Radio's Livest Magazine

RADIO'S LIVEST MAGAZINE

July 25 Cents

NULO GEUNSBACK Ed tor

The Radio Robot See page 24

What Radio Manufacturers Are Showing - The New Pentode Receivers - Home Recording

Latest Data for Service Men - Improving Short -Wace Reception - Rules for Coil Winding 51 XL Tome aNiZóRion come t.n /eÁe locals JUST AS CLEAR-JUST AS LOUD

ATRULY international receiverhas been the desire of radio enthusiasts for years, and the hope of engineers since radio began. ITT And what listener hasn't wished for a receiver that would bring him -not only the whole of North America-but the major stations on the other conti- nents as well, and as easily? 1931 sees the perfected realization of all such A dreams, in the new and genuinely excellent Scott ALL -WAVE Receiver. The new receiver tunes from 15 to 660 meters. Actually- without exag- geration-it brings in Rome, London and many other foreign stations below 200 meters, just as clearly and with the same volume as a local broadcast. Grand Opera -the real Grand Opera. comes in direct from Rome to afford Scott listeners the musicalthrillofalifetime. And Big Ben, tolling off the hours in the House of Parliament in London, sounds as though it were right over head. Such reception is a REGULAR, DAILY event in homes equipped with the new Scott All -Wave Receiver. New Standards for Short Wave Reception The performance of the Scott All -Wave below 200 meters is not to be confused with the unsatisfactory short wavereception of the past.There are no sharp edges -no irritating squawks -no mushiness orotherdiaturbing receiver noises to take from the thrill of listening to the other side of the world. The short wave broadcasters un- roll their music, voice and song thru the Scott All -Wave. with the same liquid smoothness as those within the 200.550 meter band. Credit goes to new kind of Intermediate Amplifier The truly amazing performance -the unlimited range- the actual 10 kilocycle selectivity - all are due to the new type intermediate frequency ainplification employed in this receiver. Never before thought of - never before attempted -- this system of amplification accomplishes exactly what superheterodyne engineers have sought to achieve, ever since the advent of this admittedly superior receiving circuit. suffice to express our confidence in the engineering and quality construc- GIVES A NEW MEANING TO "TONE" tion that makes Scott performance possible. So -we guarantee each The tonal reproduction of the Scott All -Wave is equally as refreshing as its sen- Scott All -Wave for five years and agree to replace any part -free of sitivity and selectivity. From a whisper to concert volume, every note - every charge - that fails to give perfect service within that time. delicate shading is faithfully reproduced. The push -pull audio amplifier employed gives results impossible to otherwise obtain. Make the SCOTT ALL -WAVE 5-YEAR Prove Itself to You MAIL NOW GUARANTEE Decide right now to have the ultimate in radio. Plug the new Scott All -Wave R.C.-74, into a base board socket in your own home. Tune in Rome -tune in London - Scott Transformer Co. tune in Chelmsford- listen to Sydney. Australia -to Buenos Aires -to Bogota. 4450 Ravenswood Ave., Chicago To simply say that we be- Colombia-enjoy short wave foreign stations to your heart's content. Then step Send me full details of the new Scott An -Wave ... new Scott All. thru the broadcast hand for the domestic stations. You'll find them all on dial. Soperheteroulyne. Iam Dealer 0 Set Builder Wave to be the finest re- and all with far more volume than you can ever use. The price of the new Scutt Service Oleo Radio rao ceiver ever built, does not All -Wave is amazingly low. Write for full particulars at once. Name SCOTT TRANSFORMER CO. .Jrcct 4450 Ravenswood Avenue - Chicago, Illinois Town filate July, 1931 RADIO- CRAFT 1

Radio Seroice

Important and far- reach- ing developments in Radio create sudden demand for specially ?iìth thif equipped and specially trained Radio Service Men. Radio Set Analyzer

THOUSANDS of skilled Radio Service Men are needed now to (sent lo everyl Ylember) service all- electric sets. By becoming a certified R. T. A. Service Man, you can earn $3.00 an hour full time or spare time, and fit yourself for the big -pay opportunities that Radio offers. \Ve will quickly give you the training you need to qualify as a Q/011 Caìi (arn Radio Service Man . certify you ... furnish you with a mar- velous Radio Set Analyzer. This wonder instrument, together with our training, will enable you to hold your own with experts who have -9 an hour been in 3° the radio business for years. With its help you can quickly diagnose any ailing Radio set. The training we give you will enable you to make necessary analysis and repairs. Serving as a "radio doctor" with this Radio Set Analyzer is but one of the many easy ways by which we help you make money out of This amazing Radio Set Analyzer plus the Radio. Wiring rooms for Radio, installing and servicing sets for instructions given you by the Association will dealers, building and installing automobile Radio sets, constructing transform you into an expert quickly. with and installing short wave receivers ... those are a few of the other it, you can locate troubles in all types of sets. ways in which our members are cashing in on Radio. test circuits, measure resistance and condenser capacities, detect defective tubes. Knowing As a member of the Radio Training Association, you receive personal how to make repairs is easy; knowing what instruction from skilled Radio Engineers. Upon completion of the the trouble is requires expert knowledge and training, they will advise you personally on ally problems which arise a Radio Set Analyzer. with this Radio Set in Analyzer, you will he able to give expert serv- your work. The Association will Help you make money in your ice and earn $3.00 an hour. Possessing this spare time. increase your pay, or start you in business. The easiest. set analyzer and knowing how to use it will quickest, best -paying way for you to get into Radio is by joining be but one of the benefits that will be yours ill, Radio Training Association. of the R. T. A. No -Cost Membership Plan Now Open The No -Cost Membership Plan enables you to secure a membership without cost. The training and the valuable Radio Set Analyzer can 1 ill Out and Mail 7 oda he yours! Now is the tinte to prepare to be a Radio Service Man! RADIO TRAINING ASSOCIATION OF AMERICA By the time you're ready, demand will exceed supply. Bigger salaries. rapid promotion, bigger opportunities! For the sake of extra money Dept. RCA -7, 4513 Ravenswood Ave., Chicago, W. made in your spare time, bigger pay. a business of your own, a position Gentlemen: Send nie details of your No -Cost with a future, get in touch with the Radio Training Association at Training Offer and information on how to make once. Send for No -Cost Membership Plan, and FREE Radio Hand- real money in radio quick. book that will open your eyes as to what Radio has in store for the ambitious. Don't wait! Don't delay! (yet started now' Name

RADIO TRAINING ASSOCIATION OF AMERICA Address Dept. RCA -7 4513 Ravenswood Ave. Chicago, III. City State H. GERNSBACK, President R. D. WASHBURNE, Technical Editor S. GERNSBACK, Treasurer J. M. HERZBERG, Vice- President adio raft FOR THE C. MASON, I. S. MANREIMER, Secretary P. SERVICE MAN. DEALER RADIOTRICIAN Associate Salter HUGO GERNSBACK, Editor -in -Chief

VOLUME III J ( 1. lr NUMBER 1 Contents of This Issue 1931

PAGE I'AG I: EDITOR IAL: Crosley "Super Buddy Boy" 20 I The Radio Dollar By Hugo Gernsback 9 The Summer's Small Radio Sets 21 New Accessories and Components 22 SERVICE MEN'S DEPARTMENT: The Walker Short -Wave "Super -Converter" 23 A New, All -Wave Oscillator By H. G. Cisin 10 Latest Testing Equipment for Bench and Kit 11 RADIO CONS'T'RUCTION AND THEORY: RADIO-CRAPE Data Sheets: Introducing Our "Mr. Radio Robot" By H. G. Cisin 24 Philc( "Ill" and "111A" Supers 12 How to Improve the Quality of Recording Clarion "Series 90" 13 By George J. Saliba 27 Operating Notes for Service Men..13y Bertram M. Freed 14 Installing Radio in a Big Hotel (Part II) Making Money in Servicing By W. E. Smith 14 By Eli M. Lurie 30 Leaves from Service Men's Notebooks By Themselves 15 Building an Automotive Set Around the Latest 'Pubes The Service Man's Open Forum 16 By C. E. Denton 33 Every Millianmleter a Direct- Reading Ohmmeter A Short -Wave Receiver -Adapter..By L. Mitchell Bantus 35 By Francis R. Ehle 16 Improving Short -Wave Reception..By Clyde A. 'Landon 36 Reference List of Commercial Circuits 16 How to Figure the R.F. Coil Secondary..By C. E. Denton 37 Replacement Resistors By Harry Georges 17 The Whole Oh Family (l'art II) By Hal Wyman 38 Hints to Manufacturers By Service Men 17 The Radio Craftsman's Own Page :39 RADIO- CRAFT'S Information Bureau 40 NEW DEVELOPMENTS IN RADIO: Better Reception Ahead Morris Metcalf 51i The New Scott "All -Wave" Superheterodyne 18 Radio Book Reviews 58

In Forthcoming Issues

MODERNIZING THE OLD SUPERHETERODYNES, by APPLICATIONS OF THE PENTODE, by C. E. Denton. F. L. Spravberry. No article we have published has at- This article will be devoted to the practical side of the prob- tracted more requests for personal information than Mr. lem. It will contain curves, data, and circuits for the use Sprayberry's explanation of his way of adapting the Radiola of the pentode to best advantage; either for the construction "28" to 2 -volt tubes. He will write also on the earlier of a new receiver, or the modernization of the older models. models, "25" and "812." THE RADIO -CRAFT PENTODE PORTABLE. In every IMPROVING RESULTS WI'T'H SHORT-WAVE ADAPT- country of Europe, the portable radio receiver is a favorite ERS, by Lewis Winner. A discussion of the principles to type; it has never reached any such vogue here- possibly be followed in obtaining goo(1 results on short waves with because of the very relative nature of its "portability." The adapters (or converters) used in connection with broadcast new pentode has made possible a very light, compact, in- receivers. This article will show many where their mistakes expensive model of good output, which will be described. have been made, and enable others to make good short -wave It is a development of RADIO -CaArr laboratories. reception better.

RADIO -CRAFT Is published monthly. on the fifth of the month preceding that of Test and Illustrations of this magasine are copyright and must not be reproduced date; Its subscription price Is 32.50 per Jeer. lin Canada and foreign countries. without permission of the copyright owners. We are lso agents for WONDER S3.00 year undpostage. ) Entered at leTraJ STORIES and WONDER STORIES OI'ARTF.RLY. Subserlptions to the,e maga- n.. a eond -class rt March a. °107a9 marksorand zines may be taken In combination with ItADlO.CR.tPT nt reduced flub rates copyrights by permission of Gernsback Publications. Inc., 98 Park flare, New Write for Information, York Pity. Copyright 1931, c.KItNSItACK PUBLICATIONS. INC.

Published by TECHNI -CRAFT PUBLISHING CORPORATION Publication Office: 404 No. Wesley Ave., Mount Morris, Illinois Editorial and Advertising Offices Chicago Advertising Office Western Advertising Office 96.98 Park Place, New York City 737 North Michigan Avenue, Chicago, III. 611 So. Coronado St., Los Angeles, Calif. L. F. McCLURE, Chicago Advertising Representative LOYD B. CHAPPELL, Western Advertising Representative Landon Agent: Hachette & Cl... Paris Agent: Hachette & Cie.. Australian Agent: MeG Ill's Agency. 3 La Belle Sauvage, Ludgate Hill. E.C. 4 III Rue Resumer 179 Elizabeth St.. Melbogrne i July, 1931 RADIO -CRAFT 3

Coyne studentsget- ting actual experience on one of my big synchronous converters!

One of my In- structors explaining the operation of a radial airplane engine.

A BIG PAY JOBforYOIJ

ELECTRÌCI JOBS PAYING Don't spend your life in a dull, hopeless job! Don't be satisfied with a mere $30.00 or $40.00 a week! You don't have to! Electricity $60 to $200 a week pays salaries of $60.00, $70.00 and even $200.00 a week to thousands of fellows no smarter than you. Power Plant Operator $50 to $70 awk. Maintenance Engineer 60 to 100 awk. LearnWithout Lessons in 90 Days Armature Winding.. 46 to 76 awk. In the Great Shops of Coyne Illumination Expert . 60 to 80 awk. Radio Service Expert 60 to 100 a wk. Come to Coyne at Chicago and learn Electricity in 90 days -not by correspondence, but by actual electrical work -on huge motors Aviation Ignition . . 60 to 125 awk. and generators, switchboards, power plants, substations, auto and Battery Expert ... 70 to 200 awk. airplane engines, armatures, etc. You don't need advanced education or previous experience. Coyne has been placing men in Big Pay Elec- Auto Electrician ... 75 to 200 awk. trical Jobs since 1899. Let Coyne help you to a good electrical position. Contractor-Dealer . . 60 to 300 a wk. Free Employment Service Signal Engineering . 60 to 100 a wk. Earn As You Learn Don't worry about a job! My Employment Department FREE ELECTRICAL BOOK Coupon gives you a FREE lifetime service. And if you need part - time work while at school to help pay expenses, we'll gladly H. C. LEWIS, PRESIDENT help you get it. MAIL COUPON FOR FREE PROOF THAT YOU COYNE ELECTRICAL SCHOOL, Dept. B1SI CAN HAVE A GOOD ELECTRICALJOB IN 90 DAYS! Get my Big 500 South Paulina Street, Chicago, Illinois Free Electrical Book -FREE Radio and Auto Electrical offers. Find Gentlemen: Please send me your big Free Electrical Book with out about my special low tuition price. This does not obligate you 151 illustration. This does not obligate me. in any way. JUST MAIL THE COUPON! ELECTRICAL SCHOOL Name H. C. COYNE Address 500 S. Paulina St., Dept. BI -S! Chicago, Illinois : t csey State E\'Ell since the advent of radio, the sum- BIG News for you mer season has been curse to the radio man because that is the time when radio activities are at their lowest In the summer time. people do not use Weir radio sets so touch and there is as a rule, little servicing to be done. This means that the average radio service man and rWlutricien finds pretty slim pick - ings during the summer months. We have given this problem considerable thought and for over a year worked quiet- ly- an the problem; and from now on every radio man. service man and radiotrician will have a steady Income all the year around. incredible as this may seem. The idea of radio people servicing nfrigeration units is self -evident and We thought has occurred to perhaps untold thousands of radio men ever since electric refrigeration started. Yet nothing was done. because the average radio man knows little or nothing about refrigeration- Our sur- vey of the field convinces us tut. compared with sera icing a radio set, the servicing of a refrigerator is abamnit). aim - pie, once you get the hang of It; and that Is exactly why the OFFICIAL REFRIGERA- TION SERVICE MANUAL Is going to he a side- partner to the OFFICIAL RADIO SER- VICE MANUAL, with which you are well acquainted. When you are called In to service a radio set, it Is easy to find out if your customers own a refrigerator. If they do. you can now tell them that you can semire the refrigerator as well. Piare your card somewhere near the re- f igeratcr so that, If trouble comes. you will be called in to fix It From whatever point you look at it, you will make money. And don't ever lose sight of Ube fact that refrigerators a ually need sersielne In the summer time and that It Is here that you will get Hew sad extra Income. But don't take our word rot all th k. Study the situatinr yourself and mea e if s e are not right. Look In your locality and find out how many refrigerators there are. At the present time the servicing nl these refrigerators goes to other trades when this business might Just as well belong to you. So we say to you, why net go Into the refrineration er eking business at once? Re- member. there Is hie money In It and the reteleeratier business is growing enormously every year; and it won't be very Ions before there will he more refrineraton than ndies. The OFFICIAL REFRIGER- ATION SERVICE MANUAL has been edited by I.. F. Wright. who is an expert anc a leading refrigeration suehor- ity. Tie is a member of the American Society cf Mechan- ical Engineers, American So- ciety of Refrigeration }Sngln- eers. The National Asanriatior of Practical Refrigeration En- gineers, etc. The new Manual. as TM will see from the photographic reprodurtion. is the same size as our OFFICIAL RADIO SERVICE MANI'.1L. It will be 9 x 12 Inches. anti will contain at least 900 paer loose -leaf. hound in leatherette. gold-stamped cover: in fact. It is a gold mine of Information on the entire art of refrigeration. Here are the chapter contents: Preface: Introduction; Eatery of Refrigeration: Fun. damentals of Refrigeration; Description of All Known Types of Refrigeration: Service Tools and Shop Equipment: Trouble Shooting: Motors: Unit Porte, Valves and Automatic Equipment: Manufac- turers, Makes and Specifications of Units; Manufacturers of Cabinets. Every pare le profusely illustrated: every refrigerator part Is explained; dia- GERNSBACK PUBLICATIONS, Ina. RC-7 grams are furnished of every known machine: special care is given to Cie servicing end, of course; all the tools needed are 96-98 Park Place. New York, N. Y. Illomrated and their use explained; there are trouble shooting charts, and other service data. This by no means exhausts the contents of the hook. and It would take much more space to give yot all of the details. Ate per your special publication offer. I enclose pre- Last year. when we brought OFFICIAL !SERVICE 111.1N1-Al,, we made is special offer herewith my remittance for (check or money out the It.tDio pre- publication $3.50 to our saved them thousands of dollars. We are now the same chance very order preferrcd) for whirl, you are to senti to me. friends, which actually giving you again for a short time. Postage prepaid. one tory of the OFFICIAL REFRIG- ERATION SERVICE ItTANUAL as soon as It comes off the mess. I understand that the price upon pub- SPECIAL PRE- PUBLICATION OFFER lication will be $5.00 Per copy and tes special offer will be void. The regular price of the OFFI(IAT. REFRIGERATION SERVICE MANUAL is $5.00 after It Is published. To you, the book will the sold at $3.50 prepaid if you send In your order at once before the publication of the book. Please use the coupon. The whole bask Is new ready for the printers and me are putting on the lest finishing touches. It will be In the printer's hands In a few weeks. Once the ( OFFICIAI. REFRIGERATION SERVICE MANUAI. Is Issued. you know from Name experience that we named allow any price reduction and. the instant the book comes off the tress, the price will be $5.00.

Address GERNSBACK PUBLICATIONS, Inc. City

State 96 -98 Park Place New York, N. Y. July, 1931 RADIO -CRAFT 5

Uur;N'1S WURKINU ON FILM SCANNING MACHINE OF OUR MODERN TELEVISION TRANSMITTER LEARN RADIO -TELEVISION TALKING PIUU RES 10 WEEKS By Actual Work In the Great Shops of Coyne Don't spend your life slaving sway in some dull, you in hopeless job! Don't be satisfied to work fora mere -right here the Coyne Shops -all velous opportunities! LearnRadioSound $20 or $30 a week. Let me show you how to make the actual practice and experience you'll work at Coyne on actual TalkingPicture REAL MONEY in RADIO -THE FASTEST- need. And because we cut out all use- and Sound GROWING, BIGGEST MONEY -MAKING Reproduction equipment. GAME ON EARTH! less theory, you graduate as a Practical Radio Expert in 10 weeks' time. JOBS LEADING to SALARIES EARN AS YOU LEARN OF $60, 870 A WEEK AND UP You Get FREE Employment -r. Jobs as Designer, Inspector and Tester, paying TELEVISION Service for Life. And don't let $3,000 to $10,000 a year -as Radio Salesman and in lack of money stop you. If you need part - Service and Installation Work, at $45 to $100 Is Now Here! time work while at school to help pay liv- week -as Operator or Manager of a Broadcasting And TELEVISION is already Station. at $1,800 to $5,000 a year -es Wireless Op- here! Soon ing expenses, we will gladly help you get erator on a Ship or Airplane, as a Talking Picture there'll be a demand for THOUSANDS of it. Many of our students pay nearly all or Sound Expert -HUNDREDS OF OPPORTU- TELEVISION EXPERTS! The man who NITIES for fascinating. BIG PAY JOBS! of their expenses that way. Mail the learns Television NOW can make a FOR- coupon below for full particulars! TUNE in this great new field. Get in on No Books No Lessons the ground -floor of this amazing new Ra- Coyne Is 32 Years Old dio development! Come to COYNE and Coyne Training is tested. proven beyond all All Practical Work learn Television on the very latest, new- doubt. You can find out everything absolutely Coyne is NOT a Correspondence School. est Television equipment. free. How you can get a good Radio job or how you can go into business for yourself and earn f rom We don't attempt to teach you from books $3,000 to $15.000 a year. It costs NOTHING to in- or lessons. We train you on the finest out- vestigate! Just MAIL THE COUPON for YOUR lay of Radio, Television and Sound equip- Talking Pictures COPY OF MY BIG FREE BOOK! ment in any school -on scores of modern A Great Field F------Radio Receivers, huge Broadcasting Talking Pictures and Public Address H. C. LEWIS, President equipment, the very latest Television ap- Systems offer thousands of golden I Radio Division, Coyne Electrical School S. Pauline Dept. ZU. paratus, Talking Picture and Sound Re- opportunities to the Trained Radio 1 coo St BI -811 Chicago, production equipment, Code Practice Man. Here is a great new field of Send me your Big Free Radio Book and all equipment, etc. You don't need advanced Radio work that has just started to 1 details of your Special Introductory Offer. education or previous experience. We give grow! Prepare NOW for mar- these 1 This does not obligate me in any way. H. C. Lewis, Pres. Radio Division Founded 1899 1 Name 1 COYNE ELECTRICAL SCHOOL Address 500 S. Paulina Street Dept. B1 -8H Chicago, Illinois 1 City State fì RADIO -CRAFT July, 1931

.1ewlse .(,iiwis.mos,rasoetwa(me1,emewwwww.,ms(mswomoms,iwosowoomr,iwss,iwsts w.omoiww..I,s.....,rwsw.owse..--..-; SHORT WAVES with a Converter

WITH high -gain radio frequency amplifiers characterizing experimenters' broadcast receivers today, and audio amplification remarkably faithful, it is convenient. economical and easy to tune in short waves and television with a converter. In that way you use your entire broadcast receiver just as it is, and besides the television band, tune in other short waves. The range is 25 to 600 meters, when the broadcast set is worked at a high frequency, around 1,500 kc.

The converter illustrated is model PR -3FS and has a filament transformer built in. There are only four external connections to make, and one of these is to a positive B voltage, 50 to 180 volts, taken from the receiver. If you have a screen grid set you may take this voltage from the screen of a radio frequency tube, by looping the bared end of the B plus lead and slipping the screen prong of the tube through the loop before reinsert- ing the tube in the set.

The converter uses three 227 tubes and plug -in coils of the tube base type. There is an AC switch built in, but there is only one tuning dial (at right). The condenser is the new Hammarlund Junior Midline of .0002 mfd. capacity. The Model PR -3FS Short -Wave Con- This short -wave converter has proved highly satisfactory, developing great sensitivity verter that is, in fact, an all -wave converter, as it enables also the reception and enabling the penetration of great distances. There are no body capacity, no squealing, of broadcast frequencies. The range is no squawking and no tricky tuning. 25 to 600 meters, so you are sure to cover the television band, too. By all means provide yourself with the complete parts for this dandy converter. as specified by Herman Bernard, the designer. vv

TI newest condenser to come from the laboratories of the Hammarlund Manufac- Iuring Co. is the Junior Midline, made especially for us, and designed for highest grade short -wave performance. The capacity is .0002 mfd. and the midline tuning i r characteristic prevails. Single hole panel mount. in a ?é -inch hole (with option of sub -

panel mounting by built -in brackets) : end stop provision at both extremes: rigid plate assembly and the fine workmanship of Hammarlund mark this compact condenser. The overall depth of the frame is 1% inches, while the rotor plates turn in a diameter of only two inches. This condenser, our Model PR -H -20, is a superb product, in line with the modern vogue of compact parts. v

RECISION short -wave plug -in coils, three coils to a kit, not counting as a coil the movable tickler. Used with .0002 mfd. for tuning. this kit of coils affords coverage The new Hammarlund Junior Midline Short -Wave Condenser, capacity .0002 of from 15 to 160 meters. These coils are wound on 97% air dielectric and are pre- mfd. The rotor plates turn in a diam- cision. de luxe products. A receptacle base, on which the adjustable tickler is mounted. is eter of only 2 inches, while the total supplied with each coil kit. This kit is our Model No. PR -AK -1 and represents the frame depth is only 1344 inches. So this pinnacle of short -wave plug -in coil achievement. It is for Short -wave receiver circuits. is an extremely compact condenser, made by one of the foremost condenser manufacturers in the world. It is our Model v No. PR -H -20, m:.de specially for us. EXTRA -SPECIAL FREE OFFERS OF SUBSCRIPTION PREMIUMS! RADIO WORLD, 145 West 45th St., New York, N. Y. RADIO WORLD, now in its ninth year. is the first and only national radio weekly. Enclosed please Ond: and publishes the latest. up -to- the -second news of circuits, both of kit types and of 1931 f ¡!t 1.00 fur two years' subscription clot issues) for 1t.\1)111 w111í1.11 at the regular rate. Please send commercial receivers, as well as news of happenings in the broadcasting field. Lists of as a premlmn all parts tu 11411111 the Short -W11ve I ,meerler. Including filament tnmsformer nd broadcast and short -wave stations, including television stations. are published regularly. :. '4 xi -hp It cabinet. but not hadpding tubes. This is Your Model PR-3F14. You get your information weekly -which means quickly -and you get it accurately, so for subscription (12 Issues) fut Enti.0u one year's be sure to become or remain a subscriber for RADIO WORLD. We are able to offer now R \11111 \\'11RI.P. ('lease send the short -Wove foil hit as n premium, your model PR-AR 1. especially attractive to short -wave experimenters, and ask you to make your consisting of three plug -ln Bolls and base re. premiums cetit Sels. choice from the parts offered on this nape. When ordering. please use coupon. 0$5.00 for Ni a months' subscription (26 Isenesl. Ilummarlund Condenser, PR- Il -20. Please send the The regular subscription rates are: $o for one year. 52 issues, one each week: $3 for

tvon.o : 8 weeks: 6 months, (26 weeks) : $1.50 for three months, (13 weeks) $1 for 15c per Address single copy. Clty State (S) ..a,xomw.=rlrrONIII.MIll,l1=1.,urlr1..14M111tr4xxIM July, 1931 RADIO -CRAFT 7 Iwill train you at home to fill a 106YAY

will giveYou my new 8 OUTFITS Radio Job. of RADIO PARTS for a home If you are earning a penny less than 150 a week, send Experimental Laboratory for my book of information on the opportunities in Radio. is It free. Clip the coupon NOW. Why be satisfied with $25, You can build over 100 d r- $30 or $40 a week for longer than the short time It takes to cuits with these outfits. You get ready for It:utio. build and experiment with the circuits used in Crosley, Radio's growth opening hundreds of SSO, $75, Atwater - Kent, Eveready, Majestic, Zenith, and other $100 a week jobs every year popular sets. You learn how In about ten years Radio these sets work, why they has grown from a /2,000,000 to work, how to make them a 81,00u.00o,0oo Industry. Over 800.000 jobs have been cre- work. ated. Hundreds more are being This makes learning opened every year by its at home easy, fascinating, SIN a week continued growth. Men and young men with the right training -the kind of training I give you practical. "My earnings in Radio -are needed continually. are many times greater Back view of 5 tube than I ever expected they You have irony jobs to choose from Screen Grid A. C. tuned would be when I enrolled. Radio frequency set - They seldom fall under Broadcasting stations use engineers. operators, station only one of many cir- $100 a week. If your managers and pay 31,800 to 15,000 a year. Manufacturers cuits you can b u i Id course cost four or five continually need testers, inspectors, foremen, engineers, service with my outfits. times more I would still men, buyers, for jobs paying up to $15,000 a year. Shipping' consider ft a good Invest- companies use hundreds of Radio operators, give them world ment." wide travel at practically no expense and a salary of $85 to 1200 month. E. E. WINBORNE a Dealers and jobbers employ service men. salesmen. buyers, managers, and pay 130 to $100 a week. 1414 W. 48th St.. There are many other opportunities too. My book tells you Norfolk. Va. about them. So many opportunities many N. lt. I. men make SS to 1525 a week while learning

The day you enroll with me I'll show you how to do 10 Jobs, common in most every neighborhood, for spare time money. Throughout your course I send you information on servicing popular Jumped from 034 makes of sets; I give you the plans and to ideas that are making $200 to $1.000 for hundreds of N. R. I. $100 week students in their spare time while studying. "Before I entered Radio I was making $35 a week. Movies, Last week I earned Slio Talking Television, Wired Radio included servicing and s e 11 in g Radio principles as used in Talking Movies, Television Radios. I owe my success and home Television experiments, Wired Radio, Radio's use Tam doubling and tripling the to N. R. I. You started in Aviation, are all given. I am so sure that I can train you me off on the right foot." satisfactorily that I will agree in writing to refund every I salaries of many J. A. VAUGHN penny of your tuition if you are not satisfied with my Lessons 3715 S. Kingshighway, and Instruction Service upon completing. in one year and St. Louis, Mo. less Find out 64-page book about of information FREE this quickway to Get your copy today. It tells you where Itadio'S good jobs are, what they pay. tells you about my course, what others who have taken it are doing 1,- BIGGER and making. Find out what Radio offers you, with- Radio out the slightest obligation. ACT NOW. pAr 'J Needs *see extra to a months J. E. SMITH, President Trained "In looking over my National Radio Institute Dept.. IGX Men records I find I made $500 from January to May in Washington, D. C. my spare time. My best Our Own Home week brought me $107. Pioneer and W o r I d's I have only one regret Largest Home-Study Ra- J. E. SMITH, President. regarding your course dio training organization National Radio Institute, -I should have taken devoted entirely to train- Rcpt. 1G X it long ago." ing amen and young men Washington, D. C. HOYT MOORE for good jobs in the Radio industry. Our growth has Dear Mr. Send R. R. 3, Rox 81s, Smith: nie your book. This paralleled Radio's growth. request does not obligate Indianapolis, Ind,. M'e occupy three hundred me. times as much floor space now as we did when or- Nanne ganized in 1911. Address Lifetime finploonentleroicetoallgradyatef City cl ,t,. S R:11)IO-CR:AFT July, P./31 The Third Supplement to the OFFICIAL RADIO SERVICE MANUAL Is READY for Distribution

SUPPLEMENTS Nos. 1, 2 and 3 to the OFFICIAI, RADIO SERVICE MANUAL NOW! are obtainable - ONE of the most important achievements in recent radio Some of the features book publishing comes with the completion of the first three Supplements to the OFFICIAL RADIO in the third Supplement SERVICE MANUAL. These Supplements, now ready for distribution, are the beginning of a series which will be pub- Completely revised index for the entire OFFICIAL RADIO lished every sixty days during the year. The pages of the Sup- SERVICE MANUAL. plements are printed exactly like those in the OFFICIAL RADIO SERVICE MANUAL, and as each Supplement is Radio -Phonograph installation, added periodically it will be kept uniform with the original book in paper stock, (loose -leaf form) and in make -up. Wattage of Radio Receivers, R.M.A. Color Code, The third Supplement to the Manual brings that useful book Fada Resistor and Condenser Values, right up -to- the -minute with the diagrams and schematic circuits of the latest radio models which have been placed on the Canadian Circuits. market during the past few r^onths, as well as with new information of sets for 1930 and 1931. LIST OF CIRCUITS PUBLISHED IN With each set of Supplements a new index is supplied. The SUPPLEMENT No. 3 pages are numbered to enable one to include the new additions in their logical places in the original OFFICIAL RADIO Sentinel Audiola Electrad SERVICE MANUAL. Erla Philco Loftin -White Kellogg Every owner of the OFFICIAL RADIO SERVICE Stewart Warner Canadian- Bosch MANUAL will be sure to be up -to -date in radio if he becomes Story & Clark Westinghouse a subscriber to the Supplements. The cost -only $3.50 a Brunswick Silvertone year -is trifling, when it is considered that it is our intention Radiola DeForest Crosley New Midget to publish enough Supplements during 1931 to make the Circuits present SERVICE MANUAL more than twice the size it Victor Ambassador is now!

SUBSCRIPTION PRICE FOR SUPPLEMENT SERVICE MAIL COUPON $350 A Year TODAY! EACH SUBSCRIPTION STARTS WITH SUPPLEMENT No. 1. This is a very small cost when you consider that for the whole year a Supple- ment will be mailed to you every other month. Those who already own the GERNSBACK PUBLICATIONS. Inc., R("7 OFFICIAL RADIO SERVICE MANUAL have concrete evidence of what 96 -98 Park Place, New York, N. Y. can be expected from a $3.50 investment in the Supplements to the original I enrlme f2. ro for which sou are to enter me tubsrrlpl lm for the Supplement% of the OFFICIA. RADIO SF;Ity I(t; book. 11.\NI.M.. It Is understood that the Supplement% will he nulled to me nt lea,t six tunes during the year. No S.W.- If you are one who has not yet recognized the importance of owning a copy ment wlll be sold singly. of the OFFICIAL RADIO SERVICE MANUAL, turn to page 56 in this issue and learn more about this valuable book. Name Future issues of the Supplements will be ready at the following dates: July 1st September 1st November 1st Address City State JULY 1931 HUGO GERNSBACK adio raft Editor VoL. I1I-No. 1 `- FOP TPE SERVICE MAN . DEALER RADIOTRICIAN " Takes the Resistance Out of Radio " Editorial Offices, 96 -98 Park Place, New York, N. Y. The Radio Dollar By HUGO GERNSBACK

IN a time of rapid industrial changes, we may easily fail The reason, of course, is that today the basic industries to recognize how thorough these changes are and, also, from which the radio industry derives its raw materials are how revolutionary in many respects is the fall of prices. all operating at exceedingly low costs, and in many cases During the present depression, all industries have, of even below cost. course been affected to a marked degree; but there is, per- Take, for instance, such an haps, no other industry that has been affected so vitally as item as copper, which enters largely into the production of - radio. It is noteworthy that the downward price movement every radio set; it is today selling actually lower than it has done in the past 35 years. in radio has exceeded that of most other industries. . The chances are (going by averages), that copper will not Few people realize that the radio dollar of 1924-26, when sell so low again for many years to come. 'l'he same thing radio activities were at their peak. is true in a proportionate degree of all is worth less than 25e compared to other nuato- riads. Many industries, in today and it is prulrthle that the fig- ruinous competition, are selling their ure of 25c on the dollar is quite (sigh product actuallyll' at a loss. Copper, for as radio goes today. It can at best instance, which costs more than Ile a only he an approximation or an aver- FIR ST! pound to produce, on the average, is age; but you can pick out any amount sold at 9c. That means, that the pub- of items where the radio dollar of TI)R the past two years, RADIO-CRAFT lie today is virtually getting radio 1924 is worth considerably less than I has brought to its readers FIRST, all new merchandise at less -than -cost prices; 25e today. Or to put it in another radii) developments, with practically no which condition, in the very nature way, because of the lower prevailing exception. In many cases, the new inven- of things, cannot last forever. prices, the purchasing power of the tions and developments are published from The same radio dollar today- is therefore $4- two to four months of idea is carried further ahead other radio into compared to the 19.24 dollar. publications. the finished product as well. Thus, for instance, radio tubes also Take, for instance, the receiving Just to mention a few which "broke are being sold at lower prices today tubes. In 1924 the average price of first" in RADIO -CRAFT: than they probably will be for at tubes was around $4.00 or $5.00 generation to come. 'l'he reason here while apiece; today, the average price Thyratron is a price war between several of of (disregarding the tubes list prices, and Automatic Volume Control large tube interests, in order using average prices to ex- in the open mar- Farnsworth Televisor terminate a n her of smaller con- ket) is about 60c. Radio Fever cerns. After this has been accom- Kruesi Radio (Airplane) Compas. Take the average radio set in 1921; plished, the chances are, the prices Variable -Mu Tubes the prices then were around $15(1.00 will be higher again. to $'200.00; whereas Long -Wave Converter today, the aver- The same situation also prevails in me price -when Cold- Cathode Vacuum Tube. the midget sets are the radio set industry; and those who figured in Radio Sextant -is somewhat less than can sec the lundwriting on $50.00 Short -Wave Prospecting the wall, if we figure the set stripped, realize that, even today, and only a com- without tubes. We st also If you wish to get the latest radio de- paratively few radio set manufactur- figure that in 1924 sets were sold for velopments FIRST, read RADIO- CRAFT. ers are left compared to the peak of $150.00 to $200.00 without a loud 1926 -1929. After the process speaker; of eli- but today practically all sets mination is over, the chances are that come with loud speakers, and the the present depression will be over purchasing value of the 19:31 dollar therefore, is proportion- as well, and higher prices will prevail for both reasons. ately higher. These are the heyday bargain days of radio. Ten years from now, we shall look back with wonder There is not a single radio item today that cannot be bought at what we were a able to buy with the radio dollar in 19:31, at prices that are exceedingly low you and we will marvel -if compare them with how it was clone. those prevailing in 1924-whether it be. standard merchandise put out by a reputable .house, or surplus merchandise thrown 'l'he intelligent radio man of today appreciates this situa- on the nmrket for what it will luring. No matter how you tion, and is soaking the best of it by stocking up with the figure it, the radio dollar today in purchasing power is bigger necessary material that he will require for some numiHis than it ever was. to come. He need have little misgiving that be is making a mistake by paying too much. As I have often said before, In many respects, it may be said that this is the radio 'Mil- there are .Still increasing opportunities, to make money in radio, len , so far as prices are concerned; and it is doubtful for the wide- awake radio man who is alive to the possibilities indeed if we shall ever see such low prices again. that are open to hint today.

9 10 RADIO-CRAFT July,1931 A New All -Wave Oscillator for Modern Servicing With features of special value in superheterodyne work By H. G. C1SIN, M.E. UI.T1MATE simplicity distinguishes the calibration charts are supplied, enabling the new Supreme "Model 70" modulated operator to determine the frequency with Oscillator; by means of an ingenious circuit an accuracy within one -half of one per cent. arrangement, both the intermediate and the With this wide tuning range, the instru- broadcast bands, from 90 to 1500 kilocycles, ment is adapted to all commercial inter- well as other in- are covered with a single set of inductance mediate frequencies, as to The Supreme "Model 70" oscillator is its car - roils and tuning condenser. One -30 Babe termediate frequencies between 90 and 550 rying case; with the output meter at the left. be employed in future is used in the instrument, and may be sup- kilocycles which may the When the A.C. line Is plied with current from dry -cell batteries superheterodynes; thereby eliminating 110 -volt D.C. line. ob- is automcaticall- modu- (the shielded case provides room for the possibility of the instrument's becoming employed, the Output of the supply volt- batteries); or it may be connected to the solete. lated by the frequency in this case, the switch Si may be light -line. An output meter (which is also age; Operation of the Oscillator it will work on an A.C. combined with an ohmmeter, for measuring closed. Obviously, the grid circuit of the tube is placed line of any commercial frequency. all resistances up to 1 megohm) is furnished; In and grid -leak re- 1.3, by the variable resistor but the oscillator non' be obtained without a grid condenser, C3, Coil shunted he short -cir- antenna, coupled output meter by those who already sistors 112 and 1t3; 112 man' R1, serves as a dummy the switch SI. With coils, from which an output meter, or a set analyzer cuited by means of the to the main oscillatory have -leak modulation" energy to be delivered to the containing one. the switch open, "grid it picks up that is, the grid condenser set under The fixed condensers C4, A dumuny antenna enables the oscillator takes place; test. receiver under C.5 and CO isolate from the os- to be couplet) to the radio antenna's output from the oscillator being cillator the d test; the grounded connection to the set. under control by a tapered variable resistor Complete shielding eliminates the possibility of picking up front the oscillator energy which has not passed through the The curve at the very left is the of the oscil- y antenna. fundamental frequency du lator; its 15 harmonics, in their order, A more detailed analysis of the instru- cover the whole range of servicing. ment may be obtained by reference to the The difference between two oscillator diagram. It will be noted that the familiar settings immediately indicates the po- is employed, in- sition of one frequency adjustment, Hartley oscillator circuit with. relation to the other. cluding two inductance coils L1 and L2 tuned by the variable condenser Cl. The plate current of the tube is fed through the By means of a single toggle - H.F. choke RFC-1; the feedback effect tak- switch (shown in the diagram ing place through the blocking condenser C2. loo too i00 moo roo 600 lao Soo soo toad 000 imo MOO 1400 KILOCYCLCS two switches S2) the The oscillatory circuit 1.1- 1.2 -C1 covers a as the can be changed over band of fundamental frequencies between oscillator immediate y from battery to lamp- socket op- 90 and 250 kilocycles. For all higher fre- e larges and discharges at an audible fre- or vice battery operation, quency- bands, the multiples, or harmonics, e tency and modulates the oscillator output. eration, versa. For volt and a 221/2 - of the fundamental frequencies are em- (The tone's slight variation over the tuning a single 4',Ç "C" battery, the equivalent, are employed. By this means, frequencies up to range is an index of the tuning multiple. - volt "B" battery or These fit within the shielded os- 1500 kilocycles are generated in the single Tech. Ed.) This method of modulation is ployed. tuning circuit without the use of compll- used only when the oscillator is supplied cillator case in compartments provided. operation, a. detach- ated switching arrangements. Complete with battery current or current from the For socket power able cord and plug are provided. From the 110 -volt D.C. line it is necessary to have R2 R3 RFC I the correct polo Mg it may be necessary 60000 to reverse the plug if it is placed in the - V OHMMETER. hump socket the wrong way at first. If a LI sl' POWER LEADS 220 -volt power supply system is encountered, C3 Cly The oscillator may be operated in series with a 200(1- olhmt, 10-watt. resistor. R6 'l'he R.F. chokes, 1(FC2 and RFC3 are 12 placed in the puiser -line circuit as shown; C2 --3I13 + S2 S2 '4%zv the.r prevent the radio -frequency energy 22y2v from the oscillator from leaking out into OSC. OUTPUT CONTROL the power line and interfering with meas- C6 66000 C4' RFC 2 { urements on the set. In general service L3 practice, the 110 -volt A.C. or D.C. line should be used; the batteries being em- G R1 RFC 3 li CS rT - ployed only is 0QQQ9- where power not available. PICK -UP COIL In this way the life of the batteries is pro- IS TOTALLY SHIELDED.) 110v., A.C. OR. D.C. (OSCILLATOR longed, and time cost of opération becomes negligible. The values used in the Supreme "Model 70" are: RI, S00 ohms (tapered) R2, R3, 60,000 ohms; 'l'he resistor R4, which cuts the 41/2:volt C4, R4, 42 ohms; R5, 300 ohms; R6, 1591 ohms. Condenser Cl, .0005 -mf.; C2, C3. battery's voltage down to the required 2 0.01 -ml. L1 -L2 have a total inductance of 6.2 milihenries. Opening SI gives .4.F. CS. C6, volts for the type '30 tube, has a value modulation. (Latest models have two more filter condensers across the light -line, outside the chokes.) of July, 1931 RADIO- CRAFT 11

al t 42 ohms. The resistors R5 and R6, together with 114, cut a 110 -volt supply down to the correct value. The 221/ -volt Latest Testing Equipment for plate supply is taken from the line voltage at the connection between the resistors Its and ltd. It will be observed that no filter - Bench and Kit ing is employed; as the pulsating or alternating line voltage is used for modulation What manufacturers have developed recently for purposes. the Service Man Extra terminals are provided for the 22'. -volt battery on the panel of the in- ufacturer of the latter has produced the strument; so that this battery may be used equipment shown in the illustration, as a in connection with the ohmmeter for meas- compact piece of equipment for checking uring resistances. These terminals are the work. A battery is included, together clearly shown in the diagram. with a meter, variable resistor and test 'l'he output- ohuuneter provided with the prods; circuits may be quickly tested, re- instrument is a very ingenious combination sistances determined, and the assembly of a D'Arsonval meter movement with a proved before delivery is made. full -wave copper -oxide bridge rectifier. An (Scott Transformer Co., Chicago, Ill.) arbitrary range is provided for the radio output indicator, together with an accurately- calibrated ohmmeter, ranging from u OUTPUT METER to 1 megoluu. This will indicate circuit COMPARISONS of output, as well as continuity of even higher resistance values. The Jewell "Pattrrn 213" meter, drsi!nucd for lJ checking and balancing of circuits, not the edification of the tube purchaser. only in receivers, but in public -address and projection equipment, are facilitated by the COUNTER DEMONSTRATION CHECKER S\I.I:S\L\NS1III'. ns well as technical a,einau , (Eel atetl the design of the tube checkers .shown, which their maker markets as "Tube- Sellers." While a small meter shows the tube salesnum the readings, the big demonstration meter facing the customer presents them in conspicuous and confidence- inspiring fashion. Psychology as well as precision is evident here. The big teeter is "Pattern 21:3," and the combination shown as "Pattern 219" includes a counter - type tester with pre-heater, rotary filament

The Supreme portail., ,.ride- rectifier meter used with the ".Model 70" oscillator; Right, the n e w its circuit appears on page 49. Weston ".11 o d e 571" output meter, The mechanical construction lias been de- a precision iustnu- signed for utaxituum compactness, light "leuf far all types of servicing. weight, durability, appearance and simplicity of operation. 'l'he black liakelite panel, with veriebrnn ed markings, presents a pleas - use of the device shown. It has live ranges: ing appearance. It is mounted on an 1.5, 0, 1.5, 60 and 1.50 volts, A.C., which are aiuuin plate which fits into a cast alumi- Left, a set -up o obtained by the range -selector switch below tester and large num tray; giving complete shielding and the dial. 'l'he non -inductive impedance of great strength. meter for ran liter nuchanic:II A hardwood Ilse; the combina 4,00(1 ohms is constant for all ranges. The carrying case (furnished separately) may uion is Jewell "Pat- instrument may be connected hcross the tern 219." be used for transporting the oscillator and output of a receiver: butt, if it replaces a output natter. The control dial is of special voice coil directly, must be shunted by a design, affording a positive vernier action, switch, and connections for the newest resistance approximating that of the coil. which is necessary for fine settings. pentodes. It is. 51,!.x:37;,x2' inches over all, and weighs (Jewell El. Practical Applications Instrument Co., Chicago, Ill.) about 26 ounces. (Weston El. Instrument The busy Service Man is called upon to Corp., service all kinds of receivers. The more CONTINUITY METER Newark, V. J.) complicated superheteroch'nes, which are FOR custom set builders, handling re- ROW becoming very popular, require very ceivers of specially high quality, the man- "DEADLINE" TUBE CHECKER accurate adjustments, to give full satisfac- BY the use of a particularly 450 1,045 "dead- heat" tion. Ifence, the use of a service oscillator moving -coil type of test meter, there has of simple design, but very flexible in its been developed for the Service Man and 25 OHMS applications, is essential; while a thorough SW. tube salesman a particularly fast- working knowledge of its use is an important factor. + tNNNI_ test instrument. The name "Deadline" is To use the oscillator, first connect the 7Ysv. derived from the graph that accompanies two output terminals of the oscillator each instrument, on which is indicated the ((arked A and G in the diagram) to the "life expectancy" (to borrow an underwrit- antenna and ground binding posts of the 0.7 er's terni) of the tube tinder test; those set wader test. Special marked leads for vaTs reading below the line being electrically this purpose are the provided with instru- T1ST "dead." ment. PRODS The circuit design makes it possible to de- The output meter is then connected to termine whether a tube will be noisy in op- the set output. Special leads, equipped with The circuit and outward appearance of the Scott corm unity meter, useful for many eration; and whether its elements are (Continued on paie 49) purposes. (Continued on page 43) 45 Radio Service Data Sheet

PHILCO "MODELS 111" AND "111A" SUPERHETERODYNE RECEIVERS

The fundamental circuit of the above listed Phileo receivers, manufactured by the Phila- CIA delphia Storage Battery Co., Philadelphia, Pa., is the subject of this Data Sheet; with particular reference to the Model III set. CON D. Available constants are listed, as follows: BANK Condensers: Cl, C2, C3, C4, tuning gang; and their H.P. trimmers, Cl.,\ CZ.\, C3.\, C4A. C5, C'6, C17, C20 are I.F. trimmers; C6A, C7, C17A, C35, .00011 -mf.; C8, C9, C10 (with resistor), CII (with resistor), C18, C19, (and resistor), C23, .05 -mf.; C13 and C16 (double unit), 0.25 -mf.; C14, .0007 -mf. C15, L.F. trimmer; C12, L.F. resonator; C'20.\, .00005 -mf.; C21, 0.5 -mf.; C22, .00025 -mf.; FA C24, .015 -mf.; C25, C26, C28, C29, C30, C31, C32, C36 (in filter- condenser bank; see illus- V7 tration of condenser connections); C27, tone control condenser bank; C33 and C34 (double 7 unit), .015 -mf. Resistors: RI (black), 10,000 ohms; R2, R3, R12, R13, R23 (silver gray, yellow tip), 100,- C20 000 ohms; R4, RS, RIO (with condensers), 250 ohms; R6 (orange), 50,000 ohms: R7 (brown 5PKR. body, black tip, red dot), 1,000 ohms; R8 (belgian blue), 13,000 ohms; It9, R14 (battle- PLU G ship gray), 500,000 ohms; RII, R18 (auto brown, yellow tip), 25,000 ohms; R15 (white), Arrangements of parts on the top of the chassis of the Phileo "111" Super-heterodynes. Two 250,000 ohms; 1(16. volume control; R17, 1(24 trimmer condensers (C5, C17) seldom requiring attention are adjusted from the underside (jade green), 70,000 ohms; R19 (long tubular), of the chassis. These two condensers connect, respectively, to the input and output grindings flat, wire - 10.000 ohms; R20, R21 (one unit, of the first 1.F. transformer, L5; and, in conjunction with this transformer, form a par - wound, center 35 ohms (each half); -tapped), selective input circuit for the first 1.F. tube, f'4. The oscillator adjustments are R22 (short, tubular), 800 ohms. ticularly distinguished as "high-frequency" (C4.4, and "low- frequency" (C15). The operating voltages for the "Model 111" are as follows: Filament potentials: VI, V2, 2.1 volts; V6, V7, V9, VIO, V3, V4, V5, V8, Note these readings are taken with a shipment. Under no circumstances are the 2.2 volts; VII, 4.9 volts. potentials: VI, that line - potential of 115 volts, and volume control adjusting condensers to be changed in the field. 190 volts; V2, 180 volts; V3, 45 volts; VS, in the off position; with the station selector This alignment requires special oscillator equip- 185 35 volts; V8, 95 volts; V9, V4, volts; V7, turned to the lowest frequency, and the range ment, which all l'hilco distributors have. If VIO, 255 volts. Screen -grid potentials: VI, for any reason the receiver needs adjustment, 60 volts; V2, 62 volts; V4. 65 volts; VS, 82 it must be returned to the distributor's service 0.2 -volt; lRli I volts. Control -grid potentials: V1, CSA RIS { !Rq ssy,.RN department." V2, 4.6 volts; V3, 0.7 -volt; VS, 2.2 volts; V6, "Model 111A" is a 25 -cycle design, and its V7, 0.4 -volt; V8, 1.2 volts; V9, VIO, 50 volts. dldrr77 R17 n-' vary from the above. RM C6A C17,1 RS CIA parts values slightly Plate currents: \'I, 1.7 ma.; V2, 0.5 -ma. (as Model 211" is a phonograph combination; (6 te - C4A CR ® read on 20 -ma. scale); V3, 1.6 ma.; V4, 1.5 C20Á --j 25 designation. jf, ,RI RZZ while '211A" is its -cycle ma.; VS, 3 ma.; \'7, 0.2 -ma. (as read on 2 C It will be ,noted, from the top -view illustra- IRU R19 ma. scale); V8, 4 ma.; V9, VIO, 32.5 ma.; i SRS 7 47 R p tion of the chassis, that two of the trimmer \ßZ11 side. CSA under VII, 50 ma. per plate. Screen -grid current - Rtl capacities are adjusted front the R12 ?RRq'TT (as read on 2 -ma. scale): VI, 1.75 ma.; V2, I W Their locations, and the positions of all the re- J R23 0.15 -ma.; V4, 1.7 ma.; VS, 1.85 ma. 's-- sistors, are shown in the under view. those models Phileo chassis; As indicated by dotted lines, Underside view of the "III- dated later than March 15, 1931, are wired to showing only the fired resistors and con- place a higher bias on the first I.I', amplifier, densers. and the trimming condensers; their V4. This connection is made by swinging the locations in the chassis may be fixed in re- resistor R9 from the chassis to a center -tap lation to the long black resistor, R19. which is obtained by changing R12 from a single 100,000 -ohm unit to two 50,000 -ohm shits, and connecting them in series. switch SW 1 in the diagram set at "normal." The intermediate frequency used in these Putting this switch in the "maximum" position models is 175 kilocycles. All final adjustments increases greatly the sensitivity of the Philco are to be made with switch Sw. 1 in its "III" receiver. Positions "normal" and "maxi- "normal" position, No. 1. A fiber wrench is mum" are indicated in the diagram respectively required for adjusting the I.F. trimmers. The - are to be adjusted at as 1 and 2. Check the setting of this switch; high frequency circuits - since its incorrect use will result in the com- 1400 kc. The single "low -frequency" con- plaint of distorted reproduction and erratic op- denser C15 is to be adjusted at 600 kc. After the overloading effect of power- adjusting the R.P. and I.F. stages, tune the Condenser bank: note circuit change (dot- eration, due to ful locals with the switch set at "maximum." receiver to the eighth harmonic of the I.F. ted)' in some models. Capacities are: C25, The factory makes the following observation circuits: the dial reading should then be 140 C26, C28, 0.5 -mf.; C29, C30, 2 mf.; C3I, concerning adjustment of the nine compensating At this time, make any adjustment of the - condenser which may be 0.15 -mf.; C32, .015 -mf.: C36, 1 mf.; in 25- or trimmer condensers: " "These receivers are high frequency C4A cycle model, C31, 0.3 -mf; C29, C30, 3 mf. accurately adjusted at the factory prior to their necessary.

(SA CS RA Cs CIO CIA . -_-.. C.1...... !7 IsR IOQtYI o MI r _ s7 IIs ári-' n cil

1l S 1 4 YQs StltnOA r; 1 r1;p Cn no 1 rlR 1 Itf O -` rT Q COI, (t7 17 ff n ñs f It. bla 1 ili } ns (R eq u7 ll )I))]a.)1))1111)'OA)>JIIsann. )'aMJj__t, Qsv,A.c. 1l-M l!'l,- n>>n,wl-nu>,)/')Alal-A ... r to three fixed condensers across the output Schematic cfrcui of the Phileo 's Iode! 111" Receiver. Tone control is obtained by shunting One not connect direetty to the chassis, but returns through of the second .4 F. tube, F8. No e that the renter-tap of the high -voltage secondary dors tgo resistors, R20 and R21. The plate of F6 connects. directly to the cathode. 1931 12 RADIO -CRAFT July, Radio Service Data Sheet 46

CLARION "SERIES 90" SUPERHETERODYNES (MODELS AG90, AC -91, AC -91A, 25 -90, AND 25.91)

The latest Clarion receiver. manufactured by cration at 1400 high - the Transformer kc.; except that C3 (the Corp. of America, Chicago, Ill., frequency tuning condenser) remains fixed, incorporates the newest advances in set design. only C3.\ bring adjusted, if Among the features necessary. Check with which the Service Man also CIA and C2A. must familiarize himself are the following: a superheterodyne circuit with variable -mu tunes; TTigh- percentage modulation at the transmit- a screen -grid first detector; a power screen -grid ter will result in increased signal strength at second detector; a pentode power stage; together the receiver, as compared to other stations for with tone control, tuned hum filter. and auto- which the automatic volume control has been matic volume control; as the circuit illustrates. adjusted. Models "AC -90" and "'AC -91" operate on Poor tone quality may be due to off -resonance 110 volts 60 cycles; and the "25 -90" and "25- timing by the listener. Check by using a short - 91,' on 25 cycles. Model "90" is mantel - wire antenna, with volume control full on; the type; Model "91," a console, and Model "91-.\," automatic volume control circuit will then cease a phonograph combination. to level the signal strength, and a tuning peak The volume control, in its extreme left posi- can be obtained. :\ poor '24 seco,ul- detector tion, operates a phonograph switch, in the Model may mar the tonal reproduction; check also V6. "90.\" receiver; Chassis of Series "90" Clarion: compare A "fluttering" signal may be due to a poor the phonograph pick -up circuit this illustration being shown dotted in the diagram; rcith the coded layout at the ground. and the loner right. switch at S. The pick -up impedance should .\ 100 -watt lamp should light brilliantly when be between 2000 and 5000 ohms; and the vol- connected between ground and one side of the ume controlled at the unit. in the following manner: the plate potential is light -line. .\ dim light indicates a poor ground All available constants are as follows: con. re-ad between plate and filament prongs, on the connection; and no light, an ungrounded light - densers Cl, C2, C3, tuning units; Cl..\ C2A, 250 -volt scale. The control -grid is checked line. If the power company corrects the latter C3.\, shunt trimmers; CS, C21, .0008 -n1f.; C6, between the black common lead (on the repro- condition, hum, fluttering, circuit oscillation, and back -ground C7, C8, C9, I.P. circuit trimmers: CIO, C15, ducer's voice coil) and ground. The space - noise may be eliminated. C16, C18, C20, C22, C23, .05 -mf.; CII, 0.25 -mf.; charge -grid is tested between this prong and Although the intermediate frequency of 175 C12, 1.0 -mf.; C14, C24, C27, C28, 0.1 -mf.; filament. Connections to the UY base of the Ice. has been selected by most manufacturers as C17, .00005 -mf.; C19, 0.35 -mf.; C25, C26, 8 'PZ resemble those of a '27-except that the the most satisfactory it is to be noted that a mf. (electrolytic). cathode prong becomes the space -charge -grid weak fourth harmonic, 700 kc., may heterodyne lead. An Resistors RI, 113, adapter which exposes these five con- a broadcast station carrier and cause a whistle. R6, 1,000 ohms; R ?, 230 nections ohms; R4, 2,000 RS, I(9, will be of assistance to Service Men Another cause of circuit oscillation is high line ohms; 100,000 ohms; nut yet R7, 40,000 ohms; R8, % -meg,; provided with modern analyzers designed voltage; look also for open by -pass condensers. RIO, 1.0 -meg.; to test pentodes. RI I, 12,000 ohms; R12, 3,800 ohms; 1(13, 4,300 Note that one side of the filament secondary ohms; R14, 1,800 ohms; R15, 1,300 ohms; 1(16, Lack of sensitivity may be duc to an open which supplies VI, V2 and V4 connects also 435 ohms; R17, 400 ohms; R18, 65,000 ohms; circuit, a high resistance, or a short circuit; to other parts of the circuit, including the cath- I(19, 20,000 ohms; R20, 210 ohms. seldom to trimmers out of adjustment. Ex- ales of VI and V4, and the plate of the oscil- ceptional care is taken Operating voltages (with volume control in to align these circuits lator V3; and that, with respect to ground, this accurately; after which they will position "full" and line potential 115 volts) retain their lead has a positive voltage of 95, adjustment in nearly are as follows: Filaments \'I, \'2, V3, V4, VS, all instances. V6, V7, 2.2 Poor selectivity is seldom volts; \'8, 4.6 volts. !'late po- due to mis- align- OFF -ON TUNING VOLUME tentials, V1, 160 volts; V2, 168 volts; V3, nlent of the tuned circuits; but, more often, AND TONE 125 volts; V4, 163 volts; V5, 178 volts; VG, to a high -resistance joint in an R.F. circuit. An 25 volts; V7, 260 volts; \-8, 350 volts. Control - ohmic test may not indicate the faulty con- grid potentials, V1, 11.9 -volt; V2. 7.6 volts; nection; but the application of a soldering iron V3, none; V4, 0.6 -volt; V5, 6.8 volts; V6, to suspected joints may clear the trouble. 4.6 volts; V7, 16.5 volts. Cathode potentials, To align the T.F. circuits, (if the procedure VI, V4, 2 volts; V2, 4.9 volts; V3, none; is imperative), use a Bakelite screwdriver to VS, 9 'volts; VG, 4.5 volts. Plate currents adjust C6, C7, C8. C9 for maximum output (normal), VI, 2.8 ma.; V ?, V4, 2. ma.; V3, meter reading; with a 175 -kc. (exact) oscil- 9.5 ma.; VS, 0.25 -nma.; \'6, none; V7, 36 lator output wired to the cap of V2, all tubes nia.; V8, 72 nia. Screen -grid potentials, V1, in their respective sockets; and all cap leads V2, V4, 77 volts; \-5, 90 volts; VG, 40 volts; connected. V7, 260 volts. The R.F. circuits arc to be aligned at 1400 Removal of the tube shields will cause cir- kc. and 600 kc. cuit instability. Use of the variable PNDMO ow 9cm -mu tube The oscillator low -frequency "padding" trim- POWER REPRODUCER eliminates the hissing sound usually associated mer C4 is next adjusted, with the R.P. _-"i with oscil- LEADS - tASLE high -gain superheterolynes. The manufac- lator (connected to the antenna and ground turer's (T.C.A.) code for the tubes is as fol- posts) operating at exactly (,Ott kc.; at the Top miro of a Clarion superheterodyne lows: VI, V2, V4, CL -51; V3, C1.-27; VS, same time, chas- the receiver's dial is to be swung sis showing the positions of the trimmer VG, CL -24; V7, CL-PZ or CI.-47; V8, CI. -80. back and forth over the 600 -kc. setting-ad- condensers. The phonograph connection ap- The above readings on the pentode were taken justing for maximum output. Repeat the op- pears only an the -Model 90 -A" chassis.

ItTM. W DET OSC. L4 11.1 11 211P Sf LS OFT RFC P col '47 TONE CONTROL 'st '2T .C6 C7 '51 C6 CS p26 PEw,OOt.'RII SW. C22 PT

--_:.---"°---"'"-'"--, vg CONTROL AFC. '' ; !y Li C1. Cl) ,Ct: T RCRUPn)IL . "-" - - 7N I7 COIn , R1

1 I tl 492 )II)IIIB.I)).)rll.l,') )I.. RtD (1M5 s ®>tllll>))1)1))l'YY»)1 INNEN C12L tr to AA Schematic eh -unit of the highly- developed midget and console Clarion "Series 90" superheterodyne receivers; these utilise both mariable -mu and pentode tubes, with automatic volume control. (.Vote: in the manufacturer's "breakdown analysis" illustration of this receiver, condensers C24 and C25 return to the juncture of RIO and R20. instead of to the chassis.)

July, 1931 RADIO -CRAFT 13 14 RADIO -CRAFT July, 1931

only three of the powerful broadcasters were picked up with any degree of vol Money Operating Notes With the aid of a schematic circuit, all Making voltages, resistances, and capacities were for carefully checked. The plate voltages of all in amplifiers were found about 40 volts lower than specifications. The condensers were Men not at fault; so either a partially- grounded Radio Servicing Service coil or a had resistor was indicated. Fin- ally, under the pack, a heavy black carbon Some Tips on Supers of More or resistor (see Fig. 1) was found which should Ideas for the Application of a Less Recent Vintage have been, according to the diagram, 20,(110 Little Salesmanship ohuls; it tested 14,(00. It was removed and By BERTRAM M. FREED replaced by a 25,000-ohm component, the handiest value obtainable. Immediately the By W. E. SMITH voltages became slightly above normal, and SNCE the trend of the radio design the set perked as it had never done before. has returned to the formerly -popular This resistor is a bleeder, connected across NEVER before have there been such superheterodyne, perhaps some notes the 135 -volt supply tap to prevent any ex- great opportunities to make money by concerning a few of the models which cessive rise in voltage; such as would occur servicing radio as there are today. The have lately made their appearance on the finest and best radio receiver, sold only a market will be of interest. OUTPUT TO month ago, may be now obsolete; since PLATE OF 'MA 0.5-44. SPEAKER In the Silver-Marshall super, a compact there have just come upon the market sev- CHOKE job (which is being sold under several eral new tubes which are a vast improve- names), the speaker cable of six wires ter- DET. PLAT! ment and, of course, these tubes will better is in- ro / minates in a. five -prong plug, which FILTER any radio. at the 135V.+ =GSM serted into a receptacle provided SYSTEM 'l'he Service Man's business is, to give rear of the chassis. One wire (the black) 250 the conuuunity which he serves the best he OHMS is not connected to the plug, but must there is in radio. 13y this I do not mean RS, grounded to the chassis before any recep- selling gadgets, but incorporating improve- No. tion is obtained. (See Data Sheet 34, 400 T-O.S-MF. ments into your customer's radio. January, 1931, RADIO -CRAFT.) 35044 J Many Service Men, as well as the general If the fine wire of the volume -control 350.+ public, regard the radiotrician's profession fili<4 TO H.V. resistor strip breaks, intermittent reception r CENTER- i1e.5a as merely a job of fixing receivers. I re- The i TAP is caused; the remedy is replacement. 291Mr. gard my work as giving toy customer the ohms. value of this resistance is 3,000 TO FIL. and, course at a 45001IM5 best in radio reception of Care should be exercised in selecting '27 (8,9,10,0 ARE WS) CENTER TAPS profit. And I find the customer ready and tubes for the new Atwater Kent pentode ' willing to pay for real service. 2 model; or difficulty may be encountered. Fig. Only this year, a great many supers have The terminal strip of the Radiola "60 "; for After a great deal of bother and fuss use distance reception, sensitivity may be increased been sold that can be improved by the a "Model 20" Majestic, over hum in new by introducing R4, especially as a variable of the type '35 variable " " tube. It will using variable mu ("Multi-Mu") tubes, the panel control. be necessary, if the set in which these tubes cause was found in an open by -pass across all the tubes were removed, and which are to he installed has variable screen bias, the 35,000 -ohm resistor which biases the if might cause punctured condensers. to fix this at 75 volts (with n fixed re- second detector. The unit contains a pair filter In some instances, a lack of a few thousand sistor), and use a variable resistor for the of 0.4 -nif. capacities. de- ohms in this resistor has caused trouble. cathode bias. The value of the' latter One of the most perplexing jobs yet en- pends on the number of tubes it is to serve. countered by the writer was a Radiola "60"; Improving Sensitivity (Fig. 1.) for a long time, volume had been decreas- While the Radiola "60" is highly sensi- You will he surprised at the sales op- ing. Naturally, the tubes were first sus- tive and selective when in best operating portunities you will find if you take along pected; those in the set were not too good, condition, the writer has been approached with you, on service trips, a short -wave but their replacement did not greatly im- more than once with a request to "do converter of the superheterodyne type. Most prove reception. The next move was to take something to it," to pick up the stations people are now "off" the plug -in adapters; clown the condenser gang, in order to check which come in very weakly. After check- the ideal short-wave converter installation and realign the I.F. transformer adjusting up the set, as described above, the next is permanently connected up, so that either ments. These are tuned to 180 kc.; trim- step was to try additional by- passes in mers and compensators were then adjusted different parts of the set. This did not for maximum efficiency. help; it then seemed advisable to increase However, all this work counted for little, the plate voltage; and this was done by replacing the large wire -wound resistor under the pack with one of lower value (about 500 ohms) but without effecting any improvement. 'l'hen resistors of different values were sl ted across the four sections of the wire -wound unit which is secured to the front wall of the receiver, next the volume control. 'l'he tuning dial had been set nearly at 30 and, when a 700 -ohm resistor was shunted across the 400 -ohio section (next the volume control) Omaha came crashing in with a wallop. When this shunt was removed, reception ceased. After experiments with different values, centering around the biasing resistors, it was noted that n resistor of 400 to 700 ohms worked best when shunted across the 400 -ohm unit; but that the vol control Fig. 1 Fig. 1 To convert a standard screen -grid set for had then no effect when a powerful station Position of the large resistors in the Radiola variable -mu tubes, the circuit is altered front "60" power pack. (Continued on page 45) ..1 to B. Values depend on the set. July, 1931 RADIO -CRAFT 15

short or long waves can be selected by Lions on Philoo "Neutrodyne -Plus" sets throwing a D.P. D.T. switch. where, upon checking the set with a set One of the ideas I have been able to cash Service Men's of analyzer, sill voltages with the exception in on is altering receivers so that the short- of the grid bias voltage on the first R.F. wave police calls can be picked up. This tube were O.K. 'l'he first R.F. tube showing can be Notebooks done on any receiver, merely by no grid bias, and the second and third taking off turns of each tuned secondary. A few leaves from the experiences lt.F. showing grid bias (whereas all tubes tin!! act iii tes it is pi.ssi I'le to realign the trim- of our readers. get their bins through the same source), mers and What have you get frequencies high enough. I tells its that there is wu open in the second- Wuu1c1 found in your daily rounds? not advise changing single -dial an- of the first R.F. circuit. :1 continuity supers, unless you are thoroughly versed in test of the secondary shows it closed; this this DEMONSTRATING THE type of receiver. leaves only the range control, which is a Then IMPROVEMENT there are the new pentode power small variatble compensator across the first which By George Gable tulles, can be installed in au» set, H. tuning cundenser and functions as a "local- whether A.C. or D.C. There are several COME months ago, the same idea which distance" switc-h when turned all the way S Mr. Freed describes (on page 651 of to the left. Examine the range -control May issue of RADIO-CRAFT) occurred to me; spring for an open from the stator to the that of improving the Majestic "Seventy" spring. If the spring sloes not slake con- series, by replacing the push -pull '71.1's with tact to the stator, when not in "local" '45's. The latter, with their filaments wired position, no grid bias is applied to the first in series, give a better output. 11.1". tube; and the set will not bring in However, customers usually want to hear anything but strong locals. In most cases - B +R.F. AFEW TURNS REMOVED for themselves before they authorize the tension can be restored to the spring by change. How is that possible? bending with a pair of duckbill pliers, or Very simple, if the adapter sketched in install a new range control (Philco l'art Fig. 1 is used. The parts required are two No. 3133). tube sockets, two 4 -prong plugs and cords, When cases of oscillation in the Philon small clips, a suitable variable resistor It N -l' sets cannot be cured by neutralizing, and center- tapped filament resistor It 1. As the trouble is usually caused by an open the diagram shows, the grid and plate con- lt.F. plate condenser in the plate resistor- nections of the adapter are wired to their condenser cartridge. 'l'he easiest wily to respective prongs on the two plugs, while test this is to remove the grounding screws the filament current is drawn from one and lift the cartridges so the condenser of socket of the set. 'l'he battery is used for the unit is not grounded and test the con- additional grid bias, using the variable re- denser with an A.C. voltmeter in series with sistor to obtain the correct value. the light -line. Open condenser will show up 5W. by not giving a reading. If a Philco part F F G P G P is not available, an .05-nf. condenser can TO be PLUG--' - shunted Fig. 2 7-7 _ _. _ c - >TD PLUG from ground to the resistor - To receive police calls, below 200 meters, it condenser terminal. Reground all resistor - is necessary to reduce the minimum inductance 45 condenser cartridges, replace bottom pact of the tuning coils. Sonne methods are shown. / and re- neutralize the set; and you will find i

'45 1 types for different filament voltages; con- the oscillation is cured. sult the table of characteristics. Upon investigating sonne complaints of A great roam' sets have the leak-con- nuise in l'hileo "Models 95- 96 -76- 111 -77," denser detector; here a power detector may All111111111 where the volume was fairly loud, it was r R be installed, with consequent increase in asV.,C" found that the primary of the It.F. trans- both CCHA selectivity and tone quality. SIS1_1 formers was the cause of the trouble. 'l'he in a district supplied with 110 volts, D.C., 1Ih__IIIr primary is a small coil inserted inside the you will find any amount of battery -oper- -ir` Bakelite tubing at the bottoms the of trans- ated sets that can be changed to work off former (meaning the end away fr the the house lines. Incidentally, there is on Fig. 1 bracket) and is wound with very fine wire. the market a new series of tithes which are The Customer wants a sample of the proposed In nearly all cases, it has been found that work. Very well; this give ideal for this job, viz..: the '36, '37, and ':38. seal it to him. this fine wire has been broken and only All these tithes operate on the same fla- lies against the tenninal. \!'hen the volume uacnt voltage (6.3) and filament current is turned up, the vibration of the speaker (0.:3- ampere). Bias can be obtained in the A HINT OR TWO ON PHILCOS causes this wire to make and break contact; some way as in A.C. tubes, by the voltage By James W. Roberts resulting in a very disagreeable noise at the drop across a resistor between cathode SF.It VICE \Ion have, nu doubt, had speaker. In cases where the wire has broken and ground. (See page 731 of June ¡tAnto- trouble in locating the cause of very nt the outside terminal of the primary CitsFT for characteristics.) weak reception of ;III but strong local staa- (Continued on paie 14) '!'here are a great many automobile receivers that can be improved by the use of these tubes. YELLOW FROM LOC. DET .O15 -MLF. '2? PUSH - PULL Very recently there came on the market .015 -MF. 5.000 ANT. AMPLIFIER INPUT A.F.T. OHMS e al midget receiver using three '21's, one TO \.t f 5 '45 and one '80 type tube. I purchased LIGHT BAND a LINE NII 500,000 lot of four of these receivers for $70 and SELECTOR OHMS changed theme to use two '35's. one '21, one ( WHITE J250,000 '47 and one '80; which increased the range OHMS and volume most 1.0 BONY noticeably. The expense CtMER for two resistors, one output transformer TAP and 4 -naf. condenser cause to about $6.(0 per set all told. However, I happened to have these on a a TO FIELD COIL items hand. salvaged from .junk AND '84, sets; anti I sold these receivers for $Ií9.50 apiece. Fig. 2 The ¡'hitro (Continued on ¡age 48) tutte control may be introduced into an earlier model conveniently, wherever the "local." distance" switch may be dispensed with to provide a place for panel mounting. 16 RADIO -CRAFT July, 1931

Right on top, and where no one can deny The Service Man's they belong, is Silver -Marshall. My experi- Every Milliamineter ence has been that they will send you any- Open Forum thing and everything to help you, and they a Direct -Reading will be doing business when these other firms who are too "confidential" are by- Ohmmeter A Place for Free Discussion gones. 'then come Philco, Hanunarlund, of Trade Problems Atwater Kent, Aerovox Wireless Corp.,'l'obe By R. Deutschmann, and a lot more of the old - FRANCIS EHLE* timers. Forget the "confidential" firms, and MR. RABE BREAKS HIS RULE let us boost the "good fellows" instead. N YONE who works with radio cir- Editor, It Anm- CRAFT: Let us use good standard products, and euitss is, sooner or later, interested ohmmeter for Every so often 1 read something in your stick behind the firms who will give us de- in a direct- reading publications which is so disgusting that I sired information. Cut out all this "gyp" the purpose of measuring unknown sl Id write you about; especially letters stuff, and especially "gyp" tubes: let us resistance values and also testing the con- from Service Men which must be corre- find the demon who started "gyp" tubes and tinuity of circuits. If the price is available, spondence school beginners. put him inside his product with about 180 a suitable instrument can be purchased for Take for example the Colonial Midget, volts on the plate -that is where he be- this purpose. However, the experimenter the article states that set and speaker :t longs. or Service Man can readily convert the usual both be removed at once. On this set there And don't forget, fellows, that it was you 0-1 milli:uumeter into a c bination milli - is at small arrow on the dial and when this ammeter and direct -reading ohmmeter, is up to the station pointer a cutout on the making use of the scale herewith re- dial will slide out under the speaker. An- produced. List of the Schematic other writer wrote about neutralizing an A Reference To bring about the desired conversion of Circuits of Commercial the millianm,eter, the first step is to remove RCA 44. RADIO APPARATUS Whv don't you get in contact with some the meter from its case by loosening the first -class Service Men and have the letters Published is RADIO -CRAFT since the three mounting screws. Remove the two checked over before printing them? On the July, 1930, issue. screws holding the millimnnieter scale in other hand, first -class Service Men are (Previous reference lists appeared in the position. Place ohmmeter scale on top of loath to put out information for the benefit April and August, 1930 issues of the maga- old scale, fastening with a few spots of back numbers of RADIO -CRAFT I not put out zine. All glue if desired, and replace the scale mount- of competitors. I know, do are still available at 25 cents each, post- any. paid.) ing screws. Connect meter, battery and H. HOWARD RABE, calibrating resistance in series. The meter August, 1930 620 Nebraska. should now read zero on ohmmeter scale; if North Park, Fremont, Bosch "Cruiser," "Royal Cruiser," and "Im- (Mr. Rabe is correct in his observations perial Cruiser" Model 35, Battery Sets not adjust pointer with zero set screw. concerning the midget's dial, as an examin- (No. 23 Data Sheet), p. 78; Replace meter in case. ation shows. It is also obvious that the All- American Mohawk "One -Vial" Receiv- 'l'he battery voltage and calibrating re- ers, "Battery" ami "A.C. 226 -227" (No. writer of the article concerning the "44" 24 Data Sheet), p. 79; sistor determine the meter reading and, put down "neutrlizing" hastily for "align- Pilot Automotive Radio, p. 91; therefore, the accuracy of the ohmmeter. ing"; it is well know,, that small condensers Dubilier "Model l'I. 1985 S -G Duratran" When a 1.5 -volt battery or single dry cell though used Aperiodic R.F. Amplifier, p. 93; is employed, in combination with a 1,500-ohm are often called "neutralizing," Delco Automotive Radio (General Motors) for other purposes. p. 106; calibrating resistor, the scale is direct read- While the service notes in RADIO-CRAFT "Radiola VII -B" Receiver, p. 104; ing. If a 4 -5 -volt battery tnade up of three are checked over, it is true that errors t Samson "Double- Rotor" Circuit, "Model dry cells is employed, in combination with TC," p. 121; we a 4,500 -ohm the scale occasionally slip through; and are glad Screen -Grid, 4 -tube "3- Circuit Tuner," calibrating resistor, to have our readers point then) out for cor- p. 122. reading must be multiplied by three. With rection. Then, too, we are glad to observe (Continued ou pupe 60) 22.5 volts as provided by the usual fresh the increasing willingness of manufacturers 'B battery, together with a 22,500 -ohm and Service Men to give out information resistance, the scale reading is multiplied by which not only their competitors, but and I who sent in our subscriptions, even by fifteen. the whole trade, may profit. "I've noticed," before RAmo -CRAFT was published, and got By employing a 221/2 -volt tapped "B" said David Harcuat, "that it ain't a bad idea behind Mr. Gernsback because we were con- battery, providing a choice of 11/, 41/ and to let the other fellow make a dollar once vinced he was right. I.et us stay behind 221, volts, together with three resistors of 'n a while."-Editor.) him. 1,500, 4,500 and 22,500 ohms, the ohmmeter S dam-, Mr. Editor, when space is not may he employed to cover any resistance at a premium, might I suggest that you readings from (1 to 750,000 ohms. Meanwhile, TO OTHER I. S. M. print a "Red" and a "I;Inek" column, listing the former milliannneter function of the Editor, R.\nlo -CR. rr: in their respective Pinar. the "good fellows" meter is by no means impaired, since a Regarding the letter of Mr. D. C. Karr, and the "confidentials"? double -reading scale is now available. a is at Gen- h:ow, T. PIIILLIrs, in which broadside delivered - The direct- reading of ter described ItADIO- CR-t }-r Mich. eral Motors radio: first of all, 15106 Chapel Avenue, Detroit, presupposes the use of precision wire - has gone to at lot of expense and a tre- wound resistors of an accuracy within 1% mendous amount of corresponding, cheeking, WHEN TO BUY A NEW SET of their rated resistance value; ordinary etc., to put in the hands of anyone desiring resistors will not do. Our recent develop- be had. Editor, RADIO- CRAFT: them, practically every diagrams to ment of precision wire -wound resistors (in- Certain manufacturers, too, have their I find your magazine very helpful to the corporating stud i unique features as a special a Service Man and my copy each month is own ideas about this; and I to afraid it ceramic form with successive sections to read eagerly from cover to cover. ')'his is is ton late for them to fall in line. Their hold the winding; the highest grade of been checked, values Inv first letter to you, and in it I would sets have dismantled, enamelled resistance wire; special im- like to record some of my observations and recorded, diagrams made, and all the rest pregnating compound which hardens with so why let us boost e nts gleaned from several years of of it; worry? Instead, high temperatures instead of softening; the out experience in this field. those manufacturers who came right moulded end contacts; and the unique submitted they could to To begin with I think there is not enough and everything method of balancing the winding to the along. cooperation between the three divisions help radio - exact resistance value) now makes the usual experience have other readers had selling, servicing, and manufacturing; in What milliammeter and voltmeter available for a Some time ago I fact at times it seems as if they are working with the manufacturers? greater variety of uses, without sacrificing RADIO- CR.tFT a lot of letters, pro directly against each other. As I see it the saw in (Continued on page 51) and con, regarding this question. Well, here manufacturer is primarily interested in I go: (Continued on page 48) President, International Resistance Co. July, 1931 RADIO -CRAFT 17

1 mil. (.001 -amp.) flowing, there is a drop of 100 volts. Replacement Now, consider the case where a replace- Hints for Radio ment resistor narked 100,000-ohms is used, but assume that this resistor has an actual Resistors resistance of 140,000 ohms. In such a case, Manufacturers the voltage drop will be 140 volts and, By HARRY GEORGES hence, the voltage at the screen grid will By SERVICE MEN be 50 volts instead of 90 volts. An examination of the ace ponying OBVIOUSLY, it is impossible to chart, Fig. 2, showing d'namic character- judge the quality, accuracy of rat- Two -Volt Storage Battery istics of the "'l'ype 12l" Arcturus tubes, NOW that we have a good line of 2 -volt ing, or duration of useful service indicates that with 90 volts on the screen - tubes, would it not be a paying propo- of any radio c by a mere ponent grid, the tube has a tool conductance out a visual inspection; this statement applies with sition for some concern to put Gni of 1050 (other values such as plate -cell that could be especial weight to fixed resistors. They all single of high amperage voltage, etc., being normal). 'l'he amplifica- recharged like those already on the market? 11 are seem to look very alike and some tion factor is 400, and the plate resistance still sold very cheaply and are announced as Such a battery would be much smaller than Rp is approximately 400,000 ohms. the air -cell type, and there would be less wonderful "bargains." At a screen -grid voltage of 50, however, The intelligent radio Service Man, how- danger of overloading the tube. The writer the mutual conductance drops to 675, the has had this suggestion poked at him so ever, realizes the need of careful selection "mu" is 800, and the plate resistance in- and discrimination in the use of replacement often, by those who cannot sec anything creases to 1,200,000 ohms. in the big air -cell battery, that he passes parts. He has learned, often through sad Without considering mathematical equa- experience, that resistor bargains simply do it on for what it is worth. tions, we can see at once that, since the mu- A. W. McVEY, not exist. tual conductance (Gm) k an indication of The cheap replacement is the cause of 821 Locust St., Philadelphia, Pa. many kinds of radio troubles. In nine cases (The two -volt "accumulator" has been in vogue abroad for years, since tubes suited out of ten, the low- quality resistor is in- '2 accurately rated, sometimes even to the ex- -13+" 90v. MAS to operation 'in this manner were available. tent of being half or double the marked (To '27 PLATE) However, the two -volt storage battery will TO value. 90 require periodical charging, even with a In many cases, such discrepancies POWER time are noticed by the Service Man as soon as PACK set of small cons ption; and therefore he solders the replacement resistor into the air -cell battery serves a distinct purpose set. Where the resistors determine plate, ti for which it has no competition except grid, or screen -grid voltages, these potentials time dry-cell.-Editor). 100,000 OHMS VOLTAGE may be so far removed from normal, that (1.0 MA.) DIVIDER it is impossible for the tubes to function. A Little More Metal Sometimes, however, the resistance, al- Fig. 1 M\NL'FACTURERS alight well use a .4 resistor incorrectly be though incorrect, is not far enough "off" marked may the cause little more iron and copper when con- of numerous faults in a radio set. An instance to prevent the tube from operating. Still, is illustrated abo:c. at R: too high a. resistance structing filament and plate -supply trans- the operation is of poor quality, due to the destroys seu.riticty. formers. After some sets have been oper- use of the wrong resistance value; and so, ated four or five hours, if the transforme- while correcting one fault, the Service Man TYPE 124 TUBES is accidentally touched, one feels like rush- may introduce another, merely through the DYNAMIC CHARACTERISTICS ing to the street and shouting "Fire!" Or 1200 2.40 use of a "bargain" resistor. X do they believe in giving extra value by 0 an Another possibility is, of course, that the `>t 1000 ' ' 2.00 W providing electric heater in combination resistor of incorrect rating may he of a with time radio? i I.fO F value which will permit the tube to operate < 800NViAfa/tifata H. A. DEAL, i N'GIB = 600 I.20 with apparent efficiency, yet overload the 1"A\fa.2`\\\I Ñ 69 Glenwood Glade, Oakland, Calif. tube, causing a serious shortening of its 400 ago a life. Even in the single case out of n bun- Less Cross -Talk ` 200 .1 °f Bred, where the cheap resistor happens to J 040 W DEALERS and Service Men. right now, o have an ohmage approximately the same as 0.00 á should have equipment to handle the i OaM1IIt\ 10 20 30 40 50 60 70 80 80 its rated value, it is certain to deteriorate SCREEN-GRID VOLTAGE large recording discs- talking -picture 16- rapidly and cause noticeably poor or at inch size; the public is not, as was suggested . least inefficient operation, resulting in tube Fig. 2 in this cohmm some time ago, quite ready burn -outs or other similar troubles. Time This graph illustrates the result of changing the for them. How mammy pickups and consoles screen voltage of a screen -grid poor- quality resistor may only burn out it- tube. could take care of therm? I have at different self; this is about the best thing that it the efficiency of the tube, it is evident that times recorded radio programs on 12 -inch could do, for it thus calls attention to the this Imas been very greatly impaired. It is discs. and had a recording time of 11 to desirability of using a good resistor. Un- always desirable to have the mutual con - 12 minutes; using an electric motor with fortunately, most of the other troubles men- ductance as large as possible; but here we a power Clarostart to control voltage and tioned above, occur before time resistor goes see it reduced 40% by reason of the use thereby speed (ti gh some high- priced "haywire." of an improperly-rated resistor. uuotars have a speed regulator.) A Service In order to obtain a more definite idea We may apply a simple engineering rule Man, free to travel, could make a nice of ,just what an improperly rated resistor to determine the effect on sensitivity. The profit, as it is estimated that 45% of pic- operating characteristics can do to the of a gain of a tube is, when it is used in an ture houses are not yet wired for sound - tube, actual data will he given, to show amplifying stage, not its theoretical ampli- 10,231 out of 22,731. exactly what happens in the case of a fication factor, or "mu," but the "mu" mul- But what I have to say, last but not least, screen -grid tube of the '24 -type. tiplied by the effective impedance (Z) in is: give time public selectivity in a cheap its plate circuit, and divided In' the sum receiver. Incorrect Screen Potentials of its plate resistance (Ilp) and the effec- Wii.mrAR A. Smmeer.sr, Suppose that there is a 190 -volt tap on tive impedance load; since the latter two 149 .hiller Are., New Castle, Pa. the voltage divider, and that the current iS constitute the series load across which volt- supplied to the screen grid from this tap; age is divided. That is: Put Back the Jacks the voltage being reduced to the normal Mu x Z "I "l ING a phone ,jack somewhere in the operating voltage of 90 by means of the Gain equals Pl set, for the use of headphones. This drop across a 100,000-ohm fixed resistor, R, lip Z would give extra enjoyment to a lot of Fig. 1. In other words, with a current of (Continued on page 46) (Continued on page 49) 18 RADIO -CRAFT July, 1931 The New Scott "All- Wave" Superheterodyne An all -purpose, high -quality receiver for the distance fan who is exacting in his demands.

Tn,, handsome radio receiver, cone - cording bead, there is available an accessory idrtn y- shielded (even to a base unit, au Control Box, Fig. 1); and, also, to rover- plate), and designed to cover watch its constants, a hand microphone and wavelength ranges of 15 to 184 me- a. 200 -ohm phonograph pick -up. ters, and 21111 to 551) meters, is the latest of Details of the Circuit the distinguished series of distance-getting receivers developed 6t the Scott Trans- As indicated in Fig. 1, there are nine former Company of Chicago. 'l'he schematic tubes in the receiver chassis; and in the circuit of the receiver chassis is shown in power pack, two more audio tubes, type '45, Fig. 1; and that of its power pack in with an '80 rectifier. Five of the tubes in Fig. A Fig. 2. the receiver chassis are of screen -grid type Panel appearance of the III- II'are Superhet- Experimenters have long wanted a receiver ('24s) and the remaining four are '27s. erodyne in o suitable console. which would get that "nth degree" of effi- The 13.F. or signal -frequency amplifier V1 ciency obtained by using inductance values is a '24; the first detector V2 is au ither; further will be stated on this subject; except rquiring the least tuning capacity, for a the following three '24's, V4, V5, V1i, are to remark that a sixth (center) pin on the riven frequency adjustment. The Scott 1.F. amplifiers; and the last, V7, is the oscillator inductance operates the switch All-Wave Superheterodyne receiver obtains second detector. Sw. Further, the control -grids of V1 and this result by the use of six sets, each of two top -engraved plug -in coils. One set of inductances, which we will call A, covers a band of 15 to 21 meters; set It, 21 -27; set C, 27 -38; set D, :38 -84; set E, 81 -184; set F, 200 -550.

Accessories for Versatile Performance As we have pointed out in the articles on sound recording in past issues of lt,cuw- ('a.vrr, a high -power audio amplifier must he used for hest results. 'l'he Scott superheterodyne is peculiarly adapted to this work; since it makes provision for the connection of a microphone output, or a phonograph pick -up, to the input circuit of the Fig. B second detector, as shown in the schematic From right to left, tuner, amplitirr -pack, and reproducer: showing the connecting tables trhids circuit. This makes available, therefore, for give flexibility of placement. Note the complete shielding nad strong constnertion. Imam recording, a first stage of A.F. amplification using a type '27 tube; a second The manner in which such circuits are com- \-2 are connected either through red leads using two of these tubes in push -pull; and pensated at the extremes of tuning range (by for the reds- dotted coil sets A, 11 and C, a lied stage, also push -pull, using type '45 the selection of .0005 - or .00007 -m f. tuning or through black leads for coil sets 1), E. F. tubes. The combination is particularly de- capacities, respectively) has been discussed 'l'he shield cans are to he used only over sirable to give an audio output, as in this in past issues of It.unn- ('ui.crr; and nothing the coils used on the broadcast range- 2110- receiver, of high quality. To enable the owner of an "All-Wave" Fig. 2 (right) The cirrn it of the power to obtain the best results in the use of park, triti, its connections microphone, phonograph pick -up, and re- to set and speaker.

550 meters. It is necessary, in order to Fig. C (left) reach the highest-frequency tuning range, .I rear of the tuner to use au '27 tube with a continuous -sheet elmssic, with all roils. It (not wire-mesh) plate at V3. is unnecessary to .shield As will he observed by reference to Fig. the ,short teate rads, tebich a low -boy console is recommended for are there /ore easily : \, e.nhanu,;1. the Scott All-Wave Superheterodyne chassis July, 1931 RADIO -CRAFT 19 and its power pack. The lid of this cabinet the full sensitivity of the receiver, which is ceivers; a mistake in the handling of a must be readily lifted for convenient ex- obtained with switch Sw. 2 in position 3. short -wave superheterodyne. The only really change of coils, etc. Just a little fatherly advice concerning satisfactory method of tuning is to set the the procedure in tuning for the short -wave left or oscillator dial at a given point, and signals. It will be found that, although the swing the right or signal -frequency dial tuning is very simple after a little practice, back and forth, slowly, a few degrees on the listener may observe a tendency for sta- either side of the I.F. resonance positions to "whip" across the settings; this is tion (which is that point where a "reso- due almost entirely to a natural tendency nance rush" is heard) ; then advance the to tune the set as though it was one of the oscillator dial's setting a fraction of a de- earlier two-dial tuned -radio -frequency re- gree and repeat the operation with the right -hand Iliad. After operating a Scott All -Wave Super- heterodyne at a selected locality in Brook- lyn, N. Y., the writer wishes to urge that clue care be given to the use of the vol control; which is the potent' ter R in Fig. D the diagram. There is a natural inclination The microphone control bo.r is obtainable as an to advance the setting teat far, thus greatly accessory for recording or speech amplification. overloading the tubes; since the amplification obtainable through the correct use of Knack of Short -Wave Tuning the screen -grid tubes is simply tremendous. The short -wave enthusiast who has been (Speaking in technical terms, this receiver accustomed to handling other types of short- has at 1,400 ke. r. sensitivity of one -one wave receivers will be pleasantly surprised hundredth of a microvolt per meter!) How- by the ease of tuning at all points through- ever, if the volume is held at the correct out the range of this receiver; this is fue, level, there will he no hissing sound and no in great part, to the subdivision of the in- hunt, but perfect audio reproduction. ductances. Taken in its entirety, the Scott All -Wave A factor in the consmnmate ease of op- Superheterodyne, with its tuning range of eration at the shortest wavelengths, right 1.5 to 18.4 meters, and 200 to 550 meters, down to 1.5 meters, is the design of the in- should appeal to anyone interested in ob- put circuit of V1. When the first five coils taining an exceptionally sensitive radio re- are in use, the antenna connects to the bind- Fig. E ceiver, operable within these wavelength ing post S.W. and designed particularly for ease Cross -section of an 1.F. transformer; observe limits, Excellent selectivity is obtainable, even at "sub -pond" position of shielded X.F. choke. in tuning and high -quality audio output.

SW. ANT. CHOKE LW. S.M.2

¡ R.F. 1$ OET. 1>Y.I.F. 2 11Lr. R.F C. I.F. 3521.F. 2sDEf. AUDIO 24u C2 '24 50 MMF. '24 50 W. 24 50 MMF. 24 SOMME '27 f 2r .002 MF. .;.C1 : , ; --t ...... 2--, o 0 o T Vt. 0 .1-MF.

a :ii4w1 z ì 400 .000 O001. MF. 5,000 MF. 3.000 MF. 50,000 2 OHMS OHMS OHMS' SW2 .Ö02{ MF CH.1 CH.2 CH.3 CI,00007MF. c Soóo 2 PLUG -IN C2,.00054MF. OHMS COILS

50 MME ,0005- 31 MF. 1 0$C

a.1

1.500 OMM .1 -MF

Fig. 1 Schematic circuit of the receiver chassis of the Scott ".911- II'are" superheterodyne. The long-wave antenna post is at the rear of the chassis; and the short -nove pod mn the shield over the tuning gang. The output feeds a push -poli '45 pack (Fig. 2); a push -pull '50 unit is also obtainable. 20 RADIO- CRAFT July, 1931 And Now the Crosley "Super Buddy Boy"

In which the "Midget" set develops a giant's reach and voice

Fig. A "Super Buddy Boy" is little, but E tried out this superheterodyne oh my-! in New York City, and were struck by the remarkable amount of SCOR E another hulls -eve for the C ros- and mechanical refinements embodied in the

power that such a small set can de- I ey Radio Corp., whose engineers have design, the outstanding features are to be velop. It is literally impossible to the happy faculty of turning out )Wald noted. 'l'he tubes required for this set are turn the power on full; as the volume sets incorporating the latest technical two type '35 tubes, three `24s, one '17, and is entirely too great for locals. advances, for a little lower suns than the an 'SO. These few words tell the whole Even on the distant stations, such next fellow. This hallmark is observed in story to the technician; that of ultra -mod- as Boston. Pittsburgh and Chicago, the the new Crosley mantelpiece receiver, the ernism in radio set design. Referring now volume was often uncomfortable when "Super Ruddy Roy" illustrated in Figs. A, to the schematic circuit, Fig. 1, we find that the set was turned on full power. I3 and C. Y1, one of the new type '35 tubes (first It was found possible, in the heart Before considering the many electrical known as the variable -nu, and now vari- of New York City, to tune in stations within a radius of a thousand miles B without interference from the locals; Fig. which we think remarkable. The upper rien' shows the compact chassis, with This receiver worked exceedingly Mc tuning paua (It the well without an aerial; it was neces- right: its ingenious flex- sary only to connect the ground lead ible tuning scale in the center, and, at the left, to the aerial binding post, and this the power unit. worked exceedingly well even on distant statiors.

Fig. C (left) .4 rear Lien' of the chassis beside its one -piece -rep:eood'' cabinet, the back of which may be used as an antenna for local reception: t h u s making the whole system self - contained, without aerial or et'Cn ground.

ously termed "exponential," "logarithmic," "multi-mu," and "super -control "), functions as a radio- or signal -frequency amplifier. 'l'he characteristics of this tube greatly min- i iii ire "crosstalk," the two-stations-at-one- time bugaboo of the type '24 screen -grid tube; the latter, however, in this circuit

\r F. POWER 07 u RF 1lU otr L4 1 35 LS RFC (a t;. '33 L3 2M áóáv°z ! fi s u lt f 1 R

_a f i i u el kig -r v CIARZ; r R6 é ll` i(b C7 L Cl2 R3 ` 11L49:1U IIII wawaRI7 ``,,,,,i11111ÇÇÇÇÇ(t111f !¡tt(it[tt(t1111R1111fit(t

May. 1931 issue of R.vnlo- Camr, this pen - do i :uuic reproducer, all with their power tode's power output very greatly exceeds supply. Ham this result is obtained is shown that of a type '15 tube, for the sauce control - grid voltage swing.) Containing the volume control and the off- on switch increases the convenience of op- The Jesse French 7 -tube "Devon" super. eration. Resistor R14 and condenser C17 constitute a panel- operated tone control; the advantage of which in acoustically re- of the compact receivers here shown ducing the effect of "summer static" is now BOTHutilize the latest developments in tubes: too well known to require discussion. the 7 -tube "Devon" model being a super- 'l'he high factor of sensitivity of the "Su- heterodyne; and the 5 -tube "'l'udette," a per Buddy Boy" has uaade it practical to tuned -radio- frequency receiver. incorporate in the rear of the cabinet a small capacity -type antenna. This plate of The chassis of the set shown above has scree s- cardboard measuring 7 x 16 in., and coated grid (two) R.F. and detector, feeding a power with a conductive substance, is connected pentode. to the antenna post on the receiver; and in the interior view; the maximum baffling is referred to as the "'l'ennaboard." The possibilities are realized by the central dis- cabinet is hued "Helmond" in the fae- position of the speaker cone. 'Three tuned simile of an old English hand -carving, no circuits, giving good selectivity, are con- nails, or glue being used; incidentally, it trolled by the tuning knob at the right; the doesn't warp. only other control -that for volume -is com- "Illuminated angular -vision ribbon -dial bined with the switch. '1'he design is attrac- with vernier drive" is the explanatory desig- tive by its simplicity, which seems to be nation of a new mechanical development, a almost the ultimate. tuning indicator mounted at 45 degrees to (I si s si J Ill (.14(.0 Bosch Corp., the vertical plane; it renders tuning con- priagfield, Mass.) venient either in sitting or standing position. The use of "quantity production" design A POWERFUL MANTEL SET makes it possible to place on this 7 -tube superheterodyne receiver, complete with tubes, 1 h French 5-tube "Tudette" midget. a list price under seventy dollars. :\ dynamic reproducer is includ, d. The former utilizes two type '51 variable- And that is not the end of the story! mu tubes, one '27, two '24's, and a type I' By removing a strap between terminals 3 pentode. The rectifier is the standard '80. and 4 on the antennas -and- ground binding - The "l'udette" mantel set also uses two post strip, a high -impedance phonograph variable-mu tubes, has a single '24, an '80, pick -up may he connected into circuit; tubes and a pentode in the output circuit. A fea- V5 and V6 then function as high -gain audio ture is seen in the "full- vision" dial. Both amplifiers. models are equipped with tone controls. It is the opinion of the writer that the (Jesse French & Cons Piano Co., Crosley "Super Buddy Boy" supencetero- The Roosevelt 'Model 19" in a mantel-type - Newcastle, Ind.) (Continued on pale 44) cabinet. (Continued ou page 47) 22 RADIO-CR AF-l' July, 1931

With this is announced also the type 447 power pentode, which is intended to give a The Latest Radio Accessories greater output titan is possible with the 445, with the same plate voltage and a smaller input. It has a filaient voltage of and Receiver Components 2.5; filament current of 1.5; plate and screen voltages of 250; plate current, 32 ma.; with AUTOMOTIVE FILTER CONDENSERS MULTIPLE UNIT HORNS a grid bias of 16.5 volts. 'l'he amplification l°l'OMOTIVE radio reception requires, factor is 80, plate resistance 35,000 ohms, A not only special tubes to stand up un- and the mutual conductance reaches the high der the exacting conditions, but special con- figure of 2,300 tnicromhos. A UY base is densers as well. To bypass the high -fre- used. quency currents of the ignition system and (De Forest Radio Co., Passaic, N. J.) eliminate noise, the component type illustrated has been designed with special reg,nd A\IPERITES FOR NEW TUBES to the high temperature and vibratory im- HE revival of interest in battery-op- pacts which it must undergo. It is desir- .1 receivers, using highly- efficient able to use at least two with a car's elec- tubes of low current consumption, has between and trical system; one generator Raton nine -unit reproducer horn. caused a demand for suitable filament bal- frame and one between the interrupter and last regulators. The manufacturers of the O single dynamic unit is sufficiently pow- two -volt types have especially urged upon 1.11 erful to meet the demands of public - their users that the filament voltage be kept address amplifiers, such as airports and large assembly grounds require. Of a line of horns designed for such service, the illustration shows one which takes nine giant reproducer units, and blends their output into one voice with a three -mile range, on the ground. It is demountable, with a heavy Polymet auto- ignition filter condenser. aluminum throat and stormproofed bell; is dmperite suited for 2 -volt pentode. thirty inches across the opening, and 51. frame, with, of course, the necessary re- constant; and that this is impossible with inches long. 'l'he weight is 48 pounds. sistors in series with the distributor and fixed resistors in series with a battery sup- Other horns, taking four -, two - and single - spark plugs. 'l'he unit shown, used ex- ply source the voltage of which changes con - unit connections, are made for installations tensively with commercial automotive radio tinually. The we'll -known self -adjusting of lesser size; and are also demountable for equipment, is made in two capacities, half - rheostat, or "Aniperite," overcomes this dif- portability. and one -mf., 11/t inches in diameter; the ficulty. Since it is a current -regulating de- (Roca'''. Electric Co., New York City.) smaller is 21/s inches long, and the larger vice, several of the former types will serve 31/. inches. for :3 -volt batteries; while for lì -volt battery ( Polymet Mfg. Corp., New York City.) NEW AMPLIFIER TUBES operation, new designs have hem made. type numbers required are (one Auuperite INTERMEDIATE TUNING for each tube): CONDENSERS Type Battery Battery SU PER HETI:RODYNE vogue has pro- 'rube 6 -Volt 3 -Volt duced a line of condensers, designed spe- '30,'32 No. (ì30 No. 4 \'199 cifically for manufacturers' use, but now '31 No.631 No.120 obtainable by constructors, and intended for 33 (Pentode) No. 633 No. 1.1 mounting to and tuning the I.F. transformers. The capacity ranges are 10-70, 70 -140, "FEATHERWEIGHT" HEADPHONES and 140 -220 mud., in single and double PPLICA'l'IONS of the headphone, in components. A servicing and reception, are still num- 'l'he bases used are of isolantite, an im- erous, in police automotive or aviation radio permeable high -insulation material; the vari- for instance; while in connection with pub- able plates are of phosphor bronze, specially lic- address and other amplifier systems for tested for hardness and temper; and the the hard -of- bearing, a comfortable phone is adjusting screws have specially -eut threads a boon to be sought for. With this in 1, and tapered, self -aligning heads, to main- one manufacturer has just produced an in- tain their adjustment. 'T'he eyelets have strument of remarkable lightness. 'l'he mag- fiber "shock pads," to absorb strains and net is of a special cobalt steel, held in ils prevent cracking. 'l'erminu!s are solder- Bakelite case bv clips; the whole phone unit weighs but an ounce and a half, or four ounces for :i !unir, with light spring -steel New De Forest .Indians: left, 451 variable- ma amplifier; right, 447 pourer pentode. MA\IJftM sensitivity, while safeguad- ing against overloading, crosstalk, and distortion on loud signals, is the purpose of the new 451 "Audion," illustrated here. It operates, like the 424, with 2.5 volts on the filament, drawing 1.75 amperes; the recom- I.F. adjusting condenser. Ilamnmrhn,d mended plate voltage is 180, with a plate 5.5 ma. at :3 volts control -grid dipped, as well as cad plated, and de- current of Trinan 1Jpl10/,c unit. signed to facilitate soldering without con- bias, and 0.65 -ma. at 20 volts grid bias. 'l'he duction of heat to the plates. The mica mutual conductance is thus decreased from band. 'l'he cord is attached to the phone dielectric sheets, it is stated, are so rigor- 1,000 to 80 nticromhos, giving complete con- unit and the ease in a manner which pre- ously inspected that four out of five are re- trol of the amplification in receivers which vents wear and strain. 'l'he standard set jected in the selection of the best. can accomplish this by varying the cathode has a resistance of 1.010 ohms for each unit. (Mammarlund 3Ify. Co., New York City.) potential. (Triamm Radio Mfg. Co., Chicago, Ill.) July, 1931 RADIO -CRAFT 23

The Walker "Model 4" Short - Wave Super -Converter

THE superheterodyne converter has al- prevent radiation and hermit use of most ready won for itself a commanding any antenna length. ('l'he signal is picked place by the facility with which it pro- up by the converter and passed on to the vides efficient short -wave reception, when receiver for additional amplification, thereby used in connection with the standard broad- utilizing each circuit of the receiver and milk- cast receiver which every up -to -date house- unnecessary the purchase of an extra hold now possesses. 'l'c hitter instrument speaker or die erection of a special an- Left a gong of metallized resistors; right. tha is designed for reproduction of good quality tenna.) An '80 rectifier is used in the snaking of a wire -wound precision resistor. on long -wave stations within a reasonable power pack. MIDGET RESISTOR STRIPS listening area; it remains only to provide The receiver is not disturbed; since there N(1W that the midget construction is in the necessary means of tuning to the rap- is no need to "plug in" to furnish the power demand, for even receivers with many idly- increasing ber of short -wave broad- necessary to operate a converter; it connec- tubes, compactness and accessibility are at cast stations throughout the world. tion is made from the converter directly a premium. 'These requirements have been to the antenna post of the receiver. There met by "ganging" .metallized resistors in the is no overloading of the receiver's power manner shown; the various units are mount- supply, for the Walker Super -Converter ed on the strip by passing through it the draws its power directly from the electric tips of their leads, and crimping them to light socket. There can be no possible dam- nIdering lugs. Such units, of course, are age to the receiver. made up to meet the demands of the re- Regeneration in the detector circuit, as ceiver for which they are intended. shown in the schematic circuit, Fig. 1, pro- The remainder of the illustration shows yids a degree of sensitivity and selectivity the method of building up precision wire - otherwise unattainable; it has been cred- wound resistors. The wire used is of nickel ited with the efficiency of an additional tube. alloy, of n cross- section as large as the re- Where is there a "(iced in the wool" short- sistance value permits, specially enameled. wave fan who does not insist upon regen- and tested through mercury contacts to de- eration? The oscillator and detector tun- termine the completeness of the insulation. ing condensers are ganged and, necessarily, It is then wound in the slots of the ceramic provided with a Inc vernier dial for sharp George W. I Nalkei s latest is housed converter tuning. A small midget condenser, used as (porcelain type) base, and impregnated as befits a modern receiver. with a special varnish which hardens at high compensator, connected in parallel with the temperatures. The resistors are again tested 'Phis, with all simplicity of operation and oscillator condenser, permits resonance at by five- minute flash loads; and then on ac- the sensitivity required to pick up signals all wavelengths. All tuning is accomplished curate bridges to determine their accuracy, from thousands of stiles away, is now ob- with the vernier dial, and with the aid of which may be from 1% down to a quarter tained through the modern unit pictured the midget compensator, insures maximum of that figure. here -the Walker Super -Converter, which selectivity. "Hand capacity" is noted by (International Resistance Co., tunes over the hand from 14 up to 200 me- its absence. Philadelphia, Pa,) ters, and uses as its intermediate and audio In addition to hearing far -distant short- amplifiers any standard receiver, of what- wave programs, there is the thrill of tuning ever type and method of operation. The in broadcasts of police departments through- VOLTAGE REGULATOR FOR Super- Converter acts simply as a pre-am- out this country and Canada. The personal MIDGET SETS plifier and frequency changer, feeding into transoceanic telephone conversations have the receiver a modulated radio -frequency also proved interesting to those inclined to signal which is within the tuning range of "listen -in." Short -wave fans have no fear The Clarostat 50-watt the latter. Only a single external connection of warns weather reception. The reduction line - voltage regulator to the broadcast receiver is required, as the of static, plus the long range and pene- has beets developed for the benefit of owners Super -Converter is self -contained. tration of short -wave broadcasts, will prove of "midget" sets. It includes an oscillator and first detector, entertaining in the hottest months when your using type '27 tubes, as well as a stage of local programs may be disturbed by crashes screen -grid It. F., using a '24 tube, ahead of of static. the detector -to increase the amplification, (Continued on. page 41) `qq \ \ l'F.\C'1't'RERS and Mr. Ultimate I Consumer will be interested in the new "Clnna.t it" automatic line-voltage regulator, in diminutive (50-watt) sire, designed especially for midget radio sets. Service Men contemplating the use of this resistor will be interested in the voltage drop to he expected when it is inserted in series with the input to the primary of the power transformer; this is dependent, in part, on the power requirements of the particular set, as follows: 0.45-amp., 10 its drop; 0.5-amp., 13 volts drop; and 0.6- amp., 20 volts drop. The unit is IN inches in diameter, and 13/4 inches long, with two prongs extending another %-in. Although intended only as a voltage regulator in the primary circuit of the set, it will function also as a fuse in sets not pro- Fig. 1 vided with one. Of course, such fuse is The schematic circuit of the "Model 4" Super- converter, which operates as a frequency changer. (Continued on liage 41) It has its own power supply and is connected to the receiver only at the antenna post. 24 RADIO -CRAFT July,1931

IN radio, as in almost every other field, productive originality is amply re- warded in dollars and cents. A clever New York radio engineer, Mr. Paul \.un 1 uni(s, has created "Mr. Radio Robot,' Introducing Our a reniarkable device which is attracting unusual attention and proving a source of The mechanical and electrical profit to its originator. 'Hie idea is passed along in this article, the "Iron Man" which is such with complete details, to other radio men, public, and is making big as "NI r. liadiO lobot" can undoubtedly he used to advantage in many towns and cities throughout the c try. By H. G. The cover illustration gives an excellent idea of the appearance of the "Iron .1a n." announcements and to entertain with the rophones, the loud speaker and the headset From a theatrical costumer was procured latest song or other nnusieal selections. If are connected as shown in Fig. 1. Complete the coat of mail used to represent a medieval desired, "Mr. Radio Robot" can be made portable amplifiers are available for this armored knight. Such ensembles are fairly tu go through the various mechanical mo- type of work; one of the most suitable common, since they are extensively used for tions by machos of switches or push- buttons ones hieing the new Electrad Loftin -White masquerades, and they can be rented or located at a distance; or manual and audible Portodile Amplifier. purchased at a reasonable price. control may be dispensed with and he may Before giving detail, as to the construc- be actuated through the mere interruption SELECTED FREQUENCIES UNIT ST tion and actual mechanism of the robot, of an invisible ultra -violet beam. 'l'hus an OUTPUTS TO UNIT SA some of the startling things ate can do may arrangement is possible, whereby he will fire be mentiuncd. In reahonse to a pre- deter- a gun, Or stand up, or start to talk-if DVN. whistled whis- walks past him. REPRO- mined series of notes, or the someone DUCER tling of a given tune, "Mr. Radio Robot" In the cover illustration, the robot is ALL will stand up, sit down, move his left arm shown answering questions put to it. 'There FREQ. or his right arm, turn his head, fire a gun, is a reproducer concealed in its chest; and INPUT FROM UNIT start to talk, etc. a microphone (within it) at a distance of MA1 He will also go through a definite series about five feet from the ground and thereof operations, which may be worked out in fore on a level with the mouths of people advance. For example, in response to a asking the questions. 'l'he operator and the a tune, Matt" nay' be located at any command in certain the "Iron portable amplifier FIELD will stand up, move his head, make a speech, convenient point, no matter how far front SUPPLY R TUNED VIBRATING-REED RESONATORS (9 REQUIRED) lift either arm to emphasize certain points, the robot. It will be noted (Fig. A) that bow at the end of the speech, and then sit the operator uses a headset and that he Fig. 3 down. While he is talking, his eyes and talks into a microphone. Its adjustments Current generated in the bobbins of this fre- teeth will 1w illuminated with a light of are made on the small control box in front quency- selector when the tanned reeds vibrate fl uctuating brilliancy. of the amplifier. with the loud-speaker signals, is later amplified. Furthermore, this robot will answer ques- ,\ portable power amplifier is used for Giving Commands by Sound tions intelligently; and eaut be used to make this portion of the set -up. The two mic- Fig. 2 is a pictorial layout of the signal - selector System, whereby a pre -determined series of notes of different pitches and timbres are used to actuate the mechanical man. Examining the layout front left to right, it will be noted that the microphone MI (the one concealed within the robot) is connected to a microphone control box (G, in Fig. A.) This connects to the input of a high- quality amplifier, such as an Elec- trad direct -coupled Type A -245 unit, Fig. 4.1. 'l'he output of this microphone amplifier, connects to a three- section selective tuning device ST, which is the portion of the apparatus that picks out or responds to the particular actuating notes or tones. 'l'he output of the "mike" amplifier (NIA, Fig. 2) is connected directly to the voice coil of a small dynamic reproducer, mounted within a sound -proof wooden box (ST) containing nine differently tuned vibrator reeds. There are nine electromagnets, one in front of each vibrator reed; three of them being connected in parallel on each of the three electrical circuits, as shown in Fig. 3. When a note of the required tone and pitch is sounded or whistled before the microphone Nf2, the microphone amplifier NIA magnifies the impulse sufficiently to actuate the speaker. The amplified sound coining out of the speaker causes the reed which is tuned to correspond to this one note to Fig. A vibrate; this, in turn induces a feeble cur- This inscrutable, armored figure stolidly moves his head, his arms, and correctly answers questions rent within the electromagnet placed before put to him-a seemingly human Iron Man. (Mr. Cisin, wearing headphones, is at the controls.) it. The reference letters indicate: A, pulleys and reproducer: B, microphone MI; C neon tube which By varying the lights the eyes; D, head and arm motors; E, selectors, relays, and amplifiers; G, microphone control position of the magnet, box; H, additional amplifiers; I, microphone M2. with relation to the vibrating reed, it is July, 1931 RADIO -CRAFT 25

third Ilnrtnonics available liv changing the plaeeunetit of the electromagnets, as shown in Fig. f), it is apparent that the "Iran Man" IIIa be arranged to respond tu a cer- Mr. Radio Robot tain melody, ow a song containing tlnc cor - rect sequence of pre- determined notes. details of the construction of fluer the circuits "A,' "11," and "C" slum ii in Fig. 6, have been closed, the an object of interest to the óc:n -duty master relay is actuated. This money for his constructor. is over:Lted by the li -Vlt battery, shown for the sake of clarity as a separate unit; in actual practice, the battery used for the CISIN, M.E. tine -delay relay may also be used for the heavy -duty master relay and for various possible to pick off either the fundamenMf, as lever syst VIII ; causing a heavy notched other relays requiring six volts, as shown the :second harmonic, or the third harmonic, brass wheel R' (NO. 1, 2, or 3) to turn in Fig.. I. as clearly illustrated in Fig. 4. Incidentally, one notch. .\ spring pulls the armature The heavy -duty master relay is used to the reed will respond also to notes either back until a second impulse again causes close any desired specific circuit; such as one or two octaves higher than the fund: - the brass wheel to be turned : timer notch. the one causing "Ir. Radio Robot" to rise, mentla. If the correct number of whistled signals or tu fire a g , to make a speech, etc. are given, it will turn until the supper Details of the mechanical- motion circuits strips A, II and C cake contact with the are shown T. The is equipped FUNDAMENTAL HARMONIC in Fig. robot 2w0 brass / (NE. 2.) studs fastened on its side. Before it with two Ford frnctiunil- horsepower start- is possible to actuate the heavy -duty master ing motors, and with a number of Knapp relay III)\Ilt all three wheels must be .h I r N4.3 toy inuturs ( "series" motors are used in ----- 1 I` .2 turned the right number of notches (since order to supply the necessarily high starting t 1 PoSITIO,J ----El the three circuits are in series.) torque). 'l'he Ford .starting motors are used I OF CONTACT The action is analogous to a NY.1 I that of Pale tu make the robot stand up and to lire the I á r lock, or to the opening of it safe. Unless gun; while the toy motors perform the 352 lei 1 / I the correct, pre -determined notes a w lighter tasks of moving the head and arms. HARMONIC I, --STEEL REED (NE 5) RESONATOR. sounded, :Ind unless the correct number if Three wires are necessary in the circuits notes are sounded, "Mr. Radio Rebut" w II front tiWI _RIGID SUPPORT the moeurs, in order to reverse their PART OF UNIT ST fail jÿß / to respond. Since three distinct fu r direction when required. \terely changing daunentals are available on each of the three the polarity will not reverse the direction circuits (not to i netttinn the second a1 d of these motors, and it is therefore neces- Fig. 4 sary to reverse the current direction in :1 "corset steel" may he used in making this '22 .01 -MF. 12-A the armature, without portion of the tamed relay. alluring the bobbin UNIT SA changing that in the may raise the pitch (positions 2, 3.) motor field. 25 OHMS , .\ The Robot's Stunts 'l'he feeble induced current flows into the (EACH)- 0.5- -signal amplifier SA. MEG. corresponding selector 4lk 10 .\ mechanical stop prevents the motor are three of these amplifiers, one for There REED 40MM5 from turning ton far. For example, in ca'li of the three circuits. (Hearst' I.oftin- IN UNIT ST. bY order to make the "Iron Man" stand up, be W l,ite A-245 amplifiers may used for the motor can turn over only a certain this purpose; the circuit connections are (POTENTIAL OF amount; reversing the motor causes hint to shown in The main function of -C- DEDENDS ` Fig. 4A.) UO+ TE 4S TO 135V sit (1uw'n. 'Phis Muter (+dung with most of AA - these amplifiers is to give voltage amplifica- i - the relays) is mounted in the platform be- 'TGE B+1- A- A +' POTENTIAL tion and hence a "space -charge" amplifier -8 +2' "C- low the robot. In turning, the motor pul s 22/0. -B,- 135 V. FIXED BY having a screen -grid tube and a '12A tube -c +- TDR DESIGN two cords, which pass over pulleys in tl e would serve the purpose. (See Fig. 4B.) knrs, :tut whirl are fastened within the to a Fig. 4B The output Of each amplifier guts figure at the rear titist line. Tension t n The .elector amplifier: a "space .separate rectifier R. Details of the recti- charge" eir- curds ruit is .down. The onlput operates a firne- the promptly brings the "Iron \fan" fier circuit, which is very simple, are shown delay relay, Fig. 5A. to his feet. Similar ingenious arrangements in Fig. 5. Rectification is accomplished by means of a '12.\ tube. 'l'he rectified cur - KEEP THIS POINT '24 V245 RFC. rent then goes to the "time-delay relay" VI J CLEAR OF APPARATUS -X

'i'r)ht. The plate voltage required on the 1 ,sC3 sl_ '12A tube will depend upon the type and 1 500.000 OHMS characteristics of the time -delay relay. 1 f 'i4F OuTPUT INPUT R. PART NR. 1 if it were possible to obtain a compara- v- 586.020 MAX. tively pure note at the microphone (for i 775 OHMS 2 100.00I instance, by the use of a flute), the time - 4700 OHMS 25,000 OHMS ONM f delay relay would not be necessary. In the R east of a whistled note, however, strong .-IMF. IMF. 24 50 000 as II :rnumics and overtones are present, which 425 OHMS TWIST Tt aim OHMS X200 OHMS w B cause the recd to "chatter." The time-delay (HUM BALANCER) FILTER CHOKE relay overcomes this trouble, preventing con - 80 úw tinued vibrations. GND B --TWIST CIA

1.OME; Controlling the Relays 40 MA / 2.57 S.S A. 2.SV. ,.75A. 5V. 2A 'l'he output of each time -delay relay 2 4 7 5 (Tilt, Fig. 5A) gees to a corresponding 11 II III 3- 1 51 PT (LOAD heavy -duty circuit -breaking relay RC. A I FIGURES

ARE MAX). common ti -volt battery actuates three heavy- L_------¡ 6b+f21Ö0000006 duty relays. See Fig. 6.) (RFC AUO C3 USED WITH 0..F TUNER: WHEN VI BECOMES DRü10R) -(AD-080-11.1-C1A AND CIB (SAME 110 V. A.C. CAPACITY3 TO REOUCE NUM.) Each current impulse through a heavy - duty relay IIDR attracts a pivoted arma- Fig. 4A ture. As the armature is drawn towards .Schematic circuit of the direct- coupled unit. recommended by the author for use as a selector amplifier. The number of amplifiers used is detrrminrd by the desired number of actions; three operates a the magnet, it ratchet through bring described by the author and illustrated in Fig. 2. 26 ..RADIO-CRAFT July,1931

of cords, pulleys and levers produce the point, were amplified and reproduced Various other mechanical motions. through 1 :IORATIO 100,000 0141411 1.0-M/. the speaker within the robot. At A.F. TRANSl (WIREWOUNO) '16A The most mystifying effects are produced stated intervals, the "Iron Man" answered TOTIME )DEI.AY A(' through the use of a light -sensitive cell; questions; and, between times, the latest SELECTOR this is ted in an unobtrusive position, song hits were reproduced by means of the AMPUFIER r,J TOR with a light -source constantly directed upon electric phonograph. Although the original SA OUTPUT VARY it, except when the light is obstructed by contract was for only one week, the robot TO SUIT u111! - someone passing in front of "Mr. Radio was so successful in stimulating business, - RELAY Robot." (It is ,ossible even to use an that be was held over for three entire weeks. 30 UNIT R. + 4 ONMS ultra -violet ray, which is invisible and hence Since the idea was first conceived, "Mr. VOLTS still more dramatic). As long as light falls 1O6V.BATT. on the cell, no appreciable current flows Fig. S but, as soon as the light -source is ob- Ocie of the :Inds rectifying the output of a structed, there is a sudden increase in cur- selector unit (Fig. 3). rent, sufficient to actuate the relay. Of course, it may also be connected in such can be operated by a store manager or sales r a way that the reverse action will take place. person and does not require a skilled at- That is to say, the relay may he actuated tendant. 'l'hose who contemplate the con- by an increase of light instead of a (le- struction of a robot can make the device crease-for example, by permitting the light cou1paratively simple at first, and after- source to strike the cell only when it is wards make it more intricate fr time to desired to operate the relay. time. For instance, it may be desirable to start out with the portable- amplifier outfit Business Possibilities of the Robot for answering questions, making announce- The commercial possibilities of "Mr. Radio ments and playing records. Later on, the Robot" are tremendous. He may he rented relays and mechanical action may be added. to stores which are carrying on special Fig. 5A This flexibility is a great advantage and This relay gives a delay of about a mimte; sales and advertising campaigns; or he may is as point which should not be overlooked its winding is connected in series with the be used at entertainments, fairs, bazaars platt circuit of a rectifier (Fig. 5). by the radio man who may be deterred from starting the construction of a robot, because of imagined complexities. LIST OF PARTS (Units M, MC and MA, Fig. 1) One three -pole, double -throw switch, Swl; One single -pole, single -throw switch, (Sw2, operated by R1); One single -pole, single -throw snap switch, 512 5W.1 SW.2 R3 Sw3; tm 2BUTTON MICRORgNE Three dry cells (1.5 volts); (OPEW.IOR'S) One Ferranti "'Type AF5M" microphone SOUND (MICROPHONE) transformer, Ti; AMPLIFIER One Ferranti "Type AF5C" push-pull input DITS M, MC, transformer, 72; AND MA One Ferranti "Type OPIC" (for direct coupling to 8000 -ohm line speaker) or Fig. 1 "OP25C" (for dynamic speaker) push - The first section of the apparatus; care must be used in placing Ml, to avoid howling. since there pull output transformer, T3; is a reproducer in the figure. The operating potentials demand high- rating filter condensers. One Electra(' 2(N) -ohm potentiometer (and R11 may be variable, to adjust the sound level in the headphones. switch Sw2), RI; One Electra(' 0.5 -meg. "Royalty" potentio- and for a great variety of purposes. In Radio Robot" has been in continuous use, meter, 112; New York, the "Iron Man" was recently and now has more advance engagements Two Durham 50,000-ohm (1 -watt) "metal- leased to a large furniture store on East than a popular vaudeville star! lized" resistors, R3, 118; 57th Street. The portable amplifier was set The entire device needs practically no Two Elect rad 100W) -ohm "flexible" grid re- up at the rear of the store; and announce- servicing, once it is set up, and consumes sistors, 114, 119; ments, made from the microphone at that very little current while in operation. It (('anlinued an palle 46)

FIG5.4A AND 46 FIGS FIG. SA FIG. FIG.7 SELECTOR- '22 45 TIME- POWER RELAYS HEAVY DUTY FIG.1 OR OR SO RECTIFIERS DELAY AND SELECTOR- MASTER AMPLIFFIER . 24 '12A RELAYS CONTACTORS ELAY

Ml(IN ROBOT) FlG53 AND 4 R. T D R. a SELECTOR NE12 nie1 w M V3 IN MA AND SA, AI I 1 CONTROL NOT USED IN T N?1 01--=e MDMRI Box ) BATTERY MODEL) ~Ì r (3 CIRCUITS) 2 0--1 fi M2 I 1MOTORS . 3 MC. VI TD R I , 0 57. I N?2 Nc2 A.( ; 3 0--1 ,) B --- D0. \ I - I I MIC. AMP. M4. FIELD RC 0--i l Y1 v3 I R. TOR (3- CIRCUIT 414 ANS" ' iNOTE 6v.A NE3 A.A COOLSwá. I BATTERY OUTPUT) I i5 11 gi - NOTE

I

7 I

Fig. 2 .4 layout of the units shown in detail in the detail sketches, as noted at the top. Most of these units (except those of No. 1) may be concealed in the base beneath the robot. The binding posts 4 and 5 in the unit of Fig. 7 (at the right of this diagram) arc for additional controls and motors. July, 1931 RADIO -CRAFT 27 How to Improve the Quality of Radio and Personal Recording Instructions for operating the microphone, amplifier and cutter, and for the choice of records By GEORGE J. SALIBA, S.B.

lli: radio eur of the olden days Microphone Technique be necessary. Some people connect the me- had no citercriterion by which to meas- 'l'oo many records are spoiled by incur- ter permanently in the center leg, to read it ure the results he obtained. His rect use of the microphone. Fig. 1 is the the stun of the two currents, but this is T Home -made radio receiving set (or schematic diagram of a single- button mi- risky procedure. If the microphone is rated "wireless receiver" as it was called in those crophone circuit, and Fig. 2 that of a two- at 20 mils per button, the middle leg will days) was capable Of receiving code signals Import microphone hook ult. In Fig. 1 the carry 40 mils. With the meter in the center very dearly; and, when broadcasting cane, millianumeter is placed in series with one leg reading 40 mils, one button may be the music and speech were clear and in- leg, and the microphone current is varied packed and carrying 30 mils, while thv telligible. The amateur did not worry about by means of the potentiometer "l'; the other carries only 10 mils. The result will fidelity. His magnetic horn or cone was not values of this current is determined by the be that the button carrying the 30 mils will nearly as efficient as the present -day dy- type of microphone used, and this infor- pit and burn out. For the saur reason it mimic reproducer; but he was satisfied with mation is usually supplied with the instru- is inadvisable that the meter should be it because he had heard nothing better. ment. (Interesting data on microphone am- placed permanently in either leg. 'l'he ideal With the home recordist the story is re- plifiers appeared in the article, "A Public - way of keeping dose watch on the current versed. For years he has been listening to Address Amplifier Unit, in the October, is to have a meter in each leg, but thio- commercial phonograph recordings of such 1930, issue of It, tom- Cs.trr. -Tech. Ed.) means added cost. quality that they are hard to ai.;iinguish If a two- button microphone is used, jacks If the speaker, or singer, stands too close from the living artist. When, therefore, in each button leg, as shown in Fig. 2, will to the microphone the reproduced recors. he starts to record he has a criterion by which to judge his results; and for tbi- reason his first few results will appear to he unsatisfactory. Yet he is not up against the difficult problems with which the radiir ham has had to contend. All recording systems are fundauentalty the same. Sound is put into a microphone where it is con- verted into small electrical currents; these are then :unplificd and transmitted ton cutting head. It is very important that every eoatponent operate at maximum efficiency to insure good records. The different integral units will he discussed later, in detail, and the precautions to be observed in the operation of each will he pointed out while the most common complaints of hone recordists are the following: (I) Volume of reproduced record low; (2) Inability of reproducing needle to track; (3) Needle jumps record when recording; (3) Sound distorted; (5) Sound comes in loud, then dies down; (U) "Echo" in the reproduced recording; (7) Record off pitch. Complaints 1, 4, and 5 are common to the pregruoved record and the blank uncut dise. The volume of the reproduced record may he low from any one of several reasons: incorrect microphone technique; lack of gain in the audio amplifier system; either insufficient, or too great, weight on the cutting head. Distortion of sound may lie due to too much a iplitication; improper impedance matching between the microphone and the amplifier, or between the amplifier and the cutting head; or to shouting into the microphone. if the sound comes in loud, and then (lies down, it is practically certain that the mi- eruphone is ''packing'' rl sound installation demonstrated at police headquarters. New York City, for the famous "line -up." Conversations between the inspector (right) and the "suspect" posed The remedies for these troubles will he before the lights, mould br recorded. .11r. Saliba (left) and li. ll. Shiepe (tenter) are operating a portable recording considered under their proper headings. apparatus. (International News Photo) 28 RADIO -CRAFT July, 1931 will be loud and possibly distorted; even if there is no distortion, the quality will he poor. The effect will he "tubby" and stifled. as when talking into a partly filled barrel. Thirty Dollars for 3 Words On the other hand, if the distance from the microphone is too great, the vohuuc of the VERY so often, in the development of an art like radio, new descriptive words record will be low. It is best to stand are urgently required; and, as a rule, the trade itself see!:s to supply them. about 10 inches from the microphone, and In putting it up to the readers of R.uno-CaArr to coin three new terms which the voice should be directed into it. If it are urgently required, we are in hopes that our readers will find exactly the right is necessary to stand closer to the micro- titles to fill the blanks: phone, the person should face the instrument and direct his voice past it. At no (1) The Professional operator of recording equipment should be called a time during the recording should the cur- (A word hitherto used, but which fails to quite fill the rent be changed by the operator; otherwise bill. i. "Itecordist. ") a crackling noise will be registered. If the current should suddenly rise, it (2) The Non -Professional owner of a recording radio receiver is a is an indication that the microphone is ( "Home- Recorder" is not sufficiently definite.) packed; this usually happens on particularly loud notes. The pressure causes consequent (3) The person whose voice is actually being recorded is a lowering of the resistance. The microphone (While " Recordee" or "Speaker -In" might be used; neither seems satisfactory.) should then be tapped lightly, to spread the granules. The terms quoted above do not seen: fully suitable; so you will not send them When starting to record, the full micro- in. However, we are sure that, among our thousands of readers, there is someone phone voltage should never be applied sud- to find exactly the right word to cover each of these ideas. denly; it should be brought up graduali!, until the millianin:eter reads the normal Here are rules, read them carefully. current. A little time may elapse, while the Each word should he euphonious (that is, sound well) and be short rather than long. It must, of course, express the specific idea as correctly and distinctly as possible. microphone is warming up, before the but- Write your entries for each word on a separate slip of paper; do not mix No. 1, No. 2, ton current readings stabilize. and No. 3. Each should loe of a size to go in an envelope without folding; or you may use It will be found that the use of a two - postal cards, also separate for each entry. Do not enclose these entries with any other com- button microphone will result in much bet- munication, or they may be mislaid. ter recordings than a single -button type. The contest closes June 30, 1931; entries postmarked after that date will not be accepted. to Editor, RADIO- CRAFT, 96 -98 Place. best, the single button will not pass fre- All letters or cards must be addressed New Word Park At New York, N. Y. We cannot enter into correspondence abut entries. quencies higher than 2500 cycles; while the All employees of the Techni -Craft Publishing Corporation, and their families, are excluded two button will easily pass 5000 -6000 cy- from this contest. cles. If the recording system is to be used The three contests are separate; the prize for each winning word will be awarded without for voice only, then a single -button micro- reference to whether or not the winner submitted entries for the other two. If two or more phone will he sufficient. persons submit, for the same one of the three definitions, the identical word which is selected as the most suitable, each will be awarded the full amount of the prize offer for one contest -- $10.00. The Amplifier end the Motor Checks will be mailed on publication to the three prize winners, to be announced in our September, 1931 issue. In the radio sets of today, where the gain in the R.F. stages, due to the use of screen - grid tubes, is so high, only two stages of A.F. are generally used; and sometimes, a sistently good records, one must depend on inch records are used, the average commer- "power" detector is followed by only a sin- a three -stage amplifier, preferably of the cial phonograph motors will be found satis- gle output (power) stage. The use of such transformer -coupled type. Fig. 3 shows a factory. an audio system is unsatisfactory for re- single -stage amplifier which was used ahead cording, unless one is willing to stand very of the two-stage audio amplifier of an The Cutting Head close to the microphone and shout into it. Atwater Kent "Model 55" receiver. The ordinary phonograph pick -up has If the radio set has one preliminary audio A motor of at least 20 -watt rating should been found fairly satisfactory for house re- stage feeding the power stage the results be used, especially if records are to be made cording hut, nevertheless, it has its limi- will he fair; but still the person at the mi- on uncut blanks. A motor of this rating tations. In commercial recording, the cut- crophone will have to stand close. For con- is powerful enough to stake an 8 -inch record ting head is given a response -characteristic, but, if a larger record is desired, a 25 to as shown by curve A in Fig. 4. (The only 30 watt machine should be used. 'These mo- function of the true recording head is to MIC. MIC. TRANS. tors are now obtainable from the manu- receive power from the amplifier and, in r' facturers. turn drive is mechanical recording stylus.) PrOTEN. When recording it is very essential that ':'his recording head operates in a linear - TO a stroboscope (See page 636, April, 1930 fashion over nearly the entire range of am- 1 AMP. issue of R.tnlo- Ca.tr-r) be used; and the plitudes involved in speech and sic; al- SWRCN -1 1 1 + P _ speed of the motor should so 1w adjusted though, as indicated in Fig. 4, the response MILLI-AMMETER is running at 78 R. P. M. falls off below about 250 cycles. It is gBATTERY that the table with the cutting head in position on the necessary to have this falling characteristic FIG.1 record, and rating. When the lines on the (volume reduction) to prevent double track- JACK I BATTERY MIC.fRANS. stroboscope appear stationary, it is an in- ing when recording the lowest notes. dication that the table is running at the In order to compensate in the reproduc- SWITCH speed. tion for this "falling" characteristic, prac- f proper rill If the records are made with the motor tically all pick -ups are designed with the i - i running at less than 78 R. P. M., the play- "rising" characteristic shown by curve II , - TO AM D. back will 1w off the pitch until the turn- MILLI- - (Fig. 4.) MIC. AMMETER POTEN. table is adjusted to the same speed at which I et us consider the use of a regular pho- 5 the record was made. nograph pickup, hooked up backward for : the recording, instead of a commercial record- JACK 2 1)o not entertain the idea that motor 14 is O.K. if it is strong enough to pull the ing bead, compensated for the mechanical FIG.2 record. It might, and will, reach normal limitations of the disc, as stated above. speed when the record is about half fin- Then, the low- frequency response would be, above, connections for the adjustment of a ished; but, on playback, the first part of approximately, as shown dotted at C; aid, single-button microphone: besace, those for a while the with the saine pickup connected as a re- double-button hookup. The narrent in each the record will he off pitch, last "leg" of the latter should be checked separately. part will be O. K. While six - or seven- producer, this high volume level recorded July, 1931 RADIO -CRAFT 29

at the lower registers would result in ac- When the cutting needle refuses to stay sharpened to a tine I t. The thorn and (10tuated bass reproduction, as indicated at in the groove during recording, the fault fibre needles should never be used more I) (providing, the record does not double- can be traced to one of two sources: either than once or twice before resinarpening with track). the volume is too great or the weight is a piece of emery board -that is, a finger- It is tints evident that the phonograph not enough. Add a little more weight to nail board! pickup is not the ideal instrument for home the head, until the fault is corrected, and The angle which the reproducer makes recording. The tendency to cut over from then record. If the reproduced record is with the record has a great deal to do with groove to groove at the lower frequencies distorted, the trouble is due to too much the life of the needle point, and an over - is very great and, when using a phonograph amplification. One or two experiments will heavy reproducer will very rapidly wear pickup, for recording, volume must he sac- usually locate the trouble. Dirt needles. Therefore, it is very important rificed in order to prevent this cutting over. When using pre -grooved discs with more that the needle be examined thoroughly be- Ile wever, "cutting heads" are now available than 80 lines to the inch (fortunately, few fore each playback. on the market at as slightly higher cost than are available) the volume must he watched Houle recording is a new art -an addi- very carefully; otherwise, echo will he tion to radio which is here to star'; but to MIC TRANS TO DET. PLATE heard in the finished product. Before these obtain good results, one tritest be patient records are used, they shnnld he carefully and willing to tin just the least hit of ex- '27 wiped clean to remove all foreign particles perimenting. Du not be too ready to give TO up. P0._N. and, if it is found that some of these rec- Commercial records are the result of a 2OHM50.000 ords have "surface noise," the application complicated and expensive process, and have S of a few drops of ordinary Imbricating oil been in the course of development for many I.MF. V will usually reduce the "surface." years. i? TO DET. To say HEATER. that the home recordist can make Recording and Playback Precautions as good 50,000 LEADS records as the commercial product OHMS -' 2.000 Not every kind of aluminum is good for would be going a bit tam far; but it is a (FILTER OHMS FIG.3 (BIAS recording; the grade that is used is of a fact that home recordings can RESISTOR.) be made, and RESISTOR) hank been CHASSIS GND. certain hardness and the discs are first maple, that conu nire very favor- polished to a mirror -like finish. 'l'hen a ably with eouuuercial records. The enjoy- Schematic circuit of a single -stage Pre- ampli- wax film is spread over the surface and ment and pleasure to be derived from real tier. The '27's pinte connects to the ter- plate rubbed right into the disc, tunas filling up goad home records justifies the care minal on the detector-tube and socket. Unless a patience "power detector" is used, the "B" voltage all the pores. It is important that only expended in the effort. must be increased to 90 r. or mue. this specially- treated aluminum be used; Chat have you found out concerning otherwise the results obtained will be un- recording; or what do you Want to know pickups; these cutters are really like the satisfactory. (The Rencsen disc is an ex- about this interesting anal lucrative regular phonograph pickup, but properly field? ample of this type, in which the groove is Address ymur letters, enclosing a stamped ¡tamped to Simula /e curve J, made by compressing the metal. No mate- return envelope, to the attention of The problem of properly matching the the rial is removed, thus preventing surface Sound Recording Department of impedance of the recorder, tu the output of lt.uno- noise.) Ca Ar r. the amplifier, is veri, important in the making of good recorda. \lust phonograph pickups are of the high - FIG.4 ANOTHER SCOTCH STORY impedance type and can work directly off \ D Great Britain, as almost everywhere the plate tube. .r of the per If the pickup 5.0 I else, a owner of a radio set roust pay a is of the 200- or 50U -ohm type, however, B\ license fee for the privilege. And, so an impedance-matching transformer is neces- ta Amateur Wireless (London) tells us, "home- sary. Sonie manufacturers have tried mar- r recording apparatus is having great sales in keting a low- impedance (1.2 --1.5 oluns) re- Aberdeen. Ily playing each prugrammre cording head, made to work from the voice i twice instead of once through the loud- coil of the dynamic speaker; but the impe- speaker the inhabitants of the Granite City dances of the voice coils, in different radio 0.20 FREQuENCV - CYCLES feel that they are getting read money's worth sets, vary from 2 -18 ohms and, consequently, for their license fee." 250 5000 the high -impedance cutter was resorted to. Aberdeen, he it known, is where the Scots The Pre -Grooved Record In the above ,graph, lines :I and B represent are reputed (by their eountryuan) to he Before the troubles of pre-grooved rec- respectively the voltage characteristics of com- Canniest. mercial recording heads and playback pickups. are ords diagnosed, the theory of this type .4t C is indicated the rise of a pickup for re- ci record will be discussed briefly. cording: anal, at P, the resulting distortion GROOVE AFTER. NEEDLE DIRECTION NEEDLE HAS 'l'llis type record 78 or 80 when using the same pickup for playback. (TOP VIEW) OF of has lines to SPREAD IT.\ RECORD the inch, as against the eventual 92 or 96 per inch to be scribed in the dise which Sometimes, when recording only on one is furnished Wank and ungrooved. The side, it is found that the disc haa.s warped groove is very narrow and merely serves slightly, and difficulty will be experienced t.:e purpose of guiding the cutting head in making the needle track. This can be across the face of the record. When the avoided by either recording the uthcr side needle is placed in the groove and pressure or cutting II blank groove therein. is applied, the groove is spread to almost 'l'he inability to track may also be due FIG.5 BLANK twice its original width. (See Fig. 5.) to several other reasons; if the tone -arm UNTOUCHED GROOVES. (i is a \s Fig. shows in acore detail, when the tilted bit, or the turntable is wobbly, SOUND NEEDLE DIRECTION OF needle is vibrated a new, wider groove is this will prevent the needle from following GROOVE POINT` RECORD made tu correspond in its tluetuatitins tu the groove. If the recording has been made the tonal modulations impressed on the in- at a high volume level, some of the grooves put of the amplifier. When the elmneet'rolls will cut into emit othr; and this also will fl are changed over for reproduction, the play- prevent the needle from tracking. I back needle follows this wider groove, and Only two types of needle should be used the vibrations are again (unverted, first into to platy hack aluminum records-namely. electricity and then into sound. It is quite fibre and thorn. The use of any type of evident that, if there is not ample space steel needle. aside from introducing con- FIG. 6 BLANK UNTOUCHED GROOVES between grooves, a heavy bass note will siderable surface noise, will ruin the record. cause the needle to "double track," or cut Do not he tam ready to condemn aluminum !bore is indicated turc marner Ill which the "pre- over into the next groove, and spoil the records until you ha ve made sure that the groove' is spread in tier path of flee urrdl,'; at the same time, the mall of the groove record. needle with which you are playing back is may be sound -impressed, as shown below, 30 RAU10 -CRAFT July, 1931 Installing Radio in a Big Hotel (Part II)

By ELI M. LURIE, B.E.E.

N the last issue of R.tnIo -CRArr a de- so, as long as the tube continues to operate scription of the radio and public ad- on the straight portion of the curve. dress installation in the Hotel New However, as soon as the variations ex- Yorker, of which the writer is chief tend into the curved portions of the char- radio engineer, was followed by a discussion acteristic, at C and i), then the wait is of the principles of designing similar equip- slightly flattened on its peak points, and a ment. The subject is resumed at the point small resulting third harmonic introduced where the problem of distortion enters. into the output. This distortion, however, It should be remembered that the re- is comparatively small while the tube is quired 40 watts of power per channel (of operated with the center point of the curve .1 bird's -eye view of the Hotel New Yorker, which there are four) must he 40 watts of as an axis, and is usually neglected. which towers over the Pennsylvania Terminal bias district of New York City. It gs the city's n,ulistorled audio output; which means that As soon as either the grid or the largest and tallest hotel. not more than 5% of the second harmonic plate voltage varies so that the tube oper- component shall be introduced when operat- ates from any other position (such as X, It should he remembered, however, that ing at peak level. Fig. 3), then variations in the plate circuit the cancellation of the double frequency or If a single -tube stage of straight A.F. second harmonic is due to the fact that this were used, then the tube would have to distortion is generated in the push -pull am- operate on the straight portion of its plate- FIG. 3 plifier itself, and is not paused into its grid current, grid- voltage characteristic curve z circuit by the preceding amplifier. The push - (Fig. 3) in order to produce distortionless at pull amplifier defies not distort or cancel out amplification. This condition is effected by v any of the applied input, but only that so adjusting the plate and grid voltages which is actually produced in the unit itself. or that, when there is no externally- impressed i With the nuove factors in mind, we can voltage in the grid circuit, the operating proceed with the design of the amplifier point of the tube falls on the center of GRID VOLTAGE to supply our load. the straight portion of the curve, at A. If a symmetrical wave is now impressed on A!f tube characteristics are curved: the dcurce The Channel Amplifiers be symmetrical varia- of curvature at the operating point determines the grid, there will Since our total load is to be 40 watts they will continue the degree of fidelity, is an audio circuit. tions in the plate circuit; per channel, and the have decided to split will not be symmetrical with those in the this load into two 20 -watt amplifiers, our THIS RADIO SYSTEM grid circuit, and this will produce a double separate amplifiers should be designed for in the output figure. The undistorted the h., been :entailed for ye., dervon and frequency or second harmonic this output of en 66666 circuit. 'l'he greater the discrepancy be- '.50 tithe is rated at 4.65 watts when recom- How,-12 noon t to 12 n,dn:gh, Ope.et.ng tween the positions of the center point of mended maximum plate potential of 450 Turn switch to the right Tern ,.itch ro left the characteristic and the actual working volts and a negative "C" bins of 84 volts is to select your program: to shot oft radio: position of the tube, the greater will be the applied to the tube. This rating is increased second harmonic. This finally results in by about 25% when the tube is used in a strong overtones which completely alter the push -pull arrangement. Since each of our original na1dulation. amplifiers is to be rated at 20 watts, it is In the push-pull amplifier, this condition evident that it will be necessary to use No. 1:,W AF INBC Chain) is a extent eliminated; for, in this more than a single pair of '50's in push - No.2 n WJZ (NBC Ch.:n) to large No. 7 is WAFC (Colombia Ch. ;.) type of amplifier, it is possible to operate pnll; since their output is ILfi watts, or No. a brings you the moments best at other positions on the plate - au little more than half of the necessary program hon snorter to the tubes lected ,taten. current, grid -voltage characteristic than the value required. Therefore, if we put two center point without introducing second - '.50's in parallel, on each side of our push - Please shoal off when leaving room. harmonic distortion. The reason is that, pull arrangement, our total output will be ?ha speaker mode especially for this system ono' when a fundamental frequency is impressed. 2:1.25 watts. ('l'he formula is: P,olal can not be u ed in with any other ne ewg Is to writ properly please the two tubes of a push -pull amplifier oper- (l'. X N) + '25 (P X N), where P. is refw.,t l uu thr Roo. Clerk. ate 180° out of phase with one another. If the undistorted output of one tube, and N this is the case, then a double frequency the number of tubes.) harmonic of the impressed fun - As our output is to be only 20 watts. Walk. (Oteo., Imou, Deily Dosen or second . gi.,n oru this ..dio damental must be 3110° ont of phase or, the extra amount is excellent as a safety deely.'..ceM Sender, et 7. 305.00 now, the output wind- factor. 'Thus a push -pull amplifier using anti e2o.m actually, in phase. If, ings are connected so that they buck one the above arrangement should be satisfac- This ,ado s wined on at 10 ..m. another, the fundamental frequency com- tory. on Sunda, Io, the nLgrous ,e,dces arise as to why ,.goody boadc.,1 horn 101a Ir ponents will add and be passed out; while A question alight '50's the second harmonic or double frequency should he used, when larger tubes such as tenu is cancelled and disappears. (The fi rst the 211E (a 50-watt tube) would operate of a series be Edgar Messing, entitled, "The perfectly and carry the load with fewer The wall card in every room of the New Ilott's and \Wht:s of the Push-full Circuit," tubes. The answer is obvious when one }'orkcr; note the absence of volume control. appeared in the December, 1930 issue of realizes that, not only is the cost approxi- since volume is regulated at the channel amplifier. Ii.Amo-CmAr-r. -Tech. Ed.) mately three times as great for this type Jury, 1931 RADIO -CRAFT 31 of tube, but also the 211E must be oper- The power transformer should have a of the peak value. The rectifier tube does ated with nearly 1,000 volts on the plate in mininmum rating of 200 watts; and, if not tliserituinate as the voltmeter floes, but oilier to produce its rated output. To ob- possible, a separate filament- heating trans- rectifies the actual applied or peak voltage. tain 1,4$)II volts the rectifiers t also be former should be used. Therefore, if a transformer gives an output of the high- voltage type; whereas, if '50's 'l'he "C" bias for the amplifiers is ob- voltage reading of (i00 volts, the actual are used, only 534 volts is necessary, 450 tained from a resistor which is incorpor- 600 for the plate voltage and 84 for the "C" ated in the power supply. The actual plate peak voltage is 848 volts. The biais. The 'SI tube is ideal for this purpose current is about 150 milliamperes; which .707 and is very efficient. means that (by Ohm's Law) the resistor The tubes used in the Hotel New Yorker should have :t value of 5(i)) ohms in order transformer feeding am arrangement similar lane been in constant operation for over to produce a voltage drop of 84 volts for to the New Yorker's load should have an a year, operating a minimum of 12 hours the grid bias. output effective voltage of about 60i1 volts per flay (n total of almost 5,000 hours) on each sicle of the center tap. As figured and, at the present date, only three UX- Peak Voltage Readings above, the applied peak voltage is 848 volts 250's have been put out of service. This per plate, but the transformer under lon:1 speaks very well for this type of tube; but Many radio men have eneuuntereti the conditions will usually have a voltage drop. the I " \ -251's have given even better serv- peculiar phenomenon of measuring the sec - Also, the rectifier tubes and filter will add ice, for the original tubes that were in- ondart- voltage of a high -voltage plate to this loss, su that the voltage on the stalled with the equipment are still in ae- transformer and then, after rectifying this plates of the amplifier tubes will be just

r--- -r------'27 POwER i IONIC i '24 I '24 1 '24 DETECTOR -. Fig. 4 Po t i REST Schematic circuit of the Q TI OF R.F. aoad detector of the SET Strom/writ-Carlson "Model - ONO AUDIO 641" used for r,uestroom SEC NOT radio servire; there are 20000 USED four of these, :chile a fifth OHMS Bile r Ill (illustrated last month in -0.3- Fias. -1 and B) is pro - IB+ DET.1 vided with remote control 1.9 M F - 500 for special services. The OHMS TO tarit 7. I, a standard "tube- OHMS POWER to -liar" type, feeds the 1[ PACE HA r "booster" stage whose out- VOL z V. CONTROL iF.F.d+ put gars to the channel 390 OHMS 1, amplifier. .- oCa[óiD tive service. On the contrary, the 21IE voltage, finding the rectified voltage read- about right. The ualues of the filter system tubes used in the public -address system ing is either equal to or greater than the are shown in Fig. 6. have not given even a comparable service voltage measured right at the transformer. :Viend of the push-pull amplifier, a good record, with reference to the '50's. l'o date The answer is that the reading obtained three -stage screen -grid R.F. amplifier and our service from 211E tubes runs to :about from the secondary winding with an A.C. detector, working into a single stage of 401) hours. voltmeter is not the peak value of the wave, A.F., will produce enough energy to supply Therefore, two '50 tubes in parallel on but the effective value; which is only 70.7 the load. In the Hotel New Yorker, four each side of our push -pull arrangement, with 510 volts supplied by '81 typt ntti furs, should be ideal. Another problem that might cause questioning is with regard to the necessary number of '8l's to be used. It is excellent policy to always use one 'Sl for each '.50 used. On this basis, it is fairly easy to design a full -wave rectifier using two '81's in parallel on each side of the wane, giving us a total of four tubes; and this arrangement will e:arry without any trouble our load of about 150 ntilliauoperes. Automatic Plate Relays In the rectifier circuit, it is important to incorporate :a method of turning on the filaments of both the amplifier and the certifier tubes before the plate voltage is applied. In the Hotel New Yorker's remote- controlled public -address sy'steut, this is taken care of by automatic plate relays which operate only :after the fib ntents have been turned OH for a period of ;about a minute. 1n the main or room -radio system, however, the interval is obtained by using special switches whirl, when placed in paration, must first he turned to position No. 1. In this position, A.C. line voltage is supplied only to the filament transformers; and then, when the switch is turned, to the second position, current is supplied to the plate transformers. In this manner, the tubes :tre given a chance to heat up before the plate voltage is actually' Fig. D applied. These switches are readily avail- Rear view of the main radio control panel of the Hotel New Yorker: its front :ras shown as Fig. able. C in the June issue- The "booster" stages are the laciest rotte of units: the volume -level indicator is at the top of the fourth panel from the left. :Ill airing is called. 32 RADIO -GRAFT July, 1931

Stromberg- Carlson "Model 641" receivers are detector produces. Thus second-harmonic fourteen "risers." Each riser is a lead -cov- used. These receivers have been modified distortion, which is almost always inherent ered cable containing 26 pairs of No. 16 by removing their A.F. amplifiers; each de- in the grid -rectification type detector, is rubber covered wire. (See Fig. 2, in the tector feeds an external single stage of quite absent from this unit. The reproduc- preceding installment.) The hotel is divided 227 A.F. which, in turn, feeds the two 20- tion from broadcast stations which have into two sections, the north and south sides. watt push -pull amplifiers on that channel. 100% modulation is noticeably improved in Seven of the fourteen risers feed the north (Fig. 5).) quality when using the linear-power detector. side and the other seven feed the south Receiver Design 'l'he receiver was originally designed to side. It is so arranged that any single pair only -two rooms. As each The schematic circuit of the "Model 641" use only a single (power) stage of A.F. feeds thirty speaker takes 50 milliwatts, any single line, is shown in Fig. 4. It sl Id be observed However, because of the high gain needed when capacity, carries only 50 that the output transformer is designed for in an installation the size of the New loaded to 32 1600 milliwatts, or 1.6 watts. u 500-ohm load. The reason for this value Yorker's, it is evident that the tube for X = is that the remote -controlled public- address this position should be of the "voltage- gain" It is also arranged so that groups of rooms on same floor that in system is located on the fourth floor of the type; especially so, when the final stage is eight the are hotel, whereas, the main radio equipment is a power stage. numerical order are all wired numerically. on the forty -first. Therefore, the transmis- (See Fig. 1.) Then, from each of the eight A "Booster" Stage rooms, lines are dropped to time sion lines used for interconnecting the two same n - To eliminate any possible chance of motor- bered room on the four floors below. Thus, systems cannot be operated at a high trans- boating or feedback, the detector unit util- 1710 mission -line impedance, because of the losses if the feeder feeds rooms to 1718, izes a separate power supply; so that, then lines are dropped from on the line which would be incurred when each of the filament the '27 in the rooms directly down operating in this manner. :Usti, the output though the of first eight four floors; so stage receives voltage from the de- 1710 supplies 1610, 1510 and input transformers of Western Electric of A.F. that and 1410; the detector's plate voltage is 1711 feeds 1611, 1511 and 1411, etc. equipment are usually designed for either tector unit, 250 -ohm or 500-ohm lines. It is interesting to note that overloading BIAS RESISTOR FOR. 50'S Y of the detector, while possible, is extremely 3 Fig. 6 10AMP FUSE 7.5V. ar improbable. This t important device is The schematic circuit of '560 OHMS operated as n "linear power' detector. That Y the rectifier system used for powering each of the is when the input voltage increases, the B: 7 CH four -tube, type '50 chan- plate current rises; which, in turn, increases nel amplifiers, such as the "C" bias by producing a greater volt- 0.2SAMP shown in Fig. 5 below; age drop across the biasing resistor (a FUSE Ì the unusual filter constants xrill be noted. 1.5,000 ohm unit). (The grid leak and Con- V The emitri. Sw4 it pro- denser in the detector's grid circuit are used, 5 MF. EACH) vided, in order that the not but to insulate the filaments of the 'S1s may for rectification, CH. 7.514Y. from the radio-frequency transformer be heated before the grid 0.53MF high plate voltage is ap- when the phonograph pick -up is in use.) FUSES plied. About a minute 'l'he plate potential on the detector is 250 is permitted to elapse. volts; and the plate current is about two The output is about 150 110V,A.C.' milliamps at 540 volts milliamperes, which results in about 30 volts - OPERATION OF 5w4 : l i! POSITION CONNECTS I AND S,4 AND 6; 259, 1 AND 5, 4 AN02; "B" and "C" added. being applied to the grid as "C" bias. The 352, ALL OFF. detector is capable, therefore, of working at high radio-frequency voltages; and, by supplied from the main rectifiers. The plate Shooting Trouble using the above system of automatic grid supply is dropped fr the nmuxinmnt of By this method, a defective switch or bias, the tube operates on a linear -variation 540 volts, to 130 volts 1w means of a ground can be located by merely examining basis, supplying audio output from radio 66,000 -ohnt resistor. The resistor also acts the radio input linearly, instead of "square -law" equipment in the upper eight as a filter to prevent possible interaction rooms. Trouble in any section of 32 rooms values, which the grid - rectification type of between the two amplifiers, due to the fact is very easily determined by means of either that both use the same plate supply. an ohmmeter or a "wire chiefs" outfit. Once 'l'he plate current of the '27 in the first trouble has developed on any line, that line I '50 - } AMP. stage of A.F. is about 6.2 milliamperes is cut out of the circuit by pushing a plug .-, I N21 which, when used in conjunction with the into a jack on the test board in the radio i TO'271 j 1500 -ohm results in 9.3 INTERMEDIATE biasing resistor, room. The line is then is not I I tested, and it I AMPLIFIER volts grid bias. Both the input and the out- 1 put back into service until the trouble has ml A HJ put lines of all amplifiers are brought out been cleared. Cross -talk, the greatest OUTPUT C' rMMIP. to the main distribution panel, where they "Jonah" of most large installations, is neg- 1 -e- RADIOOFSET NE2 are connected to jacks. Thus it is possible ligible in the New Yorker. to connect any amplifier or group of am- Radio Service Men should feel that there plifiers, as the operator desires. An am- is a promising field in this type of work; plifier may be taken from any channel and since all of the men employed in the radio transferred to any other channel by merely division of the New Yorker are Service plugging "patching" or cross -connecting Men and were all at one time actively en- cords into the proper jacks. When all cords gaged in radio service work. are removed from the panel, the line -up of There are many details in this installa- !!_ is is, detector 3.9 OHMS amplifiers numerical; that tion that are not of the ordinary in that unit No. 1 feeds the primary amplifier No. they are rarely heard of; yet almost every- TWISTED 1 which, in turn, feeds the amain amplifier one in the radio field would like to learn r I rack No. 1, etc. about them. For this reason, subsequent 7.s V. I 516 Distribution of Load issues of R.mmm-Ca.mt-r will deal more full' Very little service work is necessary on with the apparatus about which complete this installation; since all the wiring is run details have not vet been furnished. At the Wiill down through the house in lead sheath, and sauce time, the writer extends an invitation branches, to various floors, from the leach to anyone interested in obtaining other data Fig. 5 sheath cables are run in iron conduit. There on this subject to write to him, in care of Below, the coaiertions of the push -pull am- are no exposed wires anywhere in the entire RADIO-CRAFT (enclosing a stamped return plifiers, using four '50s earls; Nos. 1 and 2 installation. envelope). He would also like to receive are alike. .4bove, the method of feeding both The distribution of the load throughout photographs of other hotel radio installa- amplifiers through a '27 "booster" stage (oat Mailed lucre). time building is accomplished by means of tions. July, 1931 RADIO -CRAFT 33

PENTODE 36

i0 R13 10 4 I 20 T REPRO- DUCER. D ffll ` 9 11A RI; Il RAISE C19 I IN. RS ' _ =ROM C5 CHASSIS CN R2 II1.: L 111Fc.: 6.3- WLT `5 r AUTOMOTIVE TUBES USED. Rl

L -4007. HONEYCOMB Nt. 01 2 VOL. CONTROL 36 5.S.C. ANT. AND RF. SEC. 5W.1.-. 3J0- INSIDE DIA. AND V4.VADE 110 T. N2.30 ANT. PRI. ENAM. 'B- B+' LOT. Nt 30 SCC. CN Iy} -01A. TUBE. 3 4 5 06 7 75V. RF. PRI. la T. Ht 30 %C. ; P IAND 201045V. -A+ BEI .0SE RRTE OTSIDE. 135V. 6.7V. 135 v. Fig. 1 This circuit, whirls works from any battery sir-volt supply, uses the new, rugged "cathode- heater" tubes for screen-grid amplification, a sensitive detector, and an output pentode. The tone fitter R13 -C19 is adapted especially for the characteristics of the final tube and its average output load. Building a Set for the Motor Car Around the Latest Tubes By C. E. DENTON

introduction TIIE of several new and s'ges, employing the new type '36 screen - that all parts are adequately shielded. Stable improved tubes, designed especially grid tubes; a screen -grid detector, also us- operation of the '36 type tube, in R.F. for use in automobile radio receivers ing a '36 tube; and a single audio output circuits designed to give maxinumm gain per 'as announced the in preceding is- stage, using the new type '38 pentode tube. stage, requires separation of the input and sues of RAmo- CRAFT) is certain to give Including the detector circuit, there are output circuit elements. In a high -gain great impetus class to this of radio con- four tuned stages, all "ganged" and con- multi -stage R.F. circuit, such as the one struction. As a matter of fact, it is no trolled by the movement of, a single dial; employed here, it is necessary to use com- secret that practically all the tubes pre- the condensers are of the "battleship" plete stage shielding in order to realize the viously used have failed to function satis- shielded type. The screen -grid detector is amplification possibilities of the '36 tube. factorily when applied to automotive work. of the grid-bias (power) type. For most Referring to the schematic circuit dia- 'l'he type '22 screen -grid tube is too fragile; sensitive detection with resistance coupling gram (Fig. 4) it will be seen that the this objection also applies to the 2 -volt tubes. (between the detector and the audio stages) various plate and screen -grid circuits are The 'Ole\ tubes lack the required sensitivity it is necessary to reduce the screen voltage carefully isolated by resistors or R.F. and gain. Other tubes used were unsuitable, on the detector tube to between 20 and chokes, all of which are suitably by- passed because of their inability to function prop- 45 volts. The detector's "C" potential is to ground by small by -pass condensers. This erly Over the range of heater voltages en- obtained by automatic biasing, using a re- is necessary to prevent interaction between countered during the charge and discharge sistor 1t8 in the cathode circuit. the various portions of the circuit. cycles of the automobile storage battery. The antenna coupler LI and the three The potentiometer 111 serves the double In most automobile sets, microphonic dis- R.F. coils L2, I.3, IA, all shielded, are purpose of providing adequate screen volt- turbances and crackling sounds were the especially designed to gist even amplifica- age regulation and also of controlling the rule, rather than the exception. tion at all broadcast frequencies. In order volume. The R.F. choke RFC, by- passed by All these troubles were clue to the attempt to accomplish this desirable effect, an R.F. the .001 -mf. fixed condenser C15, keeps the tb employ tubes which were primarily de- choke L is connected in series with the R.F. currents out of the audio portion of signed for other purposes, instead of being primary of each coil. The chokes L are the circuit. specifically made to operate under the ex- tuned by small fixed condensers C of such ceptionally difficult conditions met with in a value as to resonate the former between High Amplification of Pentode automotive work. As a result, the 500 and 600 initial meters. The secondaries of the As mentioned above, only one audio stage keen interest in automobile sets waned, coils are radio tuned by the sections of the four - i' necessary when using the new '38 pen- and failed to bring about the gang universal variable condenser. (The principle tode; this is a screen -grid tube designed application of these receivers, involved so freely pre- is described in the article "Design for the special purpose of giving large audio dicted several years ago. of R.F. Transformers," May, 1931, issue of output with relatively small signal voltages Now, however, with the advent RADIO-CRArT. of the -Tech. Ed.) impressed on the grid. This result is made special automobile tubes, intense new interest is The C -336 screen -grid tubes used as possible by the addition of a "suppressor' again being manifested in the R.E. subject of amplifiers and detector, and the C -338 grid, located between the screen and the automobile radio sets. The mere announce- pentode, incorporate quick-heating, oxide - plate, and connected inside the tube to the ment of the tubes has resulted coated in a flood cathodes. cathode as indicated in the schematic dia- of requests for a suitable circuit in Because which of the special cathode design, gram; therefore it is operated at the saine to use them. In answer to this demand, the heater's voltage may vary from 5.5 to potential as the cathode. As a result of such a circuit has been designed and is 8.5, during the charge and discharge cycles this construction, the suppressor eliminates presented in this article. of the nut hile battery, without appre- practically all of the "secondary-emission" ciably affecting the performance or serv- effects which Efficient Circuit Features limit the power output from iceability of the tubes. Since these tubes four -electrode screen -grid tubes. The five -tube receiver described takes ad- hase uniform heating over a wide range of 'l'he pentode is capable of producing vantage of every practical possibility offered heater voltage, no resistance is required in h greater power output than three -elec- by the new tubes, and hence this receiver the heater circuit; which is to be operated trode power amplifiers of the same plate will give results closely approximating the from the "6 -volt" ant bile battery. dissipation; in addition, the pentode has a modern, well -designed home radio set. It will be noted from the illustrations that h higher gain than could he obtained The circuit consists of three tuned R.F. the receiver uses an aluminum chassis und from the three -electrode amplifiers without 34 RADIO -CRAFT July,1931

50,000-ohm poten- great loss in power output. The actual the shields have been fastened over the R.F. One Electrad "Tonatrol" figures, showing the important character- coils, each individual circuit sl Id be tiometer, R1; 4(H)-ohm wire grid istics of the typc '38 tuile, are illuminating. checked over and traced out carefully. If Three Electrad flexible, It has an amplification factor of 1(X), a different colored wires have been used for resistors, I(2, 1(4, 1(6; this check - Four Durham 50,000-ohm "metallized" 1- mutual conductance of 9011 utieromhos, and grid circuit, plate circuit, etc., simplified. watt resistors, I(3, R5, 117, 1112; ana undistorted power output of 375 toil- lack will be greatly The receiver is now counectcd to a 20- Two Durham 10,000-ohms "metallized" 1- that to he used watt resistors, 118, 1(13; the pentode to its best fusd aerial, approximating In order to utilize speaker One Durham 1(X),(00 -oluu "metallized" 1- of the speaker in the ear. Batteries and loud are advantage, the impedance watt resistor, 1(9; winding should be close to 15,000 ohms; TUBE SHIELDS Two Durham 250,000 -ohm "metallized" 1- in order to this value has been selected watt resistors, 1(10, 1(11; second- harmonic distortion to a t) t1 limit the 0 0 One 7 -wire cable, 1, 2, 3, 4, 5, 6, 7; audio output 0 minimum. (Because of the 0 Four Type X -L binding posts (antenna, which rise with fre- load characteristics, ground, and output), 8, 9, 10, 11; is Ei. quency, a tone -compensation circuit fol- La t LEl Ll Four shielded R.F. transformers for .00135- lowed; this includes 11 13 and C19. -Tech. ` a mf. tuning condensers, L1 antenna, L2, Ed.) RI / \ SIDE L3, 1.4 radio -frequency; VOLUME Constructional Notes CONTROL Four l'olynut .0()044 -ref. mica fixed con- SHAFTS !, A sheet of No. 12 garage aluminum is densers, C, for the primaries of the It.F. transformers. bent on all four sides to form as chassis 7T 16" x 7" x 3" high, as shown. The five Four 85 -tait. 11.F. chokes, RFC, 1, 2, 3; socket holes are drilled and the sockets are SHAFT One power -type toggle filament switch, Sw; CONNECT- Too Five screen -grid clips; mmmttl; then the four -gang condenser is ION FOR Ic y aale down and the four R.F. coils FLEX. -cu-cam +j Five alumimuu tube shields; turned upside COUPUN are mounted on the side wall underneath Five CY -hype sockets; the tuning Iisers. All other parts (ex- Four Cunningham 'l'ype C -336 6.3-volt cept the resistors of pigtail type) including screen -grid tubes, VI, \'2, V3, V4; fixed condensers, R.F. chokes, potentiometer One Cunningham Type C-338 (i.3 -volt pen- in the PWR' tode tube, \-5; It 1, etc., are mounted as indicated SWITCH SS - s 9t7TTM RESISTORS bottom view of the receiver, Fig. 2C. The CcBV-PA Une aluminum sheet, 12- gauge, 22 x 13 in.; chassis is then turned right side up and the Hook -up wire, etc. Fig. 2 four binding posts are mounted. (These Speedometer cable, of the required length, lap.at of apparatus st be very carefully insulated fr the Three views showing the to be used for operating the variable con- which is most compact for this automotive set. the volume control from chassis.) transformers are mounted denser gang and The shielded K.F. the car's instrument panel, or other po- 'l'he set is now ready for wiring. The horizontally, with their small resonating con - dcnscrs C in front sition. This may be obtained from auto- is wired in first (one filament circuit motive service stations. Adjustments side of the battery is automatically indi- must be macle for smooth operation. grounded by the car wiring). The switch then connected. The only adjustment trimmer Con- S \\. is wired in on the end of a two -wire cated is that of the four condenser. a to reach from the place densers on the four -gang variable cable, long gh operate per- where the set is to be mounted, to the con- The receiver now should NEW RADIO SYMBOLS should be first trol panel on the dash. 'l'he grid circuits fectly; however, the voltages THE progress of the art of radio is con - me then wired iri; tue connections which accurately checked with a high -resistance tinually enriching us with new devices go the caps of the type '36 tithes are clearly voltmeter. and, of course, the symbolism which is tht On the shown on the diagram. 'l'he 135 -volt grid The arrangement of the parts shorthand of radio t enlarge its gallery. be on the pentode goes to the socket chassis is such that the receiver may connection any terminal marked "G"; in fact, all screen - ted below the dash of the car at with its grid connect' s a re made at the sockets ennvonient out -of -the way point; by means of in the regular way. Plate circuits are wired vol and tuning controlled shaft- in next; then cathodes, b-pass 'misers, flexible shafts (similar to speed ter of an negative returns, antenna circuit, volume ing). Details :as to the mounting control, etc. automotive receiver: including the problems placement of "13" batter- for of the car aerial; All resistors except ltd have clarity dash controls; modi- view, Fig. ies; flexible shafting; been omitted from the bottom connection for "grounded by soldering fication of "A" 2C. They are held in place or "gr led negative" storagc- respective terminals during positive" them to their hattery leads; and methods of interference the process of wiring, as follows: 11.2, cath- symbols, is true, be elimination have been the subjects of exten- Some few it might cde of and ground (chassis); 1t3, screen - the Last \I sive articles in past issue', of l(Amo- CR.vr-r. cleared away, like the dishes of grid terminal of It t, cathode of \'2 course when the next is brought on. \'I; (:\ list of these issues. by dates, is as fol- dinner and ground; Its, screen -grid terminal of are the new tubes which have lows: Dec., 1929; .1an., Feb., Mar., May. Especially \'2; It6, cathode of V3 and ground; It 7, appeared during the past few weeks a chal- ,tune, .duly, Aug., Sept., Oct., Nov., Dec., screen -grid terminal of \"3; ItS, cathode of lenge to the ingenuity of the radio artist. 1!130; April, 1931.- 7'reh. Ed.) \'4 and ground; lt9, screen -grid to al Here, for instance, we have one which has of \'4; R10, soldered to RFC; It II. to C17; been suggested by Mr. J. Geartner, of the 1112, to R11 and C18; 1113, binding post List of Parts Arcturus Radio 'l'ube Co., for a new prod- No. 10 and C19. One I- (aunnarlunti "battleship" hype 4 -gang. uct which is intriguing the industry ,just After these resistors are soldered in place, .(1MH35 -n f. variaable condenser, ('1, C'2, C3, now. and all other wiring is finished, the bat- C4; We shall offer no prize for the solution tery cable should he fastened in position. Nine Polynret 0.1 -ref. rectangular-type by- of this rebuts, which represents a seven - Extreme care should be taken to prevent pass condensers, C5, CA, ('7, C8, ('9, CIO, letter word. But we invite renders who possible short -circuits later in the leads Cll. C'12 ('13; have other suggestions for new radio sym- brought up through the chassis deck. Most 'l'hree Poh'uet 1 -ntf. 201 -volt rectangular - bols and illustrations of radio terms to send of the wiring will be on the underside of type condensers, ('14, C16, C18; them in for appropriate illustration. (It the deck; and should be short and direct. One l'olymct .001 -ref. mica fixed condenser, may as well be stated, here and now, that "Solid core" wire will be found most con- CIS; variations on the hackneyed theme of "Ohm, venient to work with. Two Polvmet .01 -ruf. mica fixed condensers, Sweet Ohm" are barred in advance.) But After the wiring has lumen completed, and C17, ('19; what have you? July, 1931 RADIO -CRAFT 35 A Short -Wave Receiver -Adapter For independent use or as a permanent addition to a broadcast receiver By L. MITCHELL BARCUS \LIXF, other short -wave adapters, limited. It may be used with any receiver, requirement being to separate the plate _ that which the writer has con- by increasing insufficient "B" voltages with prong of the detector tube from the plate structed becomes an integral part one or two "B" batteries, or cutting down of its socket, and to bring out a lenci from of his broadcast receiver, giving in- anything over 180 volts with a suitable re- each. For this purpose an old tube base stant choice of short or long waves, by sistor. In districts where A.C. supply is and a socket (t'X or l'Y as needed) may operation of its built -in switch. It nay, not available, the three filmlents may be be bolted together; connecting the other however, be attached or removed in but n wired in series, omitting the center -tap re- prongs to the socket with short lengths of few minutes. Aside from its use as an sistor, and mused in conjunction with n suit- wire. adapter, it is not, as might be supposed, able battery. The new tubes available give Operation practically useless. Without changes of any a wider choice of amplifiers than hitherto sort, it serves as a complete receiver, using available. To attach the tuner to the broadcast re- either an eliminator or "11" batteries for ceiver, only a few simple connections are Construction the plate voltage. By getting the "B" po- of the Tuner required. The two leads f the socket - tential from the last R.F. stage of the 'l'he layout diagrammed (lower left) was plug are soldered to two of the wires of broadcast receiver (which has a tendency chosen bec use it permits more direct lends; a four -wire cable. 'l'he socket -plug is then to throw the latter into oscillation) and which is of utmost importance in an instru- placed in the detector tube socket of the tuning the broadcast receiver to some broad- ment of this kind. 'l'he R.F. and detector broadcast set, and the tube is replaced in cast station on the lower portion of the stages hieing side by side, the shortness of the socket of the adapter plug. On the end the lead dial, harmonics may he easily picked up between the two eliminates both of another of the wires u small loop, which the need of a shielded wire clown to It) meters or lower. This method at this point, will fit tightly over at tube prong, is made is invaluable in calibrating wavemeters and and the capacity between the wire and its and soldered. This is the tap to the plate oscillators. metal covering. The condensers and re- of the audio tube. 'l'he remaining cable lead sistors not shown are mounted beneath the Because it was designed for use with the goes to the ground of the set; if quick subpanel, taking great care to have dynamic speaker, the tuner is followed by them changing is desired, a small test Blip may three as near their associated coils or tubes as be fastened to this lead. audio stages, when used with most possible. sets. Although this is unsatisfactory The cable is then connected to the proper (and 'l'he separate filament entirely unnecessary), with head phones it transformer used binding posts of time tuner; the antenna is here is placed several feet away, has been found that it enables the most to lessen connected; the filament supply is switched any chance of inductive 1 and distant stations to be clearly received on simplify on; and the builder sits down to enjoy one of the problems of A.C. operation. the speaker. And, when the tuner is An Samar of the true marvels of short -wave at- individual switch for this transformer tached to even a fair receiver, hunt and al- reception. lows the tubes to warm up while the broad- If the tuner is placed on top of the broad- mechanical noises are almost completely cast wanting. receiver is operating; this may be of cast receiver, it may sometimes set up a In addition, the use of three any type satisfactory stages permits to the constructor. very objectionable hum, clue to interaction the filtering out of the high - All filament frequency leads and wiring are of shielded with the power transformer of the set. In static by use of a suitable tone cable and grounded. control; thus providing more enjoyable re- this case it is necessary to turn the tuner To facilitate changing coils, time construc- ception without seriously cutting down on at right angles, or remove it a few feet tor may find it a good plan to mount the volume of the signals. A -ultm the away. 250,(100 lids of the aluminum shields on the under- variable resistor and an á0)1i -nf. For best results with any slmrt -wane re- condenser, side of the cabinet's lid. 'l'he shunted in series across 'sub/land ceiver, it should be placed as close to the the secondary of sl Id be raised the set's first enough to assure that the antenna lead -in as possible, for the losses audio transformer, make a lid rests firmly very on the shield; if this is incident to long, straggling leads mount up satisfactory combination for this pur- unhandy, the metal lid may be lowered by a rather terrifyingly when dealing with pose. thickness the of wood. higher frequencies. It is not Although the tuner is shown as used with at all neces- Because it. is difficult to specify definite sary to provide another aerial for this a modern A.C. broadcast receiver having components tuner, which are readily obtainable in if the broadcast antenna is of first class. two audio stages, the constructor must - real any locality, the details of the socket -plug construction with as few turns ize that its usefulness is by no means or sharp so needed are left to the constructor; the only (Continued on page 51)

12 24 RFC AT R6 'Z7 J5 J 00 (=, C3 Oó (paoa v°.lPs VS

sC6 I R1 C8 R7 Ri C91 FEED - RS SMIEID STATIC SHIELD TO FILS 11-4, Ñ A FC / vMO`- 0++ 110v,At. C11 3 GND. j 4wnR[:'dtBLE - - -f- -'I -

Above, the layout of the tuner as it was built by the author: the filament ransformer is placed elsewhere. Attaching the shield covers to the cabinet's The circuit is a standard short -wave detector, preceded by a tuned lid makes changing coils easier. The unit may connected R.T. be to the broadcast screen -grid stage, and followed by an A.F. stage to obviate troubles which set by a plug, as shown, or by a -in built snitch. might follow its connection directly ahead of the set's A.F. amplifier. 1931 ,1; RADIO -CRAFT July, Improving Short -Wave Reception A discussion of the special features governing short. wave receivers, with constructional hints By CLYDE A. RANDON VERYONE with any experie always causes losses, to some extent; an whatsoever with short -wave re- effect which is quite pronounced at the higher frequencies. A shield should be Fig. 9 ceivers (operating below 200 meters) a -grid stage waves, than long waves, Methods of coupling tuned screen is aware of the fact that seldom larger for short to a short -save detector. L2 is a short .cave are they very sensitive; in the use of short - considering coils of equal size; nevertheless, R.F. choke. same shield sizes are, in general, used WUVC adapters, particularly, very mediocre the fac- with the result that the losses are con- However, there are other contributing results have been obtained. This has caused so that siderable. (See Fig. 1.) tors which lessen the amplification; dissatisfaction to ninny users of short -wave total amplification obtained from an short- In general, the diameters of short -waive the sets. If the sensitivity of the average R.F. stage operating at short -wave lengths wave receiver could be radically improved, coils have been too large; therefore, their in high is considerably less than tuait obtained at many users would find a new satisfaction fields have also been large, resulting design is broadcast frequencies. (See Fig. 4.) in tuning in foreign stay losses. The trend in present with The causes of this relatively poor sen- toward coils having smaller dimensions, Great Frequency-Range the sitivity, although perhaps apparent to the shields giving more "breathing" room to It will he recalled that the tuning capac- short -wave specialist, are less obvious to the coils they contain. ity in a broadcast receiver man' be between in average short -wave experimenter. It is, of Choke coils, also, are not as effective .0003- and .0005 -111f., with a shunt "trimmer" in broad- course, useless to discuss the causes of in- short -wave receivers as they are of perhaps 20 to 75 mint. The short -wave in effectiveness sensitivity in such sets without giving prac- cast work. The difference job seldom requires a trimmer (a requisite will discuss also ganging tuned stages). III fact, the tical remedies; this article BROADCAST SW ORT- WAVE for the practical application of methods for . BAND BAND Inning capacity often has a maximum value improving the sensitivity of the average of 75 f., and seldom do builders use Ca- short -wave receiver or adapter. pacities of .0003-inf. The smaller tuning Since ordinary "broadcast" receiving sets condensers used in short -wave receivers (operating between 200 and 5511 meters) "spread" the dial tuning (bear this in mind, are more or less familiar to the reader, a if you find that short -wave stations whip comparison will be drawn between them and in and out "like lightning. ") Remember "short -wave" receivers. The most important also that, on the basis of 10-kc. separation contrast and, of course, the most obvious, between stations, there are only 96 10 -kc. in frequency between or- "channels" in the broadcast frequency range, is the difference Fig. 3 signal:. while in the short -wave dinary broadcasting and short -wave Believe it or not, the short-wave hard from 550 to 1500 ke.; 11igh- frequency phenomena cause all oar 10 to 2011 meters is thirty times as raide as sped from 1500 kc. (200 meters) to troubles. the 200 -545 -metre broadcast band. :.),000 kc. (I0 ureters), there are 2,850 coils there are eddy- 111 -ke. channels. (Fig. 3.) Within the R.F. is partiv due to the fact that the ordinary losses, difference between short- current losses, ordinary resistance short -wank R.F. choke must be operated Another striking all these sets and ordinary broadcast receiving and dielectric losses; in general, over a great frequency- range. If the range: wave is, values of the tuning are greater at higher frequencies. There to he covered were limited, very efficient sets, lies in the relative condensers, and the however, :a counteracting effect: the number choke coils could he designed for the con- condensers and grid es of the set. of turns used in the coils for short war ditions. But this is not the ease; so that capacities within the tubes and is less; so that the neistannee titre to the the usual choke coil is more effective at Ily -pass condensers across resistors, often have wire itself (the "copper" loss) is reduced. some particular frequencies. (The "hy -pass voltage leads, in short-wave sets, value .01 while a condenser However, the eddy -current and skin -effect effect" in R.F. chokes is illustrated in Fig. the low of -mf.; at broadcast set losses are increased. 2.) The usual choke coils are not as effec- in the same position in tive at very high frequencies as at the Wright need to be '2 -m f. or more. Use Ample Shielding (since the ad- lower. At broadcast frequencies shielding is least) the As at broadcast frequencies. 'Dien, too, the ratio of inductance to vent of the screen -grid tube. at receivers. Shielding barn made negli- also used in short -wave capacity, (the I. /C ratio) lergues such grid -to -plate capacity has gible. However, this capacity has not been at large change in tuning over the enormous so at very high frequency -ranges used in short -.wave re- entirely eliminated; that the smallest ceivers, that the usual short -wave tuned cir- frequencies the effect of even I cuit must have a set of about three in- FOR SNORT -WAVES ductance coils. Bi' means of the three coils, TURN-TO-TURN W and this condenser (usually of the "midget" CAPACITY, CI type), the entire range from ten to perhaps LI one hundred meters is covered; a very wide I. frequency -band. (See Fig. 3.) '. 'l'he ratio of inductance to capacity, in L the tuned circuits of an R.F. amplifier i I stage, has considerable effect on the total ------_---__ value of gain of the amplifier. If a large R.F. is WELD 2 `------SHIELD inductance is used, the amplification \TOTAL OR. OVERALL COIL greater than if a large value of capacity CAPACITY, C2 Fig. 1 is used, at the same frequency. Thus, it is Fig. 2 The big long -wave coils may !rare shields much that, were all other factors the saute, evident the wavelength, the greater the closer that is practical with short -71.1M' roils. The shorter the amplification of short-wave radio fre- -turn capacities to lessen the volt- which arc more sensitive to metal in their effect of inter fields. quency amplifiers would be considerably less. age across the coil. July, 1931 RADIO -CRAFT 37

the signal amplification as well as the selectivity of the tuned circuit. How to Figure the Regeneration could also be used in an R.F. amplifier to increase the amplification; but the tuning range is normally so great R. F. Coil Secondary that an extra control would 1w necessitated. The very intimate relations of the tuned (With Tables of Coil Constants) circuit to the capacities within the tube itself are shown in Fig. 6. Evidently, the By CLIFFORD E. DENTON relative values of time tube capacities: compared with the tuning condenser must have THE procedure to be followed in de- a considerable effect on the operation of termining the inductance to be used the circuit. with a given condenser, to cover a The size of the detector grid condenser given range of frequencies, is a GC is quite important, because the entire "closed book" to all too many radio workers.

parallel arrangement of condensers is It is the purpose of this little article to Fig. 7 coupled to the tuning circuit through the shed some light on the subject; and the The screen -grid detector, the value of which is grid condenser. Therefore, a small value of recognised on long is (comparatively) writer, after an effort to simplify the prob- naves, grid condenser is desirable at short -wave more efficient for short watts. lem to the Xtb degree, hopes that the ex- lengths; in fact, a .0001- or .00015 -mf. value planation will not be found too sketchy. capacity again enters. :1n outstanding fail- is normally used. broadcast (At wave However, if this article raises any questions ing of the screen -grid tube at high fre- lengths, the grid condenser is generally in the minds of ltADio-CaAr-r's readers, com- quencies is its large screen -to-plate capac- .00025 -nef.) prehensive consideration of every angle will ity which causes a loss within the tube, so be found in that famous sixty-cent to speak, from plate to ground. text- book of the Bureau of Standards, Such internal "Cir- losses are especially evident cular No. 74." in short -wave oscillators which will not "perk" at the very high frequencies. The (The article, "Design of Radio- Frequency Transformers," introduction of losses necessitates increasing by Sylvan Harris, in time May, 1931, issue the feedback, and a point may be reached of ItADio-CHAST may well be consulted where the feedback, under existing circuit for valuable data on time design of the primary conditions, can not be increased farther; of modern R.F. trans- then the tube refuses to oscillate. formers.) It is generally Losses in Five -Meter Receivers known that a capacity and an inductance force If the increase in frequency materially a resonant circuit; that is, the combination decreases the sensitivity of short-wave re- of a coil (inductance) and a condenser (capacity) will ceivers, one would nturolly expect an ultra- time to a particular frequency or wavelength, high frequency receiver to become very in- Fig. 6 'lire tube capacities, input and output, as and, by changing the electrical value one sensitive, indeed. This has been found time trrll of as the grid -plate feedback rapacity. determine unit or the other, the wavelength to which case, by the writer and n few other experi- finally the efficiency of e circuit. the combination will tune will be menters in this most interesting short -wave changed. But, if the electrical value of one field. Sixty thousand kilocycles is a very "Numerical Sensitivity" unit is increased, while that of the other is propor- high frequency. indeed, corresponding to a Another difference between an ordinary tionately reduced, it is possible wane length of five meters. Here the tun- ,port -wave set and a broadcast set is in to maintain the ber resonance at the same frequency; that ing condensers must be so smell that the n of stages of radio-frequency is, keep tuned to the same tube capacities approach them in magnitude; amplification that are used. Perhaps the a station. In other words, we have altered only the in fact, half the tuning capacity, so to speak, foremost reason why short -wave receivers ratio between the electrical value is often within the tube itself. Exagger- do not use more stages of radio -frequency of the coil and condenser -we have "changed time ated conditions like these, show, in a very L/C ratio," to use a common striking manner, the effect of increasing the expression. But the "LxC product" remains the frequency to be received by a short -wave same. receiver. It is customary to vary the capacity of a condenser, In Fig. 5, the essential connections for to time in stations; consequently an ordinary short -wave receiver are shown. if knowing the capacity in use, we apply the A small choke coil Ch is connected either "I.xC product" figure indicated for a particular at the point X or the point Y in the wavelength (Table I) we imme- diagram diately learn the coil value required. We are In st well -designed sets, the choke coil then in a position to go ahead and design this inductance. This is connected at the 1 t Y; because at this table is extremely point it is most effective. convenient for coil calculations and for that Coil 1.1, connected in parallel with Fig. 5 matter, in capacity calculations, too. Cl, In a short-stave is the tuned circuit of this detector receiver, the importance of outfit. the R.F. choke, Cil, is considerable. Its induc- Coil I.2 is the tickler winding, used to fur- tance need not be high, but its self -capacity Calculation of Tuning Range nish regenerar and mast be very io.v. thus greatly increase The values of inductance and capacity amplification for "numerical sensitivity," employed at radio frequencies are small, and /BROADCAST -WAVE CIRCUIT (that is, to increase the product of multi- generally stated in microhenries of induct- TUNING CAPACITY\ 751414F. plying the figures of gain in the several ance and microfarads of capacity, as in stages) is the difficulty of operating with a Table I. Time relation between the product single (of the inductance and + control all the condensers of the time capacity) and various tuned stages. The effects of dis- the frequency is given by the following R tributed formula: 3 WRNS small capacities, differences in wir- ( ing arrangement, etc., make it difficult to SWAMP. `Sp MMf. SNORT WAVE = 159,200 CIRCUIT line up the tuned circuits of the various ItS TURNS (TRIMMER) LxC stages. In view of the fact that time amplification of short waves is less, and Fig. 4 the num- In which f is expressed in cycles, L in ber of stages ordinarily On short waves, the tuning capacity should It employed also is microhenries, and C in microfarads. The very low,: since it is the "L /C" ratio that less, it is obvious that the sensitivity of table covers the broadcast band. governs the impressed signal voltage. (Continued on page 53) (Continued on page 54) 38 RADIO -CRAFT July, 1931

Computing the Impedance In a circuit containing resistance alone, The Whole Ohm Family the current and voltage are in phase; in a combination of resistance and reactance, the impedance may he determined graphically by the construct' of a right -angled R, X and Z triangle. (You may remember that, according tu a famous geometrical theorem, the "square on the hypotenuse of a right -angled (Part II) triangle is equal to the . of the squares on the other two sides.") Our formula is: A Simple Explanation of Reactance and Impedance 7.2 = R2 By HAL WYMAN +X2 Then, as in Fig. 5, we can construct a triangle with It as the base, and XL the voltage, and I the back current which it Capacitative Reactance and measure the hypotenuse to causes): altitude; The familiar phenomenon of the charge find the value of the resulting impedance. and discharge of a condenser, under direct - In the case of a capacity and a resistance, current conditions, gives rise to a complex I = 21T-Xf XCxE the triangle is constructed in a different effect in A.C. circuits. Just what this effect \Ve therefore shall find that, while the in- manner with the altitude extended in the may be is readily understood by a review ductive reactance increases with the fre- opposite direction as shown in Fig. 6. This of the basic relations. A capacity differs quency of alternations, the capacitative leads us to a simple solution of the complex from an inductance, not only in its physical reactance decreases with the frequency. The problem of inductance, capacitance and re- constitution, but in the manner in which statement of Ohms Law, however, takes sistance in A.C. formulas. it is operative. the sauce form: We saw that an inductance gives a back E.M.F. in direct proportion to the current E=IXXc; I=E/Xc;Xc=E/I through it. A condenser is rated in farads Hence: to find inductive reactance, mul- according to the quantity of electricity tiply the inductance in henries by the which may be added to the charge by rais- frequency in cycles, times 6.283: the result ing the voltage across it by one volt; that is, is in ohms. a condenser which holds one coulomb (or 'To find capacitative reactance, multiply ampere-second) of electricity for every volt the capacity in farads by the frequency in across it has a capacity of one farad. This The series resonant circuit, unlike the parallel, cycles, times 6.283; and divide 1.0 by the unit is so large that we employ the micro- affords no path for direct current; but the product: the result is in ohms. resonant voltage developed is limited only by farad in most ordinary calculations. (Note: since all capacities actually used its losses (resistance). While an inductance opposes any change are small fractions of a farad, this rule is in current by producing a back E..I.F., a As shown in Fig. 7, we first lay off the not very convenient. It is better to use a condenser opposes any change in the voltage resistance; then the inductive reactance; capacity stated in microfarads and divide across it by charging while the potential then the capacitative reactance. The altitude 1,000,000 by the final product.) rises, and discharging Os it falls off. That of our triangle is then found by dividing is, there arises a current opposing any the distance A -11 by two; and the hypotenuse voltage change. If we plot (as in Fig. 4) + CURRENT + RENT or impedance line may be drawn and meas- the current and voltage relations in a /..'.... VOLTAGE ured. capacitative circuit, we will find that the AIL se. This gives us n simple solution of the when the voltage impedance, which is: current is at a maximum INDUCED formula for finding change is greatest; this condition arises as VOLTAGE FIG.3 FIG the voltage curve crosses the zero line. We z = v R2 +(cL xc)2 can see that the current is leading the In inductive circuits. left, the current is con- voltage by 90 degrees; exactly the opposite sidered to be behind t re voltage in phase; in Alternating currants .ar uuenable to be of it. of the condit' in the inductive circuit capacitative circuits. to ahead Ohms law in the sauce sense as direct cur- whose characteristic is shown in Fig. 3. rents -the fundamental relation being I - have also noted that inductive react- By a process of mathematical reasoning, We E //,. It is necessary however, in considering the current to lag; similar to that in the case of inductive ance in the circuit caused complex circuits, to consider the phase rela- reactance caused the reactance, we shall find that (when, as whereas capacitative tions of the currents in the different branches lead. (We ass a purity of st b fore f is the frequency in cycles, C the current to he fore a solution inaay be achieved. We capacitative reactance u pacity in farads, E the impressed A.C. either inductive or therefore resort to algebraic equations or in the circuit when we specify a lead or lag graphs in order to obtain solutions. of 90 degrees; if the circuit is not purely inductive or capacitative the reactance of Resonant Circuits the circuit as a whole is "complex. ") In a We have shown that a series circuit com- XL xc simple series circuit of inductance and posed of resistance and reactance has an capacitance, the capacitative reactance is impedance equal, not to their arithmetical R. subtractive from the inductive reactance. s , but to their "vector" sum instead, FIG.S FIG. 6 example: In a circuit having across it because of complex phase relations in the A For an inductance of 1.5 henries in series with circuit. The current through a series circuit XL a 40- microfarad (.0004- farad) condenser, is of course the same in each element; but what is the total reactance to 60 cycles A.C.? the voltage (auross each element) is deter- z -3- )(a.+ xc XL =6.28 X 60 x 1.5= 565ohms mined by the resistance, impedance or re- 1.0 _ 6.283 actance of the individual element. It is 4 XC = X 60 X .0004 = 66.3 oluus therefore possible for the voltage across any Xc X = XI, - X(7 = 498.7 ohms one element to be greater than that across FiG 7 Had a pure resistance of 10 ohms been in the combination. B series with the combination, this would also In series resonant circuits (by "resonance" but the total impedance would we describe the condition in which, at some for a complex impedance is rep- inerease it; The formula have one given frequency, the capacitative and resented by the above graphs: the hypothenuse not be exactly 5(18.7 ohms, but world that the sum are we find a 7, is the impedance. Remember to be determined by a more complex inductive reactances equal) that is, they are of XL and XC is algebraic; formula. (Continued on pale 56) in opposite senses. and one cancels the other. July, 1931 RADIO -CRAFT 39 Letters from Radio CRAFTSMEN

We all like to hear what the other fellow has been doing: and he would like to hear what you have done. C'mon in, Craftsmen!

TING -A -LING -LING I Editor. R auW- CRAF-r: Mr. Sprnyvberry's article in the May issue, on adapting the Hadiola "28" to two-volt RUDOLPH tubes, was well received L. DUNCAN, President, RCA bv the writer, as Institutes, Inc., Member, Institute of Radio well as by six other readers Engineers: Member. Radio Club of America in this city. I Member, am Veteran Wireless Operators Associ- anxiously waiting the publication of the ation: Captain. SCR, United States Army. next by the same author on the '25" and the "H-8l2." Can't be too soon. RADIO- CRAFT rings the hell. BERNARD M. ireIlR, A Radio 1316 Fannua St., LaCrosse, Wis. "A= A B= -B+12}V. (Mr. Sprayberry, who has been working The fundamental circuit of the Regenerative on these sets, has promised us another Interflex, which old timers will renumber for message its sensitivity article, which will appear at the earliest and quality. This receiver used a "Flexicou pler" to control regeneration. moment-probably in the August issue. - To men who are Editor.) I could not get along without RAmo-Ca,srr each month. looking ahead! EDWARD TREADWAY, by R. L. DUNCAN ERIAL CRYSTAL Reno, Ohio. 'w -FORD COIL-CONDENSER ONLY ì -A tteir correspondent is, no doubt, blessed a few men will read this mes- i '01 sage ... but they will be with a good location and one fairly free the type of .001- i men in whom I am personally inter- STOP from MF. interference; in such a spot, ai simple ested. For such men ...I want to open the set will do wonders. For comparison with door to thorough training in radio. And the coupon this little set, we below is the first step! PHONES-1 r ;how also the fundamental circuits RCA Institutes, Inc., ( formerly the Mar- of the Interflex and the Regenera- coni Institute ) 30-0HM was founded 22 years ago RNEO2 tive Interflex which found so many friends for one purpose. To produce graduates who will }L among constructors a few years ago. be amine to the radio industry. If our `TAPPED 1frPLATE Editor). - Institute never made a penny ... but did COIL COND succeed in lifting the standard of radio GROUND -B + technicians, engineers, and merchandisers, DOUBLE CHANGE OF FREQUENCY we would consider our work Editor. a success! It soul- Ca.trr -. Naturally, we want our message to reach 11r. Treadway's set is extremely simple, and After lying in a semi- as many men as possible. So we founded somewhat inexpensive. lt'e ca a,not recommend dormant state for a nuiuher resident schools in four metropolitan cities. it for distance or volume. of years, it now appears that the Then we opened superheterodyne our courses to men all over circuit has become quite the world who cannot afford to give up their A REDISCOVERY popular; and I desire to present to you an positions. Thousands of our students study home Editor, RADIO-CRAFT: at in their spare time. With theequip- ment we furnish, they have their own radio Yes sir, this is a swell set. I hope you ANT. HIGH LF. LOW I.F. laboratory right at home! You, too, can start print it. It uses a ti-volt "A" battery and FOR'ONE SPOT' FOR HIGH your course at home any time! TUNING 10 volts "ii''; one variable condenser, AMPLIFICATION Our courses cover the entire radio field. and We train beginners one fixed condenser (out of who have had no pre- a Ford coil) 53 vious knowledge of radio. Advanced stu- with a crystal as a detector. The tube is DET dents take our more technical courses. But an 'OIA. The tapped coil is wound on whatever branch of radio interests you... is a all ready for you to study. The tube three inches TO cost is sur- in diameter and six Indies ONLY THESE AUDIO prisingly low for the training you get. long; it is of No. 22 enameled TWO TUBESTD AMPLIFIER wire, tapped BE TUNED IN" As the oldest radio school in America, we every eight turns. It looks simple, but it have given training to nearly 20,000 men. Many of these are now execu will do its work well if it is built right. I he arrangement suggested by Mr. Sutton. a tives and engi- well- kuuren neers in the largest broadcasting and manu- Unlike most one -tube sets, there are no experimenter, actually follows the some facturing companies. Butnoneof these whistling noises; but will principle as a .super -converter used with arrived overnight. it sure bring in the a broadcast set. the latter Nor will you. Your suc- If alco Terre a super, cess depends on distant stations. ter would find triple frequency-change. how well you train yourself .. how hard you work. But we will help you. I personally idea that ocenrrei to nie hack in invite you to write to the days me for our free book that gives you the Before all the manufacturers Began to complete PHONES fea- story. DET. ture suit wring receivers. In choosing the intermediate frequency to RCA INSTITUTES, Inc. be used in a superheterodyne circuit, it is L'.1 desirable for uifaximllln amplification to have INSTITUTES, Inc. Pi lit NP -7 the frequency quite low, sae" alomut 70 ke. 75 Varick St., Now York, N.Y. However, so low a frequency brings about Gentlemen: Please send me your FREE " the undesirable "two-spot" tuning book which tells about your laboratory WO effect; method of radio instruction at home. I1 + Illlll which gives two separate points on the oscillator dial for every station, and causes Name loud squeals of protest to emanate The original Interflex circuit of 1925: in whirs fr Address the aerial the loudspeaker when the "high" spot capacity is smoothly variable. 7 h for actual receiver, however. included more audio one stat happens to coincide with the amplification. (Continued ou pupe 50) Occupation July, 1931 40 RADIO-CRAFT

Radio - Craft's Information Bureau like, but SPECIAL NOTICE TO CORRESPONDENTS: Ask as many questions as you please observe these rules: to explain your meaning; use Furnish sufficient information, and draw o careful diagram when needed, only one side of the paper. List each question. interest will be published here, to the hose questions whirl are found to represent the greatest general i the receipt of a question and the extent that space permits. .It least fire weeks must elapse between appearance of its answer here. Replies, magacines, etc., cannot be sent C. O. D. 25 cents (stamps) for each separate question. Inquiries can be answered by mail only when accompanied by Other inquiries should be marked "For Publication," to avoid misunderstanding.

and December, 1930, ERLA "224" SCREEN -GRID (íl -) In the September (IV wean( LW AMPLIFIER BECOMES THE DETECTOR) issues of RADIO-CRAFT were described two varia- Ll ' 24 L2 (124) \Ir. Joshua Colvin, Phoebus, \ a. I tions of the direct -coupled audio amplifier. I'ira- (í).) What are the probable causes of hunt or or advise whether the Electrad Loftin-White "T. a burnt -out volume control, in al, Erla Model 224 .\ -224" screen -grid tuner crut 1.e-dirtied to these A.C. Screen -Grid receiver? audio systems; and whether it is_nece_ssary to add 1. \.I As the circuit of this receiver indicates more tube as a detector.?.. (Fig. 11.124), the switch Sw3, which is of "clip" nue -r ('.\.) The cireoitl of this "Type .\ -224" t tye, connects one phonograph- pickup tip -jack to is shown in Fig. í),I25, with the wiring cross- the chassis; and, if this is not done, hum will it to a direct -coupled audio amplifier. the volume control is set in "phone' connecting result. when This ttming was designed for use in con- position. :\ quick- heater tube may canse a portion junction with the Elect rad Loftin-White ''Type hum. Test also for the usual opens or of the .\ -245" direct- coupled audio amplifier; when it is shorts; and resistors or condensers of incorrect connected to such an audio system. the first tutor rating. audio amplifier functions as a detector, no -out" volume control may not actually in the .\ "burnt additional tube bring needed. VOLUME toe so; lint only open- circuited from friction of the CONTROL of the - \245" will be found in the VELLOW/ TO '24 FILAMENT wire. Replacements may The circuit ' 3.000 VP slider cutting through the "Radio Robot" article on page 24 of this issue. TWIST SEC. IN AMP. with the following values; OHMS be made in accordance (Continue,/ on pane 59) and voltages checked against figures given below: Resistors 14I, R6. R7, 70,000 ohms; 22, 5.600 Fig. Q.125. R3. 6.01)0 ohms (wire -wound volume control): ohms; FREQ. OF NOTE LOWEST INSTRUMENTAL (Above) R4, 80 ohms; RS, R8. 100.000 ohm.; R9. 1.000 FREQUENCIES (ti PER SEC.) - ohms; RIO. I411, 10,000 ohms; RI2, 6,000 ohms: INANO.LOWEST ri-clrad 1. of ti n- 20 o NOTE usco -32 R13, R14. ohms. }pe .1 -224" tuning BASS VIOL - 40 II luite "1 Condensers CI. C2, C3, C4, are the usual 20 irre,., -Grid Tuner. capacities. shunted by trimmers (not shown); CS. BASS TUBA -42 40 BASSOON-GO Jrsigned to operate CIS, 0.5 -mf.: Co. C7. ('K, 12, C13, 0.25 -mf.; C9 60 CELLO -64 :ritte the 'Type :I- CIO. .001 -mf.: I'll. C19. 1. mf.; C14, 0.1mf.; TROMBONE -8O I:" Direct-Con pled CIO. C17, 2 ml.: C18. 3 mt. Bass CLARINET BASS VOICE .lu .IHIp(ifirr. its push -pull output di, The reproducer. with built -in 100 KETTLE DRUMS 85 the receiver chassis, :s transformer, plugs into BARITONE VOICE % shown. It is important to et the Erta Type 120 FRENCH HORN -105 ()126. l' -62 pick -up correctly to the chassis (R. red. to 140 grill and III, black- to chassis/ since. otherwi -e. VIOLA (Left) 160 BANJO --128 there may result hunt or lack of phonograph voltinc. TE NOR VOICE voltages Isitential 110 volt-.I 180 I his graph, repro- The operating tline- TRUMPET _ 16o per- are as follows: Filament potentials, VI. V2, V3. CLARINET duced by .phial 200 mission of the au- \4. VS, 2.4 v.; \ o, V7. 2.5 v.: \'8, 5v. Screen - VIOLIN-192 grid to cathode. VI. \'2. V3. 80 v. Plate to cath- 220 thor. .tar. .4lfred :1. SOPRANO VOICE 240 the Pi- C2, VV3, IoS v ; \'4, US v.; VS, 95 v.; 240 Ghirardi, and FLUTE Tit be VG, \'7, 245 v.; V8, 350 v. Ground to cathode. HARMONICA -256 lot Radfit. and 260 OBOE is from VI. \'2, V3. 2 v.; V4, 7 v'.; VS, 4.5 v.; Grid to reprinted 280 KULELE 268 1931, filament 50 v. th.,e Spring, I)L- Weak signals may be due to leakage through the 300 of Radio it illustrates condenser stator shielded leads; and broad tuning. 320 F PICCOLO -Ste of the to leakage in the tuning condenser or its stator (cads. the relation die's this. 1Iì0 190 Inn length to ihr (leaning with alcohol should ci,rrvet O i0 zo 30 40 SO 60 70 60 90 100 110 120 130 140150 160IÁ zoo , -Lr - off frequency NCHES column of S REQUIRED BAFFLE LENGTH IN Urfa ELECTRAD A -224 -G TUNER figures). t125) Mr. faul It. Churrund. Gary, Ind.

PHONO 5W 3 r--- 1 ---- ®á1 To OUTPUT DE TRANSFORMER RFC Cl2 T '43's CH 2 ÓLI L2 ! 21 I'24 I'24 '24 21 Q CI0 SW áó C9 C4 L.A. CÌ TpG (S C11- - 4 5 , R7 -R5 SuiCaiíST. 03 FIELD It COIL VOLVME (DNTROL' -- 1115111 C7 OWNS GND C5

TRIMMERS SHUNT CI TO CO. t« I,LOW CURRENT; NIGH CURRENT R14 EN CH. 2. 2.SV.° 110 V. RESISTOR R] MO SW. ARE GANGED i . A.C.

Fig. 0.124. .\,- le,m,tie rfrnl it tif the Fria "Mode/« 224 .1.C. Screen -Grid" receiver: trimmer condensers. not Slln n t the ttln ira Rde u.e'r.r. .Vote that the external repredaeer field, by- passed by ewers CI5 and C19, and the .duurt R11, is connected l in the ,entcrdap lead to /nigh- rolMae secondary. July, 1931 RADIO -CRAFT 41

The Super-Converter (Continued front page 23) Housed in an GEORGE W. WALKER attractive, beautifully fin- i ished, compact all -metal cabinet, the Walker Super -Converter blends in harmony with the most beautiful and correct furniture set - ting. The '50 tube, used to furnish plate SUPER - CONVERTER voltages solely for the converter, has a longer life at smaller cost. None but the Convert Your finest of materials are used in the converter; and every effort has been exercised in the Present Radio Receiver constriutititi of a truly reliable and efficient into a short -wave device. This is perhaps the very first short -wave Short -Wave Super -Heterodyne converter offered to short -wave enthusiasts in which the design parallels that of standard broadcast receivers. 'l'he faun may Listen to have confidence, because of its attractive Foreign Programs with cabinet appearance, on introducing to the family Walker Model I, Super- Converter. Pleasing Volume New Accessories WALKER SUPER -CONVERTER FEATURES (Continued front page 23) Four A.C. Tubes. including Screen metal cabinet, which measures but 78 Grid and No. 180 Rectifier. All A.C. 7 x 12 inches long. rather an expensive item; but it is cheaper operated. The Walker Converter represents the to replace one of these little resistors than TRULY SINGLE DIAL result of several years of experience in as more expensive item, such as a power the design of Short -Wave equipment. transformer. TUNING Each device tested in actual operation Its installation is simplicity itself. The No changing of coils for the popular at the factory, insuring uniform effi- two- pronged regulator plugs into a light - Short -Wave Band. ciency in performance. line receptacle, while into its opposite end Adaptable for use with either battery COMPLETELY WIRED AND is plugged the power plug of the radio set. or A.C. receivers. ASSI,Mitt I Less 'fuses) (Claroatat Mfg. Co., Brooklyn, N. Y. City.) Attractive in appearance with its neat and compact two -toned moire finished $65.00 "FOUR- PILLAR" TUBE DESIGN LATELY tube types have been appearing, not sings-, hut in droves. Their aver- FLEXI -UNIT age characteristics, in various makes, are A FLEXIBLE RADIO DEVICE OF usually very much the saule: however, a UNLIMITED APPLICATION difference of opiihion has been manifested Short- Wave Receiver, Short - Wave in the new variable -nut tubes, of which two Adapter, Regular Broadcast Tuner, type numbers are mow standard. Ihre man - R.F. Pre -Amplifier (Booster), Radio ufachn'er, however, ha. brought out "ri,blr- "Experimental" Unit, Oscillator and mu tubes in both the '3.5 and th '51, to Wavetrap. USE THIS UNIT AHEAD OF YOUR SHORT -WAVE TUNER AS A R.F. BOOSTER. Should your dealer be LIST PRICE unable to serve you SHOWING No. '01 .tD:1PTER promptly - Mail your *AO. WU order direct to factory. Including Coils Efficient reception of the entire wave hand of 15 to 550 meters. Can be used No.'01 Adapter Plug (Battery) $2.00 with either A.C. or Battery receivers, No.'27 Detector Plug (A.C. Set) 2.50 or as an individual single tube receiver No. 27 R.F. Adapter Plug (A.C. for short or long waves. Serves many Set) 3.00 purposes. Indestructible! Simple to Write for Free Literature - Liberal operate -and inexpensive. Discounts to Dealers and Service Men. One of .America's 'Pioneer Radio Manufacturers 18 30th Street THE WORKRITE RADIO CORP. 08 East

Two of the now Evercady pentodes. The ROOSEVELT Super -Heterodyne suit different receiver designs. 'l'he former Uses new Pentode power tubes in push -puai. also For the has a plate resistance of 300,1)01) oints anti new type variable -mu screen grid. 9 tubes an amplification factor of :HS); the latter in all. IO KC. sepa- RADIO MAN ration. wonderful has a resistance of 400,000 Ulnas and am tone and distance. amplification factor of 421), drawing there- The most perfect ra- ELECTRAD Resistors, Voltage Con- dio ever built. trols, Amplifiers and Sound Systems fore a slightly smaller plate current. Id are used 1 4 W CUB and praised by perts addition, this line includes the new pentodes, throughout the world. The products ofx long Midget experience -highly perfected and moderately both A.C. and D.C. types, and the 6.:3 -volt Uses new Pentode priced. power tube and vari tubes introduced for automotive work. ablemu screen grid. Write Dept. RC -7 ¡or Complete Fine tone. selectivity The feature of their construction is in and distance. Com- New 36 -page Catalog. the arrangement of the supports for the plete with tubes, 979.75. 17S Varick Bt. New York, N.M elements of the tubes, which gives not only COMMONWEALTH RADIO MFG. ÇD. rigidity, but maximutii clearance and low 873 W. Harrison St.. Cable: RADCOM. CHICAGO mELEÇTRAD 42 RADIO -CRAFT JuIy,1931

capacity between the electrodes. Its dis- eration made it certain that this design of Official 1$3.50 p 1Ce, tinctly rugged appearance marks the illus- tutte would be forthcoming. Radio Service Manual trations of two of these "four -pillar" tubes, 'l'he C -333 tube, which has just become showing the assemblies. available for set constructors as well as and Complete Directory of on all cammereial wiring oie - (Notional Carbon Co., New York City.) manufacturers, draws 260 milliamperes prams (352 pages-9 by 12 ") FREE the filament at 2 volts -double the current To Dealers and Servicemen of the '31. It gives, however, four times the with our special introductory deal on OUTLET PLATES 650 milliwatts undistorted out- RADIO wiring, as in hotels, apartments, output, or both plate and screen. T?`A new homes, etc., requires special de- put, at 135 volts on as 14 nilliamps, METALLIZED velopments, of fixtures suited to the many 'l'he plate current is given at 3. The tube has diverse circuits employed. The with plate and the screen current 1 q `Lui factor of 63; a plate re- RESISTORS illustrated, for instance, is adapted to a an amplification of 45,000 ohms; and a mutual con- Using New "K" Filament five -channel radio distributing system with sistance ductance, therefore, of 1100 microntbos. It I/1 1, 2 and 3 Watts, master amplifiers, and affords volume con- Cartridge and Pigtail Types has next the plate a "suppressor grid" which 1 trol as well. Other models combine a 110 - to the filament. volt receptacle also. Some twenty -five types is connected internally load in the are available, in brushed brass or brown 'l'he recommended impedance ohms; and this value molded bakelite face plates, ranging from tube's output is 7,500 should be maintained fairly constant, to See complete details of l' distortion to a minimum. 'l'he manu- Manual on page 56 't against the use of this pen- WRITE TODAY FOR DETAILS OF .aa,a4ala,a,l a lllllll 1111,11,/1.1.1,,,,,,.,,.,. facturers advise THIS UNUSUAL LIMITED OFFER tode in series with the filaments of other LYNCH MFG. CO.. INC. One of the numerous tubes, and reconunend that a proper meter 1775 Broadway Dept. C New York. N. Y. types of Carter radio be used to cheek its operation. convenience outlets for Inc., New York City) single and multiple (E. T. Cunningham, installations. BEST VOLUME CONTROL UNITS Sectional Itotary a simple antenna connection to the more e plex devices. These plates are approved SWITCHES by the Underwriters Laboratories. are ruggedly and accurately (Carter Radio Co., Chicago, Ill.) ( constructed to give exacting

` 1 - service. They may be fur- Wished with any number of NEW RESISTOR TYPES tt]i, C t sections with either type are 1 y non - shorting or RESISTORS of the metallized 1 -¡ shorting make con- now available with a filament of a new 3 tacts, or with break un- rlt contacts. All cur - design, described by the manufacturer + Ç., Carter volume control 1 s rent carrying pans of the Best der the term "K," which is stronger as well Sectional Rotary Switch are of resistor e a d poorer ¡71I well insulated with bakelite, as more durable, and therefore capable switch combination.

AY 0471. from the shaft, mounting stricter tolerance requirements, as well as bushing, and each other. Made for mounting on any thickness panel and for WIRE -WOUND volume controls, in the switching any number of circuits desired. resistances demanded by various cir- Write today for your ropy of illus- cuits, are available, with or without included trated price list and data sheet. switches, in values from 0.5 to 20,000 ohms; BEST MANUFACTURING CO. LIN with resistance values uniform or tapering resistor or 1200 Irvington, N. J. at either end; and in straight Grove St., Lynch "type mctalli.ed- filante,tt resistor. potentiometer arrangements. The units are very compact and rugged; they are fur- able to endure greater overload. 'l'hese re- nished with single -hole mountings. manufactured in cartridge and sistors are (Carter Radio Co., Chicago, Illinois.) Sl«dy RADIO úz pigtail types, at wattage ratings from 0.5 to 5. PORTABLE PROJECTOR AMPLIFIER CANADA In addition, improved wire-wound resist- A\ amplifier which is completely A.C. CANADA'S PIONEER COLLEGE, endorsed are also available in both types, to meet ors operated, yet so carefully macle as to by leading radio manufacturers, offers DAY, requirements, in all values from EVENING. HOME STUDY and SPECIAL individual fun 'tion perfectly in field service in con- with free scholarships one "luu to half a megoluu; cartridges also TRADE COURSES nection with photoelectric cells in sound and trip to Toronto (all expenses paid). megohnis. In the wire - to Principal. from 0.5 to 2.5 Write for booklet units, contact RADIO COLLEGE OF CANADA wound, as in the metallized Limited 310 Tongs Street - - Toronto

PATENTS TRADE MARKS - I.S All rases submitted elien oen,.nal attention members of the arm. Information and booklet tree. Lynch teire -wound precision resistor. Patent Office and Federal Court Practice is made permanent by the use of a molded Lancaster, Allwine & Rommel deteri- Patent Law Offices metal end cap which protects against The wire- 475 OURAY BLDG., WASHINGTON, D. C. oration and therefore noise. wound resistors are rated at one watt, with a tolerance in value of 1% plus or minus. (Lynch Mfg. Co., New York City.) I ELLIS TWO -VOLT PENTODE f6,(, tube provided a :. WIIILE the '31 type IFor- THE power amplifier suitable for two -volt sets, the qualifications of the pentode as the [ LUIS ELECTRICAL LABORATORY np- 408" portable amplifier. Ile W MADISON IT Sl., C...e..l:.- c ... c power stage par excellence for battery Operadio "Type July, 1931 RADIO -CRAFT 43

work is illustrated here; it is designed espe- common to the other. The dual control il- cially for use with sound -un- filma, in con- lustrated being wire -wound, will operate junction with caesium -hype photoelectric lu iii-iii icru) 111(111 ii ill V in circuits carrying rela- cells. It takes its input energy direct from tively high current. 'l'he standard case, il- the PE cell, the voltages necessary for which lustrated, is P+¡ inches in diameter, and as well as for the filament of the exciter two inches high. tae inch being duc to the Lump, are delivered by the amplifier. shaft. It will accommodate a 7,500 ohm re- Emphasis is placed upon the fact that sistance strip. l'or higher values, there no batteries are required or used in this are special casings. amplifier. 'l'he design is such that the portable projector amplifier may he mounted on the FREE with 10 wall of a projection booth, between the pro- Metallized jectors; or it may be put in a convenient Resistors carrying case. It measures 19 x 21 x 8 in. deep. (Operadio Mfg. Co.. I. ('harles, Ill.) The I. R. C. Resistor UNDERGROUND SOLDERING ASELF -SOLDERING ground post has been produced by an English manufac- Replacement Guide turer, which is rather 'el in this feature. It is a pipe with a brass point, so that it Wirt dual variable resistor nui, in o new may be driven the into ground until only f o r volume - the end protrudes. At the upper end is a coatrol circuits. brass cap, to assist in hammering down the Pocket Size pipe; under this is a small cup to hold de- The resistance wire is wound on bakelite, natured alcohol. After the pipe has been and over it ride two nickel- silver spring So remarkable has been the growth driven home, the end of the ground lead contacts; six soldering lugs are provided for in popularity of this Service Manual - from the set is placed in the cup, with sol- connection to the twin potentiometers. The so constant its use by thousands of der; and the alcohol is lighted, melting the unit fastens to the panel by means of the Servicemen, that - solder and completing the connection. usual lockmut. we are now publishing it in smaller l'he construction is of "noiseless" tpe, and more convenient size - DUAL VOLUME CONTROL lubricated; and, to prevent dust particles a size that can be readily slipped MANY radio receiver circuits demand causing noisy operation, is provided with a into your pocket -more variation of resistors simultaneously in metal cap which fits tightly over the convenient two entirely isolated portions of the cir- mechanism. to carry and use. cuit; where neither circuit has a e action (Il'irt Cutup -in/, Philadelphia, Penna.) Furthermore it now has a substantial leatherette binder, adding to its appearance and durability. Latest Testing Equipment There are more pages than ever be- (Continued front page 11) fore in the I.R.C. Guide. It gives all the resistor data you need to know consumption; and the D. C. meter being a about any popular receiver -the 1000 -ohm- per -volt type. With the elaborate proper types and values to use in every switching equipment illustrated, care has set placed on the market since 1926. been taken with the circuit arrangement so Write us at once and become the that it is impossible to damage it by incor- owner of this wonderful manual. rect ()pest Nleter readings cover up to FREE with the purchase of 10 800 volts and 100 milliamzps; higher scales I. R. C. Metallized Resistors may be uhtained on special order. 'l'he -or it may be bought in its new form for equipment is housed in a black molded Bake - $1.00. New sheets, mailed period- lite carrying case, which affords room for ically without charge, keep always the necessary it test leads and other acces- up to date, sories. (ran Horne Tube Co., Franklin, Ohio.) INTERNATIONAL RESISTANCE CO. Philadelphia Burton-Rogers "Model 3" tube checker.

rpry' cFtr shorted. Six sockets enable testing any type ^L-lr 'O tube -and under rated filament, grid and plate conditions (grid -bias adjustment for each tube being obtained automatically). (Meta.(fc Three push -buttons are provided to control the circuits. (Burton- Rogers Co., Boston, -(lass.). w Sewr Ñar.scr.» RESISTORS All orders for Resistors referred to Jobbers ANALYZER AND CHECKER INTERNATIONAL RESISTANCE CO. Ca 2006 Chestnut Street, Philadelphia COMPLETENESS in servicing equipment Flcaclling Van-Horne ".tlodel II" aaolvtcr J is excellently illustrated by this com- Gentlemen: - (Check offer you ore interested in) bination instr nt for precision testing, I enclose $1.00 for Replacement Guide, Please send price list of Metallized Resistors. I wish to both of receivers and of their tubes sepa- NEW TUBE CHECKER purchase assortment of ten, which will entitle me to rately. Eleven meter ranges are also avail- TIIIS instrument indicates the "end of Replacement Guide Free. able for external tests, by means of pin - life" or at least the stage of service, of Name jacks. The meters are precision instru- all types of amplifier, power and rectifier Address ments; the A. C. meter (left) having a tubes; tests separately the plates of '80- double movement to permit lowest current type rectifiers; and, through an ingenious City. .Stare 44 RADIOCRAFT July, 1931

arrangement upon which patents are pend- A "midget" two-tube adapter is also avail- ing, tests for noisy tubes. It is self -biasing. able; it has a black molded Bakelite case, Six sockets are provided, so that tests 7x5xl ía inches, and uses two type '27 tubes, Out each waveband, over Just may be made at the rated filament voltages. with but one coil for Colored buttons simplify the operation of the 15 -180 meter range. 'l'he sole control AALjQ the tube checker. The ureter incorporated required is a vernier dial. In this model, has a. 0 -40 scale and a D'Arsonyal move- the panel is horizontal, and the tubes are Latest Price Sheet- showing hun- nient. It is supplied with or without lid, mounted externally. dreds of adapters of interest to (l'an Honte Tube Co., Franklin, Ohio.) service men, experimenters, inven- tors and manufacturers. Service Notebooks New Analyzer Plug that locks to (Continued from pope 15) adapters. spool, it is only necessary to unwind one ADAPTERS for pickups, micro- turn of wire and then connect and solder a little slack so phones, voice recording outfits, to the terminal; leaving the wire won't break again. If the break sets, tone control, tube short wave is at the inside terminal, it will be necessary changes, the new 2-volt tubes, set to install a new R.F. transformer unless analyzers and tube checkers. the end of the broken wire is long enough ADAPTERS for testing new pen- to resolder. tode tubes in your present analyzer 'l'he tone control used on the "96 -111" -biasing tube checker. or checker. Dayrad "Type L" self series can easily be installed on the "Model 95" by doing away with the "local -distance" carrying case, for SOCKETS for replacement and and in a professional switch. Cut off the wires leading from it at at all commercial voltages experimental work. A.C. operation the small 20-ohm resistor which is located PLUGS, multi -wire and frequencies. on the antenna coil; then remove the switch. SPEAKER (Radio Products Co., Dayton, Ohio.) cables and outlets. To install the tone control, bend the lip on the chassis (which held the "L-D" Send for Price Sheet Today SHORT-WAVE ADAPTERS switch) forward to allow the shaft to enter ALDEN MANUFACTURING CO. SHORT -WA \'E adapters, exhibiting a hole in lip. After entering shaft in hole, Operated by Alden Products Company fancily resemblance, since they are the bend lip back to original position and 715 Center Street Dept. T latest children of the well -known short -wave fasten tone control in position. Run a wire Brockton Mass. designer, E. T. Flewelling, are available in from the terminal on the tone control, to several models. That illustrated employs plate of first A.F. tube, and installation is three tulles; a '24, a '27 and an '80, since its finished. The tone control is Philco part power supply is self- contained. It works on No. 4037A, and is only 65 cents list price. the frequency- changing principle, feeding into the antenna circuit of a broadcast re- NTA-AL ceiver. 'With the three sets (each of two) of plug-in ('oils supplied, the band from 15 operates on "It's the contact that counts" to 180 meters is covered. It 110 volts, 60 cycles, from the light line. A switch gives the choice of long or short - wave reception without disconnecting the :3s/4 and Full details about the OFFICIAL adapter. The size is 10x7x inches, RADIO SERVICE MANUAL and the weight about 12 pounds. the RADIO SERVICE MAN'S A two-tube model of similar type, but HANDYBOOK appear on page 56 of without the rectifier, derives its plate sup- this issue. If you have not yet famil- ply from the receiver, or a suitable dry bat- iarized yourself with the contents of tery; its filament transformer may be ob- these important radio servicing books, tained for 25 -cycle or for 220 -volt opera- to read the announcement do not fail needed. Flavelling "Modcl L" (three -tube) adapte which tells all about them. tion, if

ALUMINUM BOX SHIELDS Crosley "Super Buddy Boy" Genuine "ALCOA" stock. silverdip 8n1s11. 5 z 9 z 6, 91.89 -14 z 6 z6, E3.85. 10 e z 7 Mlonitor size $3.25. 3 X 5 z ., Coll (Continued from pope 21) Shield (like pire ore on tabu l 91.00. Any Sire te Order. O.E. 110 vols Toggle Switches, 19e; 3 for l-ne receiver, measuring only 153/a x 151/4 C4B are I.F. trimmers. Condensers C5, .Ar. Make and break push buttons, 20e. 0.5- Flexlbis -hafts for Auto Sets. Relays. In- X 9 11/16 in. deep, is a model of efficiency C7, C11, C13, CIS, have a capacity of for 91.00. notated flexible coupling, lare; a a possi- CO, C9, 0.1 -tuf.; C8, I. inf.; C10, C14, PROD and notable demonstration of the Ulf.; "BUDDY" TEST .002 I Aix ais sharp pointed, using bilities of the newest vale tubes. C17, .02-mf.; C12, .001 -ouf.; C16, -ulf.; 4 wires, phonograph needles. -ft. 8 condensers. w spade or phone tips. Colored For the consideration of technicians and C18, C19, inf. electrolytic nipples ident ity each lead, the Average operating voltages follow. Fila- 51.50 pair. the convenience of Service Men, follow- We specialize In radio parts ing technical data are appended: ment potentials: \'1 - \"6, 2.4 volts; V7, 4.8 exclusively -puts fund -hell for any kit in any magazine. Volume control resistor R1 has a value volts. Plate potentials: VI and V4, 180 l'Iraae Include 1'°stage. 0LAN, THE RADIO MAN, lue. of 2.50(5 ohms; 112, 1100 ohms; R3, R12, volts; V2, VS, 200 volts; \'3, 33 volts; V6, 89 Cortland( St. Dept. RC -731 New York, N. Y. R15, 1.11 liwg.; R4, 45 ohms; R5, 1220 ohms; 280 volts; \'7, :300 volts (each plate). Rti, 2150 ohms; 117, 3,000 ohms; 1t8, 6,500 Screen -grid potentials: VI, V4, 50 volts; ohms; 119, 3.500 ohms; R10, 300,000 obtus; V2, VS, 7 volts; V:3, 90 volts; \'6, 280 volts. j PUBLIC ADDRESS EQUIPMENT liII, 601,000 0110 ; R13, 0.5 -meg.; R14, Control -grid potentials: \'l, V4, 2 volts; 25,00- 40,000 ohms; RIO, 2,000 ultras; RI7, \-2, 7 volts; \'5, 9 volts; \'6, 20 volts. Plate 20,000 ohms; R18, 10,000 ohms; R19, 220 and grid potentials are measured with a ohms; R20, center- tapped resistor. meter of 600 ohms per volt, or higher re- C3, the sistance; with reproducer connected, vol- 1 MILES REPRODUCER CO. t Condensers Cl, C2, constitute and CIA, C2A, C3A, their ume control full on, and line-potential of 26 E. 22' ST. NEW YORK CITY tuning gang; trimmer capacities. Condensers C4A and 1171/2 volts. July, I')31 RADIO- CRAF'1 45 Operating Notes Now Ready (OAnt in tied fruin lm ye lt) was being received. To priavide for this, The NEW 1931 a S.1'.S.'l'..switch was mounted on the cabi- TROUBLE SHOOTER'S net front, in series with one leg of the 4(I( -ohul shunt, and marked "Lord -Dis- MANUAL better more tance." An even stunt. though by diftìeult, is to mount a variable resistor (about 1(1,1)(11) ohms) on the cabinet front, John F. Rider and connect it across the two lugs on the terminal strip. When the full resistance is Complete with the FREE Question used, it will have no effect on the circuit and Answer service. be but, as the resistance is varied, it will This volume is the most extraordinary hook found that hest results with various stations ever prepared for the radio service matt! It are obtained at different settings. Opera- represents the data compiled during the past 11 years and nothing ever published for use tion with this nietIiiid is more efficient than by the Radio Service Man is as complete and the first, but less simple. as comprehensive as this work by John F. Rider. More than 950 pages! Adjusting Compensating Condensers More than 1500 diagrams! 'The new l'hilco "Model 111" super pres- Endorsed by the Whatever your problems in connection with ents a formidable appearance when it comes Radio Service Managers' radio service work, the 1931 Trouble Shooter's in for realignment. It has nine adjustments; Association of New York City Manual will supply you with the vital data con- and Philadelphia cerning the circuit. the socket layout, the set these for the first I.F. primary and second - analyzer voltage data, the color code, the in- ary are made from beneath the chassis, ternal connections of enclosed units, chassis in the radio receiver. the rest from ahoye. This set uses an inter- structure, peculiarities If you have any special problems John F. Rider will be glad to furnish you whatever mediate frequency of 173 kc.; first adjust additional data you may require. If you purchase the manual your questions will be the I.F. stages at this frequency (in order answered free. 3, 2, 1). and then adjust the high- frequency For the first time since the existence of the radio service industry, ONE hook contains ALL valuable data. We want you to understand that John F. Rider spent nineteen (19) condenser at 1,400 kc. when the dial reads months compiling this hook. In it you will find the WHOLE line of receivers manufactured in conformity with this frequency. The by the popular American and Canadian receiver manufacturers. low -frequency is then adjusted at 600 kc. COMPLETE- CO\IPREIIENSI \'E- UP- TO- DATE-it covers the entire radio and public address field. 'rile two antenna compensators may be ad- The book is divided into eleven (II) sections. justed before or after this procedure; at Section I. --À modern Radio Service and Trouble Shouting Course. Seil ion 2 --tn rspóomt ion of the principles and application ut Set .tnalzers. al t 1400 . kc. for maximum reception. \Il Section 3.- Vacuum Tube Data and Tables. 9 dju sullen is are nla(le for maximum re- Section (.- \ylrlug diagrams of .11.1. popular commercial receivers manufactured sines 1920. Section 3.- Wiring diagrams of public address and power amplifiers, inelusl,e Of the products of the most sponse with an accurately- calibrated oscil- Lumens ma ouf act urers. Srrmou u Wiring dia orals, of ALI. popular eliminators and poster park,.. lator. I)o not forget the detector com- Seel Ion T. -is -i ring diagram, of .11.1. Popular abort nave Brel, ers and adaptors. pensator. (See Data Sheet 45, page 12.) Section S.- wiring diagrams of ALL popular kit receivers. old and new. Section 9.- Wiring diagrams of the popular Sel Analyzers, old and nets. "That elusive hum" was recently en- serums Io.- wiring diagrams of midget receivers. Sert lot 1L- l'eevliarlles in radio r Geis et a. sert ion width Issu r:oi o,e Iron the book, bind seps countered on a Majestic "90" chassis; the rarely and r rty e Wilk loue 'rills srctlon is a: dLtinet Inuovaliso in radio service was apparent literature. It ,till tell ) u of any special features sthirh Son must know of when testing hunt off the station, but at the reveller. C,cry commercial rerei,er in Mu 1931 Trouble Shmter's alumna) by Miler resonance it was very loud. This condi- is ment tuned In this section. No other tion was caused by an open filter condenser matter what books you may have, YOU NEED TILE 1931 TROUBLE SHOOTER'S MANU: \l, because it includes many diagrams and details which have NECI.1( in the pack; hula on resonance may he I 1 EFOItE appeared elsewhere. ... This (rook contains many diagrams which are not available caused by my condenser after the choke. from any other source. .. . Remember that one diagram with color code may save you enough time and enable you tu complete a successful repair in such fashion that it will repave your cause of for .\ intermittent and noisy re- the entire cost of this look.. . . plut off the press! ception on Kennedy "Model 526" has been The free question and answer service personally conducted by Tulin F. Rider will be worth found in :t faulty compensating condenser; a lot of money tu you. ... It is FREE with the 1931 Troudde Shooter's \lauurd there are two of these. Ire order to adjust The book is bisse leaf, beautifully bound. -I'he pages are 84i x II inches. The drawings are large and easy to read. . 'sI.I, of the vital data is shown upon the sanie page. Electrical theme, the shields must be taken oft the constants are furnished . . . No expense was spared to compile this Stook. IT WEIGHS screen -grid tutees. The adjusting screw's 6 l'OUN D5. .. . Every man who is doing sers-ice work should have this book: look like simple mounting screws; they are SOLD \CI'fll .\ MONEY ItA('K GUARANTEE. IF YOU DON'T LIKE It SEND IT BACK ANI) )'OUR \ZONE' \\'ll.l. BE REFUNDED. WE .\RI: CERTAIN i-ii.vr located on the condenser housing between YOU AVILI, 111: Mom.; 'I'll. \N l'1.1:.\SEIl. the first and second '24's, and between the We are in a position to supply individual diagrams of receivers and tu answer questions third 24 and '27. When the insulation fur service men. Write to us. erarks, it is usually necessary to replace PRICE $5.00 Postpaid. We will send the book these. C.O.D. The Itadiola "441" and "46" include a RADIO TREATISE CO., INC. "local - distance" S. switch which - - - - uunds the antenna loading coil through a 1440 Broadway New York Ci .il023-m f. Cl ndeli ser when at local setting. When a complaint of feeble reception on tee "local" position is received, it may usu- Soft Aluminum Pregono wed Blank Rec- :'Ily be corrected in the following nnnner. ords for Instantaneous Home Recording. It e E - E remove the chassis; the compensating con - Double Faced. VOLT -ME CONTROL d :nser adjustments are located in the front. Give GUIIIE They are phi') flat -head screw's, flush with Volume Compiled By Engineering; Staff of the chassis. .Align the set with the switch Brilliancy in "local" position. It may be that replare- Durability CLA 5IAT itcnt of the .0u123 -uif. condenser is neces- List Prices $0.:0 sary; if this opens, or alters its capacity, 0 inch Fiore is a mot helpful bulletin for Seri ice sien. the 8 Inch 0.75 Dealers. its aotriclans and Experimenter. it is sot receiver will not be properly grounded. 10 Inch 1.00 .d,.,,lot ely FREE upon request. I'L.t fllsST.tT'S On the Brunswick "S till. esperlenre manufacturing t'olunte comme -31" phonograph laide ea -tors has Also yI it rnph ones- Double and Single r r made It pas s l Me to I r. this , nr Vol : td cnmibinatt , intermittent action may be Button. Transformers. )Ismints. table. lost runt lie booklet. It i Ihat all y radio anti i squid egninntent men hate a top's, roused by the B.l -nlf. tubular condenser, one )'lugs. tte. New :l2.I age Catalog Just out. n rite tsd'at anti own ion RADIO- CRAFT. terminal of which is soldered to one of the l'NIVElts.tL MICROPHONE CO.. Ltd. CLAROSTAT MFG. CO., Inc. lugs of the radio- transfer switch. Inglewood Dept. R.('. California 285 North 6th St. Brooklyn. N. Y. 46 RADIO -CRAFT July, 1931

SKINDERVIKEN Construction of the Radio Robot (Continuel! front piffle '-'li) 'rwo Durham 10,000 -ohm "metallized" re- KNAPP TOY sistors, R5, R10; RELAY- t__... MOTOR ti sw_1 Two Durham 1 -meg. (1 -watt) "metallized" resistors, Re, R7; (WADm 1 ROT A} 10,000 -ohm Type B -100 re- ma One Electrad i2 RI1; m sistor, 'WAD TO 4 250" volt- One Electrad 21,000 -ohm "Type LEFT &o age divider, 1112; 6V FORD 750-ohm "Type B 7.5" wire - STARTING One Electrad wl MOTOR wound "Truvolt" resistor, R13; STAND Ai One Electrad 50 -011111 "Type V" resistor, 1114; Four Polymet 1 -naf. "Type A" by -pass con- SIT C2, C4, C5; B The Most Sensitive Microphone Button densers, Cl, L b One Polymet .01 -oaf. mica- dielectric fixed KNAPP (ACTUAL SIZE NOT BIGGER THAN A QUARTER) TOY condenser, C3; MOTOR You can easily make a highly sensitive detecto- Two Polymet 4 -Ulf. "Type C" filter con- ;RAISE LEFT; phone by using a Skinderviken Transmitter Button ARM I densers, CG, C'7; to collect the sound waves. You can build your -111f. filter con- J own outfit without buying expensive equipment. One Polymet 2 "Type C" Think of the fun you can have with such an denser, C8; TIEFTB instrument. Two UY sockets, for \-I, \-2; 0 You can install an outfit in your home and hear Four UX sockets, for \-3, V4, \-5, \-6; RAISE R. 0- the conversation being held all over the house. 124" screen -grid tube, ARM o- UNIT One Arcturus "Type o- SW. MANUAL Full directions for connecting up the button for 4,LOWER R. CONTROL HDMR VI; :ARM o use as a detectophone are given in our 12 -page One Arcturus "Type' 127" tube, V2; o- SW ITCNES booklet. :SPEECH Two Arcturus "Type 150" power tubes, V3, o- 6V These wonderful little SKINDERVIKEN micro- Si ME o- 1zo AMP. BATTERY phone buttons may be used for hundreds of uses, V4; ',CAIN o- "Type 181" half -wave rec- such as: 'l'wo Arcturus \-5, V6; Fig. 7 RADIO AMPLIFIER PHONOGRAPH AMPLIFIER tifiers, turn the head out tray, raisc DETECTOPHONE TELEPHONE AMPLIFIER Three channels the left arm, or the whole figure. Three snore STETHOSCOPE LOUD SPEAKER AMPLIFIER HEAVY-DUTY RELAY TO A HEAVY - reverse the directions of motion. MICROPHONE CRYSTAL SET AMPLIFIER HDR A DUTY Two Aulcrtran 30 hy. "Type 854" filter HOME RECORDING OUTFIT, ETC. MASTER

S RELAY chokes, Ch1, Ch2; HDMR -250A" power EACH Two for $1.755 One Amertran "Type 'PF 95c transformer, PT; 12 -PAGE INSTRUCTION BOOKLET containing suggestions and diagrams for innumerable One Auaertran "Type H-4648" power trans- uses, furnished with each unit. former, PF; (SPRING) Two Universal two -button microphones, Ml, TWO OR THREE F 1,11[° EVERY AMATEUR SHOULD HAVE M2; OF THESE AMPLIFIERS IN HIS LABORATORY 6V. 5 BATT. 1, W Four binding posts, 2, 3, 4; WE PAY $5.00 IN' CASH One control -grid clip for VI; for every new use developed for this unit (PIVOT) CONTACTS accepted and published by us. - + One alunlin chassis (size optional). and UNIT RC 6V. BATT. (In August RADIO - CRAFT, Mr. Cisin will SEND NO MONEY explain light -ray and phonograph record delivers your order you pay him Fig.6 - of robot, with other details of When the postman the three toothed wheels have been pulled control the for whatever you have ordered, plus a few cents II"F.nt operation.) postage. around, then only does the relay operate. (Canada and Foreign: cash with orders)

PRESS GUILD, Inc., RC-721 Choosing Replacement Resistors 16 Murray St., New York. N. Y. (Continued from paye 17) !'!gate mall me at once as mans of the following Items as I have indicated. If we reduce this to plain figures, for the owner cannot be blamed for losing con- ..Skinderviken Transmitter Units at 95e. for 1; $1.76 for 2: $2.50 for 3: $3.20 for 4. the ease given above, we shall find that at fidence, if it promptly develops new troubles When delivered I will pay the postman the cost of the a screen -grid voltage of 90 and a normal or stops working altogether. 'l'he natural specified postage. items plus effective impedance load of 100,000 ohms, inference is that the Service Man did not Name the gain is equal to understand his work, or that he performed 400 x 100,000 an inferior repair job. It goes without say- Address _ 80 ing that no radio man wants to risk the Cite Stata 400,000 + 100,000 loss of his good reputation in this or any whereas, when the screen -grid voltage is re- other such way. for Free Guide Book, Man, however, invariably has "HOWWrite TO OBTAIN A duced to 50, the gain is only The Service PATENTS PATENT" and Record of 800 x 100,000 many other things to worry about, besides invention Blank - Send model or sketch and deecrip- _ 61.6 rigging up meters to test every resistor that Lion of your invention for our Free Opinion whether it comes within Patent Office Rules. RADIO and ELEC- 1,200,000 + 100,(00 he uses. How then, can lie be reasonably TRICAL Cases a Specialty. prompt. Efficient Service. he is using the specified rallies? PAYMENT OF FEES IN INSTALLMENTS The above shows how seriously the gain certain that VICTOR J. EVANS & CO., 923 - 9th, Washington, D. C. per stage (i.e., sensitivity) has been af- The answer to this important question fected through the use of a poor quality should serve as a guide to every reputable Ne Wind SOMETHING DIFFERENT resistor. radio Service Man. All uncertainty can be Can l Mystery Cigar Lighter Many kinds of trouble may appear when eliminated by the use of standard, advertised It if such re- Out {YW cheap replacement resistors are used, hut, and guaranteed resistors. Even Make Big Money regardless of the exact way in which the sistors cost a little more at first, they are Shorting tilt Scientific Martel to Men. in since they New Principle of Ignition. What Makes trouble manifests itself, it is sure to con- cheaper the long run; give It Light? No Flint or Friction. All a direct reflection on the ability perfect performance and thus establish cus- D STMfI Guaranteed. Sample with Sales Plan. 25e. stitute L1GnTtR Sample Gold. Slicer or Chromium Plated, skill of the Service Man. tomer confidence and build up a lasting busi- $1.00. and -NEW FPGr CO,om When to radio set has just been repaired, ness for the Service Man. Desk SF- New Method Bldg., Bradford, Pa, July, 1931 RADIO -CRAFT 47

The Latest Small Sets (Continued from pale 21)

AN ATTRACTIVE MIDGET A switch -operated tone control connects THE "Vitatone" Midget radio set fea- n .02-ud. fixed condenser across the pri- titres a "full -vision' type tuning scale, mary of the output audio transformer. Vol- graduated from 0 to 1110. A 3 -asap. auto- ume is controlled by varying the potential motive -type fuse is the protective device in on the cathodes of the two '51's used as am- the power input circuit; this fuse clips into plifiers; the circuit includes, between cath- one of two positions, thus adjusting the input odes and chassis, a 10,5110 -ohm variable re- connections for high or low line voltage. sistor and a 230 -ohm fixed resistor. 'l'he Three type '24 tubes are used in the R.F. detector is resistance -capacity coupled to circuit; their amplified output is fed into the pentode. The reproducer's field coil is a type '27 power detector, the output of connected in the "B-" lead. which feeds a type '45 power tube. In the Inner carve shows Stenode's selectivity, outer curve that of ordinary receiver. Lines BB are 5 k. c. dis- plate circuit of the last is connected, from tant /rom Line A. All background noise included in plate to chassis, the tone control, consisting the light Portion between A and BB is eliminated by the Stenode. of a 10,000-ohm variable resistor in series with an 0.5 -mf. fixed condenser. An '80 completes the tube kit. Volume is controlled by the simple pro- STENODE cess of shunting a 1,000 -ohm variable resistor across the first R.F. transformer's TUBES primary. The volume control in this receiver is combined with the off -on switch. Until the American Tube Manufac- The dynamic reproducer used in the "Vita- turers licensed by the Stenode Cor- tone" receiver has a 2,500 -ohm field; which poration of America are in sufficient connects in the "Il +" power lend as one of production, we can supply the the two filter chokes. rapidly growing demand of labora- The instruction sheet which this manu- tories and serious investigators for: facturer furnishes to the set owner contains al piece of advice which, though not pro- QUARTZ CRYSTALS found, is at least uncommon in this form. It reads: "In all cases, do not attempt to Suitably Mounted in Tube Form repair the set yourself. Call a competent To Fit Standard Tube Sockets Exterior of the "Model 90" Clarion, These crystals are all approved by our own laboratory after actual tests Automatic volume control, added to the circuit used in the "80" Series Clarion re- in a standard Stenode developed ceivers (and the circuituit modified accord- under the patents of Dr. James A. ingly) produces substantially the connec- Robinson, M.B.E., D.Sc., Ph.D., tions that constitute the '911" Series Clarion M.I.E.E., F. Inst. P., and former receivers; as shown in the Data Sheet (No. Chief of Wireless Research, British 46) previously referred to. 'l'he autouuatic- Royal Air Force, by the engineers voluuæ- control tube is a screen -grid '24. of the Stenode Corporation of 'l'he tone control in this model is snutothly America. adjustable. (Tranxfnrtner Corporation of America, All crystals are ground to respond to a frequency of 175 kilocycles, Chassis of the "Model 54" l 'itatutie. Chicago, III.) which is the frequency accepted as Service Man; otherwise your guarantee will A RADIO PHONOGRAPH standard in all modern superhetero- he nullified and void." It is accompanied I1 the combination illustrated here, a dynes, and are mounted in vacuum by the circuit diagram and operating French manufacturer has found what is tube form. voltages. ('faneg-pill Corp., Chicago, III.) very nearly ultimate simplicity. The receiver is of the regenerative type still very STENODE (Standard UX\J Price NEW SUPERHETERODYNES mammon in Europe, with two stages of audio TUBES ` Socket Bose / $15 FOUR superheterodyne receivers havz following; the latter are used with the heert introduced under the Clarion ban- phonograph pickup. While the arrangement "If it isn't a STENODE is not ner: "Model 80" 7 -tube, mantel -type: especially attractive, compared with it isn't a modern receiver." "Model 81" 7-tube console; "Model 90" 8- the elaborate consoles used here, it is quite inexpensive. An tube mantel -type; and "Model 91" 8 -tithe external loud speaker is re- console. 'Their two outstanding circuit dif- quired. STENODE ferences are described below: at the same CORP. OF AMERICA time, attention is called to a Data Sheet, (Formerly American Radia:tat Corp.) covering the Clarion "90" series, in this Hempstead Gardens, L. I., N. Y. issue. Six tubes are used in the fundamental "80" series STENODE CORP. OF AMERICA superheterodyne circuit. "\'ari- Hempstead Gardens, L. I., N. Y. ahle -um" and "pentode" -the latest words in Enclosed find D Personal Check, O P. O. or tubes -are found in both the "Model 80" O Express Money Order for which please for- and the "81" receivers; three of the former, ward me Stenode Tubes. of '51 type, being used as first R.F., first (stale number) detector, and first I.F., positions, and the Name latter as a power output tube. A screen - grid type '24 is used as the second detector; Street and a type '27 functions as the oscillator. The rectifier is an '80. City Slate a.ru,ler, is n Fr, nah nnhlhrnlrni 1931 4R RADIO -CRAFT July,

notes and other technical information from Making Money in Radio lilt!nufacturers whose sets you do not handle; I can't understand why, if you are capable Servicing other standard slakes. (Continued front page 15) of servicing severed house 1 ant a dealer's Service Von, and my l'se your own ideas, coupled with those repairs all makes of radios. I think the of others. To amplify this statement, I cite evil of supplying would -be Service Men one instance where I used another fellow's ttith notes is lib ro' than offset by depriving idea but did the job differently; I refer the deserving ones of then) (that, I be- to using the new 2 -volt tubes in the 'Itadioltt lieve is the general excuse). 28." I made two adapters, one containing In closing, I would like to say that I a 4 -ohut it 50 -uhul resistor and one with get more renal information from your maga- resistor; this saved opening up the cata- zine (and other publications I subscribe tit) comb. All changes were made externally; in one month than I do from the manufac- thus saving a great deal Of time and Labor. turers themselves in several months; ,Ind it be Don't tell your customer, "It can't is at my own expense too. 'l'hink this over, you clone :" because it can be done and, if fellows. Service don't do it, s other enterprising Following are a couple of "Hints to the Ian will do it and you will lose both Manufacturers." put son n kind of hacks business and the {rood will. to cabinets; the lack of this has been com- will impress you Dr. T. O'CONOR SLOANE I hope these few lines mented on numbers of times by tustonmrs. with the fiut that our job is to sell service; I think all service notes should be drawn awl real service pans. with condensers, t'hnkes, resistors, and etc., Home! his with a gen- Will Teach You at (Mr. Smith closed letter indicated as to value and not by color erous offer to assist any Service Man with ONE: VS!IO CAN HEAD AND WRITE can study scheme (as some are doing for resistors); NI YOU Al'heso bry through our simply prepared course. advice on these jobs. However, all these need as harder to substitute when don't nerd a higher edit. athm, and you don't this makes it experience or preparation. Chemistry is not subjects have been the themes of articles any pre, loua Just plain defective part is not readily procurable. harder to understand than electricity or radio. in recent issues of RAUro-Cam-r. 'l'one con- sense and ordinary observation powers. I and making a list of ailments were discussed in the trols, for instance, of sets which we handle, that may he of and issues of this year; We Can Teach You At Home January February use to some other Service Man. Wishing you operating battery sets from the D.C. line Our faculty just IS you continued success I am, laboratory wkker. TiIi HEAmoldF STAFF II -leak SLOANE. scientist. engineer and author in the October, 1930, issue; power grid DR. T. O'CONOR or Very truly yours, of wide repute. He has had more than fifty years detection and conversion of old Itadiolas teaching experience. Our VOUrse fits you for an Immediate and you do not have May, 1931, issue; position In a chemical laboratory, for 2 -volt tubes in the Georgia. to up what you are doing now to leant lt. During Aflauta., gist home the and there have been repeated articles on you (We shall be Terry glad to hear again fascinating experiments and they delightfully simple but frequency -changing, short-wave converters. comprehensive lessons. from our correspondent. who made the over- should consult all sources The Service Man sight of omitting to sign his name before Laboratory Outfit Free of published inforntat before writing for closing the letter.- Editor.) CHEMICAL OUTFIT and APPARATUS advice; and when writing to a fellow Service THE COMPLETE extra supplied to you a s pan of your Course. without charge, makes you the owner of laboratory. containing Man, or an author, for personal advice on all materials used it specific problem which is not covered, he LICENSES FOR SERVICE MEN hemist. This orkinlni g kit, Is shippedpg flto you at the outset of the course,co bmutcha es your permanent property. should enclose, not a stamp but a stamped Editor, IIADIo-CaArr: It is a sturdy fitted wooden cabinet eont aining over 100 pieces of laboratory apparatus and chemical supplies. and self -addressed envelope of good size I see by the papers, and sonic of the and quality.Senice Editor.) magazines, that some states are considering Big Money in Chemistry pleasures to tvmupel any man wishing to our 'tanbetter Not only do radio work to pass an examination as raining help you to'get but oM- while start on a new inri. You can patent the work of to his qualifications. This certainly would millions of The Open Forum ands and youM1e brain, perhaps nuke the your new discovery.nd (Continued from page 16) be a very great boost for professional Every day the newspapers and magazines are full of new in Service Van; as the radio field would be Items reporting n new chemical discoveries-In mining. appli- electricity. in foodstuffs, In sanitary and medicinal selling his product, not in keeping it sold. cleared of is great number of those over- ances, in paper -making. rubber. steel, Iron. dyestuffs, tel- tiles, In fart in every well known Industry-and behind 'l'he manufacturer advertises his product night radio mechanics. Any honest, thinking each of these discoveries stands a well -trained chemist who knew how to take advantage of opportunity! and creates the dentand -the Service Van iadio nun who hams spent his time and conies along and says: "Keep your old set money and burned the Midnight oil in No Exaggerated Claims and let ale nuke it like new." The sales- studying the advanced science of modern THE INSTITUTE DOES NOT CLAIM that every chemist man: "'Throw it away or trade it in for radio, and to keep abreast of the new de- maker ouilllons, nor do we guarantee that you will immediately get job paying $10.000 a year. But many a nett up -to-date one." I don't pretend to velopments, will certainly welcome such a. hate done it and there is no son witty you can not do it pas. Often enough you read e or hear about men who know the solution to this situation but I pleasure and clasp the hand of the man hate found the highest recognition. from small. inconspicu- be ous beginnings, and you wonder how they got the "lucky have an idea which might of help. putting it over. Any ;mod electrician in any be 1 rent." Why, you wonder yearningly, couldn't you I think a cult r's radio should give of our cities must pass an examination such "lucky" fellow i Yen can ke-but you hate to meet luck half way. hint the best of service which the type before being eligible to do any work in Get Started Today! owned is capable of, until the time comes his profession, and he is reinllsursed with when the customer wants to ban a new at least :Fl an hour for his services. Why IF YOU WOULD LIKE TO KNOW \LORE ABOUT CHEMISTRY, and If you are sincere in your desire to one; as there is no one who dots not wart shoud not the Radio Service Man have the get out of the tread -mill of job anxiety and wage de- pendence, If you hate unbftlon enough to want to become to take advantage of the improvements and same privilege, both as to the examination a chemist, and perhaps famous one some day, you will This not wait until tomorrow to find out how to go about It. refinements that conic with progress. and the reimbursement? MAIL the coupon below today. There fs no charge and cannot be clone witl t manufacturers' co- Any radio elan worthy of the name will no further obligation. You will he simply asking us to write you about something that you want to know, operation. The salesman sl Id thoroughly undoubtedly pass the examination; of course r d strate his machine and acquaint the it will be the acid test to a great ninny prospective owner what to expect from his who think they are Service Men. Only the Chemical Institute of New York. Ins. fleet. RC -731 set, and what it will not do. It is not a best will survive, but those remaining will 19 Park Place, New York, N. Y. Service Man's job to go out and explain the be only more proud of the place they fill

send n once. without any obligati,. Please at phenomena of fading, and why they can't in today's industrial world. After such a my part. you 1 Free Kook "Opportunities for Chem- ists,' and full panlculars atout the Experimental get the old home town every night, etc. pleasure is put through, the organizing of Equipment given to every student. It is my policy never to advise a customer radio servicing as at profession will he the NAME to spend more than one third of what the follow -up to make the field clean. I hope set would bring at market prices in order that printing these few lines will help to ADDRESS to repair it. This I think is fair to the foster the proposition. cITY STATF customer, the salesman, and the manu- MICHAEL J. REEFF, facturer. It is very hard to procure service Alton, Iowa. July, 1931 RADIO -CRAFT 49 An Oscillator for Modern Servicing (Continued from page 11) L'\ tube adapters, serve to attach the :wetly across the voice coil of a dynamic output meter to the two plate leads of a loud speaker; the output meter is so ar- push -pull amplifier output or to the plate ranged that it will not materially affect the lead of a single output tube and the set's impedance of the voice coil. This instru- chassis. ment will also be found useful, when ad- First turn the radio set "off." 'Then re- justing for minimum 1 level in A.C. remove the set power tube or tubes; place ceivers. these in the adapters; and put tubes and It will be noted that the modulation of adapters back in the sockets. The other the oscillator signal is fully 100%, when ends of the leads should then be connected using the A.C. lighting line; it is also to the terminals provided for then: on the nearly 100', when employing grid -leak output meter; of these, there are three: modulation. This is it distinct advantage a coi uiion terminal and two others marked when making tests on receivers which use "1" and "2." Terminal "2" has in series power detection. For, if a strong unmodu- with it a fixed blocking condenser to pre- hcted signal is applied to the input of a vent the passage of D.C.. but allow the set's power detector, it is possible to overload A.C. output to pass through. the detector svitl t obtaining any I I- The common terminal and terminal "2" speaker output. 'Then, too, if the R F. should be used for all sets; but terminal energy is only slightly lulnted, in some "1" and the common terminal may be con- sets this :nay result in two apparent reso- nected across a voice coil when so de- nance peaks; and the set appears to he sired. The switch on the output meter broadly tuned. 'Therefore, it is necessary should then be thrown to the "output" posi- that the oscillator signal be modulated as tion, and the attenuator control knob to the near to 100r/e as possible. full counter -clockwise position. Then turn To use the output meter for measuring the set "on," and place the oscillator in resistances, simply throw the switch to the c peration. "Ohms" position, and connect the proper xxbe clier leads provided with the instrument to the 222/.2 -volt terminals on the oscillator panel. With the test leads shorted, set the "zero MODEL 19 ohm" adjuster till the meter reads zero; then the meter will indicate the values of COMPARE the Model 19 with any resistors, placed between the two set ter- tube checker-you need the features minals. listed below in the instrument you Alta gh fundamentally simple in de- purchase. Try the SUPREME Model sign and operation, this instrument can be 19 and you will have no other. used for all oscillator tests outlined in the various manufacturers' service manuals. It Model 19 Features offers servicing possibilities heretofore PENTODE TUBE TESTS available only with highly -complicated and Tests Overhead Filament Type Tubes expensive apparatus. Plate Current Reading Circuit of the output meter, showing the use Grid Tests on all Amplifiers of the rectifier to measure alternating cur- Pin Jacks Insulated rent, with uniform accuracy to 51)00 cycles. Accurate Plate Current and Grid Tests Limits on Panel Hints for Manufacturers All Tubes Tested with Rated Filament Potential The oscillator is now supplying a signal, (Continued from ¡sage 17) 2-Volt Tube Tests which is received and detected by the radio. people who are very hard of hearing. In Tests Both Plates, '80 Type Tubes without As soon as the radio tubes warm up, the this manner, also, radio listeners, who enjoy Adapters signal will be indicated by a reading on the Screen Grid Operating Tests late programs, may listen without disturb- Available with Detachable Portable Cover output meter's scale. It will 1w necessary ing persons who are asleep or who may Full Size Transformer All Tube Circuits isolated from Power Supply to tune the radio and the oscillator to the want to enjoy different programs. I am desired Circuit signal; and also to adjust the employed in a radio store where quite a few Both Meter Scales Accurately Calibrated Full 3 F," D'Arsonval Type Meter attenuator control on the output meter until inquiries have been made on this suggestinn. the scale reading is properly indicated at CHARLES VITA \7.A, a convenient point on the arbjtrary scale. Your Guarantee 3606 Atlantic Are., .- INnntic City, N. J. The output from the oscillator may be "Satisfaction is Guaranteed." In brief, if ('This is the experience, evidently, of ninny after investing a 19 varied by means of the variable resistor Ill in SUPREME Model dealers and Service Men. Some have made Tube Checker you do not feel that you have in the diagram, and the attenua tor on the obtained the maximum value in this type of additional money restoring the jack which instrument it fails to prove "Supreme output meter may he varied also; thus, a -if by was once found in every audio stage. Comparison," return it within 10 days from wide range of outputs can be covered. In receipt thereof, transportation charges prepaid, this way, -Editor) and GET YOUR MONEY BACK. We make the necessary aligning adjustments this offer based on our confidence in Your can be made, on both hurtuil:ast and inter- judgment and the quality of Our product. mediate scale Wanted, Hinged Fronts Mail the order blank below at once -You amplifiers, the maxinnun read- can't lose. ing on the output meter indicating the con- IT seems to me that it would be n good dition of resonance. plan, when building cabinets for receiv- SUPREME INSTRUMENTS CORI'. ers, to make the front side swing out on 407 Supreme Bldg., Greenwood, Miss. Measuring Pentode's Output limas; permitting and inspection testing of oCounter Type, Dealers Net The pentode output tube is now becom- the receiver without having to twist the Price, F.O.B. Greenwood, Miss. 26.95 ing very popular, and manufacturers are cabinet around on the floor (or rugs as the Portable Type Dealers Net $29.95 Price, F.O.B. Greenwood, Miss. V beginning to incorporate this type of tube ease may he) in order to get at the back in their receivers. As this tube has five to do the ,job. This is a complaint that prongs, it will be necessary to use it five - is very often made to me, when servicing Name - .------'--- hole adapter on the output meter leads for receivers. Street ...- -.- snaking connection. As an alternative, the C. L. MERREI.L, output meter's leads may be connected di- Selmer, Tennessee. L City -...... - ...__._ _.- State 50 RADIO -CRAFT July, 1931

for all stations. J1 ix the output of the sec- camuses cross- modulation in presence of Craftsmen's Letters ond detector with that of a second oscillator, strong local interference. A similar idea (Continued from page 39) and pass the resultant difference in fre- has been employed in transoceanic com- quency through a low-frequency amplifier. mercial c 7ttion for sonie years. - "low" spot of tiler, or vice versa. This The .IV'ond oscillator, once properly "tuned Editor.) makes the low -frequency type of super- in" Itctwt'en the second detector and the heterodyne more of a 'sa ncc than a prac- low- frequency amplifier, will require no MISCALLING TECHNICALITIES tical receiver, especially in localities where further tuning. Editor, It.4nurCa,4rr: there are nuuueruus broadcast stations; and An arrangement such as that shown in The miniature edition of the February these disadvantages outweigh the benefits to the ace ponying sketch would require a ue of It.\mo-Ca.srr, of which I recently be expected from its high amplification pus - total of t d stages; seven of which slhilities, are fixed hi tune and only two need to be On the other hand, Iry using an inter- "tuned in" in operation. mediate frequency sufficiently high, say about I must admit that I have not tried out 475 kit, stations will be received at only titis plan in practice, and no doubt some one point On the oscillator dial, and heter- difficulties would arise, as they do in almost odyne squeals are e1 ated. However, the all experimental circuits. Itut, if you think intermediate amplifier is working at al t an arrangement such as this is worth ex- as high a frequency as if the stations were perimenting on, I shall be glad to have you being tuned in direct, as in the case of a publish this letter; as it may he of interest tuned radio- frequency receiver; and the alu- A new radio thrill for you! Listen In DIRECT to London. to other experimenters. Paris. Berlin. Buenos Aire: and other broadcasting stations plificatiun is therefore not much better than Co1.E3r. SUTTON. throughout the world via short oases. Enjoy unique for- x eign programs from strange lands. Your ordinary rerelver could he obtained from a tuned radio -fre- 319 West Grand Are., .Alhambra, Cal. cannot tune in the low ware stations. WORLD -WIDE RECEIVER gets 14 to 510 meter stations with surprising gluency set. clarity. SEND NO MONEY! .lust write your name and (Our correspondent's suggestion will he address on a 1osb and and ask us to send you this won- In order to retain the advantages of both derful guaranteed short wave set. Pay postman $6.45 plus of interest to many experimenters, who wish a small delivery charge. All orders West of the Rockies the high -frequency and the low- frequency to try their ingenuity on something differ- cust be accompanied by Si.l10 deposit. Price in foreign ountries. a $7.7deposit.delivered. Order today! amplifiers and, at the su time, eliminate ent. With the parts of one of the old super - their disadvantages, submit the following I heterodynes -such as the lea diola 25, which NEW RADIO BARGAINS plan with reference to the accompanying Lw Power Transmitter adaptable for phone or code. has an intermediate frequency of 45 k.c.- With plug rolls sketch: -In $14.75 preceded by a high- frequency I.F. amplifier, B Eliminator. Leone Dry with 2280 tube. Igo volts, will operate up to ten tube set, fully guaranteed Let there he two separate intermediate 6.75 of the kind which several constructors have AC-A B C Power Packs. completely assembled 8.75 amplifiers; the first of which is of the high - lately described, very high and very selec- Tubas: 1X type. 30 -day replacement guarantee. No. ^In. $2.25; No. 250. $2.45; No. 281. $1.85: No. 245. 51.25; frequency type and the second of the low- tive aunplificat might be obtained. To No. 224. $1.25; No. 227. 75e: No. 226. 65e; No. 171. 75e. frequency type. 'there will then he only one put hand -pass filters ahead of the first stage Int tonal Microphone. two button for public address system and transmitters. speech or music spot on the first -oscillator dial fur any of a receiver lowers sensitivity and the pos- $9.75 station and the untplt of the second de- sibility of extreme distant recept ; while CHAS. HOODWIN CO. tector will always be at the same frequency, indiscriusilate amplification of all signals 4240 Lincoln Ave., Dept. G -15, CHICAGO

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National Radio Trade Directory NAME Established since 1922 ADDRESS 303 FOURTH AVE., Dept. L, NEW YORK, N. Y. CITY RTATE July, 1931 RADIOCRAFT received a copy, is very interesting. How- THE HARD -TO -SELL RADIO SET ever, on looking over the book, I find a By M. N. Leibowitz. very bad error on page 480 (Fig. 2) in Mr. NU other industry has achieved the Bernd's kink of using a ruling pen to handle standardization of the radio industry IT'S EASY TO small nuts. The illustration shows a pair in products as intricate as radio sets. The of dividers instead. only variety is in the cabinet's design or Being a draftsman Of long experience, I general appearance. IDENTIFY don't like having the dear public misled Several large radio retailers in New York about the working tools of our profession. City have hit upon an ingenious and inex- KARL. H. SF.F.nr.RS, pensive weans of individualizing the hard- 1931 TUBES (On consulting our chief draftsman, Mr. to -sell radio set. Such a set is provided with T. Pent; we learn that this criticism is an automatic line -voltage regulator, which just, from an artistic standpoint. Mr. is nothing more than a socket and a suit- Bernd sent a description of the use of a able Amperite inserted in the connecting ruling pen with an illustration of n pair of cord and screwed inside the cabinet. ('the dividers, which was reproduced on page 481, cost is about $1.75.) The salesman, after of the issue referred to. Either tool, how- pointing out the standard features of the ever, might be used as described; and the set in question, climaxes his sales talk by pen would in ninny cases be more useful, calling attention to the additional feature- giving a longer reach. Incidentally, this is a "and in addition to all these features," he testimonial to the readability of this minia- explains to the hesitant buyer, "there is a ture edition; of which n few copies remain unique and indispensable feature, the auto- which we shall be glad to send to the first matic line -voltage regulator, which you see inquiring readers.-Editor.) back here. It insures uniform, positive, satisfactory operation at all times, and saves you untold money in longer tube life and diminished servicing costs." That generally clinches the sale and moves the hard -to -sell set. Milliammeter into Ohmmeter (Continued from page 16)

The scale reproduced corresponds to those of the Weston "301" and Jewell "88" million:- Look for meters (which differ in the positions of the serewholes). Corresponding resistance readings may be entered on any milliampere scale. Clean -Cut

the expected accuracy. Unless precision Screen -Grids resistors are employed, the conversion of millianttneter and voltmeter instruments for Minimum metal for maximum electrical a Itiplicity of purposes is a sheer waste and mechanical strength -that is the true of time. test of o screen.grid tube. De Forest engineers have attained those prerequisites Short-Wave Receiver -Adapter by 1. plate instead of mesh for greater degassiicoa (Continued frota page 3.5) tion. increased strength and closer tolerances. 2. perforations to decrease possible secondary angles and as far from detracting influ- "Type 225" or "255 "; ences as the location permits. If but one AFC -Audio filter choke, 80- henry; 3. Patented De Forst notched cathode insuloto, aerial is used, the operator may mount a FT- Filament transformer, 21/2 volts, 6 am- for practical quick.heoter performance. small S.P.1).T. switch on the back of the peres; 4. Molybdenum wire for both grids, costing 20 tuner's cabinet. The saune ground is used, JS- Yaxley jack switch, "Type 45 "; times as mach as nickel. Higher melting point permits greater dega"idcotian. providing it is satisfactory for use on the RFC- Hmuuuarl nd shielded, polarized S.W. short waves. choke; s. Continuous support for outside screen, insue. ing mo.imum rigidity. Parts Used LI, I.2-6 Pilot or Silver- Marshall UY coil CI, C2 -2 National S.W. condensers, "Type forums; S.E." 125 f.; Four Pilot UY sockets; one Eby UY wafer 03- National equicycle condenser, 250 f.; socket; C4- Polyuiet molded fixed condenser, 150 One aluminum double can, 8% x 7% x 5gß mint.; inches; C5, CO, C7, CIO, C11- Polymet molded fixed 7 x I8 -inch metal panel; 9 x 17'/2 inch metal condensers, .01 mf.; subpanel; AUDIONS C8-1 -mf. by -pass condenser; Four -wire cable, hook -up wire, hardware, C9 -2 -mf. by -pass condenser; etc. C12 -X -I. Vario-Denser, "Type N "; A very effective resistor, for R3, may be RADIO 1U-2000 -olun fixed resistor; one of the windings from a discarded pair R2 -2-meg. grid leak; of bead phones. If the ends of the coil TUBES erwsy estom R3- 500 -ohm fixed resistor; are carefully soldered, an absolutely silent rre.Y R4-3 -meg. grid leak; and permanent resistance will result. R5-Clarostat volume control; The layout of the front panel is left R6-Centra lab Radiohny 5(M),000 ohms; somewhat to the choice of the builder. Two DE FOREST RADIO CO. R7- 1800 -ohm resistor, preferably variable; vernier dials may be used for the tuning RR --Clarostat "Hum -Dinger" hum balancer, controls; a more balanced appearance will PASSAIC, N. J. 20 ohms; result, however, if a very small vernier con- \'l'- Silver- Marshall audio transformer, denser is placed above CI (in the respective 52 RADIO -CRAFT July, 1931

positions of C3 and RG) and plain knobs - - no greater magazine .... set testing are used. This construction will also make for quicker tuning, it being difficult to turn published on development reduced a high -ratio vernier with the left hand as to quickly as with the right. The jack switch of Short Waves may go beneath the dial of C2. On all large newsstands Simplicity It has been found hest to use a filament transformer which comprises an electro- MAGAZINE with the New static shield. By this means, a noticeable RADIO EXPERIMENTERS improvement in the operation of the tuner lias is effected; the shield grounding many of the A.C. line noises, which otherwise might : shoRi, prove exceedingly annoying. Should such 1 at transformer he difficult to obtain, a trans- wAVE former of the proper size may often be readily taken apart and a shield added. This is done by placing around the primary winding a sheet of soft iron as wide as the core t permits. Care should be taken to insulate the overlapping ends of the shield from each analyzers other, to prevent a possible short of the .....r ACHIEVEMENT in perfecting and simplifying single turn. A lead several inches long testing equipment for servicemen, dealers and experimenters is still of prime importance -and for should be soldered to the shield before giv- the past twenty -seven years Readrite engineers ing it a layer of tape and replacing the have periodically placed on the market testing equipment of advanced design. Good testing equip- secondary. ment today is indispensable-and for rapid adjust- l'he coils are wound on standard L'Y ments, expert servicing and testing, Readrite products are increasingly being demanded. In- coil forms, 11/2 inches in diameter, with No. vestigate the advantages of using Readrite equip- 24 D.S.0 wire. The grid winding is at the ment- -the products that have been sold for over a quarter of a century. top in each case, with the tickler 1/-inch or the primary /. -inch below. Beginning 4 -Color Corer 9" s 12" in size ' Oyer 200 Illustrations at the top of the form, leads are taken off RAPIDLY increasing each day are the number as follows: Grid, "F" (Gnd.); F (to "11" of experiments in the Short Wave field -de- supply) Plate; and, for the primary of Ll, velopments which are bringing to this branch of radio thousands of new "thrill seekers." Experi- "F" (God.), C'r (Ant.). menters, as in the early days of Radio, again have Turns L1 'Turns L2 the opportunity to bring abort stirring new inven- Meters (Grid.) (Pri.) tions. Read in SIIORT WAVE CRAFT, the (Grid.) (Tick.) Experimenter's Magazine, how you can build your 18.5 -32 61/, 5 4% 51/, own Short Wave Sets, both transmitters and receivers. SHORT 31.5 -52 91/2 6 83/4 6t/ WAVE ('RAFT is exclusively a short ware magazine -the kind you have wished 50.0 -85 1811, 7 171/ 81/-- for so long. Regular Departments in RAFTERS, BOLTS AND NUTS SHORT WAVE CRAFT Photographic Section -pictures of latest short wave By John Hardt sets and stations: Transmitters for short wave and how to build Model them; 700 THE idea I am about to describe has Short wave receivers- construction of all types and kinds; THE \IOI)EL 700 Meter is equipped with a prac- served me lots of times and I am sure tical selector switch for checking all parts of the The Short Wave experimenter; tube circuits by cnunecting to the set sockets. it will be of interest to many others. It is Television on Short Waves; Short Waves for the broadcast Selec ' for testing voltages of plate. grid. cathode illustrated below. listener; and screen -grid is done quickly and accurately. tItra Short Waves; Plate current. filament volts, also line and power Aircraft Short Wave sets; supply volts are measured. The grid swing test for How to build Short Wave aerials; tubes is used. Just push one button for screen- Short Wave tlitestiou Box. grid and allot her button for other tubes. Makes Interesting Articles in testing of all type tubes simple and thorough. A the Current Issue 41/2 volt grid battery is furnished. The battery is Short Wave "Amateurs" link Trail - Blazers with used for the grid test and also continuity testing of !lase; transformers, chokes, etc. Capacity and resistance Short Wave Converter with "11" Supply Built -In; charts are furnished showing the use of instruments A Single control Short Wave Receiver; for testing eon lensers, also measuring resistances up The "Ham's Own" Receiver; In 100.0110 ohms. The eight scale readings of the Investigations in Ultra Short Waves; meters may be used separately with jack terminals Getting Started on Five Meters; provided. The scale readings are 0 -60 -300 -600 D. C. The DeForest Short \l'arc Receiver; volts, 0-10 -140 -7011 A. C. volts and 0. 20.1110 milli- 'l'he Leutz Short Wave Converter; amperes. Both A. C. and D. C. filament voltages and many other articles by well -known authorities are accurately measured on one meter. as, Lee DeForest, C. IL W. Nasoni, A. I;innrweg, Jr., R. \Vm. Tanner and others. This misled is housed in a strong case with leatherette covering; it is attractive and compact, as well as complete. Cover is removable. It tills every "The Short Wave is the most im- need for the expert serviceman or the beginner for radio set analyzing. Size 10-Ç x ,iri x 3 inches, portant thing in wireless." No. 700 - - - List Price $25.00 This is a .space- .mtinn idea: but be soc to screto the jar rap tight. '/i/qlLC07t t- MODEL 600 te4.4- contains exactly the same testing equipment as No. T'.very mechanic has his choice collection 7110 Lut the carrying case is much larger and is of bolts, nuts and washers; which often are equipped with a lock. Room is provided for carrying SPECIAL OFFER COUPON tulns, tools and supplies. The test equipment and carefully filed in lettered boxes, or in cans, panel is in a removable tray in the top of the case. but still more often, are not tiled at SIIOR I' WAVE The tray may be used separately as a complete test all! CRAFT RC-7 99 Park l'lace. New York, N. Y. panel for shop purlioses. Size 14! e x 7 x 7t2 inches. It lases ha Ili iy it is for anyone to reach I enclose herewith my remittance of $2.00, (Can- 600 - - - - Price $30.00 as No. List overhead, unscrew glass bottle froth its ada and foreign $2.50) check or money order pre- threaded cap, select the desired part, and ferred, for which you are to enter my subscription Send for Catalan "R" or Order Your to SHORT WAVE CRAFT Meters .V011'! for One Year, also replace the bottle by a turn of the wrist. send me the last two issues gratis. I understand If not at your jobbers order direct. This arrangement is the result of fasten- that the regular subscription rate is $3.00 and this Di set nut tu dealersa and service nient, offer will be void after June 30th. SHORT \V. \\-E ing the metal cover to an overhead rafter CRAFT is published every other month. by means of a couple READRITE METER WORKS of screws. A number NAME of these present a neat appearance, and 17 College Ave. Bluffton, Ohio are very handy. (If the rafters are low, ADDRESS Manufacturers of .4 CCU rate Testure Instruments Since 1904 "watch your head! ") CITY <-l'.\TP 14MNNN41104M1A,% 4 July, 1931 RAD1O-CRAFT 53 Improving Short -Wave Reception (Continued from gauge 37) an ordinary short-wave receiver is consid- grid lt.F. amplification and a screen -grid Data, Parts List erably less than that Of gut ordinary Iaroad- detector is quite sensitive, and will give cast set. very good results, when compared to the The superheterodyne overcomes, to some ordinary short -wave arrangement. It must and Blue Prints extent, the difficulties mentioned; but it is, be remembered, however, that a screen- Complete Schematic Diagrams as usual, more eoni iiicated in comparison. grid tube lam n high plate impedance and, and Construction Details for Constructional Suggestions for this reason, it must have a high value building: r There ,are various refinements in short- of ?date inductance (L2). This may be an wave receivers on which the experimenter ordinary short-wave choke coil of good de- can work, but they are not practical for sign, provided the constructor couples the manufactured receivers. A manufactured winding of the choke-coil L2 inductively to receiver is it comgnomise reached by the coil 1,3 of the detector (Fig. 9). If this design engineers, taking into consideration cannot be done, the choke cannot be used. many conflicting factors. However, an ex- Instead of the choke, a winding of about perimenter is not l' 'ted in any way, per- 200 turns of No. 36 wire on a piece of haps, other titan by the contents of his one -inch tubing may be used. This coil (L2, pocketbook. For instance, to increase the Fig. 9) should be closely coupled to I.3, amplification of short -wave sets witl t, at the secondary coil of the detector. the sane time, increasing unduly the ber The dotted lines in Fig. 9 show an alter- of tuning controls, a screen -grid tube may native arrangement in which a small coup- be used for a detector. Experimenters who ling condenser of .0002 -mf. capacity is used have worked with screen -grid detectors, on to couple the R.F. amplifier to the detector. short -waves, report that the single detector In this case, L2 and 1.3 need not be coupled carve Stenodes curve tube gives results equal those of an inductively, and 1.2 may be any Inner shows selectivity, ostler to or- available that of ordinary receiver Lines BB are 5 k. r. dis- dinary detector tube and one stage of audio xhc.rt-wave R.F. choke coil. tant /rom Line A. All background noise included in the light portion between A and BB is eliminated amplification. The circuit of a screen -grid The expiry nter may desire to increase by the Stenode. detector is shown in Fig. 7. the amplification still more. (It is not de- THE Ordinary short -wave adapters are not sirable to do so, unless tuned stages are very sensitive; one possibility of increasing used; untamed stages are poor amplifiers, the sensitivity is to use a screen -grid tube and usually not worth adding.) 'l'he addi- STENODE in the adapter itself. The reason, perhaps, tion of more tuned stages means more con- why these tubes have not been used to a trols, but the signal strength, especially on CIRCUIT greater extent in adapters, is that n slight foreign stations is greatly increased; so Developed under the patents of complication results because an extra volt- that the addit al controls nuty be well James A. Robinson, M.B.E., D.Sc., age tap is required for the screen -grid ter- worth while. Each of the stages of R.F. Ph.D., M.I.E.E., F. Inst. P. and For- mer Chief of Wireless Research, al on the tube. However, this sl Id may take the form of either of the two British Royal Air Force, by the en- not be difficult to overcome. arrangements suggested in Fig. 9. Each gineers of the Stenode Corporation grid circuit is tuned; and each plate circuit of America. REGULAR TUBO SCREEN-GRID TUBE is coupled, to the grid circuit of the next tube, either inductively or capactt Lively Price $10.00 coupled (through a condenser of about Several reliable American manu- .0002-m f.) The signal strength obtained facturers are now making all parts with two stages of lt.F. amplification ahead meeting Dr. Robinson's specifica- of the detector is very good. tions for the Stenode circuit. The special quartz crystals tube form (Do not make the mistake, as many ex- -in for convenient handling and mount - perimenters do, purchasing of low -grade ing -ore obtainable From us until screen -grid tubes, they will not give good Fig. 8 the American Tube Manufacturers results at short wavelengths.) licensed by us are in sufficient pro- In the usual adapter, a tube is connected to the duction to supply the demand. detector socket through two or more leads. In- Options in Design genuity may be needed to use a screen -grid tube The Stenode Corporation of America 'l'he tuning condensers of the R.F. stages as the S. -!t', detector. now throws open to serious investi- should not be htrger than .I0)35-inf. in gators the study of this revolutionary One method would be to connect a re- capacity and, prefer.l'lg, much xnualler. The circuit, which is the greatest single sistor (R, Fig. 811) of suitable value, to amplification of an H.F. stage falls off advance since Morse invented the the plate lead; thus reducing the voltage quickly as the value of the tinting capacity telegraph. sufficiently for the screen -grid. This re- is increased beyond a certain value. sistor should, preferably, be variable; be- If one desires to receive some particular "If it isn't a STENODE cause individual screen -grid tubes vary con- foreign stations, small midget condensers it isn't a modern receiver." siderably in their characteristics. can be used for tuning and correspondingly Another way to increase the sensitivity larger inductance coils. This will result in of the ordinary short -wave receiver, or greatest amplification at the desired fre- STENODE adapter, is to add a stage of R.F. amplifi- quency. (See page 29, Jul-, 1930 RAnto- CORP. OF AMERICA cation ahead of it. There are two types of (te %r-r, "Spreading Shot -Wave Stations on (Formerly American Radiosaat Corp. ) R.F. amplifiers which arc ordinarily em- the Dial. ") Hempstead Gardens, L. I., N. Y. ployed. In one, the input is unluned: a With small condensers, more plug -in coils ------choke or a resistor of suitable value being are, of course, necessary. Large condensers STENODE CORP. OF AMERICA - eonnected across the input to the R.F. stage. require a smaller number of coils, but give Hempstead Gardens, L. I., N. Y. However, this type of circuit arrangement less amplification from the stage. The ex- Enclosed find O Personal Check, P. O. or gives only low amplification. By using a perimenter should Express Money Order for á10.00 for which choose between these please send me complete diagrams, details and tuned stage of amplification ahead of the extremes; it would seems, however, letter to list of Pans for constructing the Stenode Circuit. detector, a considerable increase in signal get fine results on a few stations than to strength will result. A circuit diagram of obtain poor results on a large number. This Name such a single -stage R.F. amplifier is shown is the failing of many short -wave receivers. Street in Fig. 9. Its addition to an ordinary short- The designers have been too ambitious to wave receiver or adapter is not difficult. cover the largest possible ranges; with the City Sate The combination of a stage of screen- result that the amplification has suffered 54 RADIO -CRAFT July, 1931

greatly, and personal satisfaction to the user, in proportion. A REFERENCE VOLUME OF Many plug -in coils are troublesome, but necessary if a wide tuning range and good CO-ORDINATED RADIO KNOWLEDGE amplification are desired, at lowest expense, (and without recourse to complicated switches). In any short -wave set the coils, if unshielded, should not be greater than two inches in di; 'ter. Good broadcast coils, having low losses, and unshielded, are often three inches in diameter. It is important, for short -waves to wind good space-wound coils; the increase in amplification will be quite noticeable. (See Fig. 1.) If a breadboard layout is constructed, give all parts plenty of spacing. Often, by i so doing, the shielding can be dispensed with (depending upon parts useti, local station power, and other factors). Otherwise, ample room in the shield cans. If the experimenter or set builder will take into consideration, when designing his short -wave receiver, the foregoing principles, he cannot help but increase greatly his enjoyment of long- distance, short -wave programs originating in many foreign lands.

knowa subject kinds. We is of two can informa- "Knowledge', s, know where we or we know Johnson Figuring R. F. Coils ourselves, » it. (Continued front pape 37) liontion upon ..rnaDEDn10K .'' handy, and quite accurate, formula for the calculation of the inductance of a simple single -lamer coil is as follows: 0.2 d2 Na L 3d + 9b 352 Pages Those not familiar with equations of this kind will understand its application more readily as expressed below: Weight, 3 lbs. Multiply the number of turns of wire bc- the diameter of the form (in inches): square the product, and divide by 5. Then add 9 in. wide by three times the diameter of the form to 12 in. high nine times its length (also in inches). Di- vide the result Of the first operation by that of the second; the result is the inductance of the coil in mierohenriee, (.\ number is squared when multiplied by it- A SYMPOSIUM self; the square of 4, for instance, is 16.) OF For example: A cylinder with a diameter INFORMATION TOPICALLY of 2 incites has 70 turns of wire wound on it, and the length of the winding is 2 ARRANGED IN ALPHABETICAL ORDER inches. Substituting these values in the This book is not a dictionary, but a true Radio enlarged and improved and brought up-to above formula, we have: Encyclopedia, covering Radio from A -date. to Z. It is Every page is replete with illustrations; a vast the first standard work ever published in America number of tables 0.2 X 2 X 2 X 70 X 70 classifying alphabetically and charts have been added. In the countless words used many instances, the definitions have been rewritten _ 163.3 mil. in this highly specialized science of Radio. The En- to conform cyclopedia to a w developments and new material was first issued in 1927. The volume has been added which makes (3 X 2) -h (9 X 2) offered is the book twice the non the SECOND EDITION, greatly .tse of the first edition. The use of the I.XC table simplifies the RADIO amount of work necessary to determine the IN ALL ITS BRANCHES, EXPLAINED various values of L and C required for DESCRIBED the broadcast hand. The Encyclopedia and ILLUSTRATED For example: A .0005 -mf. variable Con- contains definitions of every The Radio Encyclopedia is published in one vol- word and phrase used in the entire Radio art- urne of 352 pages, bound in denser is available, and it is desired to every circuit, part flexible red morocco find and apparatus, formula, abbrevia. keratol, size 9 x 12 inches and gold -stamped cover. lion. outfit accessory, the value of inductance which will enable etc., is thoroughly explained. Heavy ledger stock is used and the loose -leaf con - The entire book is written in everyday English, struction enables new material to be added. the combination to tune to the highest wave - easily understood by anyone. length in the broadcast hand. Referring to Table I, we find that the S. GERNSBACK CORPORATION $3.98 98 product of L and C corresponding to 545.1 Park Plane. New Yank. N. Y. Postage Prepaid Kindly send flit one ropy Of the Sri ,d Edition ut S. GernOtio k': Radio En meters (or 55e key.) on the chart is .08128. cyclopedia. I enclose herewith $3.11) for whirl 3,111 are to send me the hook Dividing titis number by .0005 postpaid. (Foreign and Canada add 35e. extra.( If the book day not COMM (the capacity up to my expectations. or is not as represented. I can return it, and have nu (Canada and foreign of the money refunded in full. condenser in mierofarads) we obtain add 35c. postage) 168.6, the inductance of the coil in nticro- Name henries. Address MAIL COUPON Now. in order that the combination of the coil City St ate and condenser shall tune from the RC -7 AT LEFT TODAY highest to the lowest wavelength, it becomes July, 1931 RADIO -CRAFT 55

As the capacitative effects of the tubes, TABLE I wiring and shielding, and the minimum ca- Ka WL .xl c. WL. I.xC pacity of the condenser add together, it 550 545.1 .08428 1030 291.1 0.2389 can be seen that the actual minimum capac- 560 535.4 .08119 1040 288.3 .02343 Experienced 570 526.0 .07827 1050 285.5 .02299 ity of the variable condenser alone should 580 516.9 .07551 1060 282.8 .02255 he quite small. In practice, 18 or less 590 508.2 .07288 1070 280.2 .02213 mmt 600 499.7 .07040 11180 277.6 .02171 is possible. 610 491.5 .06808 1090 275.1 .02130 '.hus we find that a coil suitable for Radio Men 1 620 483.6 .06593 1100 272.6 .02090 630 475.9 06383 1110 270.1 .02052 use over the broadcast range with a .0005 - 640 468.5 .0618i 1120 267.7 .02016 tuf. tuning condenser should have an in- 650 461.3 .05998 1130 265.3 .01980 YOU Have 660 454.3 .05823 1140 263.0 .01946 ductance of approximately 160 to 170 utie- 670 447.5 .05658 1150 260.7 .01914 robenries; the exact value depending upon 680 449.9 .05501 1160 258.5 .01882 had enough 690 434.5 .05348 1170 256.3 .01852 the actual uutxinnuu capacity of the con- 700 428.3 .05198 1180 254.1 .01821 denser. Most ".000.5 -mf." variable condensers 710 422.3 .05051 1190 252.0 .01789 Experience 720 416.4 .04997 1200 249.9 .01760 are not exactly .0005 -mf., but slightly over 730 410.7 .04767 1210 247.8 .01731 or under that value, unless made with spe- 740 405.2 .04630 1220 245.8 .01702 in Radio 750 399.8 .04495 1230 243.8 .01675 cial precision. 760 394.5 .04.180 1240 241.8 .01648 Those not interested in the above simple 770 389.4 .04268 1250 239.9 .01622 780 384.4 .04164 1260 238.0 .01596 mathematics of the coils will find in Tables to appreciate 790 379.5 .04060 1270 236.1 .01571 II and III some tabulated data of var- 800 374.8 .03960 1280 234.2 .01546 ous sizes 810 370.2 .03866 1290 232.4 .01522 coil to be used with the more the need for 820 365.6 .03774 1300 230.6 .01499 standard values of capacity; namely,.0005- 830 361.2 .03684 1310 228.9 .01476 and .00035- microfarad. 840 356.9 .03596 1320 227.1 .01452 ENGINEERING 850 352.7 .03511 1330 225.4 .01432 In tabulating these coils, the largest size 860 348.6 .03429 1340 223.7 .01411 of wire possible, 870 344.6 .03351 1350 222.1 .01390 in proportion to the length 880 340.7 .03275 1360 220.4 .01370 of winding, is specified. TRAINING! 890 336.9 .03201 1370 218.8 .01350 The various coverings on wires are not of 900 333.1 .03129 1380 217.3 .01330 TODA)'! 910 329.5 .03059 1390 215.7 .01311 absolutely standard thickness, in one make Mail coupon for details 920 325.9 .02991 1400 214.2 .01292 of wire as compared to another; and, since 930 322.4 .02926 1410 212.6 .01274 940 319.0 .02864 1420 211.1 .01256 this table is for shop or experimental use CAPITOL RADIO ENGINEERING INSTITUTE, INC. 950 315.6 .02804 1439 209.7 .01239 it is advisable to wind more turns than 960 312.3 .02746 1440 208.2 .01222 3166 Mt. Pleasant St., N. W., Washington, D. C. 970 309.1 .02688 1450 206.8 .01205 specified here, to compensate for any dis- without obligation, your new issue 980 305.9 .02634 1460 205.4 .01189 crepancy in the maximum. value of the con- Please send me, 990 302.8 .02582 1470 204.0 .01173 of "Modem Radio" explaining your advanced 1000 299.8 .02532 1480 202.6 .01157 denser, and for difference in the thickness course in Practical Radio Engineering. 1010 296.9 .02483 1490 201.2 .01142 of the insulation. 'l'he additional turns a re 1020 293.9 .02436 1500 199.9 .01127 Name removed after testing the coil in conjunction with the condenser for which it is in- Address necessary to know the minimum capacity of tended. Position -_ RC-7 the condenser and its associated circuits. Thu first col of the tables represents The table is again consulted and the the diameter of the coil form, in inches, value of the LxC product for 199.9 meters and the second, the length of the winding (1500 kc.) is found to he .01127. Substitut- in inches. No attempt has been made to GET OUR LATEST ing this in the formula: maintain the ratio of 2.46 to 1 between .01127 diameter and length; which is, theoretically CATALOG .600067 (uff.) at least, the most efficient in obtaining : 168.6 (nth.) given inductance with the least wire. 2 -Tube High Grade "HAM" Receiver Kit $20.00 Net TABLE 1I TABLE III Pilot Universal Short Wave Receiver Coils for .0005 -mf. Condensers Coils for .00035 -mf. Condensers s National AC 5 SW Short Diaur. Length Diana. Length Wave Receiver I n, In. Wire No. Turns In. I n.. 11'ire O. Turnt Mershon Condensers 3 1 23 Enwn. 42 3 1 26 S.C.C. .50 3 11/2 20 Enmu. 45 3 l'/z 24 D.S.C. GI Send Tex Cents for Catalog 3 2 19 S.C.C. 49 3 2 21 S.C.C. 60 CHICAGO RADIO APPARATUS CO. 3 21/ 18 S.C.C. 54 3 21/2 19 Enaut. 65 Established 1921 Dept. CF -7 3 3 16 Emmm. 57 3 3 18 D.S.C. 68 415 S. Dearborn St., Chicago, Ill. 21/ 1 25 D.S.C. 46 2 1/2 1 27 D.S.C. .55 11/. 22 Enam. 21/ 56 21/2 11/2 24 D.S.C. 5:3 21/ 2 20 Ennui. 60 21/2 2 22 D.S.C. 69 19 BEINSURAN 21, 21/ Ennm. 61 21/2 21/2 21 S.C.C. 75 2,% 3 18 S.C.C. 66 21/2 3 19 Ennnt. 80 THAT PAY.* 2 1 25 Emma. 53 2 1 29 D.S.C. 66 11/2 corrects line volt. 2 231:mmm. 62 2 11/2 26 AMPERITE S.C.C. 75 Lengthens tube 2 2 22 age variations. S.C.C. 70 2 2 24 D.S.C. 89 life. Protects power equip- 2 21/2 20 l:nanm. 75 2 21/ 22 Enant. 92 ment. Improves tone. Reduces on set 2 3 19 Ennm. 80 2 3 21 Enam. 99 noise. Saves money You can install 11/2 1 28 Enant. 75 upkeep. Write Dept. 11/2 1 32 D.S.C. 84 AMPERITE in your radio in 26 Ennm. RC -7, 86 11:-, 11/2 27 Ennan. 97 5 minutes. No chassis changes. giving set, including make and 1J!. 2 24 F:naun. 94 11 <2 2 25 Enam. 104 A type for every 21i, midgets. $3 at model num- '1% 23 Enaut. 100 11 /2 24 Enant. 21/2 115 your dealers. ber of your 22 Enant. 108 11/2 3 11x 3 24 S.C.C. 12:3 set. 1 1 30 F,mun. 95 1 1 37 D.S.C. 1.21 braes I 11/4 32 D.S.C. 106 1 11, 35 D.S.C. 132 sn, woow.v. KEW Vas 11/ 28 Ennm. 112 á j1/2 30 Ennm. 136 1 2 28 D.S.C. 132 1 2 32 S.C.C. 168 Self -Adjusting 1 21/2 26 Enam. 140 29 S.C.C. 16.5 1 3 25 Enam. 156 1 3 28 S.C.C. 180 C OL 56 RADIO -CRAFT July, 1931 Better The Two Latest Books on Reception Ahead By MORRIS sIETCALF5

Ati a rather bright and promising cor- ullary to the business depression, RADIO through which we have been passing in the SERVICING the radio industry, comes a prophecy fr radisi engineers and scientists concerned with the present unusual effect of "sun Manual spots" upon radio reception. This prophecy Official Radio Service is already making itself manifest in actual- ity and shows a silver lining to the clouds and Complete Directory of All Commercial Wiring Diagrams which have darkened the sky for the radio industry. Edited by HUGO GERNSBACK The financial statisticians have shown us rather conclusively that periods of business THE OFFICIAL RADIO SERVICE and depression Ink ye followed one MANUAL is the greatest achievement prosperity ever attempted in the Radio Service Field. another in a regular cyclical order. Ex- It is not only the OFFICIAL RADIO SERV- perience has shown them that ,about 10 or ICE MANUAL and Complete Directory of all 11 years elapse between successive depths Commercial Wiring Diagrams, but it contains of business depression. a complete and comprehensite course of in- 'l'he astronomers tell us that the ber struction for radio service men. Just off the of sun spots also passes through a similar press and more than 21,000 copies sold. And cycle and, strangely enough, this cycle is of why not, when it fills such a universal need among Manufacturers, Jobbers, Dealers, Service about the sane period. 'l'he fact has been OIfiN:d Men and all interested in radio? The OFFI- recently recognized that, when the number Ratto Scrvin \lanual CIAL RADIO SERVICE MANUAL is com- of sun spots reaches its minimum, radio replete and gives you every circuit of every set ception conditions become exceptionally n.a+o i.,.o.., manufactured of which there is any informa- good. This is due to the fact that magnetic c,.n.,.r,..a .,, o..._ ,.. tion. Its looseleaf and flexible leatherette storms which cause severe variations in ra- covers enable additional servicing data to be dio conditions are also at the and added periodically. There are hundreds of time- saving kinks which will help to increase the height of the hypothetic Kennelly-Heavi- your business and profits. side layer, which reflects back radio waves As the NEW YORK SUN says, "It is diffi- to the earth, is also at its minimum; which cult to see Lain any service ntan can conduct provides the greatest intensity of signals his business satisfactorily and efficiently with- over the distance usually encountered in ra- $3.50 out Ibis 310 -page tolume." dio broadcasting. 'Flutse of the radio industry who can recall the \'inters of 19.20 A Copy Over 1,000 Diagrams and and 19.21 can verify the fact that, during Illustrations - 352 Pages that period, radio reception w'as excellent. It is well known to scientists that the great radio reflecting plane a Iitindretl miles Radio Service Man's Handybook about the earths surface (which is called the Heaviside- Kennelly layer) has been fall- With Addenda Data Sheets ing steadily for several dears, and that this has changed the trantslni.ssiun constants of THE RADIO SERVICE MAN'S HANDYBOOK con- radio waves. Prominent engineers have esti- tains a tremendous amount of authentic material and mated that radio reception conditions dur- practical information on Modernizing old receivers; ing the past season have been from two to RADIO Servicing obsolete sets; Repairing power packs; Construction four times as gout) as a year ago. 1)r. H. of _est laboratory equipment; Vacuum tubes; Set testing T. Stetson, the great astronomer who has SERVICE MANS with analysers and hundreds of other similar subjects. Among been measuring radio reception as at func- HANDYBOOK the contributors are Bertram M. Freed, Leon L. Adelman, solar phen 'VOR Paul L. Welker, Sylvan Harris, C. W. Palmer and others. tion of na, reports the strong- ADDENDA DATA The HANDYBOOK enables service men to record notes, est signals in years It is predicted that diagrams and charts on the special 48 -page section of spe- reception will probable get better in 1932 cially ruled sheets included in the book. Over 200 pages in and the spring of 1976. all -size 9 x 12 inches. '!'resident Midi. il,,." (rrtI,,s Is.s,,,,atin.. Hundreds of Diagrams, 200 Pages, $2.00 9 x 12 inches Reactance and Impedance (C'on/inlied frot" pour :38)

GERNSBACK PUBLICATIONS, Inc. RC- ; condition in which the voltage across the 96.98 Park Pleas. Nevi York. N. Y. BOTH BOOKS total circuit is zero and theoretically infinite I endoso herewith cheek sir Money order for i for each which you are lu end tu Inc postage prepaid the across element. The presence of resist- ( ) Off Hal Radio Sen Ire Manual 83.50 for $5.00 ance lessens this effect, but does not prevent ) Sere he Man's Nand>hok 2. nO ( Radio its use in radio circuits. For example, we OR BOTH BOOKS FOR $5.00. may design an amplifier stage (such sis that shown lit 8) and Name Fig. have the voltage across MAIL COUPON the inductance I. rise to an extremely high Address value at the resonant point. This allmvs us CITY TODAY! to obtain in an . \.l'. amplifier at bass response which issugtensates for the Lack of State II I "lows" in reproducers, transformers, etc. 57 July, 1931 RADIO -CRAFT

In parallel circuit*, having single induc- GREATEST TUBE SALE OF 1931 tive and capacitative arms, the voltage The Largest Variety of Tubes in the World circuit is the same for each first across the THIS SALE has been especially arranged All tubes are guaranteed to be -grade branch; while the current through either comparable to the best obtainable on for service men, dealers and radiotricians quality- branch is (determined by its reactance. At the market today. We will replace within 30 and a large supply of tubes are always on resonance in a parallel circuit the impedance days any tube that has not given complete by one of the of the circuit as a whole is theoretically hand. These tubes are made satisfaction. infinite; the current will be zero; and the largest Eastern tube manufacturers. This is Such an amazing tube sale has never been buy tubes at prices. conducted. voltage will attain a inaxiuuun value which your opportunity to lowest is l' 'ted only by the presence of resist- COMPLETE STOCK ALWAYS READY FOR IMMEDIATE SHIPMENTS Order from this page and note the following terms: accompanied by 20rí of the value. ance in the circuit. That is why we attempt No orders accepted for less than $5.00. Shipment will go forward to you by express or to maintain the resistance in radio circuits It is not necessary to send the full amount of parcel post C. O. D. cash with the order as long as your order is All prices are F. O. B. Newark. at a low value. Jai 1-X -2ots s .20 20t.í- tluodrode 5 -prong .60 t'X -232 l'X -a!i .30 2un.t- sots dal detector tube .00 U 210 55 -°'S an 201.5 -Special radio frequency... .60 1' X-250 85 Il" 1.00 l'X -171.\ .30 171 Special A.C. Y4 atop. extra All bakelite shield tube 201. '.... l'X -171 .a0 POOol filament .60 Ballast tube t)IIe 1). and M. to l'X -240 .40 T -14 (201A Itigh Mu high ends- present tones front binning 1-5 -120 .411 'ion .60 out 1.00 1'X -199 .41) Switch tube. 2111.5 or 112 or 171 CX -22 --Sc reen geld radio fre- I'V -199 .40 double life .60 que,u mnplifier 1.10 I'\' -199 Short prongs .40 Adapter tube 226. 227, 171A, to CX- 247- Pentode s.í l'X -112 .40 rumen battery sets Info A.C. .611 ('X -235 55 1-X -112,\ .40 w-n -ll ,6a Tenon trlcvi'fon tube 't s5 I'X -2a0.t .40 w'14-12 .60 Phutoeleo Irk cell, 2 -luck 3.83 l' Y -221 .40 l' X -230 .110 l'X -245 .40 1 X -231 .60 Rectifier and Charger Bulbs type) 1.40 rectifying (nil >1 2.00 The tuned circuit C -L would present infinite G Amp.\cl,. Triante chargerew bulb 1, our ' R.F. impedance at its resonant frequency, ex- 2 Amp. Nd and new type charger bulbs $t 3..5 1a rharger 1,11111, Ig.00 t, Ile its innate ohmic resistance. and .tnse, aid typa Insu Vrlrr .40 cept for as tube for high mission l'X- 1t1 -Gerd t full -,vane rectifia .85 l'X -281-C T,,bt.terisllcs similar to the 280 hut used as half ware reel (fier of high mission is Tube. designed use with Freshman Master "It" Eliminators, l'y brass base, limited quantity .30 The impedance of a parallel circuit the Rectifying especially for 7.00 CX -866 Mercury vapor saline as that of a series circuit at all other 10 and IO;é frequencies than that at which resonance Discounts: 500 tubes and over °o occurs. At resonance, the "effective resist- ARCO TUBE COMPANY, 38-40 Park Place, Newark, N. J. ance' of a tuned parallel circuit would theoretically become infinite; actually, the effect of the unavoidable of (or pure) in the circuit moderates the effect CLAR-A-TONE resistance sir that the effective resistance becomes equal to Gives Volume - Reception and 21T' X f x L)2 Tone Your Radio Never Produced R Before For eXatnl lc, if al desire to know the load presented to a vac tube by the resonant circuit shown in Fig 9 -in which the coil $1.95 has an inductance of 200 nlieruhenries (.(M)02- heny) and a resistance of 12 ohms Postpaid at 1,IXI0,0(X) cycles -we may readily find the effective resistance of the circuit when tuned to resonate at that frequency, which cor- Money Back Guarantee responds to 3013 meters: Pure. clear tone -greater volume- intorfereucc ant out instantly: Attach R (effective) = ('lar -. \- 'Pone to your set and enjoy toue yutt never thought your radio could 6. 28 X 1,000.0011 .0012' prod lice. X Thousands of owners say (lar..\ -7'uuc is amazingly ingenious. And radio - ohms ------= 131.000 engineers will tell you what a tine technical accomplishment it is. 12 lt1gular price, $'.:10 -bun now as special introductory offer, we will ship pou a l 'Iar --\ -T direct for only $1.95. ?tail the coupon !clin with check or uwuey. order. or currency. No (',(1.11,'x. \lumy hack any tinte within lo days if ynn'rc not satisfied. Simple installation instructions rumplete ou box. l'on are cordially invited to visit are c.rhibit at the R. M. .1. Trade .Shun., t'euinnin,, .111M. Stlu, .Strrrvl.a 110lel, Chicag, Exhibit H,,,,tr \',,, 12: i)c,ncnrsfrufiou Ruorna 1207 and 5:1, Stevens note/. }ISSENISEE RADIO DEVICES CO. Dept. R. C. 732 Mather Street. chicano. Illinois. Enclosed find my payment of $1.115 for ( 'lar -.\ Two., ,sent pea pa id. same Address City State

The New POWER Pentode 247 AUTO .ell. the heavy arc is a radian; impedance formulas take frequencies. not in whole cycles, used in place of the 245 Semipower Tube ReR¢AD10ceiver

but in radians: Right, why a generator creates is an improvement of more than 25', over 1 AmazingLowPrice! , i a in its revolution. hack. sine-mare the old. Guaranteed or your money Quality Performance Use No. 47 adapter, $1.25. In pushpull sets Noir: The presence of the number 6.283+ Sis tube triple screen -grid use 2 No. 47 adapters. using 3-224. 2 -227, and (2 "pi ") its the reactance formulas is accounted 1 -245 power tube. Easy fact that in higher mathematics it is to install. will fit any car. for by the BUDDY MFG. CO. Single dial contro We f I more convenient at times to measure angles guarantee that this set in radians. The radian is the angle whose arc is 89 Cortlandt St., New York, N. Y. will pull in stations within a radins of 1,000 mil.* and that it will de- just as lung as the radius; there are therefore 1:nc dosed find $ check or money liver the volume and tune qualities of 6.283+ radians in 360 degrees (Fig. 1a.\). The order. for which you are to send nu, postage au elect tic set. or y money refunded. by 6.283 +, to convert cycles prepaid, No. -17 Adapters. PRICE OF SET ONLY $20.00 frequency multiplied Price Complete. including tubes. bat te rien, dy- of 360 degrees into radians. is commonly repre- N :ltaie, namic speaker nd suppress/ rs. all ready to Install sented in formulas by the Greek letter "omega;' and use, $39.60. Sen $5.110 deposit with order, Address balance C.0. D. Ort foreign rders remittance in which is like a w and is often used also for ohms. full required. ORDER TODAY. lu the sine wave of Fig. 1C, the slope of the City State CHAS. HOODWIN CO. 4240 Lincoln Avenue, D.pt.(2.150 Chicago, Illinois 58 RADIO -CRAFT July, 1931

curve represents the rate of change. It is therefore least at the top and bottom, where it is theoretically level; and greatest at the zero points, where it Hotel Directory of the Radio Trade equals 6.283 x f x I (maximum); from which the maximum induced potential is found to be 6.283 x f x Lx I (maximum). Since the factor determining the effective value, as regards the maximum, is the sanie for both current and voltage, it may be disregarded here. For Those Delicious German Apple Pancakes - 50e The reason for the sine -wave form of generated voltages, in general cases, may be seen by considering a coil of wire, in the armature of a THE VILLAGE GROVE RESTAURANT generator, revolving in the magnetic field (Fig. 72 GROVE STREET, NEW YORK CITY 1011). The voltage generated in that coil is pro- portional to the sine of its angle with the position DINNER 90e $1.00 $1.25 of greatest flux; and its maximum at right angles, - - - from which as unity (sine 1) the ratio is com- puted. The generation of a sine wave in an oscillating circuit is a matter of more complexity. Visit the Village Grove Restaurant for Dinner and Then for Laffs The resonance formulas are all based funda- THE WORLD FAMOUS mentally on VILLAGE GROVE NUT CLUB I= 1 99 Seventh Avenue, So., New York City 211" LxC "In the Heart of Greenwich Village" in which L is in henries, and C is in farads. To with ttNUTSY" FAGAN reduce this to more practical units, every time a Here's what the critics say- unit under the square root sign is reduced a million times, the numerator is increased a "The goofiest place in town ... I really get a kick out of it." thousand times. When I. is in microhenries, and -LOUIS SOBOL, Evening Graphic. C in micromicrofarads, for radio frequencies:: "Hurrah tor the Nut Club -long may it rave. "-RIAN JAMES, Brooklyn Daily Eagle. "A fast, furious show, something going on every second." f 159,200 Kc. -NICK KENNY, Radio Editor, Mirror. = "Nothing like it anywhere in the world." -MARK HELLINGER, Daily Mirror, Y Lx C "You can be made to laugh." -MAE WEST. The standard work on this subject, for those RESERVATIONS - SPring 7-9139 who wish to go into it with considerable thorough- ness, is Circular No. 74 of the Bureau of Stand- ards, "Radio Instruments and Measurements." In THE SHOW PLACE OF NEW YORK this and other issues of RAoto- CMAPr, the matter of resonance and coil design will be treated in a more simple manner, with practical tables of informa- VILLAGE BARN tion.-Editor. with The Sensational Crockett Mountaineers and REV. DAVE BARNUM and His DEACONS Old- fashioned homestead dinners with dance music Book Reviews served from 5 until 9:30 p.m. - $1 by gosh! S. GERNSB.\CK'S lt.\1)10 ENCYCIO- Later on rural entertainment in a rustic setting, square dances, cider, l'EI)IA (Second Edition). 352 pp., 9 x 'n everythin' 'till curfew! 1.2 in. loose -leaf red leatherette binding. BARN DANCING Published by S. Gernsback Corporation, - at - New York City, Price :F2.98. This volume, when placed beside its thinner 52 WEST 8th STREET, NEW YORK CITY predecessor the First Edition, which was the first Between 5th and 6th Avenues Radio Encyclopedia published, bears witness to the the five years, of Reservations SPring 7 -4348 rapid development, during past - Its appearance has the most -rapidly growing art. been impatiently waited l'y many who will appreciate, on seeing it, how much time has been be- stowed upon its production. as well as expense. and what efforts have been made to revise its con- Around the corner from the tents up to the very moment when the last pages were committed to the press. Little Church around the Corner The hook contains over 2,200 definitions and, since it is an encyclopedia rather than a dictionary, many of them are of considerable length. Tele. vision, for instance, covers S pages; Short Wave, with its associated headings on short -wave antennas, coils, receivers and transmitters. 10 pages; Sound HOTEL SEVILLE Projection, 6 pages; Vacuum Tubes and allied headings, 15'/, Consecutive pages -all these containing information of the latest date. The original First MADISON AVENUE Edition had a very thorough foundation of the principles of radio, and those branches of elec- & 29th Street tricity, physics and chemistry bearing upon them; this matter remains still useful and unchanged, but New York City the remainder of the book has been rewritten and doubled in size, with regard to the more recent A hotel of distinction and comfort, applications of radio in the light of the growth of broadcasting and of other important developments. within walking distance of shopping The illustrations number over a thousand; hun- and amusement centers. Five minutes dreds of them are photographs, which reproduce to especial advantage in the new method used for from Times Square, Pennsylvania Sta- printing the second edition of the Radio Encyclo- pedia. There are 38 practical tables, charts and tion and Grand Central Terminal. maps in the text; and an appendix of 21 pages of data on commercial receivers, their layouts, trade- marks, types, etc., which will be especially appre- Room $ Per ciated by every one who is connected with the and Bath Day Up radio trade. 3.00 In the revision of the Radio Encyclopedia, it is obvious that especial care was taken, not merely Convenient to all to make its contents as comprehensive as possible, but also to increase its value to the reader by deal -. points of interest ing with every subject from the ground up; i.e., July, 1931 RADIO -CRAFT 59

in such a way that even a person who knows little or nothing of radio will he able to read intelligently. This is facilitated by very elaborate cross - references, and the simple definitions, either under Hotel Directory of the Radio Trade separate headings or where first used in any article, of all words which might prove a stumbling -block to the lav reader. The addition of a short reading guide, in fact, would make of this book a course in radio which the novice might follow to secure a thorough grasp of the theory of the subject and much of its practical details. In its new and attractive dress, the Radio En- cyclopedia bears witness to the fact that progress in radio may be expected to continue. It is provided with Extra Data Sheets on which the owner CONTIN.NTAL may conveniently index additional material of value, obtained from periodicals or otherwise; and, in Conveniently located later years, it is not impossible that supplementary just across from the. sheets may be issued. As we have said, its present Union Station Plaza contents are timely up to the moment of publication. The pages are very readable and easy to ALL OUTSIDE ROOMS consult; and the substantial binding well fits the ô/ce / /ent Mood volume to be, as intended, a tool for daily use and f requent consultation. The radio expert, no less DINING ROOM than the radio student, will find it a tine -saver and E, COFFEE SHOP a trustworthy guide. u RADIO - FREQUENCY - MEASURE- C. J. COOK MENTS; by E. 11. Moullin, M.A.; 487 Manager pages, cloth, li x 9 inches; 288 illustrations; RATES published by J. B. Lippincott Co., Phila- WITHOUT BATH delphia, Pa. 529OtoS2SO single The three years spent in revising and enlarging 53 °Oto$35 °double this intensely interesting work are but an indication of the thought, care, and sincerity of purpose WITH BATH which Mr. Moullin has given to his subject. $2? °to15 °°single The hook is written in the style of a laboratory 54° °to$7. °°double manual and, by virtue of its arrangement, is useful as a handbook or reference guide. To advanced students at universities and technical colleges, the GARAGE book will be a valuable addition to their libraries IN CONNECTION and text book collections; because it serves as a connecting link between theory, which is oftimes irksome and hard to correlate, and the reality of practical measurements. The electrical engineers, who have been working with commercial low frequencies, will find that the certainties of low -frequency practice must be discarded and a new conception of the foundation of I 9101! their faith brought forth in studying the phenomena [ _V1 : Mel[e 3 &] `.I of radio frequency. The work starts with the equations of the electro- magnetic field; not a full exposition, hurt the essential ideas with a well worded description passing "SOUTH OF THE then into circuit formulae covering Inductance, Capacity, and Resistance in various combinations MASON -DIXON LINE" of circuits and conditions. is but another way of saying The valve generator receives much attention and is nicely handled with the remaining pages more "Hosoitality" or less evenly apportioned to the following headings: "Measurements of Potential Difference and Cir- HOTEL LUDY cuits." Resistance, Capacity, Inductance, Antenna Characteristics, Intensity of Radiated Fields, and South Carolina Avenue at the Boardwalk a miscellaneous section which contains a few extremely interesting descriptions. The author brings Atlantic City's Newest Centrally Located Fireproof Hotel within two covers, logically and in gaol order. IS South of the Mason -Dixon Line the wide ramifications of this fast moving and vitally important field. Its RATES are as PLEASING as ifs hospitality C. E. D. $5 up Daily - American Plan - $30 up Weekly Information Bureau $2.50 up Daily - European Plan (Continued from page 40) Fireproof Garage Attached BAFFLE BOARD SIZES R. B. LUDY, M.D. (126) Mr. hasard May, East Springfield, Mass. (Q.) Is there available any ready reference, which will indicate the size of baffle recommended for various cut -o0 frequencies? (A.) This information appeared recently in the form of a graph which is reproduced in these col- umns (Fig. 0.126). It was developed by Mr. A. A. Chirardi of the Pilot Radio and Tube Company; and appeared in the spring 1931 issue of Radio De.rign. MAJESTIC "MODEL 70" (127) Mr. Alfred N. Bacon, New Dorp, S. I., N. V, (Q.) What can le the explanation for exces- sive hum and generally horrible noise in a "Model 70" Majestic receiver? I have tested all resistors BE sure to read the message on page 8 of this for change, all condensers for opens. shorts. at, capacity rating, and all voltages appear to I issue. It is an important announcement and tells standard. The reproducer diaphragm will n1! S as much as one- quarter inch. There do not seem all about the Supplements to the OFFICIAL RADIO to be any loose leads in the set and all the tuned circuits appear to lie in tune. Have had this ex- SERVICE MANUAL. perience with several of these receivers. 60 RADIO -CRAFT July, 1931

(A.) Loose connections are the usual explanation for this effect; check over the joints once again, using a soldering iron. Defective tubes can caust HOTEL CUMBERLAND the same effect or it may be due to loose variable condenser plates. Resistors and condensers will sometimes test okay but develop trouble in service. 54th Street and Broadway In this motel, changing an A.F. transformer has New York City been known to eliminate the fault. Check up the centering of the reproducer cone. 3 Minutes to Times Square It may be necessary to float the chassis in the cabinet; using rubber or cork for the insulation. In sonic instances, the trouble has been cleared by to tightening the adjusting screws of the trimmer Close Everywhere -but Removed leasers, and only backing them off slightly (this prevents the movable plates from being set too from the Noise and Clamor loose, thereby wobbling and causing the disturbance.) A modern fireproof hotel with every modern hotel convenience. List of Commercial Circuits Within walking distance of the- Published atres, shops and business sections. (Continued from patio 16) September, 1930 Colonial 31 and 32 D.C., 110 -volt D.C. Receivers DAILY RATES: Room and Bath, $2 and $3 per day (No. 25 Data Sheet), p. 144; Fada "Special" Model 265 -A and Loop Special Weekly Rates Fada "7" Set Model 475 -A (F -A.D. Andrea, Inc.), (No. 26 Data Sheet), p. 145; Under the Personal Management of Joseph Goulet U. S. Radio & Teks'. Corp. "Model 30" Auto- formerly of Hotel Woodstock, New York City motive Receiver, p. 149; Crosley "Buddy" and "Chum" Receivers, p. 164; FREE CATALOG FROM ANY RAILROAD DEPOT October, 1930 Atwater Kent "Model 40" Power Pack, p. 201; Majestic "7BP6" Power Pack (similar also to "7P6- 71'3," and "711P3 "), p. 201; Freshman Masterpiece" (early 5 -tube model), p. "AN ADDRESS OF DISTINCTION" 205; WELCOME to Kolster K 20, K 22, K 25, K 27 and K 37 6-tube Receivers (No. 27 Data Sheet), p. 206; NEW YORK and Columbia "Screen -Grid 8" Receiver (No, 28 Data Sheet), p. 207; tII ROTEL Radiola "18 D.C." Receiver, 110 -volt D.C. circuit, p. 209; eiNERNOR "Stenode" Crystal -Control Receiving Circuit, p. 211; (LINTON RCL "Models 5, 10 and 15" Public - Address Adapter (-nits, p. 218; Priess "Nine-in-Line" Models R ST. Aso 7r "AVE. and C Receivers, Exceptional 3I'r p. 224. opposite PE N NA. R.R. STATION November, 1930 in Every Detail Radiola- Victor R 80- Westinghouse WR5-Graybar 700 -General Electric 11 -31 A.C. Superhetero- THE finer character of TEE dynes (No. 29 Data Sheet), p. 268;

DRAKE accommodations, Grebe Super- Synchrophase - : \.C. Receiver Model foods and service is reflected 5K -4 (No, 30 Data Sheet), p. 269; in the continued patronage Brunswick Models '5 -14" and "5.21" Receivers, p. 272; seasoned travelers... and of Crosley "Model 54 -New Buddy" Midget Set, p. in the extra comfort the 1200 Rooms each 274; enjoys. Rates begin at Jackson -Bell "Model 62" Midget Set, guest with Bath, Servi - p. 275; $ .0 per day. Permanent Work -Rite Radio Corp. "Flexi- Unit," p. 275. Suites at Special Discounts. dor and Circulat- Lincoln Radio Corp. "Model 31" Screen -Grid Su- ing Ice Water. perheterodyne, p. 276; Radio Receptor 50 -watt "Powerizer Model PM' THE 245 Driver" and "Model P50W Power Amplifier," p. 289; DQAEF\ Stewart- Warner "Series 950" A.C. Screen -Grid HOTEL, Set, p. 290. Under Blackstone Management ROOM AND BATH 3s° UP December, 1930 Howard "Model SG -A" Screen -Grid Receiver (No. 31 Data Sheet), p. 332; All - American Mohawk "Model I)" Lyric Receiver (No. 32 Data Sheet), p. 333; Delco "l'olice" Short -Wave Receiver, p. 344; CLASSIFIED ADVERTISEMENTS Crosley "Models 5 -50" and "5 -75" Sets, p. 360; d Art each Advert i... insert, th, ,..-t of ten cents per word for Crosley "Model 52" Receiver, p. 360. each c,unt u word. Cash should accompany all classified adv e r t i'i Hie lit, tin It ss (,laced by a recugn i zed advertising agency. No less than January, 1931 ten words are accepted. Advertising for the August issue should be received not later Victor "Micro - Synchronous" Radio, Models "R -35," than June 7th. "R -39," and "RE -57" (No. 33 Data Sheet), p- 396; BUSINESS OPPORTUNITIES ELECTRICAL Silver- Marshall Superheterodyne, with "Model 36.t" Chassis and "32A" Power Pack (No. 34 ELECTRIC FUN! 300 stunts, 110 volts, $1.00. Data ARTIFICIAL MARBLE. Make it yourself. Beau- l- erring Sons. Campbell, Calif. Sheet), p. 397: tifully colored glossy tiles- no polishing, sums Supreme "Model 90" Set Analyzer, p. 425; unreal. Sawable and planeable, or hacksaw proof. FORMULAS Van Ilorne- Flewelling "Model I)" Tube Checker, Make floors, bases. inkstands, novelties. tabletops, MAKE AND SELL your own products. We will p- 426; garden furniture. Cement composition. fireproof, Pilot "Midget enamels wood. Write before opportunity furnish you any formulas. Write for our litera- Set," p. 406; cheap, Chemical 19R Park Place, New passes. Liberal astonishing samples with particu- ture. Institute, York. M. Y. lars 10c. John F. Pay-n, 945 Grande Vista Drive, $5,000 ANYONE PAW O Los Angeles, Calif. PERSONAL PROVES THAT THIS IS not the actual photo of myself BOOKS IF YOU want to get acquainted? Send for my showing my superb physique big (free) list of descriptions. Membership over iand how the Ross System has set of LaSalle Extension nereasea my own height to FOR SALE -Complete 30.601. Box 100 -AAA, Detroit, Michigan. 8 ft. 3 3 -9 Inches. Hundreds University's Banking Finance Books. Ayan, of Testimonials. Clients up 965 Freeman Street, New fork City. RADIO to 45 years old gain from 1 to e Inches In few weeks!! DETECTIVES SERVICE MEN. ATTENTION - Speakers rewound, magnetized. repaired, $2.00 to $2.75. Com- No Aaalianees -Ns Drugs -Ns Dieting. ROSS Pack Transformers rewound, SYSTEM NEVER FAILS. Fos Ton Dollars Com- DETECTIVES Earn Big Money. Excellent oppor- plete Power Service- pete. Conrineing Testimony repaired, resistors duplicated. and Particulars 5 tunity. Experience unnecessary. Particulars condenser blocks ants .stamps. "Allow time for return malls arrow Free. Write, George Wagner, 2190B Broadway, Guaranteed. Clark Brothers Radio Co., Albis, the Atlantic." D. MALCOLM ROSS, Height Specialist. New York. Iowa. Scarborough. England, (P. 0. Boa 15). July, 1931 RADIO -CRAFT 61

Federated Purchaser "Cathedral Tone" Melorad Midget Receiver, p. 406; Jesse French & Son Piano Co, "Model G, Junior" STATION H -O -M -E BROADCASTING! Midget Set, p. 407; Master Radio M fg. Co., Ltd., "Model 421" Midget MILLIONS OF LAUGHS WITH A Receiver, p. 407; fierce -. \iro, Inc. "De\Wald, Model AC-524" Midget Surprise your guests at parties and Set, p. 418; social gatherings with a new Gem Transformer Corp. of America, "Clarion, Jr." Midget Hand Mike which you can Midget Receiver, p. 408; use for broadcasting through your Render Division, Gray & I)anielson Mfg. Co., own radio. All you need to do is "Cameo Model 14" Midget, p. 408; Keller- Fuller Mfg. Co., Ltd., "Radiette Model 14F" press the button on the top of the Midget Receiver, p. 408; 5S ATtON Mike and the program is cut off or Northern Electric Model "R -50" Pc; -Tube Re- H-O-M-E diminished and your voice is heard ceiver (Resembling the "Everyman Four "), p. clearly -there is no interference. 420. When you have finished talking, just February, 1931 release the button and the regular Sparton "Model 301 E1i,asonne' A.C. Set, p. 459; program returns. \[ajestic "Models 50." "51," and "52" Midget and Low -Buy Superheteru,lynes (No. 35 Data Sheet), Any one can attach the Midget p. 462; Hand Mike in two minutes. No tools Kennedy "Model 82611" Combination Long- and are necessary. Complete instructions Short-Wave Receiver (No. 30 Data Sheet). p. enclosed with each Mike. Made of 463; white bronze, beautifully designed Silver - Marshall "Sargent- Raymeut 710" Receiver and Model "S.M. 675" l'ow'er Amplifier, p. 475; and chromium plated. Size over -all Moore Radio Laboratories Model '1)a-I.ite R'' 3% ", Price S7.50. Screen -Grid R.F. Ch:.: - :, p. 478; 6I are cordially invited to 'Left our \\-albert "Penetrola," p. 488; l'll at the R. .11, .1. Trade Shwa Knight "8/9 -\.C," Set, p. 488. I nniug June 8th, Stevens Hotel, Ch iraao. March, 1931 L.rlhfbit Booth . \'o, 12; Demonstration Room 1207 and 8.I, Stevens Hotel, l'hiteo "Screen -Grid l'In:" Receivers, Models 92, MIDGET HAND MIKE 95, 95E, 96, 96.\, 96E, 296 and 296 E (Phila- 'Ho t;I m is :tl.,, ui uawled for l'u bl,, delphia Storage Itattery Co.), (No. 37 1)ata Address Work such - Advertising Trucks. ESSENBEE KAHI( DEVICES CO., Sheet), p. 524; Golf Links, l'ale-. I )anct flails, Hotels, 732 3Iittltrr Street, Dept. K.C, Brunswick Model It -1S "Uni- Selector" 2 \oit Tube Schools und Stores. Ilace your dealer I Chicago. Illinois. tinti cheek or money $7.710 Type Radio Set (No. 38 Data Sheet I, p. 5 demonstrate the Midget Rand \like to you. order for 1f he cannot supply you, IEnclosedfor Gent Midget Hand \1i k,. Electrad, Inc., Loftin-White "Model C -2511" Direct. write direct to us +ts per the attached cool and mention the I Nume Coupled Audio Amplifier, p. 534; dealer's naine. Insuline Corp. "Companion" Portable I- Tube A.C. I Address Set, p. 535: 1 City Stat.'

I lammarlund "Hawk" 22 -vult Tube Short-Wave Re- ceiver, p. 541: "Aires ABC" Eliminator, p. 552. April, 1931 Erla Model 224 A.C. Screen -Grid Receiver, (Elec- trical Research Laboratories, Inc.), (No. 39 Data Sheet), p. 590 ensationally LOw 60 (American Bosch Magneto Corp.), S Itosch Model Prices

(No. 40 1 hita Sheet), p. 591; Supreme "Model 19" Single -Meter Tube Checker, p. 593; All- American Mohawk "Model II -94" Lyric 2 -Volt on all Radio Tubes -- Tube Receiver, p. 595; l'hilco "Model 30" 2-volt Tube Set, p. 596; Lincoln "Model t). C. 8" 2 -volt Tube Superhetero- DAY dyne, p. 597: 60 GUARANTEE l'ierce -.\iro "I ,e\Wald Model 1)C 632" I10 -volt D.C. Midget (2-volt tube) Set, p. 597; Pilot "Universal Super-Wasp" .\.C.- Operated Multi - ALL PACKED IN ATTRACTIVE THREE -COLOR BOXES Wave Receiver, p. 605; Ilayrad "Type 1811" Service Oscillator (The Radio 222 $ .70 201A $ .20 226 $ .25 280 $ .30 Products Co.), p. 614; Crudcv "\\'igit. Model, Model 48" and "Johnny 384 .50 171A - ...... 30 227 .30 210 1.00 Smoker," p. 619. 182 .50 112A ...... 30 224 .50 281 1.00 May, 1931 183 .50 200A .30 245 $ .30 250 1.00 Silvertouc Models "F." "FF " "(; " "if;' and "1" Radio Sets (Sears, Roebuck & Co. early bat- 2% off for full remittance with order minimum order $10 tery ;nid . \.(. receivers), (No. 41 Data Sheet), - 1, 65 20t CASH - BALANCE C. O. D. Radiuta ' "28" 4uperheter.slync and "11)4" Power Speaker (No. -12 Data Sheet), p. 053; "I. -32 ('Itradyne" Screen -grid. All- Wave Super- RADIO TUBE SURPLUS CO. heterodyne. Trawl Radio Co.). p. 066; "S \WS -9" Short-Wave (and long -waves Superhet- 31 Marshall Street Newark, N. J. erodyne (Wireless Egert Eugineeriug Co.), p. 663; làaliola "28" Circuit (without power connections), p. 670. Right Now!! June, 1931 Zenith Model 'l1E." p. 716; Send for Our C'rusley Model 120 ("Super-Sondo," "Super -Ron- deau." "Super -Administrator ") Senior Super- heterodyne ( I'liodyuatrnu l Chassis (No. 43 Data Sheet), 0. 72(1: \Westiughansc "Colo omaire" Models Wit-8 and NEWEST CATALOG \WR -8 -R (Remote Control) (Representative of R(-.\ -Victor Radiala Models R -80. R -82, R -$6; Largest Assortment and Biggest Bargains in Westing] se Models \VR -5, \WR -o, \\'R -6 -R, \WR -7. \\'R -7 -R: Orayb: r 700, 770, 900; (le- RADIO SETS AND PARTS eral Electric II -31, 11 -51, I1 -71). (No. 44 Data Sheet), p. 721: All Merchandise at Wholesale! ". \ir King" Soper Converter, p. 734; \tayulian "it" Eliminators (Models 609, 611, 612. S. HAMMER RADIO 614 and 615). p. 742; COMPANY Silver - Marshall Model: 37, 38 and 39 Midget 142 Liberty Street, N. Y. City Dept. R Hltchock 4 -1152 Superheterod. nes p. 759. NOTHING IN RADIO EVER APPROACHED THESE VALUES! SONORA! Known everywhere as QUALITY Radio. Now offered to you in LIMITED QUANTITY at Prices LESS than the AC- tual cost to manufacture. A ready market awaits your sale of these famous sets. RADIO CHASSIS WITH MATCHED These Sonora Chassis are of the very latest design and con- ELECTRO DYNAMIC struction- Screen Grid - 24 onor SPEAKER Push Pull Amplification. Total- CLEAR AS A BELL ly shielded. Battleship Con- struction, with oversized transformers and condensers assur- ing long, faithful performance. Chassis measures 21 in. long, 8 in. wide and 8 in. high. NOTE: Do not confuse this genuine Sonora built Radio chassis with similar type mod- LATEST MODELS els offered elsewhere. SCREEN GRID 4S's IN PUSH PULL SONORA Model A31 SONORA Model B31 7 TUBES -3 SCREEN GRIDS 8 TUBES -4 SCREEN GRIDS Uses: Uses: OUR OUR 29.50 26l e, 4-224, 1 -22 1 Net 3 -224, -227, PRICE PRICE 2 -245 & 1 -280 Tubes 2 -245 & 1 -280 Tubes Super Push Pull Power 245 and 250 Amplifiers CLEAR AS A BELL And "A-B-C' Power Supply SONORA CONCERT SONORA AUDITORIUM Power Amplifier Theatre Amplifier 2 STAGE 2 STAGE 245 Push Pull 250 Push Pull With "ABC" Supply With "ABC" Supply POWERFUL Enormous Volume QUALITY UP REPRODUCTION IS AS NEAR PERFECT AND Faithful Reproduction LIbE -LIKE AS POSSIBLE! ITS POSSIBILI'T'IES CAN BE SUMMED UP IN THREE WORDS: ABSOLUTELY DISTOR- Here is a truly fine amplifier affording volume galore with TIONLESS VOLUME! The full benefit of the 450 volts pro- astonishing faithfulness and realism. Constructed of the high- duced is obtained, using this as a PHONOGRAPH AMPLIFIER est quality parts, to give long life and the finest performance. -PUBLIC ADDRESS AMPLIFIER SYSTEM -RADIO TUNER PHONOGRAPH AND RADIO INPUT AMPLIFIER. Self -contained unit. Supplies all necessary A, B The Concert Power Amplifier supremely efficient for reproduc- and C power to its own tubes. Operation requires two type tion of phonograph records, radio programs and speeches. X250 power tubes, one Y227 A.C. tube, and two type X281 Operation requires: Two x 245 Power Tubes, one Y227 AC rectifier tubes. tube, and one X2'Ù Rectifier tube. Regular OUR Regular OUR Value PRICE Value PRICE 50 5.00 2Z5 $14 5.00 Net Genuine T U N G - S O L ISN'T THIS WHAT YOU'VE SONORA ABC REPLACEMENT BEEN WANTING? HANG -UP At Last A Real Noise and Hum POWER TRANSFORMER CONDENSER SECTIONS Eliminator For Models A -31 and B -31 FOR For -2224 is GENERAL REPAIR 2- 245 and 1 -2N0 AND POWER -PACK Tubes. For Models WORK A -31 and B -31, 6% Every Service Man in. wide, 6% in. should always have on long. 4 in. tall. hand several units of Also Furnished for each capacity a n d 25 Cycle lurrcnt voltage to meet every for $5.50. emergency! No More Working Voltage Our Hum -mi OUR PRICE 3.75 Capacity D. C. Price 2 Mfd. 500 V. $0.35 CUT DOWN USELESS SERVICE 1 300 V. .40 Mfd. CALLS: You will find this article to be 1 450 V. .45 Mfd. a money- saver, as well as a money- KO D E L STEP -DOWN 1 Mfd. 500 V. .50 .60 maker, for you. The majority of your 1 Mfd. 600 V. TRANSFORMERS .70 service -calls are due to line -noises. How 1 Mfd. 700 V. much time and material has been wasted HEAVY DUTY 1 Mfd. 800 V. .80 by your Service -Department making Primary 110 -120 Volts, 1 Mfd. 1000 V. .90 special apparatus to cut down line - 50 -60 Cycles AC current. 2 Mfd. 300 V. .60 installation of the 2 Mfd. 400 V. .70 noises? Now a simple Output 14 Volts AC al "MAXIM FILTERAD" and your troubles 234 Amp Suitable for A 2 Mfd. 500 V. .80 on all currents -Auto- 2 Mfd. 600 V. .90 are over. Works Eliminators, Dynamic 1.00 matic-Requires no adjustments -Take Speakers, Trickle Char- 2 Mfd. 700 V. advantage of this off,r now! 2 Mid. 800 V. 1.10 gers, Bell Ringing and 2 Mfd. 1000 V. 1.25 Heavy Duty Model Toy Transformers. 3 Mfd. 300 V. .85 C 3 Mfd. 400 V. .95 OUR PRICE Net 500 V. 1.05 OUR PRICE 75c 3 Mid. 2.65 3 Mfd. 600 V. 1.15 Net All otters are F.O.B. New York, and subject to prior sale. Terms: A deposit of 20% is required with every order. Balance may be paid on delivery. Or, deduct 2% if full DO NOT WRITE FOR CATALOG! amount is sent with order. G R E N P A R K CO., Dept. WC 245 Greenwich Street, New York, N.Y. Famous Model "G" Gordon R. C. A. Radiola New Type Elkon Dry Phono -Motor and Turntable Magnetic Chassis Disc Rectifier First time at this price. Ruggedly constructed Will stand up to 600 volts without Standard on "A" Elim- output trans- throughout. Spanish felt gears assure silence. distortion. Contains inators for Majestic, Equipped with automamtic atop control. In- former. Used in 100B, and 103 9 Mayolian, Webster, El- duction type, no brushes. Easy to install- speakers. Outside diameter in.; depth over all 4,/,3 in. Ideal for any exceptionally quick starting torque. For 110 kon, Bernard, Fada. radio installation. Complete with 5 Knapp, Sentinel, Metro, volt 60 cycle alternating current. Proven de- ft. radio cord. pendability has made this New Gordon Electric G en era I Instrument, OUR PRICE Phonograph Motor and Turntable the accepted .. $2.95 Philco (Elkon equipped) standard of ex- and also on Elkon 3 cellence for the R. C. A. Loudspeaker 103 induatry. amp., and Briggs & OUR PRICE First time at A beautiful speaker, superb in its Stratton chargers. faith ful reproduction. Molded t h i s price. frame and pedestal resemble hand List $7.00 $3.45 Make a nice carved oak. Mechanism concealed profit and build by attractive tapestry. List $30.00 Baldwin Rival Unit good will with OUR (Genuine R.C.A.) er cry one. This Nathaniel Baldwin unit is l'RICE $9.95 List $18.00 one of the finest. For phono- OUR PRICE $4.25 graph, automobile and portable Farrand Dynamic Chassis radio outfits. We offer this fam- Atwater -Kent ous unit now at a sensationally Famed for its simplicity reduced price. and reliability. Easily Condenser & Filter Block installed in all types of For Model 37 and 38 Sets OUR PRICE ... 65c radio or phonograph Ideal filtering system for ANY consoles. Tonal range make A. C. set using 171 -A VICTOR ABC and fidelity superior to tube. Contains proper chokes any other reproducing and high voltage condensers. Power Transformer unit in general use. Flexible wire colored leads same as Dimension: Height 9 original. For use with 6 -226, inches, width 8vl inches, HOOK -UP 2 -245, 1 -227 and 1 -280 DI R PRICE Green wire to 280, black to P(C depth 7 inches. For tube s. Magnetically R.F. plate, yellow to Power shielded hum. A.C. current. $5.95 Tube plate. white to first preventing audio by -pass. white to C.T. Can safely be overload- of 226 resistance, ed High voltages, Condenser Block red to detector OUR 400 volts at 150 mila uu for plate. Wire from PRICE $3.60 either side of center Majestic can to ground. tap. Extra large case especially designed to "B" Eliminator Kolster K -6 Speaker prevent overheating. Replacement f o r defective Magnetic type rune speaker. Can Be Used For Any Power Amplifier blocks Remarkable tone quality: vol- in "B" Eliminators - ume to spare. Beautifully carved. Using 245 Tubes identical in electrical character- fine wall cabinet. Equipped wRh highly sensitive oversize Size: 41/2 x 5 re 5tr[a inches. istics and outside dimensions. 9 and 14 (5 volts). OUR PRICE magnet and driving unit. Faith No. 1- Center tap of Can also be used in any make ful reproduction from the faint No. 2 and 4 -21/2 Volts. to fullest rolu,n, of .t ed whisper No. 5 and 7 -1 in. V. High amp. (226). "B" Eliminator as well as most Iras band. 3 List $20.00 No. and 6- Primary 1110V. input). $2.75 power packs No. 8-Center tap of 12 and 17 (2t%j V.) No. 9 PRICEUR + and l4 -5 Volta (280). 95 No. 10 and 15 -High voltage for B supply. No. 16- Center tap of above. Gordon Acme 4 Pick -Up AIR -KING No. 12 and 17 -2V in. volts high amp. (224). with Volume Control Superheterodyne Converter OUR PRICE ...... $2.75 The greatest converter Genuine Bakelite arm with ever built. FREE Catalog -means money to you beautiful natural wood fin- Brings in European station. clear as a hell. Convert._ These are only a few samples of the values be ish will not show wear as any get Into a short ware be found in our catalog. It is full of items on will plated metal. Faith- receiver. Employs 3 which sou can make front :11';, to 300'; profit. tubes; from 20 to And the best of them is, they are sound, well fully reproduces the entire 115 meters. ('mil salt, h all wave length. known, trademarked articles you can depend musical range. single dial control. u pon. ',Loy cape. ity. no squeal. f OUR PRICE I.,. built -In filament Send 20'; with the order and articles will be - $4.50 n.foruwr to heat the shipped C.O.D. Order any of the above ar- All you need ticles direct from this page. And be sure to receivereceiver is a ask for the catalog. It means money to you! a necessity to the t I.C.A. Test Leads- i tare R. wllage front dealer , to Igo von:. voltage OUR PRICE Ilnu-pa ed for List lug set, and tracing short.,ort not critical' no moles. RADIO CIRCULAR CO. opens and other common defects. Easily at Lion of the remise,. ladled to te-ting meter or electrical apparel u,. 7x10x5 fn. Weight 225 Varick St. New York City 40C I hi. $14.70 ORDER DIRECT... from this page! TEAR IT OUT NOW! 1 RADIO CIRCULAR CO..225 Varick Street. New York City

Enclosed find 5 This is 20;., of item, listed below, 1 will pay balance upon receipt of merehandi RADIO CIRCULAR CO. 225 Varick Street. New York City Pleae send me your catalog of radio bargain. I can o made a profit o u I understand this obligate, me in no way.

Nome

Address Alto pleas, send catalog.fili...... _...u..uuJ City Sfate STOP SHOPPING ! ! HERE'S a NEW plan, which save-e- sou 111011C). SI)p shopping X011 the late.' and loss c-t prices up to the time this ad is printed. the lowest prices are right on this page. Yee, lower than in We %ateh our competitors and do not allow anyone to undersell our own catalog. Why? Because no house can get out a new cata- us. We meet ANY price on NEW merchandise. Order direct from log every month. but by advertising in this magazine we can bring this page and save money. 11th ° - satisfaction on seen' transaction. Dry Electrolytic Condensers Utah Dynamic A.C. Power NEW READRITEAnalyzer Speaker -Model 33A Mount In any position! Guaran- 110.vett. 60 -ryete .Ie, n meter teed never to blow mitt Remark - analyzer has selector snitch for checking all of rirenits Ivy A.C. light socket compact and very inexpensive. parts ruin supply field ally Cngnteet l rag to the set snkets. Selection for for permitting generous use of filter- testing voltages of grid. excitation w i t h plate, cathode and screen- Westinghouse dry ing systems. The greater the mid. grid dune quickly and accurately. Plate eurr,nt rapacity employed, the less A.C. rectifier. fiiallleltt rolli. title 11111 lamer simply volts ale 9% hunt 500 volt peak rating. 9 lu. high. remain.. measured. Grid suing test for tulles used Just in. wide. 7% in. - 215 power Ideal for all 171A push one button for sereml -grid amt other button d e e p, Speaker parks -use two of each rapacity for other tubes. Makes I sling of all UTU tubes conies packed in desired for 250 power packs (1,000 simple and thorough. 145-volt grid battery' Is Tie den c r a t e . cult peak thereby assured). Turn ishetl. Battery is used fur grid test and Weight 19 lbs. It YOU R continuity testing of trausfottners, chokes. etc. Is one of the No. Mfd. Diameter Length PRICE Capacity and resistance charts fuml.lted almu- must powerful as well as best re- 1801 1 In. 2.. hl. $0.27 Ltg else of Instnuneuts for testing candengem, 't producers in the marker. 9- Ino 'b cone. 1802 2 1 in. 2'w in. .44 also pleasuring resistances up to 100.000 ,alums. in. .83 List Price 350.00. 1804 4 115 In "l' Eight scale readings Of nu furs may be used sep- $7.45 8 In. 41.5 in. 1.20 No. 1506-YOUR SPECIAL PRICE 1808 l'. pith the terminals provided. Seale 10 'l In. 411 in. 2.10 arately jack 1816 -G00 volts. 0 -10 -110. 3 In. 2.70 readings are 0.60 -300 D.C. 1824 21 in. 'l's filament voltages are accuratelY 1832 32 3 In 4lí In. 3.30 700 A.C. et Its and 0.20 -1'211 wi iii a nlpetti. A.C. and D.C. Olt one r a4e with leatherette covering. Attractive. i iii pact. ! ! ! 1854 54 3 is 4!3 in. 4.73 measured the meter. Strom. NEW NEW Slzo 1,' ,X3!iXS Inches. Shipping weight 13 ohs. Litt Price $25.00. Qs t 7 .70 NO. 700- READRITE ANALYZER. YOUR PRICE $ T Superheterodyne S -W Converter THORDARSON At last a short wave Dayton Adapter Earl Power Transformers concer'ter tlla[ - Flewelling- SW rmts any hrnalleam "245" Power Transformer This uvnderful lost ru- revamping te set Into a superhete- Supplies All on Is tu anY Make money A Miniature Power Plant - the und battery set. This rodyne hart ware re- 80 Watts A.. radio set by put- ceiver. Employs three ABC Voltages - ting Into tube socket in power transformer used In Earl Model 22 receiv- 227 tubes anti r In addition tasuP- Waal' 44 the tube iw Melt er s rl.pl les "A. "'11" (runt 20 to 113 r plying a full 230 mu -i hr a p'pe '27. or No -In to the platen and '1" potentials for: tern. plug its 'beater- tuber the plug is n - 50 volta to the two _ (or screen- Coil ...itch and which Is an the end of '26's. corer all wave!. r : ids hf two Iype its 2.ft. eablr; then put grid 21'sthree í. two ';1.1's and one 'SO Single dial '45 tubes In puah- MIN' into tube - socket of re('t filer: total current no 1.1y eat. Irv.. 1 ell. this trans- adaitel. Remove sonal of vultago Eglleats. This want I former in a Y ber truer broad cast set and output high- winding at 1111X111111111 ter has built -in fila- tisad tu light the conneiI to antenna post 200 ment transformer t lamrtt. of seven on adapter. Special plug - output (about volts) le so ma. Iligh-s 41 huge se ndary. filament heat the three 227',. eight 2.5.volt `n coil Na,. 1 cuves a winding for '27's and for ';IA's( are +'1 ter - All rot need to obtain from y u ', :lamentn l it lies; wavelength 11 (rand of 3 161 long a positive 11 voltage anywhere from and by connecting No. meters: colt tapped. Sise. 3.1 x X 2 inches. Ito 29 meters; coil 2. 27.211 wiring direct lues. Shipping 1.0 volts. Voltage is not critical: n in series Iwo of Na. :t. 17,1 nab r-. fluai' in nil induct- leads and full weight e ohs. ninon of the run it.. So simple 11 a lo a all: the three 2.1vott ant es mono with the adapt,. 5!¢X713 X4" ListPelee. 37.50. operate it. Size x 10 . Inrhe -. Phonon enalla- high, overall. Ship. weight 4 lbs. No. 1410 Transformer (with- -Earl $1 73 Ships I , Ì1n7 L)st Price $25.00. ea It is possible out brackets). YOUR PRICE.... 1 No. 1814 -Super Converter (less 5.93 to light 5 -volt fil- No. 1613 Dayton Flewelling Short -Wave $1 aments too. Five - tubes). YOUR PRICE 11 e7 Adapter. List Prive. $15.00. ,,f$ No. 1411 -Earl Transformer. the 9ó SI 2 Y. 93 measles: --5 V.. .tnlp.: `2-310 YOUR PRICE (without tube).... $st same but with mounting brackets.. . T. S3 -2'o V., 3 .Une. rent. T. _ . r.. I0Si, .in'.n.: r., Amp. High -Voltage Condenser Units T. lust the power transformer for build- Speaker Columbia Phonograph Pick -Up Ws ruuncondi onall theycon- er,' Baldwin D.C. Dynamic up a high- publie address amplifier .i bi .uns m a Idltlun to An extort Iona sly tine are alto. these .Tuley to use a screen -grid A.F. amplifier to boost the fatuous Baldwin line phonograph are Ideal for general re- the output et a microphone er phonograph d Never before uh tit Pairposee and can with Issu -mgrs of -Peakers. ',Mk-up: following this has a. speaker of mill tone arm. 'lade for he installed In any new rash -pull amplification rnnslsting of two '27's uall size olTered such Holster tw the fa- Inw,.r- plank. All or tinned are unYa I the first stage and two 43's in the second. lldelìn' of response. ll in. mous COLUMBIA Simla lengths of tinned "push-push-back" -back" stiri I:.. m m of has bakelite panel on transformer diaphrlgul, 25ui. alois field v organ's:O lt. I'l'k- v are mounted all tat n. It outperforms 600 VOLTS 800 VOLTS mi die: w itb 1"3-ohm voice - tip seines hark over ANY similar transformer. Many S r ire Men Cat. Mid. Your I Cat. Mid. Your ull. Fer tti s. a ass 1r.,'. arm ovine changing !.Is oie] Iransform, ut t hand for No. Capee. Price I No Capar. Price ,. line u slly field m11 reseed. (u.Hon sinn Presents jarring of Lu11is In hundreds of makes s'ils as aller choke in irk -up head. Handsome bnrnze finish. :Us 1702 %2 $0.25 I 1706 t $0.40 11 -120 vous. 10.60 cycles. I 2 .70 stn ply cive °nt. SFI19id had clll ideal pick -up for home, theatre or auditor- 1703 I .30 1707 1 x 31_ In. Shipping Shilming 1704 2 .40 1708 4 1.05 'coupling n weight. lÓ ium. Brand new inert handle List Price, $15.00. 1705 4 .60 I lbs. List Price. 312.00. cu lei Or - List Price, 319.75. Vo. 1450- Thordarson Power Trans- Phonograph $9.85 No. 1513 -Baldwin D.C. Dynamic No. 2304-Columbia $4,58 former. YOUR PRICE eS $4.73 PRICE Speaker. YOUR PRICE PickUp. YOUR Pacent "250" Amplifier Television Receiving Lamps Power Auditorium 'Huse Television Receiving Tubes Edition One of the have been designed ta astid high FREE! New Summer 'I of ;;really en- spare charges. and at the sante IS lni.at our Most Pow- I has time [online the light to the ii ..rI It St do SI itvllE 'l'ItE.vTISE erful Super ta the ere -s. If you liked the \\9n- useful portion of the tathl,le Power Am- Brilliant Tight spots usually found ter Issue. yon trill Ilk, this to e a Inmdred- un the cathode and r sell by Odd. It cuntahis one 73 haok -ups cir- plifiers ever 310 high frequency r uner nt vibrations cuit diagram, and SUMP 8v illustrations. EVER made. have been entirely g c llntinalwll by POSITIVELY THE GREATEST BOOK a !medal Ienrrss whit h tali loues PUT OUT BY ANYONE. -tngoag the new ".puttering' under the 1Influence RADIO matters listed are: of the discharge. Rigid .ttpporl VACUUM TUBE TREATISE, with many il- ..f the elements Is obtained by the u of SERVICE lushatiuns: full rg. Varunlrl Tube Average -I11rdv glass rods. I's lu. x :{f In. sawila rhuarlen u i. l'hart: How to 'rake l'are of CONTAINS 2 STAGES SUPER POWER athmle 1 in. square. ShiPloing weight. 15 Ifa, Your Ides: iluw to Cannent Phonograph A.F. AMPLIFICATION I -ins Tune Ona I ily of Old No. 775 -Television Lamp. List TREATISE 3'itk -ups: the Thi. fa wons anti lilies I: ..In. $1.9$ St Add il I.. ts: Cent. ..tine i.nal Lod Slackers; rad output Price, $4.00. YOUR PRICE 1 all fully ill ustrautl alti diagrams. umntromrls phonograph pick -tip info .1 Old Sets; Other article.; Modernizing Radio mission line or into the I /Ana Se- RADIO BARGAIN How to Convert Battery to Power Sets; foil -had aiilti nm!.t . A.C. Short Wave Converter lection of Tubes: Posa. Poll-Amplifiers: Re- CATALOG Attach - The thrill of tuning In pinriog Anatol Trmufonnm -: l'boma . a.rr S,,..0401- R.0.o "ru..v Raw.0e.cres power Itert stare, is your,. mmHg; lino to Ctsaose Transformers: Power Trans - ' n'anse you can c n- \-ultage Dividers: wa n a'reuf clot tot m,

Replace- a onnot abort -ware RADIO fonurs: Sele,h log and Installing take= are of Ih.. Ihls Sets: Filter Cundrn- nnrerte r to our nt l'arli In ItaJlo The nntlIsttuted pro. TRADING CO. Whalriug Eilmnuntnrs. enough for four small Alm rte .r oadaast receiver. t no 2SWEST BROADWAY matt, what type re- WRITE TODAY. Enclose 2 cents for post- NEW YORK CITY by return mail. I.n r Ier yam have. Tunes age. Treatise sent In to 100 ine- t erv, using only two bud .025 selIs. plug - In rolls. Coils. 6 31ONTHS GUARANTEED NEONTRON TUBES Ideal for theatres seating approximately 3,000 already wound, are schools. hasp. nPpllmf tvl!n alti lit. Concerter has Loin -In GT-.\R.'INTEE paoOta. dance halls, Iectul.-. Solt a 6 MONTHS FREE RF.PI..MEME.NT tals, auditoriums. outdoor gatherings, etc.. A langent tra tsfurmer to A I tubes are carefully heat three 227's. All BASIS. PROVIDING TI'l1E LIGHTS! is at all you need obtain fri no sol invfnre mad carefully parsed. Du not etc. The gigantic power times r receiver is er it's'cd sldpment. that matter. It can be tnsil ire "R" vrillage, anything from 45 to -. QUALITY tubes with aril other' "low within control -for mdu -e the II It1II used In any home. as the volume can be ISO volts. Voltage tat cril irai. No moles- sal is au '' Onnes- our low pries are possible because we do tation of the receiver No tr1.ky regenera- regulated down to hiss, V01.t'S1E l,n- loess' A PHONOGRAPH aAMPLIFIER- PUBLIC turncontrol, only a Angle. slnnmh- Operaling ADDRESS AMPLIFIER SYSTEM. ETC. Hal to manipulate. Na -weals. no grunt- NEW Choi. - e of I Choice (larice Moth' Choice I . no capnrlty. All pails for 3-taille 1'hnir r I ('Moil 220 1 112.5 21: I wavy converter. in. hiding 1 idol, llr 1]e ivtis I 199X 's0 210 filament Iran-former ire 250 231 I 217 171A I r. 1\ 1"0 171 Lad Prue. $90.00. rad pictorial do;,latti. Ships m. ' 211 \ 321 I No. 1925 Parent Model 250 Power $1 List Price 320.00. 1 Ile -s In bes . Your Price 11 ea. . 1.50 ea. Amplifier 410 : I 1.58 ea. 1.08 No. 1617 -YOUR PRICE. $9.45 63c ea. . 69c ea. 79c ea. I101'SE AND ORDER FROM THIS PAGE. You will find special WE ARE A WHOI,ESAI.Ii CAN- time in this magazine. Get ORDERS FOR LESS THAN Co. Prices from time to our NOT ACCEPT $3.00. Radio Trading big FREE catalog for the greatest Radio Bargains. If C. O. D. shipment is desired, please remit 20% remittance. which must accompany all orders. 23 West Broadway Should you wish goods shipped by parcel poet, be sure include sufficient extra remittance for same. If full cash accompanies order, deduct 2 °o discount. to Send money order -certified check -l'. S. stamps. New York, N. Y. Any excess will be refunded. Announcement! . OFFICIAL RADIO SERVICE MEN'S ASSOCIATION - - EVER since the appearance of the com- The following firms are co- operating with us: mercial radio broadcast receiver as a household necessity, the Radio Service GRIGSBY -GRUNOW CO (Majestic), CHICAGO Man has been an essential factor in the STROMBERG- radio trade; and, as the complexity of electrical CARLSON TELEPHONE MFG. and mechanical design in receivers increases, an CO., ROCHESTER, N. Y. ever -higher standard of qualifications in the CROSLEY RADIO CORP., CINCINNATI, OHIO Service Man becomes necessary. COLIN B. KENNEDY CORP., SOUTH BEND, The necessity, also, of a strong association of IND. the technically -qualified radio Service Men of the country is forcing itself upon all who are familiar The schools who have consented to act as an with radio trade problems; and their repeated examination board are: urgings that such an association must be formed International Correspondence has led us to undertake the work of its Schools, Scranton, organization. Penna.; Mr. D. E. Carpenter, Dean. RCA Institutes, Inc., New York, N. Y.; Mr. R. This is the fundamental purpose of the L. Duncan, President. OFFICIAL RADIO SERVICE MEN'S ASSOCIA- TION, which is not a money -making institution, East Bay Radio Institute, Oakland, Calif.: Mr. or organized for private profit; to unite, as a T. T. Tonnehilt, Director. group with strong common interests, all well - Radio qualified Radio Service Men; Training Association of America, Chicago, to make It readily Ill.; Mr. A. G. Mohaupt, possible for them to obtain the technical informa- President. tion required by them in keeping up with the School of Engineering of Milwaukee, Milwaukee, demands of their profession; and, above all, to Wisc.; Mr. W. Werwath, President. give them a recognized standing in that profession, and acknowledged as such by radio manu- Rider -Goil Radio School, New York, N. Y.; Mr. facturers, distributors and dealers. John F. Rider, Director. To give Service Men such a standing, it is Radio College of Canada, Toronto, Canada; Mr. obviously necessary that they must prove them- J. C. Wilson, President. selves entitled to it; any Service Man who can pass the examination necessary to demonstrate Radio Division, Coyne Electrical School, Chicago, his qualifications will be elected as a member Ill.; Mr. H. C. Lewis, President and a card will be issued to him under the seal of this Association, which will attest his ability We shall not attempt to grade the members into and prove his identity. different classes. A candidate will be adjudged as either passing or not passing. If the school The terms of the examination have been drawn examining the papers passes the prospective mem- up in cooperation with a group of the best -known ber as satisfactory, we shall issue to him an radio manufacturers, as well as the foremost Identification card with radio educational institutions. his photograph. If the candidate does not pass this examination the first time, he may apply for another examination three or six months later. There is absolutely no cost attached to any service rendered by the Association to its mem- oers, no dues, no contributions. If you wish to become a member, just fill out the coupon below and mail it to us. We will send you all the papers necessary to become a member.

O. R. S. M. A., cio RADIO CRAFT, 98 Park Place, New York, N. Y. I wish to become a member of your Association. Please ail me the examination papers and application blanks.

Naine

Address Town... State. i Pilot Achieves Radio's Greatest Sensation ! ,A-e/ 631/zr /iC of did toG

PILOT C N 1 VE RSA L= RECEIVER.

Partly Complete embled "Universal" "t7 nivertta)' F a c t o r y ..for the Man assembledlaboratory and who likes W- wal- "roll his own ". tested, in With walnut nut cabinet. cabinet. hss Less tubas and -tubes and speaker. speaker. 9950

circuit . wonderful wave band changing switch. sensitive and-selective Pilot's plus Screen Grid incorporated in the new Universal SuperWasp. Screen Grid TRF amplifier . . First Audio Stage Two revolutionizes the short wave art. No longer Detector 227 output stage . . . Atations need numerous coils be changed to cover the 2l5s in push-pull on dial . . . Regen- .various wave bands. No longer need dial set. can be logged permanently does not alter tuning . Pro- zings change each time the saute distant stations eration control Phonograph Pick -up . Earphone are tuned in.. You can log permanently all the vision for . Illuminated Dials stations you can get throughout the world. you Jack on Front Panel . . . Walnut Cabinet . . . Most ad. tune from the short waves to the high ship handsome can yet used for short wave waves without removing your hand from the vanced construction work . . . In kit forni for easy h assembly; single control knob. no drilling or cutting. all parts fully prepared. Universal Features Revolutionizing t the Short Wave Art Complete coverage all wave hands from 15 to NOTICE TO "HAMS ": Pilot will continue 'building changing. Complete the original Super -Wsp in kit form for -licensed 650 meters without coil amateurs and others who want to spread the tuning A.C. operated chassis in cabinet. (Also avail. on their pet wave bands and add their own udiu models. able in battery model . . . All Metal Chassis features. A.C. and battery

PILOT RADIO & TUBE CO IF I'., Lawrence, = ass. 1278 Mlissiou Street Chicago: 234 S. Wells St. New fork: 525 Broadway San Francisco: D : O 1 N ' l ' R I E S O F T H E R' O R L O F F I C E S I N P R I N C I P A I. t