANELS CABINETS Let us start at the factory where the neces- junior engineers, and they must have quick re- FOR ALL RADIO AND O.A. NEEDS sary equipment for television transmission and sponses, good judgment, and manual skill in Write for your Free Copy Today! reception originates. getting the picture and sound results which will Visit Our Exhibit at the RADIO SHOW - Here are needed apparatus engineers who are best please the audience. Booth No. 204 Bell Street at Stevens Hotel, Sometimes, the television transmissions will Chicago, June 8th, 9th, 10th and I lth. Reprinted from Occupations, the Vocational be from sound- motion- picture film which has Guidance Magazine for April, 1938. (Copyright been previously made. For example, a film news- PAR -METAL PRODUCTS CORP. 1938.) Published by the National Occupational reel may be transmitted. This requires that there 3527 41st St.. Long Island City, N. Y. Conference, New York City. (Continued on following page) Please Say That You Saw It in RADIO -CRAFT www.americanradiohistory.com 62 RADIO -CRAFT for JULY, 1938 LOOKING AHEAD TO TELEVISION OCCUPATIONS (Continued from preceding paye hall be projectionists who will handle and pro- swaP° ject the film on the television pick -up whereby 2cFRff it is sent to the audience. Here too there will be necessary film -sound control men and film -picture control men who will carefully monitor the Q l'ACE in this department is not sold. It is these transactions and therefore you are bound by transmissions. O intended solely for the benefit of our readers, the U. S. Postal Laws. Describe everything you who wish to exchange radios, parts, phonographs, offer accurately and without exaggeration. Treat CAMERA MEN cameras, bicycles, sporting goods, books, maga- your fellow men the way you wish to be treated. The television- camera men will constitute a zines, etc., without profit. new profession as well. These men handle the Since we receive no money for these announce- NO ADVERTISEMENT TO EXCEED 35 WORDS, ments, we cannot accept responsibility for any INCLUDING NAME AND ADDRESS television pick -up or "camera' which is trained statements made by the readers. We welcome suggestions that will help to make on the action and carefully and continuously Use these columns freely. Only one advertisement this department interesting and profitable to focused. The reactions of these camera men must will be accepted from any reader for any one RADIO -CRAFT readers. be instantaneous. they must work with perfect issue. All transactions MUST be above board. Copy should reach us not later than June 4th for coordination in groups where several angle -shots you Remember are using the U. S. snail in all the August, 1088 issue. of the same scene are to be transmitted, and they must be resourceful and artistic in their WANTED: r a 5' FOLDING WILL SWAP COLLECTION OF WILL SWAP VELOTRON MICRO - plate captera with plate holders. or radio manufacturers old catalogs and phone like new for Candid camera. G. pictorial sense. It should be remembered that the 4' a Eastman folding Kodak with circulars for radio parts. What have Milon, 2342 Crotone Ave., New York television broadcast cannot be altered after it is plate bark and holders. Good condi- you? B. Sunshine. 4408 10th Ave.. t Yty. tion. Otte diaphragm scale numbers. transmitted. The transmission to the audi- Brooklyn. N. Y. HAVE SUPERIOR ALI.METER, first Will trade good radio. Edw. Seymour. ence is the bast transmission, in general. and 40 Manning Ave.. No. Plainfield, WHAT HAVE YOU TO OFFER Ultra Precision Signal Generator, N. J. for Midas combination camera and Readrlte 430 Tube Tester. Philco radio there is no opportunity to rectify errors or limi- Projector, electric motor driven, plus 602. No. 32 S.C.E. wire. radio tubes. tations by a succession (as is WANTED: ISSUES OF IRE PItO- leather case. Brand new, used only parts. books. Write your needs and of "takes" com- ceedings prior to 1920. Offer photo- once. H. N. Memel. 1627 Foul St., offers to T. Woiclechowaki, 2880 Ful- monly done in present -day motion -picture pro- graphic sup- W. Fort Lee. N. J. ton Street, Iirooklyn, N. Y. duction). Accordingly, the job of television- plies. Doane Bernard. ` Room 1114. 9 Hudson Street. New YorkIt City. HAVE AUDIO TRANSFORMERS 4 TUILE IIEGEN. BATTERY RE- camera men will be exacting and important. 7 prong analyser plug and adapters eeiver (3 sorite). Also mag. speaker, WILL SWAP LOFTIN- WHITE -RCA phono. ose. -National 803 8 p.d.t. switch. (31 370 mmfd. vari- The television- camera men in the studio will amplifier with tubes. excellent condi- socket. Want 80 meter crystals, crystal able condensers. Trade for battery be a of a larger group. is tion for portable part for it clear that electric drill or headphone.. electrical books, course. "DU". camera. or what have you? the outdoor television -ups other tools. Allan Stuart, 1627 Pons' or? Newell Kelly, 208 Congres. Howard khcElfreeh. Marne, Iowa. pick (or "spot" pro- St.. Fort Lee, N. J. Street. East McKeesport, Penna. NEON TUBE TRANSFORMER. grams- Editor) will require the services of men WILL SWAP COMIPLETE SIT OF HAVE MODEL 430 TRII'LETT Three G. E.- 115 -15,000 secondary of similar qualifications and perhaps as great golf clubs, all steel shafted. Including meter tube checker -Model 554A All - renter -ripped. 30 a[.A. Iligh reactance resourcefulness to meet the 3 woods and following Irone. multitude of com- No. 2, 5. Wave Oscillator, with output meter. -will stand direct secondary short! plicated, 7, 9, and putter, with bag. for any Want good auto -radio, tubes. Rider Valued 87.00 each. Swap for oscillator partly unforeseeable, and sometimes un- standard 1937 -8 auto -radio set. N. manuals. Send list. Radio Service, or Instruments. Elroy. 4306 Horrocks controllable conditions to be encountered in out- Gray. 160 -22 97th St.. Howard Beach. Box 404. Ashdown, Ark. Street, Philadelphia. Penns. L. I., N. Y. door jobs. The outdoor camera man will neces- DE YRY PORTABLE MOVING 4 TUBE, BROADCAST, "MAJES- sarily be of somewhat the same type as the WANTED: RADIO PARTS VIN - with lamp. tic" receiver, dynamic speaker. built tage of 1920 -earlier, want Murdock in. present successful newsreel camera man who can pt`cÚ`dmotor 1300a roll film a A.C. -D.C. 110 volts. Exchange for crystal and loose coupler set. Want 2 or 3 tube S.W. receiver or trane- of rewind machine. Exchange. Make offer meet an emergency promptly and effectively. any type roherer. Exchange radio or what have you? Inetruments wanted celver. Also have 1 tube audio oscilla- or photographic parts, or what you tor. Albert E. Hartman, 419 91st Since a fair portion of television programs want. any." INTR. Marier, V.E.2It.J., Le lt. D. Tilletsonn, 40 w Manning Malbade, P. Canada. Street, Itrookbm, N. Y. may be, as stated above, from film, it will be Ave., No. Plainfield, N. J. G.. WANTED ONE OF THE BETTER WILL TRADE 4 TUBE RECEIV- necessary to film program material, recording ELECTRIC AUTOMATIC DICK er, 1500 stamps in book, small motor. mimeograph; R.F. mllllammeters; All -wave broadcast receivers that covers both picture and sound in the same way as now all broadcasts from five meters up with radio course 67 lessons, and other noiseless portable typewriter Ilke new; equipment for receiver or transmitter. done by the motion -picture studios and newsreel other items. Want photographic good quality reception. Write giving range all particulars. Holstein, or other short wave equipment. B. B. companies. This will lead to a demand for film finder, Weston exposure meter. or what C. 246 East Trine. Sheridan, Oregon. have you? Write before shipping. 149th St., Bronx. N. Y. camera men, sound recordists, editors, cutters, HAVE ACME TYPE A.V.E. PORT - Eichberg, 782 West F}sd Ave., New ALL -STAR SII. 7 -TUBE S.W. RE- and other men of the found able 35 M.M. projector with 1000 types in the motion - York. N. Y. mirer . . . perfect condition, beat watt lamp and 5 Inch lens picture studios of today. The demand in these Parts, new tubes, 8' Utah speaker and in Al WILL SWAP (AAH'LErE Sad,- complete condition. Want reflex type camera fields may develop fairly rapidly as the program hut course of National Salesmen's set coils 80 mc. to 540 kc. with F.3.5. lens or 32 watt high gain Trade for Rider's manuals. S. Lyehak, "hunger" of television broadcasting rapidly in- Training Association. consisting of 16 53 Hadwln Street. Central Falls, R I. beam power amplifier with mixing brand new text books (value $501. facilities. F. Bosch, 69 -02 87th St., creases after its commercial inception. Want movie camera of equal value. In HAVE A NUMBER OF 456 KILO- Glendale. I. I.. N. Y. absolutely perfect condition. Or what cycle Iron core I.F. coils -swill swap. WILL SWAP REMODERNIZED TELEVISION SERVICE MEN have you? B. N. Lenta. 232 West 07 E. J. Kujanik, 62 Bruce Street, Galt, 804 Dependable Tube Tester for port- St., New York City. Ont., Canada. able typewriter or small electric drill. Still considering work of primarily technical Joim H. Lesko, 206 West HAVE JANETTE DC -AC CON - HAVE OLD COPIER RADIO fine Street. nature in the television field, it is clear that the Mahonoy City. Penna. verter, W.E. 211E's, old p.S.T.'s, Broadcast, Popular Radio, Radio News television receivers of the future must be RCA Service course, movie projector; Radio -Craft exchange for other copies HAVE 250 WATT AND 750 WATT many other Items. Want kerosene needed to complete files. Who has ball bearing 110 volt AC generato s. installed correctly and kept in good operating refrigerator, mantle lamp, gas- electric copy of Alden -Na -Aid booklet on Practically new. Also Triplett test condition. ant, water photo - p pump, surveying. modernizing tube checkers and analyz- equipment. Want acetylene welder, This requires the existence of a good -sized p aphic instruments. Joseph Leeb, 1380 er.. Pioneer Radio Service. Box 663, printing press. shop tools. J. L. O y- Merriam Avenue. New York City. Lincoln. Nebr. sen. Kerman, Wisconsin. group of television Serriee Men. Such men must be familiar with the circuits of television receivers, their operation, the testing of the receivers for faults, the location of the faults and their correction, and the best method of install- SWAP & ing and the receiver SELL maintaining in the home. is the great, big, new magazine that shows you how The public response to television will depend in to get more than 1000 different articles, such as some measure on the skill, honesty. and diplo- camerae, rifles, books, magazines, clothing, tools. macy pets, etc., without having to buy them! of these Service Men. particularly during It nuns your own swap ad free! what may be the more or less difficult early days of commercial It prints letters from men and women who seek exploitation of television. new friends! It publishes true experiences from real life! RELATED ACTIVITIES It tells you how to swap and how to make money! Governmental regulation of radio broadcasting. It helps you get all the things you've always longed as at present, will lead to the need for a num- for, yet never could afford! ber of radio supervisors in the various districts You NEED a copy to help you get more out of life! of the country charged with the inspection and supervision of the operation of the stations to NOT SOLD ON NEWSSTANDS determine that the Federal regulations are ob- Send only 10c for sample copy, or get all twelve served and to report on matters of service to big issues for the coming year-only $1.00 if you the Federal Communications Commission. Fur- order at once! ther, the staff of the Commission will necessarily SWAP & SELL include engineering and legal experts in the new 99C HUDSON STREET NEW YORK, N. Y. field of television. Those interested in entering the Government service may find openings of this sort congenial in the future. There will necessarily be a considerable number of related or adjunct activities to those mentioned above in related fields. For example, once Be Sure to Read television broadcasting is carried out on a nation -wide scale. it will be necessary that the programs. in part at least, be syndicated or carried the Announcement which appears by wire or radio. If wire methods are used. the "coaxial cable" will likely find considerable application. The construction of such cables, their installation, their operation and maintenance will on Page 60 of this Issue then form one of the fairly extensive activities of the Telephone Company with the creation of (Continued on page 64) Please Say That You Saw It tin RADIO-CRAFT

www.americanradiohistory.com RADIO -CRAFT for JULY. 1938 63 BOOK REVIEWS A NEW NOKOIL IIIIIIIIIIIIIIIIIIilIR110111111111111111111111111111CIIOIIIIIIIIIl1111lllllllllll11111111lllllll1111llllllllllll111111111111111I1111111111111111111111111111111111111II11lllllllllllllllll1111111111111111

RADIO ENGINEERING, by Frederick Emmons of radio, including aviation, navigation, and Terman. (2nd Edition, 1937.) Published by industrial control, photoelectricity. photocell McGraw -Hill Book Co., Inc. Size. 6 x 9 ins., applications, sound pictures, public address sys- cloth covers, 813 pages, 474 illustrations. Price tems. television, telephotography, electricity and $5.50. magnetism. Almost everyone in the radio field at one time "Radio Engineering" in its new 2nd Edition or another will probably find this volume useful. is an eminently successful text, and is prac- It's a radio library "must" book. tically a new book; over 34 of the text has been completely rewritten and more than 2/3 of the illustrations are new. Besides bringing FORTSCHRITTE DER FUNKTECHNIK. Pub- all material up to date, and adding a complete Halted by Franckh'ache Verlagschandlung. Stutt- set of problems for each chapter, the author gart. Germany. Size, 7% z 10 ins., 174 pages. has added a considerable amount of new ma- Price, approx. 60c. terial which is here presented in print for the first time. In addition, many changes have been Written in German, this beautifully- prepared made to improve the presentation of various volume is probably the most comprehensive sections. cross- reference to practical German radio tech- Each of the I8 chapters in this book is sub- nique of any so far published. Every sort of divided into 5 to 15 sections. The chapters are commercial radio equipment is beautifully illus- titled as follows: The Elements of a System of trated; and, insofar as possible, described in 20 Handling Capacity Radio Communication ; Circuit Constants: Prop- technical detail. Watt -Power erties of Resonant Circuits; Fundamental The section devoted to vacuum tubes contains Maximum Efficiency Properties of Vacuum Tubes; Vacuum-Tube an extensive listing of technical characteristics; -Characteristics Amplifiers; Vacuum -Tube Amplifiers (Con- and tube terminals of German tubes of all Outstanding Frequency tinued); Power Amplifiers; Vacuum -Tube Os- types. A second chapter breska down various performance will convince you there i- cillators; Modulation; Vacuum -Tube Detectors; circuit arrangements to their fundamental com- Its Sources of Power for Operating Vacuum Tubes; ponents. An exceptionally interesting chapter no 12" Permanent Magnet Speaker its equal. Radio Transmitters; Radio Receivers; Propaga- is one devoted to antenna coupling circuits of tion of Waves; Antennas; Radio Aids to Navi- various types. Another unusually interesting List gation; Television; Sound and Sound Equip- chapter is the one devoted to loudspeakers - P $31.00 ment; Appendix A (Formulae for Calculating with emphasis on permanent- magnet types. Inductance, Mutual Inductance, and Capacity). Sound recording of all types is treated in con- ¡('rite for our special introductory oiler. siderable detail. Various methods of measure- Wright -Decoster D istributors are always anxious use cathode -ray equipment including the of to cooperate. ment are described. A chapter of importance DICTIONARY OF RADIO TERMINOLOGY IN one devoted FRENCH AND to the short-wave experimenter is THE ENGLISH, GERMAN, to -shortwave technique. A chapter on by A. S. Litvinenko. ultra RUSSIAN LANGUAGES, television brings the reader up-to -date on Ger- WRIGHT-DECOSTER, INC. Published by Technical Encyclopaedias (1937) man developments in this direction. Two pages 2251 UNIVERSITY AVE., ST. PAUL, MINN. and Dictionaries. Moscow (available in U.S. from 50 of diagram symbols introduce the reader to New York Booknigs). Size, 7 x 10% ins., cloth covers, 560 Export Dept. M. Simons & Son Co.. pages of European commercial radio receiver Cable Address: "Simontrice" pages. Price $4.00. diagrams that will interest designers of equip- Canadian Representatives: ment for export. Wm. F. Kelly Co.. 1207 Bay St.. Toronto. Ont. Here is a truly monumental work of interest Taylor & Pearson, Ltd.. Edmonton. Alberta to the advanced technician who may find himself called upon to translate a radio technical TECHNICAL MANUAL TT-3, by Commercial term, abbreviation or symbol either from or Engineering Section. RCA Radiotron Div., RCA into the English. French. German or Russian Mfg. Co., Inc. 5rh x 8% ins., paper covers, 192 language. This so- called "preliminary" volume of merit in pages. Price, 25c. radio terminology has exceptional "Air- Cooled Transmitting Tubes," is the sub- enabling international standardization interests title of this most useful new publication for the to make better headway. For those technicians transmitter specialist. Note that much of the who can use a book of this nature we highly material contained in this Manual is also of im- recommend "Dictionary of Radio Terminology portance to short-wave diathermy technicians. in the English, German, French and Russian Big value; note Contents: Languages." General Vacuum -Tube Considerations, Generic Tube Types. Transmitting -Tube Installation, Transmitting -Tube Applications, Technical De- RADIO IN THE CLASSROOM, by M scription of Tube Types, Transmitting -Tube Harrison. (1937) Published by Prentice-Hall, Ratings, Transmitter Design Considerations, Use- Inc. Size, 5% z 8 ins., cloth covers, 260 pages. ful Formulas. Transmitting -Tube Charts, Recti- Price $2.50. fiers and Filters, Circuit Section, Index. Read- ing List. Although this book is primarily concerned with the use of radio as a supplementary tool to education it contains a certain amount of RADIO TUBE DATABOOK. Published by Ray- technical information regarding radio equipment theon Production Corp. Paper covers, size 4% for the school that will be of interest to the z 9 ins. (just pocket size), 200 pages. Price, 25e. progressive service and sound man who wants This tube "databook" contains the chief tech- of the extensive business to to annex a portion nical data on all tube types-from the oldest need in radio. it's available in the field -of school radio and sound as a -size book, it Everything you the newest. Prepared pocket all in this new RADOLEK RADIO installations. includes a wealth of information on tube ap- PROFIT GUIDE. Every repair part Note, however, that this book is mainly de- plications and uses -maximum ratings, values of for every receiver. Newest radio re- signed to aid supervisors, principals and teach- essential characteristics and the more important broadcast ceivers. Teat instruments. Technical ers to help make use of programs characteristics in operating curves for each books. Special equipment. Leading throughout the country. The tenor of this book active tube. following list- standard brands. Every item guaran- may be visualized by noting the Much of this information has previously been teed. It must be right or we make it ings of its chapters: Educational Objectives and obtainable only by a limited number of receiver Available to right. And everything under one roof. the School Radio; Radio Programs design engineers. Data are given on all tubes You get what you want promptly, and ex- Schools; Selection and Classroom Use of Radio that have been at all widely used in the past actly what you want. Radolek's immense Programs ; Classroom Activities Related to in receivers and amplifiers that are still handled stock, plus Radolek's efficient organization, 25,000 service Radio; Supervision of the School Radio; Radio in the trade as replacements ; also on all types insures you fastest service. Receiving Equipment for the School; Radio's men depend on this service and benefit by announced up to the end of 1937. For complete- help Contribution to the Activity Program and the Radolek's Radio Profit Guide. It will ness there are included the necessary data on re- you make more money. Development of the Units of Classroom Work. sistor, radio receiving, special receiving tubes, and panel lamps. Literally a treatise on tubes, "Databook" gives RADOLEK RADIO ELECTRONIC DICTIONARY, by definitions of the various tube characteristics and AND 601 W. Randolph, Chicago, Dept. C -19 Howard P. Manly. (New 1938 Edition.) Pub- terms. and explanations of how these quantities lished by Frederick .1. Drake & Co. Size. 6 z 9 may be determined from the characteristics send me the 1938 Radolek Radio Profit Guide FREE. ins., cloth covers, 300 pages, 550 illustrations. curves ; simple circuit diagrams showing the Price $2.50. essentials of the various sections of a modern radio receiver, including the newest features. Name This long -awaited book is right-up-to-the- and convenient charts for determining the proper Address minute, with more than 3,800 definitions of the values of certain tube circuit constants and Serviceman t Dealer t Experimenter t technical words and terms used in all branches operating voltages. Please Say That You Saw It in RADIO -CluFr

www.americanradiohistory.com 64 RADIO -CRAFT for JULY, 1938 LOOKING AHEAD TO TELEVISION OCCUPATIONS aduwdaphl (Continued from page 62) D.1UITABIf a -cable REP corresponding television staff. To the ex- A tent that radio -relay methods of syndicating net- Aerovox Corporation 5' work programs television ,.. made paiioie Gy are used in the field. Allied Radio Corporation there will have to be established a radio-relay American Television Institute. Inc Back Cover staff. consisting of engineers, maintenance men THE ACOUSTIC Amperite Corporation 64. 43 and the like to keep the connecting links in Amplifier Co. of America perfect operating condition. Amy, Acmes & King. Inc 51 COMPENSATOR Arrow OPPORTUNITIES FOR Sales Company 5-t (pat. pend.) WRITERS Leaving the field of technical television occupa- B is a be- tions, it evident that there may exist Ill- Phonic Reproducer Labs 46 II per- wildering multiplicity of opportunities for Brush Development Company 46 sons necessary energy, and of the originality, Burstein- Applebee Company 54 9Higheror application. Programs cannot be there are lower pitch started until C authors. Since the television lookers may be prac- with the Capitol Radio Engineering lust 511 tically insatiable in their demands for same micro- program Central Radio Laboratories - 40 and phone. material, it will tax the inventiveness Classified Section tiiu strength of the authors to the utmost to supply Continental Carbon. Inc .9 the steady flow of interesting and usable material Coyne Electrical School 3 for the television programs of the future. The material prepared by the authors will, in some 0 With the flip of a finger you can now (1) lower instances, require revision or adaptation by re- Grenpark Company 41 or raise the response of the microphone... (2) write men or script men who will have to be adjust the microphone for most desirable re- high -speed literary lights of special ability to N Rammarlund Mfg. sponse for close talking or distant pickup.. . meet the instant and considerable demanda of Company (3) adjust the system to any "taste", room con- the program staff. Hudson Specialties Co dition, or equipment. Ifygrade Sylvania Corp 4- DIRECTORS, ACTORS, MUSICIANS MODELS RBHk RBMIL with Acoustic Compen- The casting and of the L sator. frequency range 90 to 11000 cps, output, production programs of specialists. Lancaster, Allwin & Rommel 50 -65 db., complete with switch, cable connector will require still another group For instance, there will be needed a number Lincoln Engineering School ,e and 25' of cable $42,00 LIST of persons, including, of course, directors who N NEW LOW -PRICED CONTACT "NIKE" will know how to build up, rehearse, and present television programs. These men can be drawn 3111es Reproducer Company 48 ModelSlaf (hi -imp); SKI (200ohms) $12.00 LIST partly from the legitimate or "little" stage and Million Radio á Tel. Labs 4i slalell's 51 MODELS RAH -RAL, excellent for speech and the motion -picture studios. In part, however, Moto scoot Mfg. Company i'i music. Reduce feedback. 522.00 LIST they will have to be trained at dramatic schools which may be established for the purpose. Write for Complete Illustrated Bulletins and At this point there is reached what may he N Valuable Helps. Sales the most serious television demand of all, name- National Plans Institute - - I ly, the demand for qualified actors. By "actors" National Radio Institute ' 1 MPERITE Coble Addeerw AikenyNew Tom are meant all those appearing before the tele- National Schools 4,ì vision camera and microphone including musi- National Union Radio Corp 41 cians. announcers. dramatic and comedy charac- ters, commentators, vatideville actors, lecturers, o interviewers, and the like. D. W. Onan á Sons It must be remembered that we do not as yet know just what are the desirable qualifications P Par -Seetal Products Corp 61 for a television actor. The nature and psychology RED HOT SPECIALS! Precision Apparatus Corp 4s of the home audience, the limitations and opportunities of home presentations, the technical BRUNSWICK 6 TUBE capabilities and resttictiona of the television R Radio Circular Continue 40 2.6 Volt Battery Console Receiver screen, and the general economic problems of Radio City Products Company 61 nest-5-30 and 1 -31 tube or 4 201 A television will all affect the suitability of a given and I -71 -A 4 gang. 4 tuned Radio Publications 16 tubes, person as a prospective television actor. Since currents. single control. Radio & Technical Publ. Co only a minor fraction of the aspirants will Please Brand new. Factory waled cases. Radio Training Association 41 the radio public. it follows that a great number nice of console, 40'21x145 ehlp- Radolek Company 65 ping weight. 70-no C.O.D. C3 of applicants will be necessary to meet the 95 RCA Institutes. Inc 52 Express or Freight nly. situation. However. the career of a television 66119 No C O.l). Shipments 11('A Manufacturing Co - Inside Front Cover Alt actor will be appealing to many and. in spite Readrite Meter tt'orks 13 WATT BEAM of the long odds against the individual. it is Reliable Radio Company 44 POWER AMPtIfIER RIT likely that there will be intense competition A beautifully' designed Remington Rand, Inc 50 from a horde of applicants for these openings. amplifier conservatively John F. Rider 52 rated at 13 watts tin Probably those who have been adequately trained Duch pull) 2 stages. one and have had successful experience in somewhat 6.170 high gain stage s and pair of the (team similar fields will stand the best chance of suc- Power 65'60 tubes cuing cessfully entering this new field. Scientific Diathermy Corp 48 8- type rectifier for staler Mfg. Company 46 he A considerable number of studio openings will AD- 110 -125 v.. 60 cy.. may used for crystal. Sprayberry Academy of Radio 51 velocity or ribbon mike and magnetic or crystal necessarily exist in the television field. for ex- Superior Instruments Co phono pick -up-complete kit with all necessary parts ample, jobs for carpenters, scenic painters. act 30 lien tubes) with pictorial wiring diagram and Supreme Instruments Corp 43 size 105E x 754- shipping weight. artists or designers, costume experts, wardrobe drilled chauds Supreme Publications 52 10 lbs. mistresses, make-up men. historical -research spe- Swap & Sell 62 AD- I12 -A. 10 watt amplifier kit complete less cialists (who will see to it that no historical in- tubes. Wiring and testing. consistencies or inaccuracies are the $2.00 extra. $4.49 present in T watt complete less performance) and the like. Such openings will AD- 112 -B. 13 amplifier kit Terhnifax . ' 4e nues. Wiring and testing, increase only rather slowly in number as time Test Equipment Co. of America 4 $2.00 extra. No C.O.D. shipment.. $4.95 goes on. since it is likely that the full develop- William A. Thomas Co 48 KIT OF TUBES. 1 82. 1 -6370. 2 -6V60. 82.7$ ment of the television field as a branch of the Triplett Elect. Instr. Co 51 KOLSTER 7IA-20 WATT art of the stage will take a generation or more because of the many and novel problems which u Public Address Amplifier Transmitter Power Supply are involved. This 210 2511 United Radio Company 64 tube amplifier unit Ptah Radio Products Co. 4^ with 12V.' 25 Watt 95 CAUTION! speaker. brand new One final word may be in order in the form in factory sealed w advice to the person who is thinking of enter- ases, costing over of Wellworth Trading Co 50. 51 $100.00. ready to field of push ing the television. Don't and run - Weston Elect. Insstr. Co Inside Itark Cover use amplifier a walk ; and watch where you are Speed and tapped power going. Wholesale Radio Service Co 59 into field not be so supply. Conversion in rushing the will nearly Jahn Wiley & Sons 53 diagram for mak- helpful as first knowing where your abilities ing 20 Watt 111th Wright - DeCoster, Inc Ó1 twit amplifier fur- lie, cultivating those abilities by training in nished free. Shipping we 80 lbs. No C.O.D. shipments. fields similar to television. and then everlastingly Send for our new money saving catalogue. sticking to the job of perfecting your talents and Containing over 1000 red hot radio items at their application once you have entered the tele- (While every precaution is taken to insure bargain prices. vision field. Remember that television success will accuracy. we cannot guarantee against the UNITED RADIO CO. come rather as the result of a prolonged marathon possibility of an occasional change or omis- Dept. R- Drawer 1000 NEWARK, N. J. of effort than from a brief gold -rush of sion in the preparation of this index.) enthusiasm. Please Say That You Saw It in RADIO -CRAFT www.americanradiohistory.com lb Ord! flow e

L] .

WESTON Model 776 Oscillator

WESTON Model 773 Counter Tube (nether (also available in portable type) AT CHICAGO

Don't fail to visit the WESTON Booth at the Radio Trade Show, Stevens Hotel, Chicago, June 8th to 11th. (Booth No. 109.111 Marconi Boulevard.)

SEE the very latest in WESTON test equipment ... take this opportunity to examine the equipment inside and out and see for your- WESTON Model 772 self why WESTON equipment leads in accuracy, dependability and Super Sensitive Aralycer length of service.

GET full particulars about the 50th Anniversary announcement WESTON is making at the Show in celebrating a half-century of instrument leadership ... an announcement which presents an unusual opportunity to every serviceman. If you are unable to attend the Show, however, full particulars on the "50th Anniversary Announcement," and .-,.e. ., on all WESTON test equipment, will be -..,-.- =,,------mailed to you. Just return the coupon today. WESTON Model 775 Sorviset Weston Electrical Instrument Corporation 599 Frelinghuysen Ave., Newark, N. J. Send the "5e01 Anniversary Announcement." and literature WE S TON on WESTON Instrumente. Radio Name Instruments Address City ._Sute

www.americanradiohistory.com HE'S ALL SET FOR A CAREER IN TELEVISION and go POSITIONS IN THESE

Read What H. L. Newton Says About A.T.I. * TELEVISION "Not only did I get the equipment I expected, but considerably more. I am proud of my A.T.I. ENGINEERING Television Transmitter and Receiver, and the professional quality of the materials used. I have already received offers for this equipment I have constructed which will pay me more than I have put in the entire training. I enrolled while in the U. S. Navy and studied the A.T.I. * RADIO STATION OPERATOR Training in my spare time. My friends were impressed with each new shipment, and the excellent texts. This new method of studying with such elaborate apparatus gave me a real practical knowledge of Radio and Television, and I say that A.T.I. offers any man who wants to get into Television the greatest value for his investment." H. L. Newton, 175 Indiana Ave.. * RADIO ENGINEERING Huron, South Dakota. Television Men Will Be Needed Soon! * SOUND CAMERA TECHNICIAN Television is already commercial in England. When it is launched here. Executives know that thousands of jobs will be opened; thousands of TRAINED men will be needed. Be ready to step into a TELEVISION JOfi. Now is the time to prepare * PUBLIC ADDRESS TECHNICIAN ...don't wait until the field is crowded. Get in on the ground floor first . . . get the better jobs and the highest salaries. Practical Television Training * RADIO FACTORY EXPERT A.T.I. Training `'repares you for God paling hobs ass a Telecl +Inn Engineer. Radio Station Operator. I.:dolt: m')' Trrludri:un. Radio Elec- tronic Engineer. Sootor Caine. Technician. Public Address }:ru: ine.la. Elerlriri:m and other fa:win:dimg profitable positions. .t 'l'. I. Training quali lies twoat during the that few loofahs m 1:.1: pow RANI) * TELEVISION TROUBLE -SHOOTER TELEPHONE FIRST CLASS GOVEtN\IENT LICENSE EXANIINt- THIN and get into a good paying juts In the radio field while r mpleting your television Instruction. .t Radio Servicing Course is also a Included. * MOTION PICTURE OPERATOR You Learn By Actual Experience The I. hard- to- understand 11 n-lmre dreamed 1'013 A.T.I.,lbe 11.rim,d soul.' . .ti ti tl. EXPERIENCEi- with YOUR OWN TELEVISION APPARATUS just like on the real job. with your A.T.I. order isin Equipment you can make slyer 3.18 amazing. Interesting * ELECTRICIAN experiments right in your owl! Slmne.n 1lott can produce your own Television programs for a local audit-sire . transmitting and receiving the fares of your friends. Conn ran build complete Television Tranemisslnn and Reception Systems. You ran make hundreds of experiments and comparison tests that show stilt the pbruonuna of Telavlsiou and Radio in a . quirk. simple. fascinating way much s i,.r to understand than a.sid otcsuy othQJi.i ! just mere words in hook. All Ilse Must rated a Equipment included with Costs No More .. Yet Definitely Better training . . . AT NO EXTRA COST. Mall the coupon for FREE boas containing m ete A.T.I. Training with Complete is Information about A.T.I. training . . . pt gr hs. Equipment farts about jobs. salaries. how to earn xpen He Available on Amazingly Low Easy Monthly Payments training. Slow we assist graduates in the ti ti. ells 7 the empiric story. No obligation. , MERICAN TELEVISION INSTITUTE 433 E. Erie St.. Dept. RC -738. Chicago. 111. Gentlemen: Please send nie your free book on Telev baton and .erature describing A.T.I. Training. It is understa d lh at is is l'Ida( No ubli4ation In ant' wit). sille tge.

!dress