WILLIS KINGSLEY WING Editor HOWARD E. RHODES Technical Editor EDGAR H. RADIO S FELIX Contributing Editor
BROADCAST VOL. XVI. NO. 6 ENGINEERING THE LABORATORY SERVICING
Contents for April, 1930 . . . among other things
Review W. K. W. 309 f\T Elmer Brown, who writes in this issue about air- Industrial Changes Problems ^\. craft radio developments since 1929, has been with The News Parade Voice in the Wilderness the RCA as an first at Van Cortlandt Automobile Radio The Pentode Again engineer, Park, Licenses New Models and a Trend New York, and now at Camdcn where he specializes Radio on Trains in competitive receivers, special receivers and equip- An Automatic Record Changer - - - - Thomas E. Piazze 310 ment. He has been with Magnavox, the U. S. Navy, and several West Coast distributors. Jesse Marsten Book Review ------Edgar H. Felix 312 admits that just thirteen years ago, he took his first Radio Law by W. Jefferson Davis commercial job in radio at the old Marconi plant at Measurements of High-Frequency Response - Jesse Marsten 313 Aldene, N. J. "Thanks to the U. S. Navy and the work was Tube Manufacturing Equipment in the Ken-Rad Factory, etc. 315 Signal Corps," says Marsten, "enough pro- vided to give us the experience that Mr. Wegeant, The March of Radio ----- An Editorial 316 Interpretation then the chief engineer, promised Carl Dreher and me Radio The of the Pentode Misleading Advertising Coining as compensation for accepting $10 a week. With the Broadcasting Achievement High Power t> City Areas formation of the RCA out of the remains of the Mar- Characteristics of Television - - - C. H. W. Nason 318 Signals coni Company, I joined Dr. Goldsmith's research staff Automobile Receiver Design ----- Robert S. Kruse 320 at C.C.N.Y. This staff was the nucleus of the RCA Technical and Test Department." For the past three High-Frequency Measuring Equipment - H. D. Oakley 324 years Mr. Marsten has been chief engineer of Freeil- - Measurements on Band-Pass Filter Circuits W. T. Cocking 326 Eisemann. During the last eight years C. H. W. Nason - - - has been with Federal and Chas. Freshman The Investor Looks at Radio - - Berkeley A. Cater 329 Telephone Companies in engineering work and has also done some Aircraft Radio - - - Elmer L. Brown 330 Development consulting. He is at present developing television trans- Strays from the Laboratory - Technical Shorts 333 mitter systems and audio-frequency amplifiers for Jen- Sun Spots and Radio A Correction kins. His chief claim to fame is his operation of amateur British Heater Tubes Pentode Articles station SYK and that he was one of the last of the Measuring Percentage Modulation Baron Manfred von Ardenne 334 amateur fraternity to lay down the reactionary banner of "The Spark Forever." Thomas E. Piazze was born in Automatic Volume Control - - - - - A. C. Matthews, Jr. 336 Arequipa, Peru, and came to this country in 1926. He - - - - - "Radio Broadcast's" Engineering Review Sheets 337 is intensely interested in development of mechanical Factors Governing Amplification Calculating Amplification of Pen- devices and for the past eighteen months has been tode Receivers in the mechanical department of the Technidyne Corp. Profesionally Speaking ------339 1930 and Service New Tubes The Balkeil Radio Company, of North Chicago, The Serviceman's Corner ------340 was never in bankruptcy we have been informed R. L. now vice of the Technique of Servicing An SOS to Servicemen by Eglaston, president company. A Hum Filter Two Simple Oscillators It was incorrectly stated on page 251 of our March is- Servicing the Radiola A Legal Question sue that Balkeit was involved in a bankruptcy action. Data on Crosley Sets More "Dope" on Noise This report reached us from a source which we "Radio Broadcast's" Set Data Sheets - 344, 346, 348 believed to be correct and was printed in good faith. We Bremer Tully Models S-81, S-82 Grebe Super-Synchrophase SK-4 greatly regret this occurrence and offer our sincere The Balkeit Model C The Kennedy Chassis No. 10 apologies to the Balkeit Company and its dealers. News of the Radio Industry ------.350 Set Data Sheet No. 36 in our January issue showing a Tube Makers Defend the Pen- News of the Manufacturers Fada receiver indicated a 171/v tube in the first a.f. tode Matters Legal stage whereas a 227 type is the tube Personal Notes In the Tube Field actually employed. Recently Issued Patents Remote-Control Patents /7T For coming issues we can forecast, in addition to all In the Radio Marketplace - - - Offerings of Manufacturers 354 ^\ our regular features, the following: an article by Radio Broadcast Laboratory Information Sheets W. R. G. Baker, chief engineer of Radio-Victor, on Howard E. Rhodes 356, 358, 360 engineering personnel problems; R. S. Kruse describes No. 337. Measuring Resistance No. 341. Reflection of Sound "R39," a new insulating material; H. D. Oakley, an No. 338. of Distortion No. 342. Grid Current in Tubes Types attenuator for the signal generator; R. C. Hitchcock No. 339. Detection Characteris- No. 343. Power and its Speech for tics Measurement on design data output transformers; Jesse Marsten No. 340. Calculating Detector No. 344. Speech Power and its on measurements of antenna-coupling systems in broad- Measurement Output cast receivers; Baron von Ardenne on a system for tube characteristics The contents of this magazine are indexed in The Readers' Guide measuring vacuum using the to Periodical Literature, which is on file at all public libraries cathode-ray tube.
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DOUBLEDAY, DORAN & COMPANY, INC., Garden City, New York MAGAZINES
COUNTRY LIFE WORLD'S WORK . . THE AMERICAN HOME . . RADIO BROADCAST . . SHORT STORIES . LE PETIT JOURNAL . . EL Eco WEST
BOOK SHOPS (Books of all Publishers) . . . NEW YORK: OFFICES . . . GARDEN CITY, N. Y. NEW YORK: 244 MADISON AVENUE. BOSTON: PARK SQUARE BUILDING. CHICAGO: PEOPLES GAS BUILDING. SANTA BARBARA, CAL. LONDON: WM. HEINEMANN, LTD. TORONTO: DOUBLEDAY, DOHAN & GUNDY. LTD. OFFICERS . . . F. N. DOUBLEDAY, Chairman of the Board; NELSON DOUBLEDAY, President; GEORGE H. DOHAN, Vice-President; RUSSELL DOUBLEDAY, Secretary; JOHN J. HESSIAN, Treasurer; LILLIAN A. COMSTOCK, Ass'l Secretary; L. J. McNAUGHTON, Ass't Treasurer 306 RADIO BROADCAST FOR APRIL ^INDUSTRIAL CHANGES Colonial SOME OF the events in the ^ VOICE IN THE WILDERNESS Out of merges with Valley Appliance, of Roch- world of radio in recent the millions of good and earnest words ester, combining, it is said, "the best fea- weeks may have escaped expended at the Cleveland convention tures of each" from sales down through you. A few of the more of the National Federation of Radio engineering. Fulton Cutting is chairman important, to our way Associations came a resolution to enlist of the Board, I. G. Maloff, chief engin- of thinking, are presented the Association actively in the case of eer, and W. S. Symington, president. on this page. better broadcasting. Says the resolution, Magnavox reorganized as a Delaware in part: "... Good broadcasting is the corporation to facilitate, it is darkly by United Motors Service which has 3000 foundation of the radio industry and hinted, a merger. Erla, of Chicago, is authorized service stations and 27 "con- should have our support on all situations of that affect said to be out of receivership; Marti, trol branches" in the United States . . . arising it, will sell "Be It Therefore that a East Orange, is reorganized and Willard Battery service stations will in- Resolved, sets direct to power companies in and stall and service Transitone automobile standing committee be appointed . . . near New York. Temple, of Chicago, radios. for the purpose of cooperating with the was bought by a syndicate headed National Association of Broadcasters by Leonard Welling, formerly a New ^ LICENSES: MORE AND LESS. Two and to be ready to make recommenda- tions to this association at time." York Majestic distributor. Bremer-Tully, tube manufacturers signed R.C.A. licen- any Dealer tube or of Chicago, is discontinued as a sales ses, Cable and Perryman. Fourteen tube discounts, policies, organization and present Bremer-Tully makers now hold an R.C.A license. exclusive wholesale territories don't sets are being unloaded. DeForest and Arcturus are not licensed. matter much if the radio listeners don't listen. . . . On January 1, the R.C.A. licenses of ^ THE NEWS PARADE President Hoo- Walbert, of Chicago, were cancelled. the entire THE PENTODE AGAIN News from ver reappointed Radio Com- Shortly after, however, tuned-radio- ^ the trademark U. S. Patent mission, seemingly ignoring the strong frequency and electric-phonograph li- division, Office: "Ser. No. opposition to some members which has censes were granted by R.C.A. to the application 293,289. as Radio of New N. developed, based on their record Story $ Clark Radio Corporation, of Corp. America, York, filed December 1929. Trade Mark: radio administrators. All have been Chicago, and to the Transformer Cor- Y., 5, 'Pentode' for electrical vacuum tubes confirmed by the Senate. Gen. Saltz- poration of America, Chicago. man was chosen chairman. Passage of a and valves. Claims use since November 1929." . . . R.M.A. Communications Commission Act ap- ^ RADIO ON TRAINS Radio installa- 25, engineering inevitable and this Commission division that the will not pears tions on important trains continue. argues pentode would have radio as one of its com- not only Stromberg-Carlson's automatic-volume- permit any accomplishments possi- ble with tubes. For plex problems. control model has been supplied to Chi- present "pentode" In the last said President Rich- read "screen-grid tube." How well the year, cago, Burlington and Quincy for three of 25 of the radio fits set of the season mond RMA, per cent, new trains added by the C. B. & Q. argument designs manufacturers maintained price levels, just closed ! . . . The industry discussion 35 cent, cut and 40 cent, raging around the pentode may have the per prices, per ^ PROBLEMS On every hand, those were in financial difficulties. This state- effect of holders of who struggle with radio problems refer bringing opposing made before the Cleveland Con- of view to the conference table. ment, decisively to the automobile industry as points vention of the N. F. R. was not re- Several such meetings have been A., a perfect example of a well-managed in- already ceived the lumin- held and further discussions between kindly by attending dustry. Says Norman G. Shidle, direct- aries who felt that such frank- tube and set makers are in public ing editor of Automotive Industries: prospect. ness was not Conferences before the fact are rare in politic. "The most vital questions in the minds radio business where the has of factory executives now seem to relate practice been to wait until the die is cast. . . . ^ AUTOMOBILE RADIO Michael Ert, to dealer relations in one way or an- of told Oscar Getz, of Sleinite: "... I feel retiring president N.F.R.A., other. Some of the questions getting Says it is time that the radio manufac- members of his association that the in- most attention are: that stallation of radio receivers in automo- turers should take a hand in the control 1. car to dealer and con- biles offered to Gearing output of their own destinies." great profit possibilities sumer demands. the radio in the industry coming years. 2. Dealer discounts. . . . State NEW MODELS AND A TREND Since New Hampshire Commissioner 3. Service policies, particularly as to ^ of Motor Vehicles Griffin says: "New whether factory or dealer shall pay we last met, in the phrase of Nation's labor charges on parts replaced during Hampshire is against automobiles equip- Business, United Reproducers has an- the standard warranty period. with radio which can be nounced a new model, K-70, to sell at ped operated 4. Junking plans. while the car is in motion. This depart- 5. To reimburse or not to reimburse $149.50, less tubes. U. S. Radio $ for losses on cars in stock ment is satisfied that the greater per- dealers any of Television announced the Apex seven- at time new model is announced. centage of accidents is due to inattention tube set complete with tubes at $101.00, 6. To reimburse or not to reimburse deal- and Model 589 to sell at $159.85 of drivers, and where a radio is being ers for losses on cars in stock when a Sparton, tubes. If two manufac- operated while the car is in motion it price-cut is made. complete with 7. of non-cancellable con- certainly would tend to divert the at- Possibilities turers of radio receivers offer models tracts. this in the seison with tention of the operator". . . . Sales and early priced 8. Closed territories. service of the Delco automobile radio, tubes, is it a Trend? Our answer is a made by General Motors, will be handled Write your own comment. slightly hesitating "Yes." RADIO BROADCAST FOR APRIL 309 AN AUTOMATIC RECORD CHANGER By THOMAS E. PIAZZE Technidyne Corporation THE WIDESPREAD use of radio during the graph easier and more convenient. There instrument into two parts connected by last seven years for entertainment pur- is no doubt but that the quality of music electric cables and is not always conveni- poses in the home has created a new ap- obtainable from good electrically recorded ent. Neither does it fully avoid frequent preciative audience for music. At the same records reproducing through the modern attention to the phonograph. time experience has developed certain magnetic pick-up unit and audio amplify- This undoubtedly suggests, why has limitations in the use of radio which prove ing system with a quality loud speaker, not the automatic record changer come annoying to those in whom the desire for as used in broadcast radio sets, is as good more into use? We asked a sales represen- such musical entertainment has already if not better than that which may be se- tative of one large phonograph company been developed. cured from the average radio broadcast not marketing an automatic record In communities a hundred miles or more program. Certainly when receiving condi- changer why his company did not have from broadcasting stations, where the sig- tions are bad the absence of noise tends one. The answer is instructive. He said, nals are relatively weak, there oftentimes de- to make phonograph reproduction a fa- "So far, using an automatic phonograph velops considerable disturbing noise due to vorite. has been like going out for a ride in a poor power line leaks, electric railways, and mis- automobile; you might as well walk." cellaneous electrical industrial apparatus. Simplified Operation This represents the nub of the question. It is unfortunate that these noises tend to Any device tending to reduce the atten- No small-sized record changer so far has become most pronounced in damp or wet tion necessary for phonograph operation proved reliable for home use. We would weather due to electrical leakage over in- tends to increase the enjoyment to be had add also that probably little sustained ef- sulators or between power lines and trees from a phonograph program. Such things fort has been exerted to create an auto- or other foliage through which they pass, as electric-turntable operation, eliminat- matic record changer which is simple, fool- as it is just during such weather that most ing the necessity of rewinding; or the use proof, and capable of handling the variety people desire to stay at home and be enter- of special needle points which need only of records, even of one nominal size, to tained by their radio. to be changed every fifty or hundred be found on the market. Possibly those The last seven years experience with ra- records go part way towards easing phono- charged with such development were es- dio broadcasting has also demonstrated graph operation. pecially interested in creating a machine that there are some sections in the United Many sales people experienced in the which would handle the records manufac- States where, for periods of from one to phonograph field believe that the greatest tured by their own company and were six months during the year, radio recep- obstacle to the more widespread use of not much concerned with what would tion conditions are unfavorable due to the phonograph is the necessity for get- happen if records of other manufacture normal static disturbances from electric ting up every three or four minutes to were inserted. storms. In such and in the record. A recent has regions, especially change attempt Record sections remote from the more powerful been made to minimize this annoyance Changing broadcasting stations, a demand has grown by building an electric turntable into a Realizing some years ago that the stimu- up for musical entertainment to supple- small end-table so that the record change lation of an active demand for automatic ment the radio in the home, indicated by may often be arranged near at hand. This record-changing phonographs would be a growing proportion of sales of radios involves the separation of the playing relatively easy with an instrument which equipped with phonographs. New Interest In Phonograph Radio broadcasting from its first appear- ance proved a tremendous novelty. People MOTOR were very enthusiastic over the variety of SPEED up-to-date music and information that CONTROL radio could supply for the home. These RECORD features proved powerful enough to cause REPEAT everyone to overlook almost entirely the CHANGE STARTING KNOB importance of the phonograph. However, REJECT BUTTON the improvement in tone quality resulting ON-OFF SWITCH from tying up the phonograph with the radio set, together with a certain novelty value in the combination, has already created a new interest in the phonograph. Sales of the new electrically recorded records have been increasing rapidly and MANUAL it is thought that this results not only MAGAZINE from the superior tone quality and rela- DISCHARGE tive convenience of the electric phono- graph, but also from a strongly stimulated desire for some pieces of music frequently heard over the radio, or else brought to mind from long ago. We believe that a more rapid growth of phonograph use will naturally follow now from the introduction of any device tend- The important parts of the Technidyne automatic record ing to make the operation of the phono- changer are identified in this close-up view of the instrument. 310 RADIO BROADCAST FOR APRIL A Description of a Simple Mechanism Handling all Types of Phonograph Records in Which the Time Between Selections Has Been Reduced to Ten Seconds. Developed in the Technidyne Laboratories. was at once universal, compact, economi- tone arm C. The magazine A has a ca- l>een played, an automatic control oper- cal, and fool-proof, the Technidyne Cor- pacity of about twenty records and is ates to engage a one-revolution clutch, poration set about the development of an loaded through a slot in the front of the starting the tilting operation. The turn- ideal automatic record changer. This has cabinet. The machine is started from the table moves down with the record and at been achieved and demonstrations have position shown in Fig. 2 by a push-button a certain angle the discharging fingers E recently been made for leading manufac- control. The first operation of the machine disengage the record from the pin, and the turers. A description of this machine show- is when the empty turntable tilts over record falls down to a discard magazine as ing the principle of its operation follows: through an angle of 90 at which point a shown in Fig. 7. The record is shown assembled changer All Records in the pictures on page 310 and the motor Accepted unit with turntable is shown at the top Any record may be played over one or of this page. more times by turning a change-repeat The record is picked up and discharged knob. This disconnects the mechanism of by the turntable rotating bodily with the record-storage magazine from the tilt- the motor. Fig. 1 to 7 help in explain- ing motor so that no records are ejected ing the operation. Fig. 2 shows the records for pick-up. It also disconnects the arms stored in a magazine ready to be played pushing the record off the center pin so with the turntable in its normal position. that the record to be repeated stays on Fig. 3 shows the turntable rotated through the table. 90 and a record ejected from the storage The tone arm and pick-up unit are quite magazine and resting against the turn- free of mechanism. The pick-up is raised table. Fig. 4 and 5 indicate the turntable by the record rising underneath it as the rising and picking up the record. table comes back to the horizontal posi- Fig. 1 Schematic drawing of the record changer. A, record storage magazine; B, motor and turntable; C, tone arm. record is ejected from the magazine, A, and falls on fingers, D, with the upper part of the record resting on the edge of the turntable as shown in Fig. 3. The turntable rotates back to its normal play- ing position. During this motion the cen- tering pin slides up the record below the center hole, bearing against the record as shown in Fig. 4. As the turntable continues to rise to its normal position the pin engages the hole in the record as shown in Fig. 5. During the remainder of the motion towards the playing position the record is carried on Fig. 2 Step one: records stored 4. three: turntable the pin and finally deposited on the turn- Fig. Step in magazine and turntable in to record normal table, as in Fig. 6. After a record has rising pick up ejected its position. from magazine. In Fig. 4 it will be noted that the center pin on the turntable is pushing against tion. This action is relatively gentle even of the record and Fig. 5 shows the record though the entire cycle change occupies 10 seconds. This is because this falling back against the turntable with the only part center pin in the hole of the record. of the cycle corresponds to the crank (which tilts the in Fig. 6 shows the record in the normal table) operating the region near playing position with the pick-up resting dead center. on it. The pick-up unit is pushed inwardly by Fig. 7 shows the turntable tilted through a light spring up to a stop so that the 90 with the push-rods pushing the rec- needle contacts with the outer edge of ord off the centering pin so that it can the record as the record rises, then the drop into the discard magazine below. spring lifts the pick-up clear of the stop. is the Figs. 5 and 6 indicate how the record This outer edge a blank margin, but rises underneath the pick-up thus elimin- pick-up is impelled slowly inwards to- small ating the necessity of any mechanism for wards the first sound groove by a raising or lowering the pick-up unit. radial component of record motion under the needle, secured by placing the tone It Works How Fig. 3 Step two: turntable ro- arm center slightly inside the tangent to at needle. In Fig. 1 there is shown a record maga- tated 90 degrees and record the record circumference the zine, A, a motor and turntable, B, and a ejected from magazine. This arrangement forms a simple way of RADIO BROADCAST FOR APRIL 311 Fig. 5 Step four: turntable Fig. 6 Step five: turntable, Fig. 7 Step six: turntable is picks up record with center pin phonograph record, and tone tilted to reject record in the while returning to position. arm in normal playing position. discard magazine. insuring the playing of all records size, say ten-inch records, vary in at their beginning and without thickness and diameter as between loss of time. different manufacturers. Records will oftentimes become Automatic Control slightly warped due to their being stored The device for initiating the edgewise in too hot a location, as, record change when a record has for example, next to a radiator. been completed is of prime impor- (Jroat flexibility and reliability in tance. It must be quick, unfailing handling such records has been and unerring. Since various makes secured in the Technidyne device of records have different terminat- by a full utilization of the prin- ing grooves, all at different internal ciple of three-point suspension. diameters, a quite universal device In the record -storage magazine is required. The problem is com- the record is first supported at one plicated by the small motions, point below and two points above. accelerations and the great di- During the operation of loading versity of normal sound groove on the turn-table the record is spacings. supported at two points below and one above, the The Release point upper Trigger point being the center pin of the The Technidyne automatic con- turntable. Large variations in trol is a simple solution for this record diameter and thickness problem which is based on new are permissible because the record mechanical principles. One of these remains in leaning engagement new principles is that a smooth with the center pin of the turn- Close-up view of tilting motor. shaft will slip through a fairly tight table as the table rises. The pin bearing at a certain low axial speed must slide by the center hole of very easily when the shaft is rotating but when the needle enters a special terminat- the record at some time, and then the for great resistance is offered higher axial ing groove, and in, about 6 seconds when record must be picked up by the turn- speeds. the tone arm stops due to the needle en- table and placed in position. A trigger release is held stopped on a tering the last closed groove of a record While there are undoubtedly many other smooth rotating shaft by a pin held bal- with no special terminating groove. good ways of mechanically performing the anced in unstable equilibrium on an arm The development of the Technidyne record changing operations we are confi- rotating with the tone arm. When the automatic record changer was guided by dent that many records will be automati- tone arm either stops moving or acceler- the desire to secure a machine which, be- cally changed the Technidyne way before ates at the end of a record this pin falls sides being simple in construction and inventive genius develops another system off and permits the trigger release to ro- operation, would be able to handle the providing the easy and natural sequence tate with the shaft and start the tilting great number of different makes of records of motions resulting from the use of the cycle. The pin falls off in a half second now on the market. Records of one nominal system herein described. BOOK REVIEWS RADIO LAW. Hy W. Jefferson Davis. writing about radio and not a radio man right decisions; a comprehensive study of Published by Parker, Stone & Baird writing about law. For example, he states: the work of the Washington Radio Confer- Co., Los Angeles, Cal. 364 pages. "Radio began as a curiosity, became the ence of November, 1927, with the lengthy obsession of small boys, progressed to the convention quoted in full; rules for hear- The recent work Radio Law by W. Jeff- stage of a popular amusement, and then ings before the Commission; legislative de- erson Davis is not to be confused with The suddenly flowered into the most over- fects in the prescribed procedure; the char- Law of Radio by Stephen C. Davis. The whelming industry in the history of com- acter and effect of General Order 40; and new volume analyzes the influence of many munications." Actually, radio has been a the problems of radio legislation as an- recent decisions which define the powers recognized method of communication for alyzed by the American Bar Association's of the Federal Radio Commission and the three decades and had a commercial com- Committee on Radio Law, are some of the rights of broadcasting stations. munication history of twenty years before subjects adequately covered in the vol- Its author is a member of the Air Law broadcasting became "a popular amuse- ume. The index is particularly complete, Committee of the American Bar Associa- ment." making the volume a handy reference for tion and, on the very first page, generously However, these are small objections to lawyers handling radio cases. disposes full credit for the passage of the a book which presents not only such a A reading of the book makes obvious Radio Act of 1927 exclusively to that comprehensive history of radio regula- the fact that the most important deci- organization. This is indeed a fine tribute tion in the United States but a brief sum- sions controlling the future operation of to the months of work performed by the mary of its progress in Europe. The Radio powers of the Federal Radio Commission Radio Coordinating Committee appointed Act is, of course, analyzed and supported are yet to be made and that amazingly by L. B. F. Raycroft and usually consid- by interpretations of the Commission's slow progress has been made in defining ered responsible for the acceptance of the legal department on various sections. the position and powers of the Commis- compromise act finally adopted. State and municipal regulations of recep- sion during its three years of operation. The book is obviously that of a lawyer tion and transmission; important copy- Edgar H. Felix. 312 RADIO BROADCAST FOR APRIL MEASUREMENTS OF HIGH-FREQUENCY RESPONSE By JESSE MARSTEN Chief Engineer, Earl Radio Corporation Sideband Suppression as a Function of the Characteristics of the R.F. Amplifier, Detector Circuit, and Audio-Frequency Amplifier. Discussion is Based on Measurements of a Num- ber of Modern Commercial Receivers. HIGH-QUALITY REPRODUCTION of sound these factors. These are gradually being too great, and in order to reduce tube presupposes an overall fidelity curve which overcome with resultant improvement in hiss and atmospheric muck, the higher is flat, or reasonably so, from 60 to at quality, and the point has been reached audio frequencies were deliberately sup- least 5000 cycles. There are two methods, where the most important failing is the pressed, either by the use of high-fre- generally speaking, of arriving at this lack of high frequencies. It may be worth quency filters or otherwise doctoring the objective. One is to design the component while to review very cursorily the chang- audio-frequency system a typical case parts of the entire system so that they ing trends in audio-frequency reproduc- of compromise mentioned above. This all have the desired flat characteristic. tion over the past few years. loss in high-frequency response was ac- The other is to design the component parts The early battery receivers had audio- centuated somewhat further by side- so that one compensates the deficiencies frequency amplifiers which were woefully band suppression in the r.f. amplifier. of the other. The tendency among design- lacking in low frequencies, and high fre- The A.C. Tube Enters ers is generally towards the former. quencies above 2000 or 3000 cycles. These While very notable gains have been deficiencies, unfortunately, were further With the introduction of a.c. tubes a made towards a realization of this goal, accentuated by the horn-type loud further loss in the range of audio-fre- an examination of the fidelity curves of speaker, then in vogue, which had similar quency reproduction was temporarily en- representative radio sets reveals that, so failings. The result was "tinny" quality. countered, this time at the low-frequency far as the receiver chassis is concerned, The transition to the balanced-armature- end. The object, of course, was reduction the rhapsodies of our advertising brethren driven cone loud speaker gave consider- of hum. However, the use of the 227- are hardly justified. "True," "Lifelike," able improvement in low-frequency re- type tube and improvement in filter sys- "Realistic," "Natural," that is what we sponse, and also extended the high range tems, remedied this condition, and the would like the sound reproduction from somewhat. Bigger and better audio-fre- almost universal adoption of the electro- our radio sets to be. We have a long way quency transformers appeared on the dynamic loud speaker resulted in quite to go before such adjectives will be war- scene, and the advent of the low-imped- satisfactory low-frequency performance. ranted. ance output tube of the 171 type improved The console type of cabinet had also ar- matters still further. rived. this time the dear had Problems By public Engineering By this time, just before the introduc- learned what it wanted in the way of tone. There have been and still are numerous tion of the a.c. tubes, high-gam, shielded, The cry arose for "mellow tone." Fre- factors which have militated against se- radio-frequency amplifiers were well de- quencies above 2000 or 3000 cycles were curing the best grade of sound reproduc- veloped, employing three and four stages not wanted. Loud speakers were even sold tion from radio sets, and our engineering of amplification. For weak signals the with filters in them to cut out everything compromises are simply concessions to noise level in such high-gain receivers was over 2000 cycles, should the receiver hap- Automatic grid winding machines. Stem forming machine. (Left) Mounting vacuum tubes. General view of assembly floor where vacuum tubes are mounted. Sealing, exhausting, basing, and soldering. (Below) Automatic aging rack. Close-up view of exhaust machine. The seven pictures on this page were taken in the factory of the Ken-Rad Corporation, Owensboro, Ay., and shoiv the wide range of equipment required for the manufacture of radio vacuum tubes in a modern plant. TUBE MANUFACTURING EQUIPMENT IN THE KEN-RAD FACTORY RADIO BROADCAST FOR APRIL 315 The MARCH How Should We Advertise Radios? Let's Reform Before We are Stamped Unreliable Misleading Radio Advertising of that range is undesirable and "colors" or modifies fidelity by a process of distortion. Wide range of response is of no The National Better Business Bureau recently compiled significance unless accompanied by an accurate statement of a list of the superlatives most frequently used by leading radio the gain throughout the band. A boast of special quality of manufacturers in national advertising. The survey proved reproduction of one ki_id or another is usually an admission of what everyone appreciates fully, that the industry is uni- unequalized gain or narrow response band. A receiver which formly making the same hyperbolic is superior in selectivity and sensitivity claims for its product. The public alone is almost certain to be inferior in knows that thirty or more brands can- its fidelity as measured at the listen- not each be the "best" and that the er's ear. claims of superiority of the cheaper Furthermore, the possession of the sets can hardly be based on fact. There- maximum audio-frequency range is fore, the effect of the large amounts a questionable advantage. Some of the spent for advertising is at best de- best receivers employ an artificial veloping mere name familiarity. cut-off below 5000 cycles because that The alternatives to a policy of advertising radio receivers reduces the background noise and secures a better overall by means of glittering generalities have become quite familiar. musical effect than is attained by permitting reproduction of A halo is built around a coined word which means absolutely higher frequencies. Sensitivity, likewise, can be excessive, nothing, claims of technical superiority are based on a point contributing not only an unnecessary background noise but which is in no way distinctive or unusual, and technical data also rendering the receiver more liable to cross-talk from sta- is presented in a form which is usually correct but often quite tions on neighboring channels and reducing the amplification misleading. of the higher frequencies. In the hope of being able to offer a specific suggestion for Perhaps the most insidious type of misrepresentation is avoiding superlatives and basing advertising claims on a foun- that based on scanty though correct engineering data. Under dation of fact, we discussed the possible use of the procedure the cloak of laboratory measurements, entirely unjustilicd formulated by the Institute of Radio Engineers for rating claims are easily made. A receiver is advertised with its re- radio receivers as a basis for making advertising claims with production described by actual figures for low- and high- the chief engineer of a major manufacturer, who is a prominent frequency limits. Sometimes the low-frequency limit is so low leader in writing the standards of the radio industry. The three that it could not be attained without a baffle considerably qualities which can be rated under the I. R. E. procedure are larger than can be made a part the average console cabinet. sensitivity, selectivity, and fidelity, the three basic factors de- A claim based on the frequency range of the audio-frequency termining a radio receiver's performance. But, it was pointed amplification system means little or nothing; a fidelity curve out, there is no specific way of evaluating the relative value of its performance but little more. The only quality curve that of these qualities. An arbitrary system of means anything is a comparison of the rating must therefore be assumed in plotting modulated radio-frequency input with the comparisons of these qualities, which may sound output of the reproducer through- easily produce misleading or meaningless out the audio-frequency range. results. It is somewhat like trying to judge All of this leads us to no constructive the personalities of two men by charting purpose except perhaps to explain why such of their qualities as perseverance, in- generalities and superlatives predominate tegrity, and the knowledge each has of his in receiver advertising. The most we can business. With such a system of rating, a hope for at this time is a definite trend plodding bookkeeper might outrank a capable executive. A toward dignified and artistic advertising and an early end common denominator is required to make valid comparisons. to the present era of flamboyance. The fidelity of an audio-frequency system can be measured One suggestion can be adopted from the automotive indus- conveniently by comparing its electrical input and output. Such try which has somewhat the same problems as radio in finding measurement, however, does not represent the overall fidelity valid advertising claims. Few of the quantity producers com- of the complete receiver, as it fails to take into account the pare their cars with those of competitors by claiming to make effect of the radio-frequency amplifier in cutting off side- the best or the finest or insisting on superiority in any parti- bands and the ability of the reproducer to convert the range cular phase of performance. Comparisons are usually made of audio frequencies supplied it into sound. Advantage is only over their own last year's models to show the features taken of public ignorance of these facts. The actual audio- wherein improvements have been made. Why not be satisfied frequency quality which the user experiences is dependent with a statement that the latest models of a receiver line are upon sound waves released by the reproducer and not upon the finest made in the company's history and refrain from the characteristics of the audio-frequency system alone. comparison with those of competitors or of the general stand- Tone quality is the subject of the greatest advertising ards of the industry? Let us reform radio advertising while the abuses. The best reproduction is attained by equalized gain public still regards it merely with tolerant amusement and over a band from 50 to 5000 cycles. Exaggeration of any part before it is definitely stamped as unreliable and misleading. 316 RADIO BROADCAST FOR APRIL OF RADIO The Pentode's "Greeting" by the Industry A Suggestion Move the 50,000 Walters Inland The Coming of the Pentode Protests were then heard from radio dealers and listeners in Brooklyn and Queens, objecting to any increase in power in The radio industry treated the announcement of the avail- that location. ability of the heater-type pentode rather rudely. The Radio The facts of the matter are that the metropolitan area of Manufacturers' Association promptly issued a statement to New York is much better served by 5000-watt stations lo- the effect that the new tube will bring about no improvement cated as near to the center of the area as possible, than by in performance, that its use in Europe is accounted for by the 50,000-watt stations sufficiently removed to avoid incon- fact that royalties are collected on the basis of number of veniencing a large part of the public. No one questions the tubes in a receiver, and that the tube is unlikely to make pos- fact that WOR, within a few miles of Manhattan, delivers sible reductions in the cost of receiver manufacture. As long the highest value of field strength to a larger percentage of ago as March, 1928, William Dubilier reported the existence the metropolitan area than any other station, while two of a German pentode receiver, giving good loud speaker re- stations of 50,000 and 30,000 watts respectively, located at production, with a retail selling price of $12.00. its fringe, deliver an inferior signal at the opposite rim of The industry naturally shivers with apprehension at the the circumference of the area. very thought that its present designs may It is wholly uneconomic to locate 50,000- be forced into obsolescence. The alternating- watt stations near metropolitan centers; current tube promptly raised mountains of they should be several hundred miles from selling resistance to battery receivers; simi- either coast. We need only consider the larly the screen-grid tube made the three- example of WLW, several hundred miles element type unfashionable. With the high from the Atlantic seaboard, which gives cost of research, preparation for manufac- incomparably the best rural service of ture, and marketing of new lines, and with any station in the country at the present the still substantial stocks of unsold receivers time. in the hands of manufacturers, jobbers, dealers, and cut- It has also been demonstrated clearly that, when the price merchants, progress is as unwelcome as a Stock Commission comes out in support of a desirable engineering Market crash. trend, the broadcasting fraternity manifests an active spirit The screen-grid tube just as appropriately could have been of cooperation. The very trend toward the removal of high- greeted with the argument applied to the pentode, to the ef- powered stations from the center of the metropolitan areas fect that the performance of a pentode receiver can be equalled and the efforts of various managements to acquire several with existing types of tubes. stations in their areas for the purpose of consolidation is evi- The resistance of the industry to the pentode tube is a wel- dence of the Commission's influence. Of course, this influence come sign. Both a.c. and screen-grid receiving sets were has suffered a serious blow because of the fact that, after en- marketed on too wide a scale before satisfactory performance couraging purchases of stations for purposes of consolidation, could be assured the consumer. For once the industry is not the Commission has failed to support them. Indeed, it is, in welcoming innovation with undue haste. However, the very one instance at least, terming such a consolidation as an tube and set manufacturers who issue publicity to counteract attempt at monopoly even though the original purpose of the sentiment toward the pentode are at the same time working grouping was a response to the expressed desire of the Com- feverishly in the laboratory to perfect the tube and receivers mission to help in eliminating stations. using it. The longer this process is preferred to the usual course However, experience has proved, first, that high-power of merchandising half-engineered receivers to an unsuspecting stations, close to the eastern and western seaboards, are public, the greater will be the ultimate contribution of the uneconomic, while they render their greatest service when pentode in broadening the market for radios. It is quite doubt- located at the center of the country and, second, that large ful that the first pentodes to appear have ideal or perhaps even metropolitan areas are better served by medium- and low- useful characteristics. A tremendous amount of work must be powered stations in their center rather than by a high- done before the pentode itself is fully developed and before the powered station some distance away. art of using it is acquired by set designers. Broadcasting Achievement Power vs. Areas r High City At the Senate hearings on the Couzens bill, W illiam S. Finding that the New Jersey State Radio Commission made Paley testified that the Columbia system is giving 75 per cent, it too hot for the Columbia Broadcasting System's proposed of its time on the air to "service programs made available at 50,000-watt trans- its own expense." * ~ mitter for Prior to the WABC, 1928, NOTICE the en- lost system's system $205,480; ONLY 10 SECONDS gineering talent during 1928, $172,000, OF ADVERTISING directed its atten- and the accounting ANNOUNCEMENT* tion to the present for 1929, it is antici- location of its 5000- pated, will show a watt transmitter. (Continiiedon page 3'i9) RADIO BROADCAST FOR APRIL 317 Pertinent Notes on CHARACTERISTICS OF TELEVISION SIGNALS By C. H. W. NASON Jenkins Television Corporation THE DEVELOPMENT of television during the directly scanned images, etc. requires that, the wave shown in Fig. 4 plus a continuous past two years has progressed rapidly. in the case of radio transmission, r.f. cir- voltage of value a -j- b/2. The transients To say that we have passed the period of cuitsand a.f. amplifiers pass this entire band effective in the circuit reside in the alter- high-pressure development would be pa- of frequencies without discrimination or dis- nating component shown in Fig. 4, since tently unwise; rather it might be said that tortion. Thus it may be seen that the am- the impedance of the amplifier input cir- television is in the same position to-day plifiers of accepted usage are unsuited for cuit, as shown in Fig. 5, is infinite to zero- as was the broadcasting of music a decade this service. Short-wave receivers in their frequency components, i.e., no portion of hack. Much has been written of television ordinary form, used without regeneration, the steady state direct current may flow. and it is the purpose of this article to re- are suitable for the reception of silhouettes Distortion view certain fundamental conceptions or "shadowgraphs," such as are now being Aperture and facts regarding the television signal, transmitted on regular schedule in the We have considered the necessary char- its generation, transmission, and recep- eastern part of the country; and such re- acteristics of a.f. and r.f. amplifiers for tion. ceivers will allow the reception of a passa- television service and have noted the gain- In considering, the electrical aspects of bly good picture, but one lacking in sharp frequency performance required. There is, the television signal we will accept as a vertical lines, should such arise. however, a distortion present not due to basis the following facts: a vertical com- R.F. amplifier circuits have been de- circuit deficiencies. For example, actually position of 48 scanned lines; a degree of veloped which are capable of transmitting the form is altered by aperture distortion horizontal definition equivalent to 64 the entire band employed without serious of the wave caused by the passing of the elements in a picture area having an aspect attenuation of the high frequencies and aperture over a change in h'ght intensity, ratio of 3/4, as in a standard motion-picture represent an extreme engineering refine- for a square aperture will not give a rectan- frame; and a picture frequency of fifteen ment of the theory of coupled circuits. gular wave form as shown in Fig. 6, as is per second. The picture is to be scanned desired, but alters the wave form in the from left to right and from top to bottom Origin of Signal manner indicated in Fig. 7. where T' as in the This the time for the of the reading printed page. degree The transmitted signal has its origin in required passage of definition allows for a 'head-and-shoul- over the line in the picture cor- h'ght impulses directed upon a photo- aperture ders" image equivalent in detail to a to the origin of the change in electric cell by means of a beam of light responding half-tone an area of newspaper having varied by the changing density of a photo- light intensity. f" 1". The effect of motion is to increase A Fourier's of the wave form in by graphic film or by the degree of light re- analysis detail the apparent by some fifty per cent. flected from an illuminated scene. Fig. 8 gives These standards are based our upon This television signal differs widely from between the ever-present compromise that of sound broadcasting, both in form Sin cut d The latest Jenkins transmitting scanning system with shielded ampli- fiers and a synchronously driven pick-upfor transmitting "radio talkies." 318 RADIO BROADCAST FOR APRIL The Frequency Band Requiredfor Televi- sion. Mathematical Discussions of the Various Frequency Components. Neon- Tube Circuits. Methods of Synchronizing. which is far beyond the scope of this tone of the trans- article. The numeric values are substan- mitted scene or the tially the same as those for the square aper- character of its ture and they may be taken as equal background. Proper without serious error arising from the reception of the im- assumption. age is dependent, The effect of the aperture distortion as therefore, upon the shown in Figs. 7 and 8 may be evaluated by initial illumination use of the Fourier's theorem which states, of the neon tubes briefly, that a complex wave may be and must be ob- analyzed as being composed of a number tained by adjust- of sine waves of differing wavelength, ment for the most amplitude, and phase superposed one pleasing appearance upon the other. or by previous The shielded room in which television knowledge of the signals Size of Aperture characteristics of are measured at the Jenkins Television Corp. The aperture as applied to the scanned the scene. Neon scene should preferably be 1/48 of the tubes employed in television reception an a.c. impedance of anywhere between total height, as overlap or spacing between must be essentially free from any effects 1000 and 8000 ohms. The d.c. resistance the scanned lines is not desirable except of hysteresis, and their curves must be of the tube involves a voltage drop which in special cases. This clearly defines the linear over a wide range. (See Fig. 12) must be taken into account where economy factor T' and the discrimination of is a but in the frequency The Neon Tube voltages factor, general may be computed algebraically. This high-impedance type is preferable when amplitude-frequency distortion may be The neon tube may be adjusted for the considered as the load circuit of a vacuum compensated by a corrective network proper background density by varying tube, as a load impedance considerably having little distortion of phase. Fig. 11 the plate current of the output tube. higher than that of the plate circuit of page 357) illustrates the distortion oc- This may be done by adjusting the grid the output tubes usually employed in the curring. Variations in the overall charac- bias of the output stage, together with the output stage means that there will be but teristic of plus or minus 20 per cent, are plate voltage in such a manner as to con- little curvature to the dynamic character- allowable without noticeable deterioration tinue the operation of the tube at a favor- istic of the circuit. able point on its characteristic curve ac- The same characteristics which make of the image. Phase distortion IT-) with cording to the circuit diagram in Fig. 9. the d.c. drop high, keep the inter-element A more suitable method, though more capacitance of the tube down and render frequency is not permissible in a degree of profligate in battery use, is shown in Fig. the impedance mostl y resistive even at the more than 10 to 20 miscroseconds except 10 where any tendency toward improper highest frequencies encountered. at the low frequencies where phase varia- operation of the tube is avoided. Here the izal ion tions with frequency may be fairly large. steady plate current of the vacuum tube Synchron This latter form of distortion is not usually is balanced out of the neon tube circuit. The synchronization of the scanning found except where long land lines are em- "R," as indicated, is made equal to the mechanisms at the transmitting and re- ployed for the transfer of the signal or plate resistance of the tube, and the volt- ceiving ends presents an involved problem where transformers are employed as coup- age of the balancing battery is adjusted not only in the field of communications ling elements. Corrective networks have for the desired current through the neon engineering, but in electrical and mechani- been developed which will compensate tube. cal engineering as well. The simplest phase distortion without affecting the The neon tubes now on the market pre- method is adaptable only where the a.c. other characteristics of the circuit. sent varied load according to their me- power networks at the transmitter and As was noted, the d.c. component of the chanical construction and the gas with receiver are interconnected. In this case it initial signal is a function of the general which they are filled. Those available have (Continued on page 357) FIG. 1 TIME CO CO FIG. 2. TIME AUTOMORILE RECEIVER DESIGN BY ROBERT S. KRUSE. Radio Consultant Complete Description and Discussion of the Characteristics of the Bosch Auto- mobile Radio Receiver. Special Prob- lems in the Design of Such Receivers. An "exploded" view of the Bosch automobile radio chassis. THE AUTOMOBILE radio receiver is older speaker signal. A very simple calculation rubber-lined channels which in turn are than broadcasting. Indeed, the combina- shows that the sensitivity must be equal carried by brackets bolted to the engine tion of a motor car and a radio receiver was to that of a good broadcast receiver; in bulkhead. The loud speaker may be so obvious that many of us made suitable other words, the set must have a sensi- mounted directly on the set or may sets in the days when there was nothing to tivity in the region of perhaps 20 micro- be located in another manner which will be be heard save dots, dashes, and static. volts total input when it is giving an out- explained in a later paragraph. Unlike When entertainment broadcasting arrived put of 80 milliwatts. This rating, not the some forms of mounting this system does installations were made in larger numbers I.R.E. standard, is used because this power not require reconstruction of the car, nor but without any popular response, despite output gives reasonable volume, a depart- any special design for a new car. No exist- pictorial publicity in magazines and news- ure to be explained later. This performance ing car has yet been found in which the papers. The lack of any general response must be obtained with economy of space, equipment cannot be installed. At this was due to apparatus limitations, not to weight, and battery demand. Furthermore, writing all service stations of the Am- any lack in the idea. the construction must be dirt-proof and erican Bosch Magneto Corporation are Many months ago the Radio Frequency unaffected by vibration, and, auxiliary to equipped to make radio installations on all Laboratories, Inc. initiated the familiar the main problem is the need for a semi- types of automobiles and several manu- process of measurement, calculation, and remote control and the suppression of facturers of cars have listed the set as test which resulted in a working model of ignition noises. standard factory equipment. a broadcast receiver for use in automobiles. and at the General Collecting signal voltages After suitable road and laboratory tests, Arrangement same time avoiding the pick-up of too this model was turned over to the engineer- There are several points of interest in much ignition and generator noise is a ing department of the American Bosch connection with a typical Bosch automo- problem which has caused the appearance Magneto Corporation where it became the bile receiver installation. In the first place, of various types of antennas on motor cars basis for additional work. A production a "roof" antenna is not used and the dash for the last 15 years or so. The antenna has model was developed and this also required is left wholly unchanged except for the usually been concealed in the car roof much measurement and testing by W. F. mounting of a small control unit. The set certainly the poorest place that could be Cotter and B. V. K. French under the di- itself is supported by flanges resting in conceived. Placed between the grounded rection of Chief Engineer rooflight and the grounded L. F. Curtis. metal portions of the roof This production receiver CAPACITOR PLATE (extended up from the FRAME OF CAR 8" 30"; is discussed in this article. car sides), the effective The background for the height cannot exceed a few earlier work on the Bosch centimeters. Furthermore, automobile receiver may the location is one nearly be obtained, to some ex- ideal for the collection of tent, from reading the pa- the maximum ignition per by Paul O. Farnham, noise, since the antenna is at the Eastern Great above and the counterpoise E'venakes District Conven- (car frame) below the igni- tion, I.R.E., Nov. 19, tion system. Also, the which will appear shortly dome light wiring contrib- in the I.R.E. Proceedings METAL CONTROL utes noise to a roof antenna under the title "A Broad- "B" BATTERY UNIT i RECEIVER which is difficult to filter BOX cast Receiver for Use in satisfactorily. In addition Automobiles." A on CAPACITOR PLATE to this the antenna cannot paper 8"x 30" the same subject by W. D. be installed in a used car Loughlin has been given except by tearing down limited circulation in the the roof upholstery. R.F.L. "Preliminary En- The use of the "sub-car" gineering Report, No. 3." antenna (consisting of a metal under the The Conditions plate car), shown in Fig. 1, altogether It is evident that the avoids the last difficulty, automobile receiver must decreases the ignition noise operate with a very lim- materially by collecting ited antenna and yet Fig. 1 Schematic drawing of a typical Bosch motor car the signal in the clear space deliver a moderate loud radio installation. below the car frame, has 320 RADIO BROADCAST FOR APRIL an equal or better "effective height," and arrangement of parts in the lower compart- offers a special advantage of its own. This ment where the fixed r.f. transformer is special advantage is that the antenna is =< located. near the set and therefore the lead-in wire In the "exploded" view it will be seen is short and moderately clear of grounded that the upper portion of the casing carries (connected to frame) metal parts. The ca- the loud speaker, The tuning control of the pacity of the lead-in wire is accordingly set is by means of a gang condenser the moderate and does not vary extremely shaft of which terminates in a spiral gear, from one installation to another, thereby meshing with another gear in the small making it possible to secure tuning con- housing seen at the upper right of the main denser alignment without the need of body of the set. From this point the con- anything beyond the normal trimming trol is carried to the control head on the condenser on each section of the gang dash by means of a splined shaft of ad- variable condenser. justable length, connected to the control The antenna system is electrically equiv- head and to the set through universal alent to Fig. 4, where Cif if the capacity joints. This seemingly complex arrange- between the antenna plate and the car ment was chosen after experience which frame, CM is the capacity between the thoroughly disclosed the unsatisfactory earth and the antenna plate, and C e f is the performance obtained from flexible shafts capacity between the earth and the car of the simpler design. The principle diffi- frame. A signal arriving at the car will pro- culty about such shafts is that they intro- duce r.f. potentials across all three of these duce considerable "slack" or 'give," capacities, the combination of which will making it impossible to calibrate the dash be effective in supplying voltage to the control, since a station tuned-in at 56 receiver. In the average installation the when turning in one direction may appear antenna-frame capacity, C af, has a value at 51 when tuning in the reverse direction. near 0.000125 microfarads, across which is In addition to this there is the troublesome 2 Thin is used shunted the resultant of the other two Fig. apparatus tendency of the usual flexible shaft to to determine the effect of con- capacities in series. This resultant is also "wind and then suddenly "flip" the tinued vibrations on receiver up" about 0.000125 microfarads in the average tuning unit in the set forward, making it installation. performance. difficult or impossible to stop at a desired Thus the whole is in one sense equiva- point. lent to a capacity of 0.00025 microfarads this r.f. transmission system produces The right-hand knob on the control head connected across the terminals of better than the vernier dial, which is of the input materially signal strengths operates" " the set. This accounts for the somewhat were obtained with the antenna led di- line-of-light type. This type of dial statement on 5: correct from vague Fig. "Antenna rectly to the set in the usual manner of permits reading any position through 250 mmfds." motor car sets. in the car. The opportunities for parallax Actually the r.f. energy is fed from an- with ordinary dials are excellent and the The Receiver tenna to set through a simple r.f. trans- precaution is worth while since it is risky mission line, the purpose of which is to Having arrived at the set we find, as for a driver to lean to the right in reading permit the transfer to be made at such a expected, that it is enclosed in a substan- the tuning scale. The translucent scale, low potential that capacity effects are of tial metal case. The design of this case is though having only 100 divisions, covers no importance, regardless of the distance such that access to the tubes is obtained an arc of 312 degrees, thus providing great between set and antenna. There is a step- by loosening three knurled thumb screws ease of tuning. To provide this ease of down r.f. transformer at the antenna and removing the upper portion of the adjustment a reduction of 3.25 to 1 is and a step-up terminating transformer in- front, which also carries the intertube introduced between the tuning knob and side the set, the latter appearing as the "fences." There are no loose tube shields dial scale and an additional 5.6/1 reduction first transformer in the general diagram or cans. If for any reason the various re- is placed between the tuning knob and of connections, Fig. 3. Between the two sistors or by-pass condensers require in- three-gang condenser. The left-hand knob transformers is the shielded two-wire spection they may be reached by removing on the control head operates the volume line in which the potentials are so low the lower portion of the casing. Both of control rheostat and at the lower center that the length of the line and its location these points are made quite clear by the of the control head is a key -switch which with regard to metallic parts of the car is "exploded" view of the receiver, the head- may be used to lock the set when desired. of little importance. In its present form ing i 1 1 1 is I r;i I ion . This picture also shows the The design of the set is such that during 0.002 25p,000 OHMS BROAD MFD. 224 BAND 112A o A A FRAME HIGH TERM TERM Fig. 3 The complete schematic diagram of the Bosch motor car receiver chassis. RADIO BROADCAST FOR APRIL 321 manufacture it may be sub-assembled, the transformer is simple. It consists of a Where space and weight limitations are main set body forming one assembly with grooved form in which two wires are as severe as in the automobile receiver the the tuning gang-condenser in place, while wound together, one later to act as primary most practical coupling to follow this type the second assembly consists of the section and the other as secondary. The winding of detector is the resistance-capacity- carrying sockets, r.f. transformers, output is a "random" one. The purpose of wind- resistance type. In order to prevent radio- choke, and the various resistors and fixed ing in a number of slots instead of a single frequency feedback originating in the de- condensers. The removable portions of the large groove is to secure an improved L/C tector plate circuit and coupling with the case are handled independently, as are the ratio and a higher output voltage for the r.f. amplifier, a "PI" section filter is in- control head and the control shaft. grid of the second tube. The winding speed, serted at the plate of the detector tube. The design of the mounting brackets is tension, wire size, type of insulation, num- This filter consists of an 11 -millihenry such that when desired the set can be re- ber and form of grooves and number of choke and two 0.0001-microfarad con- moved 'from the densers. In series with the grid of the audio- car either with frequency tube is placed an 0.25-megohm or without the resistor, the function of which is to modify brackets. The the character of an audio-frequency over- alignment con- load in the grid circuit of the last tube, densers are ac- and incidentally to provide another section cessible when the of r.f. filter in the detector circuit. General vietv plate set is in The effect is unmistakable and im- place. of receiver quite mediately calls attention to the volume The Circuit chassis. control, but does not mistreat one's ears as To be of any unmercifully as an ordinary overload. This real use to the is not equivalent to saying that the full average auto- output of the tube is in any way sacrificed. mobile owner On the contrary, the tube is being operated an automobile with 180 volts on the plate, with proper r a'd i o receiver grid bias, and is as thoroughly capable of must not merely delivering its rating as in any other re- perform within ceiver. 40 or 50 miles of a station but must be useful in a goodly percentage of all -the Tlie Audio Level possible locations in the United States, at Most motor cars have closed bodies and least. It has been said that under motor- the automobile receiver designer assumes car conditions this calls for sensitivity of turns all contribute to determine the re- such a body in making his design. Even a the order of 20 microvolts at the antenna, sponse curve. large sedan is very small when considered for 80 milliwatts of audio-frequency out- The screen grids of the r.f. tubes are as a room and the sound levels to which put. This performance calls for a voltage maintained at a fixed potential by a tap we are accustomed may be obtained with gain in the vicinity of 2,000,000 between from the plate battery at 90 volts. Control a relatively small a.f. output from the set antenna and loud speaker, using the cus- by variation of the screen voltage is not and loud speaker. In addition to this, the tomary reference to equal impedances at regarded as suitable since the sensitivity dimensions of the ordinary car are such input and output. This may be obtained of an r.f. amplifier varies in anything but a as to introduce a tendency towards strong in a reasonable number of stages with linear manner when the screen voltage is low-pitched resonances. This can be under- screen-grid tubes by allowing some of the changed. The control is accordingly re- stood easily by recalling the deep rum- gain to take place in the detector and audio- ferred to the cathode bias which is ob- blings of many sedans of 5 or 6 years ago. tained frequency amplifier. by plate-current drop through an In such a space a normal a.f. system uwuld The first question to be decided is that adjustable resistor in the control head. be wholly intolerable; in fact one may say of the number of r.f. and a.f. stages to be This rheostat has a maximum value of that a good a.f. system for this purpose employed. By general agreement a single 20,000 ohms, which is adequate in the must be one which will sound very weak a.f. stage is preferable if the amplification presence of very strong signals. In series on the low notes when operated in the of the r.f. system is adequate. On the with the volume-control resistor is a 500- open. This is fortunate since the low notes other hand, multiplication of the r.f. ohm fixed resistor to provide a minimum are the ones which usually enforce the use stages cannot be carried to extremes since bias suitable for weak signals. of large output tubes with their resultant this tends to increase the size of the set heavy battery drain and bulky loud Detector by adding bulky r.f. transformers and and A.F. Amplifier speakers. Since dry-cell batteries must be condensers. In the Bosch automobile re- used in the present automobile receivers The fourth screen-grid tube is operated ceiver three r.f. stages are used to secure it is most fortunate that the conditions as a "plate" detector and adds somewhat a voltage gain of about 60,000. With 20 not only permit the 112A-type tube but to the overall r.f. gain. The cathode bias of microvolts input this amplifier delivers almost enforce its use especially as its this tube is obtained in the usual way about 0.6 volt to the detector. gain is some three times that of the 171A- through IR drop. The screen-grid is sup- From the diagram of connections (Fig. type tube. with a positive bias from the same 3) and also the pictures it will be seen that plied battery tap which feeds the other screen Circuit Features the coupling between the first and second Special grids in the set. However, an 0.5-megohm r.f. tubes is of the "untuned" variety. Some motor cars have the negative ter- resistor is placed in the lead to the screen Special design of this broad-band trans- minal of the storage battery "grounded" grid causing the bias to assume a "rest" former permits a gain-curve which is not to the frame, while others ground the value below 90 volts. For low signal levels only comparable to that of a good tuned positive. Provision is made for this by a on the detector-grid, the screen-grid voltage transformer as to height but also has an circuit arrangement shown in the general is such as to provide maximum sensitivity. advantageous shape. Inspection of the circuit diagram. The B is not returned For strong signal levels, the d.c. screen-grid chart of sensitivity curves (Fig. 5) will to the A battery but to the junction point voltage, as well as the d.c. plate voltage, show a general tendency of the tuned of one of the series pairs of 224 heaters. is lowered so as to maintain a reasonably stages to off toward the low-frequency Thus if we assume the A battery to be drop of difference. In this a end in the familiar manner. The broad- large margin way reversed the bias of the 112A tube will higher audio-frequency output rnay be band transformer is accordingly designed simply be shifted from a point 2| volts obtained before the plate circuit of the for maximum response in the region of 600 removed from A+ to a point 2j volts detector is overloaded. At the same time, kilocycles, causing a sharp divergence be- removed from A or a total shift of for large impressed signals, the response of tween the "first-grid" and "second-grid" approximately 1 volt. Even at the "Bat- the detector will be nearly a linear function curves, and a nearly flat curve for the an- tery gassing" potential of 1\ volts the of the input voltage. tenna. Thus, the fixed coupling is not a 112A tube filament operates at a voltage mere concession to space limitations but a very slightly above 5, hence the change in means of obtaining a desirable response CAR FRAME-x. bias is negligible. The plate voltages are curve for the set as a whole. all changed slightly but the percentage is The selectivity obtained with three unimportant, as is the change in screen- tuned circuits in an amplifier with such grid voltages. The cathode bias of the high gain would not be satisfactory for 224-type r.f. tubes is changed very slightly ordinary home use. It is to be remembered, '-ANTENNA but this merely necessitates altering the however, that the pick-up is very limited setting of the gain (volume) control for and the general level quite low so that the jCef iCea a given signal. Even for weak signals the "useful selectivity" (the term is admit- GROUND change is small enough to escape notice tedly home-made) is entirely satisfac- under ordinary conditions. tory. It is accordingly satisfactory to install The construction of the broad-band Fig. 4 the set "as is" in any car regardless of A 322 RADIO BROADCAST FOR APRIL polarity, simply grounding the battery^ by anyone wearing a heavy overcoat which assume the frame" A terminal and the charge form of a pulse rather | ( connecting obstructs the free radiation of sound. This than a train of oscillations. Such "high" terminal to the remaining side of is most noticeable resistors in the rear seat. are with the the A hattery. supplied set. They have stand- ard terminals and are The choice of the proper readily applied. audio-frequency Battery Supply Since output tube has been discussed The dirty charging-generator commu- sufficiently, filaments are supplied through an tators cause and the tube is may noises, or disturbances 112A-type considered satis- armored cable from the car's storage bat- may wander into the set factory from all standpoints, The from the ignition including tery. plate supply is obtained from switch, a of filament demand. In the r.f. of the pair by-pass condensers is pro- portion four medium-duty 45-volt B vided the -battery for shunting across these two units. system present standard types of tubes blocks carried in a metal battery box under There is no leave no choice that between other shielding or alteration except the the car, as shown in 1. This box has a Fig. of the ignition system, the noise screen-grid 222 type and the screen-grid yet level 224 type since the 201 A and similar tubes with full sensi- are is clearly incapable of providing a gain tivity barely which will give comparable performance. perceptible at The 222 is somewhat attractive because the low-frequency of its low filament demand but its ex- end of the tuner tremely microphonic nature and associated scale and rises at the fragility rule it out. Also, like the 20K, it high-fre- is rather hopeless in a situation where the quency end only to A potential varies rapidly from 6 to ?| sufficiently per- volts as the engine speed changes. Both the mit one to hear it 20lA with the car and the 222 will follow these voltage sta- changes rapidly and give intolerable shifts tionary and no of intensity unless Of signals arriving. specially protected. The the present tubes the 224 is by far the best. level is lower than The considerable time-lag of the heater- that of the emitter system comfortably smoothes over hum from a good a.c. the voltage fluctuations, also normal receiver. performance of the tube can be obtained To test the effect over a wider of continued vi- range of fixed voltages 'than is This view illustrates the possible with the 20U or 222. mounting bration without Thus a of the r.f. and a.f. transformers. unreasonable de- partly "flat" battery or one being steadily overcharged is not fatal. The use of three to lay the machine gasket make it weatherproof. The cable shown in 2 has 224 heaters in series has been Fig. been used. It consists proposed to the set is again an armored one. The of a but when the IR spring-mounted platform which carries repeatedly, drop in the total filament current taken from the car's two leads is bearings in which revolves a shaft allowed, such an arrangement is is 3.75 battery amperes. an eccentric on the ragged edge and will carrying weight. The shaft is drop rapidly revolved at 1800 in performance whenever the r.p.m. by means of a flex- battery is Ignition Interference ible shaft "down." connected to the motor. The set is Even with sets of very modest perform- secured to the The 0.02-microfarad low-inductance con- ance, motor car spring-mounted platform, installations have been ither in the denser across the A terminals of position shown or in the nor- battery characterized by extensive ignition shield- mal the set is an r.f. mounting position. The present con- bypass. ing and numerous by-pass condensers struction survives this vibration test in- under the hood. These things are almost The Loud Speaker definitely without damage to either set or unnecessary in Bosch installations, despite tubes. The loud speaker is a free-edge cone the unusually high amplification. This has Many road tests have designed for motor car that is been made over conditions; been partly accounted for by the collector of to for such a trips some length. Also there has been say,_ response-curve as will system and the armored cables from bat- result in much testing in and about different satisfactory reproduction inside teries, as well as the metal case for B cities, a bat- as many sets will be used motor car, and to survive the severe me- teries. The A certainly princi- battery by-pass condenser pally under chanical and climatic treatment received. at city conditions. the_set contributes also. As the writer Because It is enclosed in a Hartford, Conn. the writer's stamped steel shell, has said many times in other the papers, home town is considered a strong enough to stand up under accidental electrical disturbances set universally up by a motor radio "hole," the kicks and jars when mounted on the set car Bosch receiver has been are mainly on wavelengths below 10 tested under the cowl, but sc finished repeatedly in this vicinity. The that it meters. A broadcast-wavelength receiver scene a of the first tests was a location ro- presents good appearance when mounted with good well selectivity, shielded, and mantically named on the ceiling or in an rear corner maintained "Buena Vista" and upper well away from any tendency considered of the car. The cone good for Hartford. Here it itself is waterproofed toward oscillation is rather was and survives inherently found that good loud volume exposure to sprays. The per- opaque to such disturbances. speaker forated rear could be obtained from WBZ at shell is constructed in a man- However, the of the Spring- severity interfer- field, Mass. (27 ner which provides a sufficient number of ence be reduced miles), wjz, Bound Brook may greatly by intro- N. J. (100 openings to prevent resonances inside the miles), WNAG, Boston (perhaps ducing a high resistance between the spark shell. Dirt and are miles), WGN at Chicago (900 miles), bugs prevented from coil and the distributor and the distributor and WMAQ, also at Chicago. Several other entering through the openings by a cloth and spark the plugs, thereby making dis- stations, received rather sack which is shown in place in the ex- well, were not identified for lack of ploded view of the set. By careful de- time. It is rash to sign the overall thickness of the shell has usualy predict radio results by been kept down to 2| inches. When analogy. However, the writer has been receivers mounted on the set the whole carrying about by bicycle, train, projects but and 10 inches from the bulkhead. This sounds wagon motor car for the past 19 years and during this larger than it is or rather the space under haphazard exploration of some 25 states has the cowl is larger than one gained much confidence ordinarily in the belief that thinks. The leg room in a small car such Hartford stands well as the down at the bottom of the scale of radio Essex coach is not noticeably inter- reception. It seems not too fered with by such an installation. rash to suggest that the A bracket is supplied with the set by quite good performances obtained m many tests about Hartford are means of which the loud speaker may be reliable indicators of a better mounted on the ceiling or in any other materially perform- ance at almost all other an position in the car interior. A phone cord points, opinion is confirmed by a number of other also provided so that the loud speaker observers. for the may be connected to the set as before by Speaking himself, writer offers the opinion that at a of means of the same pin jacks. The loud majority the places in the United States entertain- speaker lead does not carry the plate satisfactory sup- would be ply voltage and may be run as desired. ment-reception possible during the hours when For compactness the location of the loud any amount of broadcast- ing is going on that speaker on the set is an advantage but _ assuming always there are there is no local thunderstorm and that acoustic difficulties. The space the road is not too under the cowl tends to cause "boomy" villainous. If the resonances; also there prediction has the sound of a free adver- may occur what we 80O 1000 1200 1400 have tisement, let it be so. I assure that it called "overcoat attenuation," KILOCYCLES you is whenever the actually quite free, and given in right-front seat is occupied apprecia- Fig. tion of a really nice piece of work. RADIO BROADCAST FOR APRIL 323 Developments in HIGH-FREQUENCY MEASURING EQUIPMENT By H. D. OAKLEY General Electric Company which measurements on a.f. amplifiers however, that the impedance of the loud are made. speaker or phone circuit is many times that Audio-frequency amplifiers make use of the load resistor so that no appreciable of vacuum tubes and, when making meas- errors will be introduced in the measure- urements to determine their characteris- ments. There is still another condition en- tics and power output, it is usual practice countered in this class of measurement. to terminate the amplifier (i.e., load the It has to do with the type of output cir- Rear rieu> of audio-frequency output tube) with a resistor the value of cuit used in the amplifier. For example, in voltmeter. which is specified by the tube manufac- some amplifiers the d.c. supply for the last turer. It is convenient, therefore, to have tube passes through the load resistor but a variable resistor with which any value in others it does not. When this second con- WHILE ENGAGED in activities concerned of resistance likely to be used in the meas- dition prevails, the supply must reach the with the development of audio-frequency urements can be easily and quickly ob- tube through a high-impedance reactor and amplifiers it is necessary to have at hand tained. Also when using a resistance load the load resistor must be connected to the apparatus by which the values of input it is wise to supervise proceedings with a output tube through a low-reactance cap- and output voltages of the amplifier can loud speaker or a pair of phones connected acitor. The circuit for this second condit- be determined. There is very little diffi- across the load resistor being certain, ion is called the shunt-fed type, the first culty associated with input voltage de- rmummlmmillmnliltil being the series type. terminations. It may be accomplished, The loading device attends to all these for instance, by measuring the audio- Voltmeter Errors little details. It consists of a decade resis- frequency current flowing through a re- ERRORS DUE TO MULTIPLIER RESISTOR tor box with which any desired value of sistor of known value across which are Multiplier Kalios Per Cent. load resistance can be obtained, a large connected the input terminals of the am- reactor and large condenser for shunt fed Nominal True Error the the of circuits, for a loud a plifier, voltage being product 1 1 pin jacks speaker, the current and resistance. But determina- 2 2.001 0.05 100,000-ohm resistor which can be in- tions of output voltage are not accom- 5 4.98 0.4 cluded or excluded from the loud speaker 10 10.01 0.1 as To the terminals circuit, and two switches. Each switch plished easily. output 20 19.90 0.5 key of an amplifier is connected a load which SO 49.7 0.6 has three positions, those for one being in measurement practice usually is a re- 100 99.8 0.2 "Choke," "Neutral," and "Resistance," 200 199.0 0.5 sistor, and in service some sort of loud and for the other "Monitor," "Neutral," speaker. Now any device placed across FREQUENCY ERRORS and "Loud speaker." On the front of the this load for the purpose of measuring the (Multiplier Tap 1. Input held at 0.9 volt) loading device are two binding posts voltage across it must satisfy three con- Frequency Meter Per Cent. marked "High" and "Low." The output ditions: the current the device in Cycle* Heading Error terminals of the which passed by 30 0.875 2.8 amplifier upon must be very small compared with that 60 0.892 0.9 measurements are to be made are con- flowing through the load; the indications 80 0.897 0.33 nected to these. Fig. 2 shows five circuits of the device must be of 100 0.900 0.00 which be obtained with this device independent 200 0.901 0.11 may frequency over the audio-frequency range 500 0.902 0.22 and it also indicates the positions of the (30 to 10,000 cycles); and the indications 1000 0.905 0.44 two key switches for each circuit. 2000 0.905 0.44 of the device must be controlled by the Circuit No. 1 (Fig. 2) is the shunt-fed 5000 0.905 0.44 effective rather than by the peak or aver- 7000 0.905 0.44 type with the loud speaker monitoring age value of voltage across the load. 10000 0.900 0.00 connection and is obtained by throwing A voltmeter has been de- one switch to the "Choke" veloped to satisfy these three position and the other to the conditions and also to cover "Monitor" position. Notice a sufficiently large range of that there are 100,000 ohms voltages to adapt it to meas- in series with the loud urements identified with speaker, thus preventing the phonograph and broadcast loud speaker circuit from amplifiers. producing an appreciable The two pictures accom- effect on the load of the panying this article show amplifier under measure- the external appearance and ment, since the load resist- the arrangement of the vari- ance never exceeds the value ous parts of the voltmeter. of 10,000 ohms and is usually An additional feature of around 4000 ohms. It is ob- this apparatus is a unit called vious from Fig. 2 how the the load device. This occu- other circuits are obtained pies the bottom panel of and it is only necessary to the voltmeter. The useful- name the circuits. Circuit ness of this device may be No. 2 is the series circuit with judged from a consideration monitoring connection; Nos. of the conditions under Fig. I Circuit of A.F. voltmeter and loading device. 3 and 4 are, respectively, 324 RADIO BROADCAST FOR APRIL PART II ADescriptionof t he GeneralElectric A.F. Voltmeter Used in Connection With the Generator Equipment Described Last Month. Part III Will Consider the Attenuator. the shunt and series connections but with a microammeter, is con- a loud speaker instead of a resistance as nected to the junction the load; and No. 5 is the calibrating of the thermocouple. or cut-out circuit. With circuit No. 5 The scale of this meter all parts of the loading device are cut has been marked in out and the voltmeter terminals (1 and 2) terms of volts; the full- are connected directly to the high and scale mark is 1 volt and low binding posts of the loading device. the lowest 0.2 volt. External appearance of the audio-frequency With this circuit calibrations of the volt- A range of 0.2 to 1.0 voltmeter. meter can be made, or voltage determina- volt is not sufficient to tions effected with the voltmeter operat- endow the voltmeter ing independently of the loading device. with any great amount of usefulness in ured is impressed across the entire resistor The middle panel contains nothing but amplifier measurements so there has been and by means of the switch the grid of the the plate battery of the voltmeter tube. provided a multiplier with which the range voltmeter tube is connected to that part of The six-volt filament battery is external has been extended to 200 volts. This is the resistor across which there exists a and is connected by a cable. a resistor provided with a number of taps potential of not more than one volt. The which are brought out to the contact but- taps have been calibrated so the ratio of The Voltmeter Panel tons of a switch. The voltage to be meas- the voltage across the whole resistor to The top panel contains all the units that across the tap is known. Therefore, which constitute the voltmeter, with the to determine the value of the voltage im- exception of the indicator. This is a mi- Voltmeler Errors pressed across the resistor it is merely croammeter connected to the voltmeter to the scale by INDICATOR SCALE ERRORS necessary multiply reading a cable. of the indicating meter the value of (Frequency of Voltage 100 Cycles) by The voltmeter consists of three this ratio. To build a mul- proper Scale Per Cent. satisfactory a Input parts: an amplifier, multiplier, and an Voltage Reading Error tiplier required very careful design. Its to- indicator. The amplifier is a single tube 1.0 1.0 0.00 tal resistance (100,000 ohms) has to be 0.9 0.9 0.00 whose bias so that it does not affect the voltage, plate-load impedance, 0.8 0.802 25 high enough and plate voltage are so related that it 0.7 0.701 0.11 circuits to which it may be connected. It operates as class "A" or linearly. In other 0.6 0600 0.00 must not possess either inductance or ca- 0.501 0.20 words, conditions have been fixed so that 0.5 otherwise its ratios would be 0.4 0.40 0.00 pacity, tap when an alternating voltage is impressed 0.3 0.30 0.00 subject to variations with changes in on the grid of the tube there appears in 0.2 0.20 0.00 the frequency of the impressed voltage. the plate circuit a current whose shape KRRORS DUE TO FILAMENT AND PLATE VOLTAGE The multiplier as finally developed fulfilled is identical with that of the impressed VARIATIONS these conditions in a very satisfactory voltage and the ratio of whose amplitude Filament Meier Per Cent. manner. The tap ratios have been adjusted Voltage Error with to that of the volt- Reading to the values of 1, 2, 5, 10, 20, 50, 100, and respect impressed 4.5 0.899 0.11 age remains constant as the amplitude of 5.0 0.900 0.00 200. These give a nice overlapping of read- the voltage is changed. Now if there be 5.5 0.897 0.33 ings on the meter so that when going from placed in the plate circuit a device that Plate Meter Per Cent. one tap to the next readings at the ex- will measure the effective value of this Voltage Reading Error treme ends of the meter scale are avoided. 123 0.82 9.0 current, and if the proportionality factor 135.5 0.90 0.0 The zero tap is simply a safety posi- between the current and the impressed 147.5 0.955 6.0 tion. When the switch is on this tap the grid voltage be known, then grid of the tube is short NUMBERS AND SWITCH the effective value of the CIRCUIT POSITIONS circuited and cannot be sub- grid voltage is easily deter- OHIGH jected to excessive volt- rninable. For this device, a ages. thermocouple is employed. There have been included It is connected to the plate in this article data by which circuit through a transformer the magnitude of the various so designed that the proper OLOW errors of the voltmeter can value of impedance is intro- 1- CHOKE - MONITOR 2- RESISTANCE -MONITOR be judged. In service, the duced in the plate circuit to greatest errors arise from low the tube as a make operate plate voltage. Therefore the linear amplifier. The circuit instrument is equipped with diagram (Fig. 1) shows a a double-scale voltmeter and switch connected across the two-position switch with heater of the couple. This is which both the filament and for protecting the heater from OLOW pi ate voltages can be checked. excessive currents that may 3-CHOKE- U.S. 4- RESISTANCE -L.S. 5 -RESISTANCE The plate battery is made (LOAD RESISTANCE SET OH (LOAD RESISTANCE SET ON (LS. SWITCH IN NEUTRAL exist while adjustments are OPEN STUD) OPEN STUD} POSIT/ON) up of large units and will sup- made a series (LOAD RESISTANCE SET ON for a being during OPEN snot ply energy long period of measurements. of time before replacement The voltmeter indicator, Fig. 2 Circuits obtainable with loading device. is necessary. RADIO BROADCAST FOR APRIL 325 MEASUREMENTS ON BAND-PASS FILTER CIRCUITS By W. T. COCKING Radio Engineer, The Receptite Co., London. Mr. Cocking, an English engineer Sorne Definite Quantitative Figures on Capacitatively whose writings have frequently appeared in foreign publications, presents in this and Inductively Coupled Filter Circuits. Band Width as article the results of some quantitative measurements on band-pass filters with a Function of Circuit Constants. Characteristic Curves various types of coupling. Although simi- lar arrangements have been thoroughly With Typical Circuit Arrangements. analyzed mathematically there has been an unfortunate lack here and abroad of definite laboratory data. An article deal- pacity must be equal to the total secon- one-half of that for the ordinary series- ing with the mathematical considerations dary circuit capacity, and the effective tuned resonant circuit. r.f. resistance of both circuits must be the The usual formulas, in the design of band-pass filter circuits simple depending same. upon the coefficient of k, for was published in February, 1930, RADIO coupling, calculating the frequencies of the two BROADCAST, pages 212-214. (1) peaks in the tuning curve of a filter are inaccurate, since they neglect the effect of the coil resistance. The occur IN MOST present-day sets the tuning is car- peaks II effective r.f. resistance in ohms of coil, at the two for ried out by a number of cascade tuned approximately frequencies when connected in circuit. which circuits, and, although it is easy to obtain L total inductance in henries of primary circuit and also of circuit, very high selectivity in this way, it is not secondary R +X = ujL- (6) since both are identical. possible to obtain fidelity as well, un- good C = total capacity of primary circuit in less a of such 2 - 2 prohibitively large number farads and also of secondary circuit, but if R is high, the term 4 R (o>L 1 /we) circuits are used. since both are identical. in the denominator of equation (1) appre- E = voltage induced in series with primary The filter, either alone or in band-pass circuit, ciably affects the peak frequencies, in conjunction with a number of cascade e = voltage developed across secondary some cases to such an extent that the tuned offers a solution of the condenser. circuits, tuning curve becomes single peaked. its e/E gain of circuit. problem, for, when components have =* At one it will be seen X reactance of coupling component, any frequency suitable characteristics it gives high values = 100 component must be equal to the r.f. re- variation in band width. The coupling Coupling Variation sistance of the coil. Now the latter, with reactance is smallest when the resistance the usual design of coils, varies in a man- is greatest, and vice versa; consequently, When a capacitatively coupled filter is 2 2 ner roughly proportional to frequency; the value of R + X tends to remain con- used, however, the coupling does not re- but the reactance of the coupling induc- stant. Indeed, by suitable design of the main constant; it is considerably less at tance is also proportional to frequency. coils it is possible to make it quite con- high frequencies than at low, and this can Therefore, the optimum coupling can be stant, but this is not desirable, since the be used to compensate the low selectivity maintained over a wide band of frequen- necessary increase in r.f. resistance at the of both primary and secondary circuits at cies. If capacity coupling be used, how- higher frequencies would make the cir- high frequencies. It is quite possible to ever, this is impossible, for the reactance cuit very unselective. It is quite possible, design a circuit which will give constant of a condenser is inversely proportional however, to affect a compromise. selectivity over the entire broadcast band to frequency. It can be seen, therefore, that when it is desired to maintain op- Table II Characteristics of English A.C. Screen-Grid Tubes timum coupling over the whole tuning range of a receiver, there is no alternative to inductive coupling. Type In most cases, however, it is desirable that the coupling should be greater than the optimum, which always gives a single- peaked tuning curve. With a greater value of coupling a double-peaked curve is obtained, and this can be used to compen- sate the usual loss of sidebands in follow- ing cascade tuned circuits. If the peaks are arranged to occur at frequencies 10 kc. apart, audible notes of 5000 cycles will be reproduced at greater strength than notes of 50 cycles; and when this is done, it is obviously desirable that the peaks should occur at the same distance apart over the whole tuning range of the re- ceiver. This, however, is usually impos- sible. In what follows it is assumed that tun- ing is carried out by means of variable con- densers; it is not applicable to the rare cases where variometers, or a combina- tion of variometers and variable condensers, are used. Band Width At whatever fre- quency wL = 1/uc, at a frequency 5 kc. dif- ferent from this the value of wL 1/iix; re- mains approximately constant; consequently, the quantity R2 + X2 of equation (6) must also be constant in value over the whole tuning range of the re- ceiver, if the band width is to remain constant. It will be seen that with inductive coupling this quantity is much greater at high than at low frequen- cies. Neglecting the effect of the resistance, when the two peaks are 10 kc. apart at a frequency of 600 kc. they will be 20 kc. apart at 1200 kc. ; the increased r.f. re- sistance at high frequencies, which always occurs in practice, increases this varia- tion in band width. With capacity coupling, however, the case is exactly opposite. Neglecting the resistance, the band width at 600 kc. is double that at 1200 kc.; but in this case, the effect of the resistance is to reduce the nearly the same with all three curves, being slightly greater with inductive coupling at the higher frequency. The side- band variation, however, is very differ- ent; at 600 kc. it is 15 per cent., and is in the form of a high-note accentuation. At 1200 kc., with inductive coupling it is only 6 per cent., but with capacity cou- pling there is a high-note loss of 30 per cent. This difference in the amount of sideband variation at different frequen- cies is not the disadvantage it may at first appear to be; as will be shown later, when considering the applications of the filter to a tuned r.f. amplifier, it is rather an advantage than otherwise. Coupling Tubes The band-pass filter may be used with very similar results as a means of coupling two tubes in a r.f. amplifier. It is usually 10 THE INVESTOR LOOKS AT RADIO By BERKELEY A. CATER Chief Statistician, Bhimenthal Brothers Members, New York Stock Exchange The First of a Series of Articles Considering the Speculative and Investment Values of Radio Stocks. This Installment Considers Conditions in General; The Next Article Will Analyse the Position of R.C.A. IT is PROBABLE that more money has been Of the 24,000,000 homes in the United made and possible that more has been lost States, 12,000,000 or more are believed in radio than in any other development in to be equipped with radio receiving sets. this generation. Surely, any industry Of the remaining 12,000,000, several mil- which has so profoundly affected so many lion will never be able to afford sets and a people is worthy of our brief attention. small portion will never want them. As The growth of the industry has been the sale of radios in 1929 was estimated at truly fantastic and has naturally aroused from 3,000,000 to 3,500,000 sets, it is public interest not only in actual receiving obvious that at this rate of production apparatus, but also in securities of radio every prospective purchaser could be sup- manufacturers. In many cases large profits plied within a few years. This growth in were realized, both because of the growth the manufacture of receiving apparatus be made quickly, (c) American manu- of the industry and the rapidly rising has been far more rapid than was healthy facturers are loath to extend credit facili- stock market, but in almost as many cases and may be compared to an over-grown ties to overseas dealers, and (d) the landed losses were equally great. The unknown child that has not yet reached its cost of American sets is much higher than element of mystery in radio was indirectly strength. sets made by European manufacturers. responsible for successful pool operations Frequently we are told that without the Although exports of radio apparatus in in many radio stocks, for it is well- drastic decline in the stock market, radio 1929 reached a total of $23,122,141, a known that such operations are seldom sales would have continued to advance as gain of $11,060,662 over 1928, the greater successful in stocks lacking an air of mys- rapidly as in the past, but if we consider part of our exports went to Canada, Aus- tery, as pool operators work on public the facts as they are, we shall arrive at a tralia, and the more prosperous South fancy rather than facts. less favorable conclusion. It is true that the American countries where merchandise of break in the market did seriously affect quality can be sold because of relatively Investor vs. Speculator sales in November, as compared with Octo- high average wealth. If we were to attempt to survey the ber. However, recovery was noticeable in In Europe the prospects are much less situation in radio strictly from the in- December, largely because of the holiday hopeful, for the quality of our merchan- vestor's point of view we could not pro- trade, but it was still not sufficient to dis- dise is not as a rule sufficiently better to ceed much further, for few, if any, of pose of stocks on hand. It is estimated that warrant the extra cost. the common stocks of radio companies are more than 1,000,000 sets are being carried A entitled to true investment ratings. Admit- over which must before long be thrown on Comparison ting that in many cases the difference be- the market. [Sale of these sets is felt to be The radio industry may be compared tween investment and speculation is not proceeding at a steady and satisfactory in a number of respects with the auto- clearly definable, we believe that to enjoy rate Ed.] The beginning of this liqui- mobile industry in its early stages. Of the an investment rating a common stock dation has already become apparent in many early manufacturers, only a few of must (a) participate in the earnings of a some of the larger centers, where radio the strongest have survived. Automobiles stable and necessary industry, (b) pay a prices have been cut materially. Although have apparently nearly reached a state of reasonable dividend in relation to earnings the break in the market with its conse- perfection, changes being of a non-essential and market value, and (c) have paid that quent loss of buying power to the average nature, such as color or body design, but dividend for a number of years, in de- investor had some affect on radio sales, automobiles of necessity will wear out pression and prosperity, thus indicating a it may more truthfully be said that it re- and must be replaced. The contrary is true substantial reserve. A few radio stocks vealed an unsound condition in the indus- of radio apparatus for, with the exception will undoubtedly attain investment rating try which would inevitably have become of tubes, and in some cases, batteries, within a few years; and a few are now known at a later date, and probably with there is little deterioration. Offsetting the reasonably attractive as a speculation for more unfortunate results. fact that radios are much cheaper than long-term holding. A modification of our automobiles and may reach the saturation Problems title to "The Speculator Looks at Radio" Industry point sooner for that reason, is the possi- would thus seem necessary. As we are not The problems facing the industry are bility of further perfection making existing interested at the moment in any particular therefore (a) to dispose of stocks on hand apparatus practically obsolete. In this company or the advantages of owning a without a price war, and (b) to improve field lies the hope for the industry. Which particular set, we shall limit the discussion receiving apparatus so materially either tendency will be stronger can be answered to the financial condition of the industry in reception or appearance that the re- only by the course of future events. as a whole and its prospects for the future. placement demand will take care of pro- Other Weaknesses Although the development of radio in duction. That this task will not be easy this country has been phenomenal, it has may be realized when we consider that Not all the ills of the industry should be been typical of the extremes of American the combined manufacturing facilities of attributed to over-production for some commercial enterprise, both enjoying the all companies in the field could produce companies have lacked one or more of the advantages and suffering the disadvan- annually over 15,000,000 sets. requisites for success, such as skilled re- tages of our aggressive manufacturing and It is possible that the answer to the search engineers, good advertising and sales policies. The industry has grown so question lies in sales overseas, especially merchandising policies, and strong financial rapidly that it has suffered from lack of in countries where the average per capita backing. The market value of the stocks of balance and at the moment cannot be wealth is high, but there are definite some companies has been made still said to be in a thoroughly healthy con- reasons why such sales cannot increase as weaker by pool operations which in some dition. This is in spite of the fact that radio rapidly as was the case in the domestic cases appear to have received the support broadcasting and receiving have reached market. These reasons are briefly that (a) of the managements, and it is doubtful if a very high state of perfection in this coun- wavelengths in many countries are dis- any radio stocks have escaped some ma- try and are being improved to fulfill the similar to our own, necessitating a differ- nipulation. The recent receiverships, of Earl best artistic and commercial requirements. ent type of apparatus, (b) delivery cannot (Continued on page 345) RADIO BROADCAST FOR APRIL 329 View of radio transmitting and receiving apparatus in a modern Navy airplane. AIRCRAFT RADIO DEVELOPMENT A Summary of the Factors Influenc- ing the Design of Aircraft Transmit- THE FIRST telephone transmis- ters and Receivers. General sion from plane to ground was Require- accomplished in England during ments of Receivers for Aircraft Use. the summer of 1915 by Major Prince and Captain H. J. Round. Sensitivity, Fidelity., and Band Width A cw tube transmitter was used for this notable achievement. Characteristics of a Typical Receiver. Since that time, radio has come to play an increasingly greater part in the development of commercial ELMER L. BROWN aviation. By Engineer, Special Equipment Division, Ignition noise has prohibited the use of RCA-Victor Co., Inc. highly sensitive receivers until very re- cently. This necessitated the use of the long, trailing-wire antenna which was un- output of the receiver is necessary for oper- satisfactory on account of landing prob- ating a beacon-indicating device. lems, time involved in reeling the antenna The trailing wire type of antenna, which in and out, frequency variation, losing the has been used until very recently for both antenna, and other factors. Mechanical vibration and noise has made the choice of non-microphonic tubes a necessity. The problems of construction, instrument mounting, and dependability are also de- pendent upon the extreme amount of vibration encountered. The placement, ac- cessibility, and servicing of the component parts must be considered. The apparatus must be simple and fool-proof, because the average pilot and mechanic are not expert radio operators and only the larger com- mercial planes can accommodate a special radio operator. Frequency choice is im- portant, and depends largely upon the purpose of the equipment. Continuous communication with ground stations along standard airways must be considered. The apparatus must be able to withstand the unusual climatic, humidity, and tempera- ture changes encountered during any kind of flight. Tuning must be accomplished with heavy gloves at times. A locking device is frequently necessary to prevent "creeping of tuning," especially for beacon work. The apparatus must be extremely light, shock-proof, and compact. The pow_er supply should be such that the equipment can be operated during emer- gencies, such as a forced landing. Sufficient UX-171A 22ov -- GEN + REDO 40 MILS O Rl-13 OHMS C1-OQ005MFD C6- 0.06 MFD R2-3000 OHMS C2- TRIMMER C7 - 0.0025 MFD R3- 0.5 MEGOHM C3 - 0.1 MFD. C8- 2 MFD. STORAGE BATTERY R4 - BALLAST RES C4- 2 MFD. C9 - tt03 MFD. R5-150 OHMS C5- 1MFD. CIO- 250 MMFD. GEN- - REMOTE POWER SUPPLY SET --' CONTROL Cll- 0.01 MFD. The schematic diagram of a typical air-beacon receiver Three types of radio receivers are in (The great demand, particularly by the beacon indicator, jack for phones, and general use by aircraft. These are: aircraft industry, for a non-microphonic necessary cable connections. (1) Military type that is required to low-current-consumption tube has resulted 10. Of such size and dimensions which cover a broad band of frequencies. in the development of the ux-864 type. permit installation in whatever space is (2) The average commercial beacon and This tube has approximately the same available. radiophone receiver required to cover the characteristics as the ux-199, except that 11. Sufficient sensitivity to get down comparatively narrow band from 285 it uses an oxide-coated filament requiring to atmospheric noise level with a 2-meter to 350 kc. 0.250 amperes at 1.1 volts. This tube is vertical-rod antenna. (3) The high-frequency receiver that extremely rugged, non-microphonic, and 12. Sufficient fidelity. Reacon signals operates on frequencies above are modulated from 40 to 120 1500 kc. cycles and the voice ranges from The first type has rather rigid 300 to 3000 cycles. specifications and usually requires 13. Must have sufficient out- the use of a specialist in operat- put to operate a beacon course- ing. indicating instrument. Ten volts The second type is a standard of audio frequency with a load tuned-radio-frequency receiver, impedance of 4000 to 7000 ohms and usually consists of three is sufficient. tuned stages of screen-grid radio- 14. A fair amount of selectivity frequency amplification, a detec- is necessary, although the prob- tor, and two stages of audio- lem is not yet as bad as that on frequency amplification with the broadcast frequencies. sufficient output to operate a 15. A well-designed helmet to beacon-indicating device. exclude mechanical noises. Use of The third type usually consists sponge rubber caps is satisfactory. of a regenerative receiver employ- 16. Should be satisfactory for ing plug-in coils for the different both visual and aural beacon re- frequency bands and sufficient a.f. ception up to 150 miles with a amplification for easy reception 2-kw transmitter on the ground above the mechanical noises. on the 333-kc. band, using an The general requirements of a antenna 2 meters high on the radio receiver for aircraft use are plane, and the bonded metal as follows: members of the plane for a 1. Single dial control. Fixed counterpoise. tuning. 17. The total weight, including 2. Rugged volume control. a 5-pound duralumin antenna Capable of remote installation. and a 10-pound battery, should 3. Sufficient shielding to limit not exceed approximately 35 signal pick-up to that of the an- The battery used for the View of a wind-driven motor generator. pounds. tenna. navigating and landing lights 4. Rugged construction in or- may be used for the filament der to be immune from vibration en- economical in operation.) It is understood supply of the receiver. countered. that a complete line of low-current, low- Plate rectification with automatic grid 5. Npn-microphonic construction. voltage, non-microphonic tubes are being bias is desirable when used with a visual 6. Rigid condenser plates. Wide spacing developed. indicator. Reversal or lack of course in- with plates of at least 0.025-inch stock is 8. Accessibility or ease of servicing. dications may result if the input is in- usual practise. The receiver mounted on a track with a creased through values corresponding 7. Non-microphonic tubes. Tubes of locking control is quite satisfactory. to the maxima of the curve into the regions the heater type such as UY-227 and uv-224 9. Dash control. This consists of vol- of the negative slope. An automatic bias are particularly adapted for aircraft use. ume control, on-off switch, tuning device,. prevents this. The sensitivity and selec- RADIO BROADCAST FOR APRIL 331 tivity of the receiver are also better with value lies in a separate small gas engine- ignition and mechanical noises made the plate rectification. driven generator. This could be used for cross-coil beacon necessary. This beacon ordinary communication service, and consists of two coil antennas disposed in The Transmitter would be invaluable as an auxiliary. two vertical planes fixed at an angle from The type of transmitter used depends Several types have been developed, but each other. In a simple form the two-coil naturally upon many factors. Roughly, a a great deal of experimental work is still system is free to be rotated about a vertical radio-phone will cover about one-third to be done in this field. A small two-cycle, axis. When the two coils are similarly the distance of a radio-telegraph trans- two-cylinder motor of about 2 H.P. is excited with a modulated radio-frequency mitter of the same power, but will weigh about right for most commercial purposes. current, signals of equal intensity will be about 20 per cent. more. However, these A battery-driven dynamotor may also heard on a receiving set when situated figures are only rela- along either one of the tive, since range vs. two vertical planes weight varies consider- bisecting the angles be- ably with equipment. tween the planes of the The transmitter is COVERS HELD BY SCREWS HINGED COVER OVER coils. At other COVERING LINE-UP THREE JACKS points, governed by the same the signal intensity ADJUSTMENT 1 - OUTPUT as the re- from each coil will be requirements 2 - VOLTAGE ceiver in regard to rug- 3 - S.G. CURRENT different. ged construction, flex- A mechanical device ible mounting of parts, ANTENNA POST can transmit the letter - accessibility, d i m e n N ( ) on one loop and WOVEN TINNED the letter A on the sions, and frequency COPPER COVERING ( ) and stability. In the latter (THESE TWO CABLES other, they are so case crystal control is a CONNECT TO ONE PLUG interlocked that a con- WHICH aid. MAKES POSSIBLE tinual buzz is heard great DETACHMENT OF THESE A range of at least 100 CABLES FROM RECEIVER along the equisignal miles of consistent com- CHASSIS) zone. A deviation of munication is accep- SHOCK ABSORBERS REMOVABLE 14 TERMINALS from 1 to 3 degrees from table for commercial (sec DETAIL) BOX COVER HELD ON JACKS the course will result in aircraft in BY FASTENED one or the other letter flying WING^UT SCREWS standard airways, since becoming distinctly pre- stations are located dominant. every 200 miles, and DETACHABLE The advantages of beacon marker stations DENTAL CABLE this type of beacon are: DRIVE -10 FT. LONG- with auxiliary equip- WOVEN CLOTH 1. No zone of max- ment every 100 miles. COVERED. imum or minimum sig- A combined cw and nal strength. radiophone transmitter 2. Location of course seems to be the desirable found by the compar- thing, because few pilots ison of two signals. have the time or pa- 3. A plane may be tience to learn the code guided along a given without sufficiently for expert 3 - UX -222 airway regard operation of>a straight 2 - UX -112A to wind drift. - - cw transmitter. As 1 UX 17 1 A 4. When considerably become off course, the beacon planes larger AV. SENsmviTY-e and the pay-load ques- furnishes a definite sig- tion is of less import- nal allowing plane to ance than at present, return to former course. 6V.-5TORAGE BATTERY sufficient weight may be METAL SUPPORT Valuable when plane ENCIRCLING RUBBER allowed for a radio- 22JV. TAPPED'C" BATT. must make detours or is forced off course. phone of sufficient DETAIL OF 135V. "B* BATTERY WITH power to communicate SHOCK ABSORBERS 5. Used on national over fairly long dis- airways. tances. 6. receiver A mechanical beacon receiver AR1286. Ordinary The wind-driven description of aircraft type and antenna may be generator is giving used. way to the more recent type which is be used to advantage for an auxiliary The disadvantages are: direct coupled or geared to one of the power supply, and will furnish power as 1. "Plane effect" or angle of plane plane motors. A voltage regulator keeps long as the lighting battery lasts. causes slight error. the constant. These 2. "Night effect" or shifting of equisig- output practically Choice generators vary in output from 500 watts Frequency nal zone at night makes it undesirable for to 2 kw, and both the filament and plate The standard allocated frequency band night flying. supply currents are delivered by them. They for radio beacon service is from 285 to (Continued on page 358) are available for both a.c. and d.c. out- 315 kc., and that for aircraft radio com- put. In some cases the high voltage de- munication is from 315 to 350 kc. The livered is 500 cycles or so. design of a receiver to cover this compara- Possibly the power supply of greatest tively narrow band of frequencies is com- paratively easy and most commercial aircraft receivers are designed for this use. The 500-kc. band may be used for dis- 1-100 tress or emergency signals. Frequencies fc 90 around 3000 to 4000 kc. are good for fairly long-distance low-power communication 60 and are not much affected by fading, skip- tj TO 7- distance, directional effects, type of an- tenna, and other characteristic I 60 phenomena TYPICAL PERFORMANCE of frequencies higher than this. These GRAPH OF AN AIR BEACON RECEIVER frequencies will undoubtedly prove of great value in the future of aircraft radio. as as kc. have been TYPICAL Frequencies high 11,000 30 for OVERALL FIDELITY GRAPH used with very good success long-dis- OF AN tance, low-power communication on trans- AIR BEACON RECEIVER oceanic and flights. flights expeditionary 295 3O5 315 325 335 10 However, they were naturally affected FREQUENCY IN KILOCYCLES by skip-distance, etc. 60 100 3 6 10OO 7000 The curve "HN" gives sensitivity CYCLES Radio Beacons in microvolts per meter for 50 The above curve indicates the The radio beacon of to-day is as prac- mW. output. The other curves overallfidelity of the average air- tical and perfect as the ordinary magnetic give band width in kc.for inputs beacon receiver. compass. High noise level caused by the of 10, 100, and 1000 HN. 332 RADIO BROADCAST FOR APRIL STRAYS FROM THE LARORATORY Sun Spots and Radio A correspondent questions the correla- tion between solar activity (sun spots) and radio reception and at the same time wonders if the steadily declining field strengths from distant stations are not due to a "saturation" or overloading of the ether. We sent these doubts and sugges- tions to Dr. Pickard whose speculations on the interesting questions and long con- tinued measurements on WBBM'S field strength have won him great credit. Dr. Pickard's answer is a chapter in the book of fundamental knowledge of radio. Dr. Pickard's curve (Fig. 1) shows such definite relation between solar activity and radio reception as to leave no doubt. Dr. Pickard says: "Signal strength at night from distant stations has been on the down-grade for at least the past three years. But the correla- tion of this decrease with solar activity has been proven beyond any doubt, and irrespective of any hypothesis. Many thousands of reception measurements, taken systematically over periods of years, have shown such high correlation with measures of solar activity that the relation of sun and reception is as certain as the relation of moon and tide. "But 'etheric overloading' is a harder problem. If the entirely hypothetical 'ether' really had the properties of matter, it might, of course, have definite tensile strength, and perhaps also exhibit fric- tional or hysteretic losses, in which case it would either break up or heat under severe loading. But the majority of modern physicists do not believe there is an 'ether'. Instead, our present-day view is that what we call electromagnetic waves are merely energy quanta shooting bullet-wise across empty space. According to this view over- loading has no physical meaning; how can we overload a void by merely projecting more quanta through it? "This reasoning may not be convincing to everyone, particularly those who still NUMBERS SUNSPOT PROVISIONAL 8SS88S8S WOLFER An untuned amplifier used by the author in his experiments with cathode-ray tubes. MEASURING PERCENTAGE MODULATION Using the Cathode-Ray Tube for Determining Percen- tage Modulation. Desirable Characteristics of a Tube Used for This Purpose. Method of Procedure and Some Typical Examples of the Results Obtained by the Author. The cathode-ray tube has always been By BARON MANFRED ment of the parallel sides is no longer a most useful device in laboratory measure- possible. If a broadcast transmitter is VON ARDENNE in which not the amount but ments on all kinds of pulsating or alternat- used, only also the of the modulation varies ing currents. Additional uses for the lube frequency then the whole trapezoid changes. This are always being found and in this artick will be true at higher frequen- Mr. von Ardenne (who has contributed particularly cies, since phase displacements take place several articles in the Proceed- published in the coupling elements of the rectifier ings of the Institute of Radio Engineers) and amplifier which completely change describes a method of using the cathode- the boundaries of the trapezoid. Further- ray lube in the measurement of percentage more, the trapezoidal form is only obtained modulation. with very small high-frequency amplitudes, since with larger amplitudes at the input of the rectifier, the corners are rounded off. THE DETERMINATION of the percentage of modulation with the Braun tube may be The Second Method made by two procedures: (1) the method The second method is free from these of standing figures and (2) the direct disadvantages. It consists in producing a of the modulation-time taking curve. time axis by means of a rotating mirror or The procedures included in the first a moving film. Naturally this method can group are the older and have been de- be used for any sort of modulation curve, scribed numerous times in the last few including those of broadcast transmitters, years. A superficial explanation of the gen- and at the same time it will allow observa- eral method for the of tion of values of excitation. production standing Fig. 1 The photographic result peak How is as follows: the figures high-frequency of experiments with standing important such a control is in order to to be demodulated is fed to a rectifier and maintain a small amount of distortion in figures. the low frequency so obtained is coupled the detector of the receiving set is gen- to one of the sets of plates of the Braun erally understood. Since the envelope of tube, while the high frequency is coupled lation of the transmitter can be computed the modulated high frequency is visible to act on the cathode ray at right angles immediately from the expression on the film or in the rotating mirror, the to the low frequency. If an oscillograph is sinusoidal form can be seen beautifully made of a high-frequency transmitter in when the excitation is from a low- this way, with the modulating current frequency oscillator and the complex shape having a constant frequency and ampli- The advantage of the method lies in the when it is due to speech. tude, and if the high-frequency axis is possibility that tubes with very weak For photographing the modulation made the horizontal one, then a figure is fluorescent spots can be used successfully curve, it is very important to have a tube to be expected which has for its maximum when the photographic exposure is made which gives a very bright fluorescent spot. and minimum widths the corresponding long enough. On the other hand, a long The brilliancy of this spot determines the limiting values of the modulated high fre- photographic exposure is necessary, and highest speed at which the film can be quency. If the demodulated low frequency in this fact lies a limitation of the use of the moved, and therefore the highest modula- of the transmitter is put on the vertical trapezoid method, if the transmitter is tion frequency which can be recognized on plates of the tube without time lag, then excited only with a constant amplitude of the film. For direct observation of the a stationary trapezoid is obtained on the low-frequency power. If the amount of modulation on a rotating mirror a bright fluorescent screen. The a and modulation then the of the of is also since parallel sides, varies, height spot light very desirable, 6, lie horizontal and the percentage modu- trapezoid also changes so that a measure- this permits observations in daylight. In 334 RADIO BROADCAST FOR APRIL AUDIO POWER TRANSMITTER OSCILLATOR AMPLIFIER o- AUTOMATIC VOLUME CONTROL A General Description of How Automatic Volume Con- trol Circuits Function. Some Details of Experiments on Circuits by the Author. By A. C. MATTHEWS, JR. A VOLUME CONTROL on a radio receiv- ing set has three distinct functions to perform, that is to compensate difference in volume of stations at various distances; to compensate any variations in signal strength due to slow fading, and to adjust the volume level to the desired intensity. An automatic volume control accomplishes the first two objectives inherently, while the last function is left to the particular likes of the operator. The setting of the volume level, however, is made only once and thereafter all stations within the range of the receiver are reproduced with the same degree of intensity, assuming, of course, that their percentage of modulation is nearly the same. Several types of automatic volume con- trols have been proposed in the past and the following are referred to as examples of the various types. 1. Plate current of the output tube in series with a ux-199 filament arranged so as to vary the bias on a preceding tube, thus preventing overload and limiting the volume. (Proc. I.R.E. March, 1928, p. 281.) 2. Varying the plate voltage on the radio-frequency amplifier by means of a control shunting the loud speaker. (RADIO BROADCAST, March, 1929.) 3. Adjusting the radio-frequency ampli- fier bias by means of a two-element rectifier tube. (Proc. I.R.E. January, 1928, p. 30.) 4. Varying the bias on the radio- frequency amplifier by means of a three- element tube connected in a simple recti- fier circuit. (Proc. I.R.E. March, 1929, p. 511.) Of the four systems referred to, the author prefers the last mentioned method, since it has several advantages over the other types. Experience has taught us that in order to provide automatic volume control without introducing distortion the device must operate on the carrier wave. Any variation in the carrier wave strength must be compensated by an inverse variation in radio-frequency amplification. The type of automatic volume control described in this article meets this requirement and is exclusively for use with the a.c. screen- grid tube (uv-224). Since it is permissible in screen-grid receivers for the volume control to vary the screen-grid potential, 250MMFD || UY-227 No. 33 Radio Broadcast's Engineering Review Sheets April, 1930 FACTORS GOVERNING AMPLIFICATION THE VACUUM TUBE is unique among realized. The amplification factor is a a three-to-one ratio transformer and a modern machines in that it amplifies term which indicates the output voltage tube with a mu of 8, are necessary? power, differing in this respect from a which would exist across an infinite re- What C biases will be necessary? The transformer which amplifies voltage at sistance load if one volt were impressed circuit is in Fig. 2. It is only necessary the expense of current or vice versa. on the tube. Unfortunately an infinite to calculate the voltage input to the Strictly speaking this is not true, i.e., resistance load is unattainable and some first a.f. stage by multiplying the the tube and associated apparatus, of the total voltage available in the plate voltage across the a.f. transformer pri- considered as a whole, does not am- circuit of the tube is used up in heating mary by the turns ratio, then, by mul- plify power. For example, if you cal- the plate of the tube and is not em- tiplying this voltage by 90 per cent, culate the total power going into a ployed usefully. Therefore, not all of of the mu of the tube, you get the a.c. tube, say a 245-type power tube, and the voltage amplification of the tube voltage across the primary of the next calculate the total useful power com- can be used. If the load resistance is transformer and so on until the voltage ing out you will see that there is an available for the power tube grid is overall loss of power. But if you neglect JU ascertained. the filament power and the waste of Now suppose you want to use two power in heating the plate and con- resistance stages and one transformer sider only the input power fed to the stage if, for example, two transformer tube as compared to the useful output stages give not quite enough amplifi- power, you will see there is amplifica- cation. Should the transformer or the tion. resistance stages come first or should What actually takes place in the the arrangement be first a resistance amplifier is something like the follow- stage, then a transformer stage, and ing; a small amount of power is utilized finally a resistance stage? The way to operate the tube acting as a valve to solve this problem is to make dia- which releases a large amount of grams of the three possible cases, fig- power from a local battery. ure the voltages that will appear on the Example: In Fig. 1 consider a power grid of each tube, and therefrom find tube getting its input voltage from a.c. what the C bias on these tubes must be. flowing through a resistor, and feeding If the transformer stage comes first, three times the tube resistance, three power into a load resistance. The in- the voltage on the grids of the follow- times as much voltage will appear is the product of the cur- ing tubes will be rather high, which put voltage across the load as across the tube (we rent and the resistance. The output will require high values of C bias, and are speaking of a.c. voltages), and power is the product of the current because of this high bias a high plate therefore the voltage amplification will squared through the load and the load voltage will be needed. Since these be mu X 75 per cent. resistance. Thus, tubes are fed through plate resistors In a transformer-coupled circuit, the in which there is a drop in voltage of Input voltage Ei = liRi = Eg r.m.s. primary inductance into which the = one volt per thousand ohms for each Input power Pi li'Ri tube works is very high and, because Po = Io= Ro current, a Output power of the fact that the total milliampere plate large plate current lo = = impedance Output (AEg/(Ro + R r ) battery will be required. For example, [J.E?/2Rp if Rp = Ro in the plate circuit must be obtained suppose the voltage on the grid of a 1*' Eg' by taking the vector sum (see "Home Output power resistance-coupled stage calls for a C 4RP Sheet" No. 10, Nov. Study 1928), bias of 3 volts. If the Output power u.' Ii' Ri- \ff Rl tube has a high- ' _" the actual voltage amplification ob- 2 will call for Input power 4 Rp Ii Rl 4R P mu this a plate potential tained will be about 89 per cent, of of probably 180 volts (so there will be the values for a 245- the mu of the tube if the reactance into Putting proper a sufficiently long straight portion of which the tube works is twice the tube type power tube into this equation, the the characteristic to handle the 3-volt between resistance in ohms. This will be true at power gain, i.e., the ratio input), and if the tube takes 0.5 mA. the frequency at which the reactance power output and power input, is at this voltage working through 200,000 about 15 times. of the transformer is twice the tube ohms, a plate battery potential of 280 resistance, and, since the maximum ob- volts will be necessary. Coupling Devices tainable is only 100 per cent., the vari- On the other hand, if the input volt- ation in amplification can be only be- The tube, no matter how much am- age to this tube is quite small, for ex- tween 89 per cent, and 100 per cent. plification it may produce standing by ample, when worked directly from the At all frequencies higher than that at itself, is useful only when connected detector, a small C bias will be neces- which the transformer reactance is with associated apparatus. We put a sary, a shorter portion of the char- twice the tube resistane, the ampli- voltage into the tube and extract some acteristic need be straight for distor- fication will be greater than 89 per out. This voltage must be put tionless amplification, and hence lower power cent, of mu and will approach 100 per in by means of accessory apparatus; plate battery voltages are required. cent, as a maximum. the power output must be delivered to Thus if a combination amplifier is some load apparatus. to be constructed it is better to place A Typical Problem The usual means of coupling one tube the resistance stages before the trans- to another are well known to every ex- Suppose then you have a detector former stage. perimenter, viz., resistance, inductance, of out one volt, and capable putting Overall or transformer, but it is not every ex- that you need to have 50 volts on the Amplification perimenter (or engineer either) who, input of a power tube to deliver the Very few radio workers have much without a great deal of hemming and required amount of power. How many conception of the total amplification at- hawing, can tell you how many stages stages of a.f. amplification, each using tained in modern radio receivers. They are necessary to deliver a do not know how this certain amount of power JU=8 JJ=3 voltage gain is distributed. into a given load when the They do know that the input is known, or how advent of the screen-grid much is the overall gain of tube has shifted the pro- a two-stage, transformer- portion of amplification 1 i fi e r coupled a m p , or that exists before and whether it is better to put after the detector. But a transformer stage ahead how much? This is an- of a resistance stage when swered in "Engineering combinations are used. Sheet" No. 34. This sheet I n resistance-coupled also considers the amplifi- amplifiers, about 75 per cation which may be ob- cent, of the amplification tained in circuits using factor of the tube can be Fig. 2 present types of pentodes. RADIO BROADCAST FOR APRIL 337 No. 34 Radio Broadcast's Engineering Review Sheets April, 1930 CALCULATING AMPLIFICATION OF PENTODE RECEIVERS THE ADVENT OF two new tubes, the transformer. How many stages are input must be 12 -=- 40 or 0.3. In other screen-grid pentode and the power pen- necessary? Three stages will give a words, substituting a screen-grid de- tode, is sufficient cause to sit down and total of 27,000, more than is necessary. tector in place of a low-mu tube and calculate the present gain of receivers, Therefore, somewhat looser coupling transformer causes a gain in sensitivity and what will happen if set designers to the antenna can be used with in- in the ratio of 2 to 1 (6 DB). choose to use these new tubes. creased selectivity and greater freedom In addition to this gain in sensitivity The new screen-grid tube is roughly from unwanted noise, or a smaller an- there is a possible saving in money due 1.25 times as good as present-day tenna can be used (the ice pick, for to the substitution of a condenser- screen-grid tubes. That is, it will de- example, as one manufacturer Silver- resistance coupling unit in place of a liver about 1.25 times as much am- Marshall advertises.) transformer. In Fig. 2 is the complete plification. The power pentode is about Think back to receivers of a few screen-grid-detector, pentode-out put- 5 times as sensitive as a 245-type tube. years ago which had a resistance- tube receiver. We now need a gain of That is, to deliver 2000 milliwatts it coupled buffer stage between antenna only 750 in the r.f. amplifier in place requires only 12 volts input whereas and the set, in which there was a of 10,000. If each tube gives a gain of the 245-type tube requires 50 volts to deliver about the same power output, DET-227 5:1 245 1600 milliwatts. Suppose a receiver, Fig. 1, has push- pull 245-type tubes working directly from a detector through a transformer with a turns ratio of 5 to 1. Across the secondary of the input push-pull trans- former is required 100 volts if the power amplifier is to be "loaded up." Therefore, a potential of 100 -=- 5 or 20 volts is needed across the primary. This is the a.f. voltage the detector must deliver. This calls for a power 245 detector, i.e., a highly biased detector probably of the 227 type. At 22 per Fig. 1 cent, modulation and working into 200,000 ohms, such a tube will deliver voltage gain of perhaps 3, plus two r.f. 30, two stages will be somewhat more one volt a.f. for each volt r.f. put on stages using 20lA-type tubes. What than enough and we have a receiver its grid. If the modulation reaches 100 was the total amplification up to the with two r.f. stages using screen-grid per cent., as it may from many modern detector? About 500 at a maximum tubes, a screen-grid detector, and a stations, the output will be roughly 5 unless there was considerable regenera- pentode power tube four tubes in times the r.f. input voltage. This is tive amplification. This meant that a place of present-day sets using five or the maximum voltage that will never be grid leak and condenser detector, which more (usually more) tubes. reached and should be just enough to is about 10 times as sensitive as a C- Such a receiver represents no great put 100 volts across the two push-pull bias detector, was necessary. Then advantage over present sets. The re- duction in the number of tubes needed 224 PENTODE may make necessary greater filtering to reduce the a.c. hum in the output; and because fewer parts are required does not mean that these parts may not the total 40JUV have to be better, thus keeping cost at approximately the same figure. If the screen-grid tube of the future is better than present tubes of this type, still fewer stages may be pos- sible, but it does not seem likely that a R F TO A:F = 1540 single r.f. tube will ever take the place 338 RADIO BROADCAST FOR APRIL kLL^^^^^Mi'^^^^^^^M PROFESSIONALLY 5 6 7 I t 2 3 4 5 6 7 i S 2 SPKAKI'NG 1930 AND SERVICE the dealer's instruments, let the serviceman something ought to be done about this take all the profits. pentode business before the public began to IF, AS THE general service manager of a The examination will prove that he is a look for the new set and to refuse the old. large and well-known radio manufacturer good technician; the fact that all the The statement of the trade association believes, the 1930 service problem will be money goes to the serviceman makes it was made with very little regard for the one of negligible importance, the entire possible for him to work as hard as he cold hard facts with which the engineering industry will have put behind it a most likes with the certainty that the money profession deals and which, we believe, serious problem. The question of whether a will be his. ought to be interpreted to the buying manufacturer should send service litera- The tendency for large dealers to farm public. The statement denied practically ture to the "independent" serviceman or out their service is a step toward the latter everything that had been said in favor whether he must compel all servicing to scheme. It is a fact that no dealer can of the new tubes. be handled by servicemen attached to afford to pay a serviceman enough money Aside from whether or not the various authorized dealers has been solved by to make it worth the while of the latter to statements were ill advised and devoid the majority of manufacturers to their stay out of the "independent" role. The of facts, the situation is indeed unique. own satisfaction. The "independent" farming out process can take place only in So far as we know, for the first time in the has no place in this picture. The rea- history of the industry a tube manu- sons as cited by the service manager facturer developed a tube in his own quoted above are: laboratory and instead of hiding his 1. He (the "independent") does not i light under a bushel until he could get fit into the manufacturer's scheme of tooled up or had sold the rights or positive control over field service or- whatever it is you do to corner the ganizations. Why the industry does not recognize the inde- other fellow's market, he distributed 2. The manufacturer has no claim pendent radio serviceman. characteristics of the tube to engi- his neers and asked their upon loyalty. A solution to the combined problems of radio suggestions. ex- 3. He is under no obligation to dealers and servicemen. Set engineers have asked such co- ecute the manufacturer's policy with operation before. They have wanted How will the pentode tube improve radio re- respect to guarantee, etc. tube designers to present their charac- ceiver design? 4. There is nothing to prevent the teristics, and ask for the suggestions of discontinuance of his activities in any circuit engineers so that the final tube locality thereby leaving that place with- large communities, and, although a large design could be worked out with the circuit out adequate service facilities. percentage of all sales is made by a smaH people in mind. While it is quite probable 5. The manufacturer cannot logically number of dealers, these sales take place that not a dozen circuit engineers in the support his own field service organization where there is plenty of service available. country have any ahead-of-the-minute on the one hand, and encourage the in- It is the customer in small districts who ideas about what to do with a new tube dependent service organization as a group needs service the most and who has the when one is presented for criticism, it is a on the other hand. least chance of getting it. good idea anyhow. Let the tube people Granting all these points, and granting But let us hope that the 1930 service make a tube, and ask the circuit people the fact that we are not on the firing line of problem will be one of negligible import- how to make it better for their needs. service but are in a comfortable office far ance. If 1930, however, is marked by an- Conversely, let the circuit people lay down from the front, we believe there is but one other race to see who can make the most a diagram and beg for a new tube to fit attribute of service that needs considera- receivers at the lowest price, we believe into it. tion is the service adequate? This means, there will still be a service problem of Let us look at this pentode business does the remedy cure the ill, is the cost considerable importance. seriously. There are two kinds, the power commensurate with the effect secured, and tube and the amplifier. The pentode power does the service require only a reasonable NEW TUBES tube delivers about the same output as a amount of time? 245-type tube but is roughly 15 DB We believe that being connected with a A new tube which had been spoken of more sensitive. Calculations on page 338 dealer is no assurance that a serviceman quite calmly in Europe finally broke into of this issue show that such a tube with a is a good one. On the other hand, we believe the public press in January, thereby dis- screen-grid detector ought to make it such a serviceman is probably not as good turbing the entire radio industry to a possible to get along with only four tubes as his brother who gets out and hustles for considerable degree. This tube is the pen- plus a rectifier and make a set just as good himself. As soon as a serviceman learns tode, a five-element tube. In Europe it had as present-day sets with more tubes. But his calling and becomes an efficient and taken the form of a power-output tube you still need two stages of r.f. amplifica- effective unit, he discovers that the of superior sensitivity and efficiency. In tion, and therefore, even if a new screen- meager salary the dealer can afford to this country there are two such tubes, the grid tube which was twice as good as pres- pay is less then he can make on his own. power-output tube and a screen-grid tube ent tubes made its appearance, it would Therefore, he gets out of the dealer's shop with an additional grid. not be good enough (because the overall and goes after business for himself. The pentode power tube came into the gain of two stages is the product and not One trouble seems to be that a dealer limelight slowly and was demonstrated the sum of the individual stages). In other cannot afford to hire a good man. The ser- before a well-attended meeting of the words, the pentode voltage amplifier is viceman can make more money on his Radio Club of America. Knowing the pro- not good enough to act with a power pen- own; therefore, he becomes an "indepen- pensity of the newspapers to exaggerate tode to make a three-tube set practicable. dent." the importance of any technical develop- It is better, but not enough. Perhaps some scheme like the following ment, the authors of the paper "hedged" The pentode power tube will undoubt- would work out. We have already sug- and said the new tube would not make any edly fit into the picture of many manu- gested that the manufacturer pick all startling difference in radio receiver de- facturers. There is no reason for everyone servicemen by a technical examination. sign. to rush into the design and production of a This would obviate the difficulty that the The other pentode was announced by a pentode set, because the public won't be dealer, not being a technical man himself, tube manufacturer with the statement that able to tell the difference, except perhaps in has trouble in knowing a good serviceman it would make possible a $50 receiver by price. It makes a four-tube set possible but when he sees one. After the prospective cutting out sufficient tubes from the present not a three-tube set. As for the screen-grid serviceman has passed the examination, type of sets. It was described as twice as pentode, it must be proved that it really is let the dealer take him on and, except for good as present-day tubes. The newspaper worth the bother of adding terminals to a percentage of the income to pay for the writers took up the matter with great glee the base and to the socket and other circuit service share of the rent and for the use of and soon the trade associations thought changes. RADIO BROADCAST FOR APRIL 339 . THE SERVICEMAN'S CORNER Technique of Servicing ting a series of by-pass condensers across Optimistic declarations on the a 15 battery and had the switch turned off BORIS S. NAIMAHK, one of our regular part of some writers to the con- in the set; nevertheless I got a short from New York sends us the iron which allowed the 110- City correspondents, trary, the lot of the serviceman is volt a.c. the notes on a sub- to run the filament circuit on the following neglected not altogether a happy and pros- through ject. a.f. side and two new tubes 'went west.'" perous one. The salary of a ser- "Did it ever happen to you -you being J. B. TEMPLE, Toronto, Ont. viceman in the a dealer a good and conscientious worker that employ of is rarely commensurate with his just as you were putting the finishing Mounting Loud Speakers touches on an ailing receiver you let your ability and skill. The independent screw driver slip and left a glaring scratch serviceman, working on his own A moving-coil loud speaker can be in the most conspicuous part of a beauti- hook, and perhaps under contract mounted advantageously in the upper ful and highly prized cabinet? or verbal agreement with several corner of a room as suggested photograph- "Anticipating the possibility of such ically on this page. An installation of this dealers, is much belter off, but it occurrences in every day service work, kind will appeal even to the discriminating is not the easiest thine/ in the world I obtained, through an authorized Philco customer, and is acoustically very fine. to so establish himself. The service- dealer, a cabinet touch-up kit known as It, is essential, however, that the louvres man is invited to read "An Philco Part Number 3809, and containing SOS be cut in the baffleboard, or the effect will Established all the materials necessary for minor cab- To The Serviceman" be drumrny. Also mount the loud speaker inet repairs. I have found that this work in this department and to write us from one quarter to one half inch behind is not at all difficult and can be handled concerning the most advantageous the opening for the best reproduction. serviceman after little The idea of by any very prac- solutions of his several problems. compensating tone dis- tice. The Editor. crepancies by moving the cone nearer to "The Philco kit enables one to touch or farther from the opening in the baffle- up scratches and white edges on cabinets, board is also suggested by H. D. Hatch, and consists of the following materials: house current is grounded; also one side of Wollaston, Mass., who writes: Burning-in Wax: Dark Red, Brown, of the radio set runs to this common "A customer recently complained that and Red. ground. It cost me two power tubes to her Magnavox electrodynamic loud Powdered Stain: Bismarck Brown, Van- find out that a brand new electric soldering speaker gave a hollow sound on voices. dyke Brown, Burnt Umber, and Malachite iron can have a short in the case. I was put- After assuring myself it was not due to Green. the set I loosened the loud Also: Liquid White Shel- speaker and moved it back lac, Alcohol Lamp, Wood from the opening in the baffle. Alcohol, Felt Block, Felt The idea was to reduce the Pad, Rubbing Oil, Steel baffle effect on the longer Wool, and Knife. waves or low notes. Turning "To touch up light fin- the set on I moved the loud ishes take a small amount of speaker back and forward 'the stain nearest the cabinet until the customer was satis- color and dissolve in a quan- fied." tity of white shellac. A little of the green stain added to A Hum Filter the darker colors will make them lighter. Having ob- An arrangement for the tained the right color, apply reduction of hum in special it with a pencil brush to cases, which, by the way, whatever parts need touch- should be effective in re- ing up. Let this dry and ducing certain forms of arti- then apply a coat of white ficial static, is suggested by shellac. If this has too high an engineer now with the a gloss rub lightly with Bureau of Standards. the felt block and rubbing "Certain radio receivers, oil. under the proper (or rather "To burn-in scratches and improper) conditions, will bruises, heat the knife over hum rather badly when a the alcohol flame. When the station is being received, knife is sufficiently warm even though the hum level apply wax of the proper color may be very low when no to the scratch and smooth signal is tuned in. This phe- it down with the knife. This nomenon has been noticed is then rubbed with the felt in a number of receivers, block and rubbing oil. If too both factory- and home- high a gloss is thus obtained made, although with the same it can be dulled easily by receiver it may occur under rubbing lightly with steel certain conditions and not wool." under others. "The effect is WATCH THE SOLDERING IRON apparently caused by pick-up from the "In using an electric iron power line as well as from on a set which is hooked up the antenna, although the it is a wise precaution to re- nature of the interaction of move all of the tubes or bet- these two pick-up voltages ter still to disconnect the to produce the hum is not receiver from ground and 110- A method of mounting the moving coil loud speaker entirely clear. A poor volt supply. One wire of your effectivelyfrom both esthetic and acoustic points of view. (Continued on page 340 RADIO BROADCAST FOR APRIL REVOLUTIONARY!* IN CONSTRUCTION AND PERFORMANCE EVEREADY RAYTHEON 4-PILLAR TUBES sell . NOW you can your customers something really new . . Eveready Raytheon Tubes! Let them hear the rich, full-voiced tone, the breath-taking realism of Eveready Raytheon reception. Demonstrate it, in their own radio sets . . . then tell them reception will always be better if they put a new Eveready Raytheon in each socket whenever the tone begins to sound fuzzy. You can HEAR the difference and SEE the reason Look at the illustration on this page, showing Eveready Raytheon's 4-Pillar construction ... a sound improvement. See the solid, four- cornered glass stem, with the four rigid pillars imbedded in it, anchoring the elements. No other tube is permitted to use this construction, for it is patented and exclusive with Eveready Raytheon. Before the day of dynamic speakers and screen grid circuits, the old, flimsy, "gas-mantle" construction may have been satisfactory. But present-day radios need tubes with 4-pillar rigidity. No legal entanglements! Eveready Raytheons are licensed tubes. They come in all types, and fit the sockets in every standard A.C. and battery-operated receiver now in use. Ask your jobber, or write us now for the names of jobbers near you. The Eveready Hour, radio's oldest commercial fea- ture, is broadcast every Tuesday evening at nine (New York time) from WEAF over a nation-wide N. B. C. network of 30 stations. NATIONAL CARBON COMPANY, INC. General Offices: New York, N. Y. Branches: Chicago Kansas City New York San Francisco Unit of Union Carbide ill Hi) and Carbon Corporation EVEREADY RAYTHEON Trade-marks RADIO BROADCAST FOR APRIL 341 (Continued from page 340) grounded connection appears to accentu- ate the hum. "The remedy is obvious a filter in a power line to eliminate the pick-up from that source. This filter should be as close to the radio set as possible. In most cases, two 0.5-mfd. condensers connected in series across the power line, with the center tap connected to the ground post of the set, provide sufficient filtering (Fig. 1). In more obstinate cases, two radio- frequency chokes may be connected on the ^1 supplemented their own independent busi- We over a two that CeCo Tubes were ness with contract work for dealers who found period of years be relieved of the of are glad to necessity the most to handle in more than one maintaining their own service department. profitable way.^' This is an to the dealer, and advantage Albert A, List, List Brothers, Distributors, Fall River, Man. certainly of value to the independent serv- ice organization. The arrangement often goes further than mere service, because a large number of service calls indicate the possibility of set or tube sales, and many who have a commission arrangement with the dealer on such sales as may be closed through leads furnished by them, are able to realize an income on selling in which they have responsibility. What have our readers done in this re- me radio service spect? Perhaps the manner in which you any solved your own servicing problems will be of vital assistance to some other service- on the fence. Do or do man sitting you man. Let him two hours you not service for dealers? If you service spend for dealers, what are the terms of your contract? How did your service start? What were the selling arguments you used in closing alone in our 3J4 acre . . contracts with local dealers, and were plant. these dealers making a profit, as far as you can determine, from their service departments? Did they prefer to have for himself mil- their service work done on contract be- seeing why cause it was not possible for each indi- vidual dealer to secure a high-grade serv- iceman to do their individual work, or lion dollar and 42 was the contract signed because of econo- equipment mies which you were able to effect for the dealer? We are interested in how particularly are needed to make you closed with the first dealer and the engineers conditions leading up to this point. Do you operate from a central point with your own office, laboratory, and work^ a better tube. rooms, or how is this done? CeCo decidedly We are interested to know the methods by which dealers requiring service work turn over the orders to your organization. How many men do you employ? What is Then when he makes his next your scale of charges? How are collections from the ultimate customer made by your organization or is the customer billed by the dealer whose work you do? Do you service call. . . there'll be a new grant a commission on gross service charges to the dealers referring business to you or what is the arrangement? How does your scale of wages for servicemen set of CeCo Tubes installed." compare with that paid by local dealers who are doing this work as part of their own retail organization? It would be of interest to know what kind of service equipment you use: whether your set analyzers are purchased complete from one of the several manu- facturers, or whether you use devices designed and built, by yourself. How many of these analyzers are employed? What proportion of repair work is done in the customer's home and what in your shop? President, Your answers to these questions will be appreciated by fellow servicemen, and CeCo Manufacturing *'.. Inc. paid for by RADIO BROADCAST. Providence, R. I. An Interesting Booklet Under the title of "Fixed Resistor Re- placement Problems," the International DO YOU KNOW? Resistance Company, 2006 Chestnut Street, Philadelphia, Pa., has published an interesting booklet on the resistor re- 1. Over 10,000,000 CeCo Tubes are in use 2. In the last 5 years CeCo has outgrown two The U. S. ocean steam- quirements of modern broadcast receivers. today. Government, sizable factories and now has the largest and ships, and countless commercial most modern devoted The text covers the of organizations plant exclusively to importance good are daily users of CeCo Tubes. manufacturing of radio tubes. resistors, their power carrying capacity, the noise factor, and how to determine the necessary resistance and current handling The CeCo Couriers broadcast every Monday CeCo Tubes are licensed under the patents and capacity required. night at 8:30 P. M. Eastern Standard Time applications of the Radio Corp. of America, over the Columbia Chain from 22 stations. General Electric Co., Westinghouse Electric Listen in next Monday. and Mfg. Co. and Associated Cos. A Legal Question The Radio Service Managers Associa- tion, with headquarters at 324 West 42nd New York is Street, City, gradualjy get- ting into swing. This is an organization with a membership made up of service managers and servicemen, providing a (Continued on page CeCo RADIO BROADCAST FOR APRIL 343 No. 43 Radio Broadcast's Set Data Sheets April, 1930 BREMER TULLY MODELS S-81 AND S-82 9 ANTENNA PHONOGRAPH JACK LOCAL-DISTANCE SWITCH MECHANICALLY ,5 MMFD. TO SWITCH TERMINALS COMBINATION ON AMPLIFIER VOLUME POWER SUPPLY CONTROL CHASSIS- > AND SWITCH OUTPUT TO CONE OF LOUD SPEAKER TERMINAL STRIP ON R.F.CHASSIS VOLTAGE REGULATOR TUBE-D-110, TERMINALS FOR A.C. SWITCH O TO FIELD OF LOUD PILOT LIGHT SPEAKER 2.5 VOLTS rpHE CHASSIS used in the Models S-81 and frequency amplifier. The power detector is a The audio-frequency amplifier consists of two -I S-82 receivers is designed for the new a.c. screen-grid tube. stages. The first stage of amplification is resis- screen-grid tubes. The radio-frequency circuit The power detector is automatically biased tance coupled to the detector tube, and employs consists of three stages of tuned and shielded for use as an amplifier for the reproduction of a heater-type tube of the 227 type. The power high-gain amplification using the a.c. heater- phonograph music when the magnetic pick-up amplifier employs two 245-type tubes in a push- tubes . the use of local- unit is into the the circuit. All tubes and type screen-grid (224) By plugged jack provided at pull amplifier amplifying ized shielding and proper grounding (each rotor rear of the r.f. chassis. Any good high-impedance the detector tube have automatic grid-bias section of the tandem condenser assembly is pick-up unit provided with a volume control control which compensates differences in cur- individually grounded even though the rotors may be used. rent drain from the rectifier system. are electrically connected in a common grounded The power pack supplies all required voltages steel shaft) the chassis and tubes are made AVERAGE VOLTAGE READINGS to the seven receiving tubes and energy for the accessible and are unencumbered by unneces- field of the electrodynamic loud speaker. The Type Position of A B C Normal sary shielding. All wiring is rigidly secured in Duresite type No. 110 voltage-regulator tube of Tube Plate position under the steel chassis maintains aconstant voltage across the primary automobile-type Tube Volts Volts Volts mA. and protected from interstage reaction by the of the power transformer, and protects the other use of secondary aluminum shields. All r.f. coils 227 1st R.F. 2.5 150 12 5.5 tubes in the receiver from line voltage changes are matched to a standard and are interchange- 227 2nd R.F. 2.5 150 12 5.5 between 98 and 130 volts. able. Volume is controlled by increasing or de- 227 3rd R.F. 2.5 150 12 5.5 The direct current filter system is tuned to creasing the screen-grid voltage. A local- 227 Detector 2.5 45 3.4 remove all trace of a.c. ripple. The loud speaker distance switch controls the sensitivity. 227 1st A. F. 2.5 145 9 3.6 h'eld acts as an additional choke in the filter The power detector uses the grid-bias method 245 1st P-P 2.4 240 27 30.0 system, and also furnishes the necessary resist- of demodulation instead of the condenser-leak 245 2nd P-P 2.4 240 27 30.0 ance to reduce the high voltage for the two method. This is possible because of the tremen- 280 Rectifier 5.0 245 tubes to the correct value for the r.f. and dous amplification secured in the radio- D98 Ballast a.f. amplifier tubes. 344 RADIO BROADCAST FOR APRIL (Continued from page , nificant of the extent to which this by placing a small grounded metal sheet rating for the latter, l>y examination, trouble is prevalent in the category of between these tubes, or by covering the which, when the organization gains recog- radio difficulties. The possibilities of rectifier with a shield. In sets having the nition, may be of significance. noise were analyzed in considerable detail rectifier in the open it may pay to shield The organization publishes The Radio in the "Corner" for January, 1930. The this tube permanently." Service Man, which is sent only to mem- following contributions may be considered CLAUDE AUSTIN, Austin Radio Service bers. It is suggested that servicemen in- supplementary to this "Symposium." Portland, Oregon. terested in communicate with joining, HUM IN RADIOLAS THE PO-VER AMPLIFIER the association. The dues for the grade "I have found from extensive experi- of membership in which the average reader "I recently had some very unusual ex- ments on Radiola 44 and 45 receivers, will be interested are $5.00 per year with periences with a that I that the hum can be reduced connect- power amplifier a $2.00 initiation fee. by believe will some of the readers of an 0.5-mfd. condenser from terminal help The January issue of The Radio Service ing the 'Corner.' No. 6 on the socket-power unit (the ma- Man presents an interesting problem: 'The amplifier in question developed a roon colored wire) to the common ground. "A customer resides in a home not terrible crackling sound, very similar to This doubles the capacity across the de- equipped with base outlets. She has been static, and a check on all tubes snowed tector cathode, and does the trick. given to understand by the salesman them to be in first-class condition. This "The Radiola 66 receiver can also be that the set will be installed. amplifier, employing a 227-type tube in improved upon in this respect. Add an 0.25- "She shows the installer where the set the first stage and two tubes in mfd. condenser across the 220-ohm reac- 210-type is to be installed. (Fifty feet from the push pull as the final stage, was used with tor coil (the choke nearest the 280) nearest current source.) by a superheterodyne receiver and was one lead from the condenser "He explains to her the advantages of connecting equipped with a switch to connect the to one terminal of the 280 filament lead locating near the current supply, calling input to either the radio or an electric and the other to the midtap of the two to her attention the fire rules regarding phonograph pick-up. chokes." (The center tap on the 280 same. "This crackling noise showed itself only filament is to be to one "The customer refuses to change her winding preferred when the radio set was connected to the leg of the filament. Ed.). mind and the serviceman has her call the amplifier and this would, naturally, in- A. J. RARRON, Radiotrician and Elec- shop. dicate that the trouble was in the radio trician, Shawnee, Oklahoma. "In some cases the policy is to install set itself. However, a thorough test of no matter how. The shop tells the man to THE VICTOR HUMS every tube and part in the set placed the go ahead. H. W. HUDELSON, Auto and Radio Ser- trouble in some other section. This seemed '"O. from his in K.,' says he, taking bag vice, Vandalia, Mo., a veteran contrib- illogical view of the fact that the am- eight feet of lamp cord and adding to utor to the "Corner," lends us a hand plifier performed satisfactorily when the this No. 18 rubber 'plated' lead-in wire, here. electric pick-up was being used. as well as I (twisted possible). "We find that the Victor is hard to fit "As a last resort suspected the first "There are cases where men don't a.f. many with a humless 27-type detector tube, stage amplifier, although nothing even the of to go through preliminary calling and even when we succeed in getting a seemed indicate such might be the case. the office. transformer good tube, with the hum considerably re- A new was tried and the for the chandelier he lets trouble Just the trans- "Reaching duced by means of the hum adjuster, an- disappeared. why down the canopy and makes an unsoldered other source of trouble is often in evidence. former was noisy on the radio set and not In the he the is still a wrap splice. retaping splice The next thing to do is to throw on the on pick-up mystery to me." to use rubber neglects tape, substituting phonograph switch, cutting out the chas- CHAS. H. JENKINS, JR., Radio Service friction. . Since N. J. ordinary" sis, and adjust the hum control on the am- 1914, Audubon, Now this carrier wave sensitizes a set to dis- just suppose wiring acquired plifier. If this does not eliminate the hum. (A a short and caused a fire. turbances in of the partial pull out the chassis and power unit, and any part system. Ed.) "The New York Fire code Department resolder all connections, regardless of how limits the of this wire to 12 feet. length secure they may appear. Hold the iron J. NOONAN sends along a few corrobora- "The insurance state ex- lines: case of interference mani- companies on the joint until every bit of resin has tory "A plicitly in their policies that all wiring must been driven out. This cures the hum in fested itself in a peculiar grating sound conform with existing regulations regard- about 99 cases out of a hundred." which seemed to keep time with the music same. received. The receiver was tested several ing (Offhand it is difficult to justify this be "Who paysP'J cure. Rut we accept it on its face value times and no trouble could found. The "We are not and don't located in a lawyers attempt from an expert with Victors.) difficulty was finally lamp the answer, however we feel that there is which was on the top of the set. The lamp THE POWER PACK is GUILTY food for thought in the foregoing." was a two-candle affair, with two shades "When the metal casing is off the power which were suspended from metal brack- More "Dope" on Noise pack of some of these compact electric ets. The vibrations from the electrodyna- sets, so the pack can be tested with the mic loud speaker set the two shades swing- Seventy-five per cent, of all contribu- set in operation, a pronounced hum is ing. The shades rubbing on the metal tions to "The Serviceman's Corner" are present in the output. This is usually standards generated static discharges concerned with the elimination of noise in due to coupling between the rectifier and which were quite easily heard in the re- one form or another. This is probably sig- the detector tubes, which can be reduced ceiver." THE INVESTOR LOOKS AT RADIO (Continued from page 329) and Kolster, the passing of the dividend of taking place but it is probable that the poration of America, giving reasons why Brunswick-Halke-Collender, and the with- profits derived from all these minor uses we think it more attractive than some drawal of Eveready from manufacturing will not equal those derived from the sale others for long-term holding, and in are indicative of the general situation in of receiving apparatus for many years. subsequent articles, we shall discuss other the industry. If large inventories are The immediate prospects for the indus- companies whose securities appear fairly written off, it is probable that earnings of try appear, therefore, to be for lower earn- priced, but in general, we should use the most companies for 1929 will be consider- ings, with a probable consolidation or greatest discrimination in buying stocks ably below those for 1928. At this writing elimination of some of the weaker com- of radio companies unless the purchaser few reports have been published but a re- panies in the field. Over a period of years, knows them to be more favorably situated port from Crosley showed actual and per the outlook is much more promising but than the average. share earnings for 1929 less than one third before real progress can be made disposal those for 1928. must be made of surplus stocks and the Asks Wavelength For Ship-to- One of the most hopeful new develop- industry as a whole, placed on a firm Shore Phone ments is the use of vacuum tubes for pur- financial basis. It is a practical certainty poses other than radio receiving and trans- that a number of the stronger companies Predicting a growth in two-way radio mitting. These tubes are essential in tele- will survive and for them earnings will telephone between ship and shore, Frank in the of H. phone and telegraph systems ; produc- show a normal increase over a period Jewett, president of the Bell Telephone tion and reproduction of talking pictures; years, but it is still too early to speculate Laboratories urged the Commission to in the metering of gas and electricity; in on the outcome of some of the weaker set aside a block of 48 frequencies for such detection of flaws in metal; in the match- companies in the field, especially when service. He recommended that channels for ing of color; in the practice of light total income is dependent on radio pro- different services be grouped in blocks therapy in medicine, and in the chemical duction. In a succeeding article we shall rather than staggered throughout the industry. New developments are constantly outline the position of the Radio Cor- spectrum as at present. RADIO BROADCAST FOR APRIL 343 imuiiJNnmmmiuiKiii.ini.'. ^ No. 44 Radio Broadcast's Set Data Sheets April, 1930)30 GREBE SK-4 SUPER-SYNCHROPHASE RECEIVER EQUALIZED BAND-PASS FILTER SECOND RF STAGE ^ f y THIRD RF STAGE y POWER DETECTOR v I R F STAGE S I I ! P , , ANT / J24 from the of a.f. the center of of rpm.s RECEIVER consists of a three-stage signal voltage secondary the series with tap the secondary A screen-grid r.f. amplifier, a type 227 detec- transformer, the primary of which is connected the transformer. This resistor prevents the tor, and a push-pull output stage using two in the plate circuit of the detector tube. Since circuit from oscillating but has no effect on the 245-type tubes supplying power to an electro- push-pull amplifiers sometimes have a tendency audio-frequency characteristics of the ampli- dynamic loud speaker. Tne receiver contains to oscillate, a }-megohm resistor is connected in fier. several unusual features. R.F. Amplifier READINGS WITH WESTON SET TESTER MODEL 547 Preceding the first screen-grid radio-frecjuency Tube A B C Screen Screen Cathode Normal Grid tube is a band-pass filter circuit con- amplifier Position Volts Volts Volts Volts Current Volts mA. Test sisting of two tuned circuits coupled by both mA. capacity and inductance. Tuning condensers associated with these band-pass circuits are 224 1 R.F. 2.4 155 0.2 38 0.5 2.8 32.0 marked Ct on the diagram and these circuits 224 2 R.F. 2.4 150 0.2 38 0.5 2.8 3.0 function to prevent any signals other than those 224 3 R.F. 2.4 150 0.2 38 0.5 2.8 3.5 from the desired station from being impressed 227 Det. 2.4 180 0.5 1.4 on the grid of the first r.f. amplifier tube. Highly 245 P.P. 2.4 225 37.0 42.0 selective circuits of this type are used, es- 245 P. P. 2.4 225 37.0 42.0 pecially in connection with the screen-grid r.f. 280 Reel. 4.9 50 .0 pfrr anode because these tubes tend to amplifiers, produce Line = 116 cross-talk. Cross-talk is eliminated if the cir- Voltage *No bias reading at socket due to resistance in series with grid. cuits preceding the first tube are sufficiently i Bias can be read with voltmeter lead connected between filament and rh.-i . selective to prevent practically all signals other than the one desired from being impressed on the first tube. To obtain this high selectivity simple tuned circuits might be used but these READINGS WITH JEWELL SET ANALYZER MODEL 198 would produce sideband suppression. By the use of band-pass circuits, high selectivity with- Readings with Plug in Socket of Set and Tube in Tester out sideband suppression is obtained. Type Impedance Coupling The following tubes in the r.f. amplifier are impedance coupled, that is, a tuned circuit is in the plate circuit of each tube. The plates are choke fed and the tubes are coupled to the tuned circuits through small adjustable con- densers, Ck. The condensers are, of course, properly adjusted at the factory and need only be altered in the event that the set has been tampered with or the adjustments have been altered due to rough handling. Detector Circuit The detector, using a 227-type tube, is of the plate-detection type. In the grid circuit of the detector tube a phonograph pick-up transformer is connected with two taps to make it suitable for use with either low- or high-impedance pick- up units. In normal operation as a radio re- ceiver this transformer is shorted out of the circuit by the phonograph switch. When the set is to be used with a phonograph pick-up unit this switch is opened and the phonograph pick-up transformer is thereby connected in series with the grid circuit of the detector. A.F. Amplifier The two 245-type power tubes obtain a.f. MEASUREMENTS OF is to start out initially with an abundance TESTING of these frequencies, as in this receiver. H. F. RESPONSE The degree to which the 1200-kc. and 600-kc. fidelity curves depart is not al- (Continued from page 314) ways a measure of the degree of side- INSTRUCTIONS band suppression, and therefore of sharp- kilocycles at which a normal output of 50 ness of resonance. Thus, Fig. 4 illustrates milliwatts is obtained at 10 and 100 times a receiver with FOR SERVICE MEN the resonant for normal very good high-frequency amplitude output. characteristics and a marked amount It will be observed that none of the very of high-frequency cut-off due to sideband one-audio-stage sets or none of the sets suppression. The 1200- and 600-kc. curves employing a low-gain, two-stage, audio- are very wide apart. Figs. 1 and 7, on the frequency amplifier shows appreciably bet- other hand, illustrate receivers with approx- ter low-frequency response than the sets imately the same high-frequency response employing two high-gain, transformer- at 600 kc., these receivers differing ap- coupled, audio-frequency stages. Less preciably in While a great hum is obtained, to be sure, but no great selectivity. deal of sideband suppression is present, improvement is noted in low-frequency most of the loss in these sets occurs in the response. In other words, the design audio-frequency system, and consequently of the audio-frequency amplifier in these the 1200-kc. and 600-kc. curves receivers is in essence very much the fidelity for each set are closer together. same, although it might be expected that, since only one a.f. transformer is em- ployed, and the squaring action of de- Selectivity vs Suppression ficiencies occurring in two transformer It is of interest to note that two re- stages is absent, a much better frequency characteristic would be obtained. ceivers having approximately the same as the of This is substantiated by an examina- selectivity, expressed by figure merit advocated the I. R. tion of the high-frequency end of the by proposed E. standards and indicated for each re- fidelity curves for 1200 kc. These curves ceiver on its curve do not neces- represent, as stated above, the frequency sheet, show the same of sideband characteristics of the a.f. amplifiers in sarily degree Thus sets 4 and 5 have the respective receivers. With two excep- suppression. the same band widths at tions, namely Figs. 3 and 4, the high- approximately 600 the former shows frequency response of the sets employing kc., yet markedly more sideband than the lat- Model two transformer-coupled stages and grid- suppression ter. This is because receiver 4 is much leak detection, is practically as good as 547 than receiver 5 that in receivers employing one audio- sharper at or very near whereas off resonance frequency stage or two low-gain stages resonance, they both show the same and C-bias detection. It would appear, nearly selectivity characteristics. This difference is therefore, that the maximum possibili- prob- due to the use of an extra tuned ties of one-stage, audio-frequency ampli- ably in receiver each fiers, or low-gain, audio-frequency ampli- stage 5, stage being tuned and the overall resonance fiers have not been exploited as yet in most broadly recent receivers. These so curve being flat at resonance and sharp RADIO SET TESTER possibilities, off resonance. far as high-frequency response of the au- It be stated that in of the dio-frequency system itself is concerned, might spite noticeable lack of these This Instrument, and this Manual are illustrated by the 1200-kc. fidelity high frequencies, receivers sound While this is curve of Fig. 4. very good. which is furnished with it, together true in some cases the sets would sound A glance at most of these fidelity curves better if the most and up- shows that, whereas a response of any- immeasurably they reproduced provide complete the to a extent. wheres from 50-80 per cent, is generally high frequencies greater to-date equipment available for ser- When do sound it is obtained at 100 cycles, and 30-50 per they good probably due to a considerable amount of radio receivers. Electrical data cent, at 60 cycles, the transmission at compen- vicing sation introduced the loud 3000 cycles is only of the average order of by speaker for practically every set on the mar- which the 20 per cent. In fact, in some instances reproduces high frequencies better than the low often ket is contained in this book which 4000- and 5000-cycles transmission is of frequencies. As as not, however, the sets do not sound so a negligible order. If this deficiency were is made up in loose-leaf form so that when the loud due only to poor audio-frequency res- good, especially speaker is not efficient at As one purchasers of the instrument who ponse the difficulty could be resolved very high frequencies. distributor of radio sets "Radio quickly. But even with a very good high- put it, turn in registration cards are auto- sets are made so that a bird frequency response in the audio-frequency canary sings bass." matically supplied with latest infor- end, as in Fig. 4, the fidelity at 600 kc. the strict re- is very poor at the high frequencies. Unfortunately selectivity mation. quirements imposed upon radio receivers necessitates sharp resonance character- Sideband Suppression This instrument has achieved wide istics with resultant high-frequency sup- The primary source of high-frequency pression. Until band-pass filters with success among dealers and service loss is in sideband suppression due to square-top resonance curves and sharp men. It is because of its sharpness of resonance. This is all the cut-off are better developed it seems that preferred more noticeable when the audio- the secure straight only way to the higher fre- dependability, ingenious design pro- frequency characteristics of the set are is to the quencies design audio-frequency ease of very good, as in Fig. 4. But even when the system with rising characteristics or in- viding operation, compact- characteristics are not troduce the audio-frequency necessary compensation in ness and light-weight portability. It of the best, as in Figs. 1 and 7, there is the loud speaker. will make all the tests considerable high-frequency loss as shown The one strong objection most fre- required on by the difference in the 1200-, and 600- quently heard against real good high- any A. C. or D. C. set. Durable bake- kilocycle fidelity curves. The severity of frequency response is the introduction of lite case and Provided with sideband suppression is illustrated in any excessive noise and tube hiss, the high- fittings. of the attached curves, which show that, frequency components of which are pre- 3%" diameter instruments. suppression starts as low as 1000 cycles. dominant. For loud signals, where the Sideband suppression may be very bad amplification of the receiver can be con- even in receivers which do not have a siderably reduced, this is not at all im- very high degree of selectivity. Thus Fig. portant. This objection is valid wherever 3 illustrates a receiver with exceptionally weak signals are concerned, but in such fine audio-frequency characteristics. Its cases reception cannot be very entertain- selectivity, as shown by the band widths, ing, to say the least, and it seems wrong is not all that can be expected of a four- to have to penalize radio sets in the way tuned-circuit set. Nevertheless, the 600- of high-quality reproduction in order to kc. fidelity curve shows very noticeable eliminate noise arising in distant reception. drop in high-frequency response. How- The reader may be interested to know ever, even with this loss its high frequency that the curves which accompany this WESTON ELECTRICAL response is very good. This illustrates that article were made from actual measure- INSTRUMENT CORPORATION the only way to retain good high-fre- ments on standard radio receivers taken even with sidebands cut off 604 quency response directly from stock. Frclingliiiysen Ave. Newark, N. J. RADIO BROADCAST FOR APRIL 347 I No. 45 Radio Broadcast's Set Data Sheets April, 1930 THE BALKEIT MODEL C An interesting feature of this receiver is the use of double primaries on obtain uniform r.f. gain over the entire broadcast band, the capacity all of the radio-frequency transformers. In all cases the two primary shunted winding being most effective at low radio frequencies and the windings are connected in series and an 0.00025-mfd. fixed condenser is unshunted winding being most effective at high radio frequencies, thus connected across one of the primaries. These two windings are used to the inefficiency of each winding is compensated by the other. THE KENNEDY CHASSIS NO 10 This is a screen-grid receiver using three 224-type tubes as r.f. ampli- output consisting of an r.f. choke and two fixed condensers, such a filter fiers followed by a C-bias detector, one resistance-coupled a.f. stage, and being essential when the detector is resistance coupled to the following one transformer-coupled a.f. stage. Note the r.f. filter in the detector amplifier tube. rtW AVERAGE VOLTAGE READINGS 90-130 ELECTRO- DYNAMIC CONE BAND-PASS FILTER tory," "Output from Pentodes Using Igranic Output Transformers." CIRCUITS October 1929, Cocking, "Possibilities of the Pentode Tube." Just Out . . . (Continued from page 328) December 1929, Rothy, "Development The loss of amplification due to the of the Pentode Tube." March and Keith use of an extra filter is considerably greater 1930, Henney Rhodes, Henney's than 50 per cent. The variation in selec- "Characteristics of Pentodes." tivity, however, is now only in the ratio Book on of 2.6-1, and it has been increased to T.R.F. Articles about three times at the lower frequency; Radio A list of articles with the tuned- the sideband variation at this frequency dealing which have is about the same, but at 1200 kc. it radio-frequency amplifier in the I.R.E. is has been reduced to 15 per cent. appeared Proceedings given below. It is doubtful whether the extra se- "The Shielded Receiver" lectivity is justified in view of the loss of Neutrodyne L. A. Hazeltine, June 1926. amplification which accompanies it, par- by "Method of Maximimation in Circuit ticularly as the selectivity with only the Calculation" Walter Van B. single filter and two tuned plate circuits by Roberts, October 1926. is fairly high. It can be seen, however, " of that the capacitatively coupled filter Selectivity Tuned-Radio-Frequency Receivers" K. W. 1927. enables a very great increase in selec- by Jarvis, May "Mathematical of Radio- tivity to be made at the higher frequencies Study Victor G. without increasing the sideband varia- Frequency Amplifiers" by Smith, June 1927. tion at the lower frequencies. Indeed, by the use of suitably designed capacitatively coupled filters for all the tuning circuits in a receiver, it would be possible to make a THE MARCH OF receiver with constant selectivity through- out the whole broadcast band. This would RADIO be with inductive cou- quite impossible Continued from Page 317 pling. In other words, with 25 per cent, of Other Advantages profit. its time sold, the Columbia system suc- Principles From the foregoing it will be seen that ceeds in breaking even. the use of capacitatively coupled filters Bookkeeping methods have a lot to do of in place of the usual cascade tuned cir- with how an annual statement comes out. cuits allows, not only of greater fidelity, However, in the case of the N. B. C. it but also of at the is difficult Radio greater selectivity higher to see, under the circumstances, broadcast frequencies. While inductive how it can help but show a very substantial the coupling permits retention of side- profit, in spite of its lavish use of high- By KEITH HENNEY bands, it does nothing to correct the low priced space and such luxuries as Director of the Laboratory selectivity at high frequencies. Schumann-Heink's services as operatic Radio Broadcast Magazine Another advantage is gained by the use counsel. of filter circuits instead of cascade cir- The N. B. C. if it could, would, perform Readers of Radio cuits; it becomes somewhat easier to ob- a service to the soft Broadcast, long great public by pedal- familiar with the -work of Keith tain satisfactory linking up of the variable ing the blatant in advertising practically in his as Director condensers. The effect of misalignment every program broadcast during the choice Henney capacity of the will with cascade circuits is a loss of amplifi- evening hours. Addressing the advisory Magazine's Laboratory, be to secure his first cation and selectivity. With filter circuits committee, which meets once a year to eager book, just the effect is rather different. Misalign- hear Mr. Aylesworth's accounting of his released from the press. ment causes the tuning curve to become the of the N. B. C. stewardship, president This book within asymmetrical; consequently, the selec- a revenue of $15,000,000 brings together reported gross one cover the kind of information tivity becomes greater on one side of during 1929. The personnel of the company on radio resonance than on the other. Indeed, the increased from 558 to 917, and clients from which will appeal to the selectivity on one side may become 96 to 199. The permanent network in- practical interest of every radio greater than that with perfect alignment. volves 32,500 miles of telephone lines, experimenter, technician, engineer, Owing to the flat topped curve, a slight linking 73 stations. The outlet stations and fan. It contains the latest data amount of misalignment does not appre- concentrate almost entirely on presenting and the most modern methods. It the ciably affect amplification. Perfect advertising features and this probably treats in a thoroughly practical way of is as difficult alignment, course, just accounts for the recent reduction of 50 everything from the production of to obtain with filters as with cent, in the made for sustain- band-pass per charges radio currents to their reception cascade circuits, but the effects of slight ing programs. and transmission. Many problems, misalignment are not usually so serious. Evidently the advertising profession examples, illustrations, experi- has accepted radio and therefore the cus- ments, are here presented in book todians of the medium can, if they will, form for the first time. STRAYS FROM THE do a little housecleaning before the public refuses to listen to the spoken word over the Keith Henney, by reason of his LABORATORY air. The act of throw- courageous publicly wide experience as an operator, en- ing somebody off the air (especially if there (Continued from page 333) gineer, and writer, has the gift of is a customer to in for the waiting step making technical information read- curves were somewhat incorrect. The particular hour involved) would effect a ily understood by the reader. lowest section of the logarithmic ordinates salutory warning to the advertising profes- of the selectivity curve, Fig. 1, was con- sion. The entertainment value of broad- tracted a correct curve will be found in casting and, in consequence, the effective- See a Copy on Ten Days' Fig. 3. In the case of the fidelity curve, ness of program sponsorship and the sales Approval the point on the abscissa marked 80 cycles of radio receivers would be markedly should have been marked 30 If stimulated if announcements cycles. advertising Price $3.50 this change is made the fidelity curve is were restricted to ten seconds, once each correct. ten minutes. No one would bother to tune out short announcements. Pentode Articles The present policy of radio advertising A Wiley Book The following articles and notes on the is to say more and more to fewer and Pentode tube may be of interest. They all fewer. The more intelligent policy would ON APPROVAL | COUPON appeared in RADIO BROADCAST. be to less words of effectiveness say greater I JOHN WILEY & SONS, INC. RB4-30 November 1928, "New Trends to the number. Henney greatest possible The | 440 Fourth Ave., New York City in Radio 1929-30." painful thing about radio advertising is Gentlemen: Kindly send me on approval Hen- April 1929, "Strays from the Labora- the growing length of the advertising dose ney's "Principles of Radio." I agree to remit the within ten after its tory," "Characteristics of Philips Pen- handed out with each announcement. The price ($3.50) days receipt or return the book postpaid. todes." does not react to a public unfavorably Name July 1929, "Strays from the Labora- few words of the most direct kind of ad- tory,' "Characteristics of Milliard Pen- vertising. The loudest groans are caused by Address tode tubes." the tediously long announcements which Reference . . October 1929, "Strays from the Labora- are now the custom. RADIO BROADCAST FOR APRIL 349 RAD NEWS TUBE MAKERS DEFEND THE PENTODE Three lube makers in the United Slates have offered pentode lubes. They are Ardurus, Champion, and CeCo. Tubes of the first two companies are power lubes to be used only as audio-frequency ampli- fiers. The CeCo tube is designed for radio- frequency amplification. We are glad to present here statements from two of the companies on this much-discussed pentode question. _THE EDITOR By JASPER MARSH Treasurer, Champion ftadij Tube Company LM Ever , The new type of pentode now being _^J Greatest Radio developed in this country is new. There is as much difference between the continent pentode and American pentode as there is between the ux-17lA and the ux-250. The tube as it now stands is surely an engineer- In southern Kanas it is common to motor buses advance for the of the becoming quite find ing improvement with a radio receiver the entertainment The art. equiped for of passengers. picture above shows one of a fleet of similarly equipped reliicles. It is very easy to conceive a real power detector which will work directly into the loud speaker. It would make possible a real many set manufacturers for their next tube engineers on a status that they have portable set, better radio sets for automo- model, and it is such people that should not not enjoyed heretofore. In the past, they tive _uses, and cut the cost of operation get an unfavorable opinion or report on have been the sort of silent craftsmen who considerably. Experimental work that the tube. labored in quiet, content to realize their has been done lines along these with the ERNEST KAUER new ideas and take satisfaction in ac- pentode tube proves that all these uses By complishment. CeCo Inc. are quite feasible. President, Manufacturing Co., The entire radio world is indebted to the the How uniformity of pentodes will run The response from the press, the trade, tube engineers; their researches have done is not known at the present time. If we care and the public over the announcement of much to make radio reception the glorious to take the English tube and compare its the pentode has been most pleasing. The satisfaction that it is to-day. There seldom cost with their power tube similar to our general character of this response evi- have been any startlingly quick develop- ux-245, we will find them almost the same. dences no idle curiosity but an expectation ments in radio tube engineering. All the The single pentode has been used in the and appreciation of the progress in the de- noteworthy results that are familiar to- here laboratory and the hum from a stand- velopment of radio science. The crystal- day, have come over a period of years of ard filter such as used in the average re- lization of modern thought to-day evi- study, application, and much costly effort. ceiver does not become any more notice- dences an instant desire for constructive The pentode tube has been in use in able than when using two 245-tyoe improvement. Europe for some years as an audio- in tubes push pull. As the Ep Ip curve is Radio's increasing development is sti- frequency amplifier for battery-operated almost perfectly flat a very small filter mulating more and more thought of its receivers. In the research laboratories of could be used in the plate supply. How- future. The development of the a.c. pen- the CeCo Manufacturing Company our at the ever, same time we must think of the tode tube ha. emphasized in the public engineers have added many improvements ripple in the drop wire from which we ob- mind the fact that radio engineering is to the original tube. They are the Ameri- tain our bias. We do not believe any great made up of two distinct schools tube can pioneers and were the first to adopt trouble should be expected from this engineers and set engineers. The pentode the pentode to radio-frequency amplifica- source, when using an average present-day tube has had the effect of establishing the tion and audio-frequency amplification filter. for a.c. and d.c. operation. Tube engineers As the load impedance for best opera- with the pentode and the screen-grid, and tions is not taken as twice the tube im- in many other instances, have invariably pedance, as in the case of triodes, but J We built up an idea which was ultimately used or Apologize j of the plate impedance, the cost of a by set engineers. In the past, set engineers very high-impedance transformer does not In an article entitled "Review" have not always been able to develop a have to .be considered and the de- circuit which the utiliza- output onpage 251 in March, 1930, RADIO receiving permits vice would compare very favorably with tion of a tube's full capacities. BROADCAST, we carried a report that now used for a single ux-245. The more efficient method seems to be to the that the Balkeil Radio In this connection there should also be effect either for tube engineers and set engineers was in the hands re- given consideration to the matter of patent Company of to consult together in advance of a de- infringements on audio-frequency ampli- ceivers. As this issue goes to press velopment, or for tube manufacturers to fiers using transformer coupling and push- we learn that the report was incor- work out a circuit capable of using the full pull output transformers. The pentode rect Balkeil was never in bank- capacity of a new tube. In the latter case, tube can be resistance to the out- the circuit should be made available to coupled ruptcy. This information was given put of a power detector, such as the 224 manufacturers of sets without in good faith as it came from a receiving tube, and hence greatly simplify the audio- This last method is the one we source which we considered reliable. obligation. frequency system. have adopted in the case of the pentode. We deeply regret the error and Our general belief is that a tube that will offer CeCo engineers are now offering to demon- our to the Balkeit Radio deliver 3.5 watts of undistorted power apologies strate to set manufacturers the possibilities output with a grid swing of 12 volts and a Company. of the pentode tubes. Our engineering staff d.c. plate current consumption of 35 mA. THE EDITOR. and our engineering facilities are available at 250 volts, would be quite acceptable by (Continued on page ,?5,?) 350 RADIO BROADCAST FOR APRIL OFINDUSTRYTHE New Broadcasting Company In the Tube Field Personal Notes of com- Two well-known Iowa stations, woe Ernest Kauer, president CeCo, on their of an a.c. and WHO have requested the Radio Com- menting development r.f. in the claims of mission to approve the organization of a John W. Million, former chief engineer of Bremer- pentode says refuting Tully, is now with Utah Radio Products, Chicago, the RMA division: "To new company, the Central Broadcasting Engineering deny 111., as research and field engineer. that CeCo's is an advance in Company at Des Moines. This company is development the radio art is as futile as was the capitalized at $500,000 and will absorb Vernon W. Collamore, formerly general sales attempt for Atwater is now of of tried to the interests of the Palmer School of manager Kent, manager automobile manufacturers who Radiola Division, RCA-Victor Company, Inc., of the delay the use of four-wheel brakes or Chiropractic, owners of woe, and succeeding E. A. Nicholas resigned. Bankers Life Company, owners of WHO. balloon tires." K. A. former Radiola Divi- It is Dr. Frank of Nicholas, manager, planned by Elliott, woe, to form sion, RCA-Victor Company, has resigned The division of U. S. Radio & to the two stations by wire, his own He will handle Apex synchronize distributing organization. has later to erect a 50-kw. transmitter and Radiolas and Radiotrons. Television Corporation placed an reduce one of the stations to a exclusive contract for its tube supply with regional D. E. who the Jenkins have Replogle recently joined the National Union Radio Corporation, status. Since 1928, woe and WHO Television Company as assistant to the president, to a recent announcement. This been dividing time on the 1000-kc. channel. has been made treasurer of that organization. according company recently announced a seven-tube Fred W. whose name is well Klingenschmidt, set priced complete with tubes at $101.00. Radio Administration known to old-timers in radio, has joined Amy, Money for Aceves & King, New York, as sales manager in of installations of the antenna lines in the radio tube field Late in January, Congress appropriated charge multi-coupler Competitive system manufactured and sold by this firm. are drawn in 1930 for the a total of $106,000 for the Radio Com- being sharpest contest in the of the mission, including salaries of the five com- Robert H. Stroud has been appointed convention history industry, Kent Co. Mr. missioners at each, and manager, Atwater Manufacturing according to P. Huffard, president of $10,000 annually T. who This Stroud succeeds Wayne McDowell, recently National Carbon. "The tube industry is for other authorized expenditures. resigned. sum does not include the entire annual cost now in a similar position to that of the G. A. Yanochowski has been elected of automobile in earlier of radio administration which is nearly president industry years. the Switchboard and Company, Kejlogg Supply From a position in which a good portion three times this amount. succeeding the late W. L. Jacoby. of the annual production came from a M. C. Rypinski, formerly with Brandos and number of scattered manufacturers, that is now of the radio de- Mexican Newspaper of the Air Federal-Brandes, manager has evolved to a stage where the of at 150 Broadway, New industry partment Westinghouse bulk of the comes from a Each night station XFX, Mexico City, York City. production very broadcasts news of Mexico both in Spanish few concerns. This is exactly the stage at K. Fearn, sales manager of The 1000 watts on a wave- Irving formerly which, in our opinion, the radio tube in- and English with Ken-Rad Corporation, has joined the French Bat- will have arrived the end of length of 329.6 meters. The broadcast tery Company as assistant to the president. dustry by starts at 11 P.M. Eastern Standard Time. 1930. The handwriting is definitely on the H. L. Williams, formerly with Silver-Marshall, station uses the service of the Trens wall and should not be disregarded. This Inc., is now advertising manager of the Rola Com- "The tube market offers one of the Agency, 43 Colon St., Mexico City, and pany, Oakland, Calif., and Cleveland, Ohio. claims it to be the of the air greatest replacement markets available only newspaper former Director of Ohio Fred O. Lange, Safety, to It is destined to from in existence. Station XDA at 4 p.m., State Industrial Commission, recently assumed his industry. grow to Eastern Standard Time, using 20 kw. on duties as director of personnel at the Crosley Radio year year." 21.85 meters, broadcasts Spanish and Corporation's plant. news in continental the English dispatches Organization of the legal division of the Federal since the creation of the Commission with ap- code. Radio Commission was completed for the first time pointment recently of two assistants to the general counsel. They are Duke M. Patrick, of Indianapolis, and Ben S. Fisher of Marshfield, Oregon. Fred W. Piper is now sales manager of the Howard Radio Company. Keith Henney, for five years director of RADIO BROADCAST'S laboratory, is now on the staff of Electronics in New York City. H. W. KaDell, formerly of National Carbon Com- pany's Research Laboratory in Cleveland, has been transferred to New York City. His new position is sales engineer in the Eveready-Raytheon Tube Division of the general sales department. Dr. It* DeForest has recently been appointed consulting editor of the new publication Electronics. Jesse Butcher, formerly with Doubleday, Doran & Company, Inc., and the New York Times, is now director of press relations for the Columbia Broad- casting System in New York. R. T. Pierson has been appointed executive representative in contacts with radio, automotive, and electrical specialty industries by the General Cable Corporation, New York. Harry Sadenwater, formerly engineer in charge of broadcasting stations of the General Electric Company, has recently joined the RCA-Victor Company, Inc., at Camden, New Jersey, as chief field engineer. Lewis M. Clement, formerly chief engineer of Kolster Radio Corporation, has resigned and has sen-ice on the S. S. joined M. S. Ripmski in the radio engineering The inauguration of two-way ship-to-shore telephone division of the Westinghouse Electric & Manu- Leviathan makes it possible for any passenger to transact business facturing Company, 150 Broadway, New York or talk with friends by telephone while crossing the Atlantic. This pic- City. on the Leviathan. To the ture shows the radio telephone equipment right Donald McNicol has been appointed editor of are re- is the receiving apparatus where voices from shore telephones Radio Engineering, succeeding M. L. Muhleman. and ceived by radio from the Deal (N. J.) station. (Other news items on pages 352 353) RADIO BROADCAST FOR APRIL 351 (Continued from page 351) Sec. 2. Whoever knowingly, malici- News of the Manufacturers ously, or wantonly by any means unreason- By the author of ably disturbs the reception of radio waves The Irving Trust of New Company used for between two York, as receivers for Sonora Products radiotelephony, ** hundred and five hundred and meters Principles Company and Sonora Phonograph Com- fifty wavelength, shall be punished a fine of Radio pany, was authorized Federal by by Judge of not less than ten dollars and not more Communi- Coxe in New York early in February to than fifty dollars to be recovered by com- continue the business of the companies for cation" plaint in any municipal or police court or two months. If it is considered necessary, before any trial justice. Approved April the receivers for an extension. may apply 16, 1927. The of An independently purpose the extension is to give the and written introduc- companies creditors an opportunity A chart to large tabulating the Federal tion to the reorganize and to free the properties subject Radio Act and amendments has been pre- Radio of the receivership. of pared by Nathan B. Williams and copies John H. Morecroft can be secured from him at the Insurance Early in February, the receivership Building, Washington, D. C. proceedings instituted against the De- Elements of Radio Forest Radio Company were dismissed by Chancellor V. M. Lewis of the Chanc- The Radio Corporation has requested Communication ery Court at Paterson, N. J. Officials of that the Federal Trade Commission dis- miss the the DeForest Company presented to the complaint against it which BY JOHN H. MORECROFT Court evidence of the solvent condition of charged that certain patent licenses the and statements which granted by RCA to makers of "We can highly recommend 'Elements Company receiving showed that the sets violated certain sections of the of Radio Communication* to those of during 18 months of Clay- operation under the officers a ton Act and the Federal Trade Commis- our readers who want a book that will present net profit of $626,424.98 was realized. sion Act. The license agreement was give them a strong, elementary ground- January 1930 showed a 24 increase over charged to require licensees to their ing in radio and leave them with few per ce_nt. equip the month's sets initially with RCA tubes. The questions to ask save those which be previous business according to only may President Garside. Trade Commission has taken no action born of a desire for more knowledge." and no date has been set for a Boston Post Radio Section hearing. Soon after March 1, the Edison Lamp Works of $3.00 General Electric, located at Remote Control Patents Harrison, N. J, will be transferred to Nela Park, Cleveland. The Harrison plant will At the present time considerable activity JOHN WILEY & SONS, Inc. be taken over is shown the radio A entirely with the removal of being by industry in the 440 Fourth ve., New York the Lamp Works by the RCA Radiotron direction of obtaining patents on automa- Please send me Morecroft's "Elements" for free tic- and remote-tuning devices. Most of the examination. Within ten Company. days after its receipt I inventions in will either return the book or send this field have been made you $3.00. The Allwood, N. J., plant of Earl Radio recently, and, therefore, a large percentage has been shut down and is Name. . . completely no of the patent applications have not yet longer operating. Address. been acted upon. For the same reason, several manufacturers do not feel sure of The plant, good will, and assets of the their present positions and hesitate in Balkeit Radio Company, North Chicago, Firm making any statement on the subject for RB 4-30 has been purchased by R. I. Mendles and publication. However, because of the R. L. Eglaston. They will operate under extreme interest in these a the name of the Balkeit Sales Company. developments list of manufacturers Offices will be maintained at North partial important and their patent holdings has been com- Chicago and at 205 West Wacker Drive, piled. Chicago. Mr. Mendles is president and Mr. Eglaston vice president and general man- Name of Company Remarks of the new Mr. Premie ager company. Eglaston AH-Aincrican Mohawk Corp. No patents filed was at one time general manager of the American Bosch Magneto Corp. Do not own any Karas Electric in patent Company Chicago. The Amrad Corporation Do not own any patent Buckingham Radio Corporation, 440 Atwater Kent Mfg. Co. Patents applied West Superior St., Chicago, on December for but not yet allowed COMPLETE 27th was placed in the hands of a receiver Carter Radio Co. No patents is- i in FACTORY bankruptcy. Certain reorganization sued yet. Sev- WIRED plans are under consideration but no de- eral applica- tions on file AND finite announcement has for yet been made. some time TESTED Colonial Radio Corp. No at UNITS patents ^_ _ Matters present time 'Band-Filter Legal Crosley Radio Corp. Do not own or Tuning"" control DeForest filed suit any pa- Screen-Grid Amplifier has against Pilot tents Six Circuits Tuned Radio & Tube Corporation, Brooklyn, Colin H. Kennedy Corp. Do not own or World-Wide Range manufacturers of radio parts, knockdown control any pa- tents kits, and assembled radio receivers. De- Kolster Radio Corp. Patent No. 7VO radio produced in mass can Forest seeks an injunction to restrain Pilot 1552919; other from an alleged infringement of DeForest patent applica- even approximate the skilled tions including patents Nos. 1507016 and 1507017 cover- of the new our basic casi- perfection Custom-Built ing the use of regeneration in a radio re- slill pending in "HiQ-30." Here is the newest, ceiving circuit. Says President Garside of the Patent Of- fice DeForest: "There is a mistaken idea at most efficient model by Hammar- Philadelphia Storage Battery Co. No patents is- large that the regenerative patent is public sued lund the climax of five years of un- Patent Nos. property, instead of the private and pre- Stromberg-Carlsou Telephone equaled custom and Mfg. Co. 1655160; 1738 designing sumably valuable property of the De- 262 famed throughout the world for Forest Company." Union Carbide & Carbon Re- Own no patents search Labs., Inc. power, selectivity and tone. A Radio Patent Nos. Maine has a law primarily affecting the Zenith Corp. for 1581145 (reis- great opportunity custom-set use receivers. It follows in full : of radiating sued 17002); builders. Choice of 1638734; magnificent CHAPTER 215 cabinets 1591417; and speakers. 1704754; An Act to Render Unlawful All Disturb- 1695919. A. C., D. C. and Battery Mod- ances to the Reception of Radio Waves els. Used for List, $139.50 to $1,175 Radiotelephony. for be unlawful to use C.B.S. Negotiating KMOX complete, less tubes. Sec. 1. It shall within the state of Maine any radio receiv- The Columbia Broadcasting System is of control of ing set which radiates radio waves, be- negotiating for the purchase tween two hundred and five hundred and KMOX, St. Louis. In addition to owner- Mail of its it has ac- fifty meters wavelength, thereby causing ship key station, WABC, Coupon with the of control of WBBM, Chicago, and for interference reception any quired 48--page other radio receiving set unless said radiat- wcco, Minneapolis. The purchase of WOR ' HiQ- set shall be rebuilt or re-designed to seems to be foreshadowed by its incorpora- 30" ing Manual prevent said radiation. tion as a separate entity. 352 RADIO BROADCAST FOR APRIL Issued Patents Single-Side-Buiid Carrier System. Estill I. Green. Recently Kast Orange, N. J., assignor to American Tele- Electron-Emitting Material and Method of Making phone and Telegraph Company. Filed September To The Same. William Henjamin Gero, Bloom- 20, 1926. No. 1,744, 044. field, N. J.. assignor to Westinghouse Lamp Combined Recorder and Reproducer. Arthur C. Filed June 1928. No. 1,731,244. Company. 29, Keller, New York, N. Y., assignor to Bell Tele- Base for Radio Tubes. Clair J. Terrill, Dayton, phone Laboratories, Inc., New York, N. Y. Filed Think of to the Kurz-Kasch Ohio, assignor Company, February 10, 1928. No. 1,744,047. Dayton, Ohio. Filed November 8, 1926. No. 1,731,832. Modulation System. Robert L. Davis, Wilkinsburg, Apparatus for Recording and Reproducing Sound. Pa., assignor to Westinghouse Electric and Man- Richard S. Arthur, New York, N. Y. Filed ufacturing Co., Filed August 6, 1925. No. February 5, 1926. No. 1,732,036. 1,744,214. Device. Wehrli D. Pack and Sound-Regenerating Audio- and Iligh-Freqnency Amplifying Tube. M. S. Salt Lake Utah, as- Joseph King, City, Siegmund Loewe, Berlin, Germany, assignor to to Utah Radio Products signors Company, Radio Corporation of America. Filed October Inc. Filed 29. 1926. No. 1,735.873. July 18, 1925, and in Germany November 13, 1924. Picture Richard Cross Screen Receiving System. No. 1,744,653. Rowland Hanger, Newark, N. J., assignor to for Short Waves. Mendel T, of America. Filed ransformers Radio Corporation January Frequency Changer 9, 1928. No. 1,736,219. Osnos and Richard Kummich. Berlin, Germany, Means for and Method of Volume Control of assignor to Gesellschaft fur Drahtlose Tele- Transmission. George Crisson, Ea t Orange, graphie m.b.H., Berlin, Germany, Filed August N. J., assignor to American Telephone and 14, 1925, and in Germany Aug. 16, 1924. No. Telegraph Co. Filed Sept. 12, 1924. No. 1,737, 1,744,668. 830. Radio Transmitting System. Georg von Arco, to Protect Loud is to Arrangement Capacitive Speakers Berlin, Germany, assignor to Gesellschaft far Puncture. Manfred von Ardenne, Ber- Against Drahtlose Telegraphic m.b.H., Hallesches, Filed 28. 1928, and in Ger- lin, Germany. April Berlin, Germany. Filed November 23, 1925, and 28. 1927. No. 1,737,872. many April in Germany December 6, 1924. No. 1.744.711. Diaphragm Especially for Sound Receiving and Think of Radiating Apparatus. Heinrich Hecht, Kiel, Germany, assignor to Signal Gesellsehaft mit Patent Suits beschranklcr llaftung, a Firm of Kiel, Ger- Filed 9, 1925. and in Germany many. February M. C. Hopkins, Acoustic device, filed Sept. 26, 20. 1924. No. 1,737,883. February 1929, D.C., E.D., N.Y., Doc. 4450, Lektophone Volume-Control Lee G. Bostwick, East System. Corp. v. Colonial Radio Corp. No. 1,271.529. Orange. N. J., assignor to American Telephone and Telegraph Co. Filed March 6, 1925. No. L. A. Hazeltine, Method and means for neutralizing 1,737,992. capacity coupling in audions, filed July 18, 1929, Means For and Method of Volume Control of D.C., E.D., N.Y., Doc. 4323, Hazeltine Corp. v. Transmission. Estill I. Green, East Orange, National Carbon Co., Inc., et al. Same, filed THORMRSON Doc. N. J., assignor to American Telephone and July 31, 1929, D.C. E.D. N.Y., 4362, Hazeltine v. A. I. Namm & Doc. Telegraph Col. Filed August 5, 1926. No. Corp. Son, Inc., TRANSFORMER 1,738,000. 4363, Hazeltine Corp. v. Abraham & Strauss, Television. Herbert E. Ives, Montclnir, N. J., as- Inc. Same, filed Aug. 3, 1929, D.C. E.D. N.Y., v. E. A. Wildermuth. SPECIALISTS signor to Rell Telephone Laboratories, Inc., Doc. 4369, Hazeltiue Corp. New York, N. Y. Filed May 20, 1926. No. Same, filed Aug. 9, 1929, D.C. E.D. N.Y., 1,738,007. Doc. 4371, Hazeltine Corp. v. Brooklyn Radio Since 7895 Piezo-Electric Crystal Oscillator. Alfred Crossley, Service Corp., Doc. 4372. Hazeltine Corp. v. Washington, D. C., assignor to Wired Radio, Colonial Radio Sales Co., Inc. No. 1,533,588. New N. Y. Filed 28. 1926. Inc., York, May L. A. Hazeltine, Wave Signaling system, filed Aug. No. 1,738.041. 13 1929, D.C. E.D. N.Y., Doc. 4387, Hazeltine Method and for Controlling Apparatus Remotely Corp. v. E. A. Wildermuth. No. 1,648,808. Radio Receiving Systems. Winfred T. Powell, Rochester, N. Y., assignor to The Stromberg- A. J. Weiss, Electrical Condenser, filed Sept. 30. E.D. Doc. Dubilier Carlson Telephone Manufacturing Co., Ro- 1929, D.C., N.Y., 4452, Transformers chester, N. Y. Filed October 15, 1925. Condenser Corp. v. Aerovox Wireless Corp. Microphone Line to Tube, Tube to Line, Tube Makers Defend The there for hundreds of years, but where are Pentode they to-day? Some people say ours will be Line to Line a great country when it is finished. When (Continued from page 350) this country is finished, its period of great- for cooperation on circuit problems. This ness will be over, for at that time the life Mixing Transformers is a service we owe set manufacturers, and will have gone out of it. Reactors we are eager to render all the aid we can. We may be thankful it will never be Coupling The Pentode represents a definite finished. Our industry will always need advance in radio. It cancels the necessity and want new ideas. Filter Chokes .... of multi-tube receivers. It permits building more into radio simplicity manufacture; Good News for Servicemen Audio Transformers makes simpler and less costly receiver re- considerable and operation and maintenance. It should After study discussion, Impedance Matching duce manufacturing and material costs, a plan has at last been worked out whereby and costs to the radio public. the Radio Service Managers Association Transformers Power Tests in our own laboratory and in is enabled to conduct examinations of laboratories owned show that out-of-town servicemen mail. by others, by Compacts ..... the CeCo a.c. pentode performs up to all The plan as worked out for the out-of- the claims we make for it. The results of town serviceman, requires that he first these tests also prove that the pentode supply the R.S.M.A. with the name Speaker Coupling Trans- tube does make possible four-tube sets, or of his employer, or if unemployed, with three-tube sets not counting the rectifier, the name of a notary public in his town formers ...... and that these sets will operate as satis- to whom the examination may be mailed. factorily as the many-tube sets of to-day. Having done this the applicant must then . . In our own laboratory, we are doing con- arrange to take his examination in the Complete Amplifiers siderable research work to develop new presence of this party and have him fill receivers for commercial use outside of out a form of affidavit to certify that all radio. I venture to predict that in less than of the requirements and conditions under a doze years the tube division of the radio which the examination was sent have been industry will be the dominant factor in complied with. radio's march of progress. All papers must be mailed to the office The CeCo Manufacturing Company has of the R.S.M.A. for correction along with THORDARSON had some criticism by set manufacturers the original questions and must be ac- because of what they call a premature an- companied by an application for member- ELECTRIC nouncement of the pentode tube, but the ship and dues. Upon correction the appli- manufacturer who does not like change is cant will be advised as to his mark and in in for an uncomfortable time. Nothing can all cases where a satisfactory mark has MANUFACTURING stop the changes that are coining. been made, certification cards will be is- The manufacturer is in for sued. Those to a COMPANY* progressive failing make satisfactory- one of the most profitable and interesting grade will be obliged to wait a period of periods in our history. It is sometimes thirty days before another examination Huron, Kingsbury and remarked that business needs to be may be taken. stabilized. When a man says that he means Any serviceman wishing to secure an Larrabee Streets . t . that he would like to get his business fixed R.S.M.A. certification should address the so that he would not have to worry any Radio Service Managers Association at Chicago, Illinois, U. S. A. more. If he wants stability in business, let 324 West 42nd Street, New York City, him go to the Oriental countries; they designating the party to whom the ex- have had their business stabilized over amination papers are to be sent. RADIO BROADCAST FOR APRIL 353 RADIO MARKETPLACE News, Useful Data, and Information on the Offerings of the Manufacturer Receivers reproduction. The unit is connected between the Silver Majestic unit and the On the instru- New Receivers pick-up amplifier. " ment are three switches marked Low Regis- GBIGSBY-GHUNOW COMPANY: The SILVER INC.: Six models of Majestic ter," "Middle Register,' 'and "High Register," MARSHALL, line ot radio receivers Silver now includes the following and a knob marked The in- Radio are now available. The three new- models: "Compensator." Model 90 at $95.00 less tubes or $116.50 strument functions to eliminate to an extent est models are the Model 60B Lowboy, $145.00, completely with tubes; less tubes, or Model equipped Majestic determined by the setting of the compensator $169.50 complete; 75B Model 91 at and with Concert $116.00 $137.50 tubes; the band of frequencies to which the switch Grand, $158.00 less tubes, or $182.50 is turned, i.e., if the switch is placed on "Low Register" the low frequencies are suppressed. If connected to the "High Register" position the high frequencies are suppressed. In this way the operator can reduce that part of the audio- frequency range which normally receives too much amplification due either to poorly de- signed sound equipment or to poor theater acoustics. The instrument is manufactured to the specifications of Simplimus by the S A F Electrical Engineering Company. Antenna Equipment M. M. FLEHON AND SON, INC.: Lightning arresters, complete antenna kits, light-socket antennas, ground clamps, loud speaker ex- tension cords, insulators, lead-in strip, porcelain lead-in bushings, and other similar items are manufactured by this company. Supreme Tube Tester SUPREME INSTRUMENTS COMPANY : The Model 50 Tube Tester is designed especially for use in testing laboratories, high-grade service laboratories, and by large dealers and distribu- tors. The unit is self contained, drawing all its power from the 60-cycle, 110-volt a.c. tine. To compensate line-voltage variations the units con- tains a constant-voltage transformer manufac- turned under a license from the Ward Leonard Electric Company. The instrument will test all Mode! 92 and 93 at $146.00 and $167.00 with types of tubes, a.c. or d.c., three-element or complete; and Model 95B Highboy, $145.00 less tubes; Model 102 at $184.00 radio-phonograph four-element. An indication of mu and Gm are tubes, or $169.50 complete. These latest models and $205.50 with and Model 103 tubes, at $203.50 obtained by a direct-reading on the dial. By use a screen-grid circuit with a de- and $225.00 with tubes. screen-grid pressing buttons the tube can be tested for gas tector. Two of the four tuned circuits are placed and emission. The unit sells at a dealer's net ahead of the first tube so as to prevent cross- Cornell Paper Condensers talk. The chassis is cadmium plated. CORNELL ELECTRIC MANUFACTURING COM- PANY: This company manufactures a complete New CeCo Tube line of small and large by-pass condensers for use in radio receivers. Based on 0.0005-inch MANUFACTURING COMPANY: The new paper linen the Cornell specifications are as CeCo 227 replacing the old type N-27 has the following features: Thickness: Two mica members, the one Capacitor tissue must caliper as spacing upper close to specified thickness as possible. In no much larger than usual. case should individual readings vary more than A grid built around two supporting bars in- 5 per cent, over or under the thickness specified stead of the usual single bur. in the order. Short cathode. Porosity: Capacitor tissue must not measure Shortened distance from glass stem to elec- less than 105 seconds in air resistance. trode. Uniformity: The tissue is to be free from Longer glass stem. wrinkles, cockles, creases, slugs, and to be prac- The larger upper mica separator holds both free from cathode and grid in positions concentric to the tically pinholes. price of $98.50. A much simpler tube checker, Width of tissue: The width of the tissue must plate and yet when the tube heats it permits the Model 17, is designed to give simple but be within inches of the width expansion without strain to cause warping. A specified up effective tests on tubes. The net price is $19.50. to a maximum width of 4 inches. The double supported grid to maintain Between 4 The Model 10 Ohmeter may be used to deter- helps inches and 8 inches the variation shall not tube uniformity. The tube is not of the be mine the value of resistors and is also useful in quick- greater than \. inch or minus. heating type, although the new tube does reach 3 plus checking apparatus and tracing circuits. Net Alkalinity: No more than one of an operating temperature than did the gram paper price: $17.50. quicker shall require more than 0.30 milligrams of old tube. In this connection CeCo engineers sulphuric acid for complete neutralization. stated, "Actually the cathode reaches its opor- Acidity: The water extract of one gram of Photo-Electric Cell ating temperature in lens time than did the paper shall not require more than 0.10 milli- New cathode of the N-27. CECo will release a quick- grams of sodium hydroxide for complete neu- heating tube when and only when a way is tralization. JENKINS TELEVISION CORPORATION: An ex- found to combine quick heating with satisfac- tremely sensitive hyoride type photo-electric tory operating life.' cell for television work has been developed. It SAF-3 Mixer is now in production and available to the public through the sales department of the De Forest Turntable Equipment SIMPLIMUS, INC. : The SAF-3 Mixer is designed Radio for use in Company. a theater "sound-movie" installation ELECTRICAL RESEARCH PRODUCTS. INC.: A and its function is to control the of quality number of broadcasting stations h ave pur- Precision Resis tance Amplifier chased turntable equipment from this company to permit the use of special or ordinary phono- INTERNATIONAL RESISTANCE COMPANY: Jos- eph Morgan, of the Engineering Department of this company, has developed a resistance- coupled amplifier which gives uniform frequency response within 1 DB from cycles up to 20,000 cycles per second. Another type of amplifier has been designed with a gain of approximately 55 DB, a power output of about 4.5 watts, and uniform response over the frequency range of 30 to 10,000 cycles. Complete engineering bulle- tins describing these amplifiers can be obtained from the company. New Bosch Models AMERICAN BOSCH MAGNETO CORP.: The two newest Bosch consoles using the Bosch screen- grid chassis and electrodynamic loud speaker are the model H listing at $198.50 and the Model 16 listing at the same price. 354 RADIO BROADCAST FOR APRIL graph records for broadcast programs. The turntables are available in either single or double units operating at either .'ill.', or 78 r.p.m. At the present time the equipment is in use at approximately twenty broadcasting stations. '1 he equipment is not sold outright but is loaned to the station under a three-year license agree- ment which includes complete servicing by KRPI. The following stations have this equip- ment at the present time. In the following list "Double 33}" means two turntables operating at 33} r.p.m. "Double 78" means two turn- tables operating at 78 r.p.m. WTMJ No. 337 RADIO BROADCAST Laboratory Information Sheet April, 1930 Measuring Resistance OF THE simplest methods of measuring re- value of an unknown resistor. The voltmeter is ONEsistances is by the use of a d.c. voltmeter con- connected directly across three B batteries and the nected in series with the resistor to be measured and potential is found to be 140 volts. The unknown re- across a known d.c. voltage. The circuit is shown on sistor is then connected in series with the meter and this sheet. the meter reads 25 volts. What is the value in ohms The procedure is to measure the d.c. voltage first of the resistance? with the voltmeter. The resistor to be measured is Since the voltmeter has a resistance of 1000 ohms then connected in series with the meter and the per volt, the total resistance, Rm, is 1000 times 250 reading of the meter noted. With these data the or 250,000 ohms. Eo as measured is 140 volts. Er is value of the resistor may be obtained from the 25 volts. Therefore formula 140-25 Ro X 250,000 25 where Ro is the resistance in ohms; Ro = 1,150,000 ohms as the value of the un- Er is the voltage read on the voltmeter with known resistor. the resistance connected in series with the voltmeter; Eo is the voltage of the source, i.e., that voltage indicated by the meter when it is connected directly across A-B; RESISTOR Rm is the resistance of the meter. SOURCE TO BE Therefore, the only data needed to measure re- OF DC MEASURED sistances by this method is the resistance of the voltmeter. This information may be marked on the VOLTAGE IS CONNECTED meter or, if not, it can be obtained from the manu- HERE facturer. In the following paragraphs are a few examples worked out by this method. f. Example: A 250-voIt meter with a resistance of 1000 ohms per volt is to be used to measure the VOLTMETER No. 338 RADIO BROADCAST Laboratory Information Sheet April, 1930 Three Types of Distortion DIFFERENT types of distortion can be produced by the tube itself, although frequency SEVERALproduced in the power tube. Distortion may distortion may be introduced by the apparatus :is- >- result from (a) volume distortion, (b) frequency dis- ciated with the power tube, such as the input or tortion, and (c) harmonic distortion. output transformer and loud speaker. Volume distortion: The ratio between the output Harmonic distortion: If a pure sine wave at some obtained from a tube and the a.c. input voltage to frequency is applied to the grid of a tube and in the its grid should be constant up to the point where output of the tube the same and other frequnu i-s the tube begins to overload. If the ratio between appear, then harmonic distortion is occurring. All output voltage and input voltage increases as the power amplifiers produce a certain amount of this input voltage increases the strong signals are am- type of distortion, its extent depending upon the plified more than weak signals; if, conversely, the characteristics of the tube itself and I In- circuits ratio decreases as the input voltage is increased, out of and into which it works. The amount of strong signals are amplified less than weak signals. second-harmonic distortion is used as a basis for In power tubes this type of distortion is slight, rating the maximum undistortcd output from a the power output per volt input squared being tube. If an ordinary three-element tubr is working constant up to the point at which the tube over- into a load resistance equal to twice its own plate loads. resistance, the second-harmonic current is about Frequency distortion: A tube and its associated 5 per cent, at a point just before the tube begjns to circuits should give uniform amplification to all overload. This amount of distortion is considered frequencies over the audio-frequency band it is small enough to be negligible. A tube may, of course, desired to transmit. If the amplification varies with generate other frequencies besides the second har- different input frequencies certain notes are am- monic and, in fact, when a tube is somewhat over- less loaded it amounts of third- plified more or than others. Over the audio- produces large second-, , frequency band little distortion of this type is and fifth- harmonic distortion. No. 339 RADIO BROADCAST Laboratory Information Sheet April, 1930 Detection Characteristics T-YETECTION characteristics; showing the rela- -L' tion between the d.c. plate current and r.f. input to a detector are very useful in determining the best point at which to operate a tube as a de- tector. Such a group of curves are shown on this sheet, being taken from an article "Detection at High Signal Voltages" by Stuart Ballantine pub- lished in the Proceedings of the Institute of Radio Engineers. 0.6 tt 00.4 U CHARACTERISTICS OF TELEVISION SIGNALS (Continued from page 319) is only necessary to employ synchronous motors of the same speed for rotating both mechanisms. Temporarily, while the television audience consists mainly of amateurs interested in results with the minimum expenditure, this method is ideal. However, as the service areas of visual broadcasting stations are increased it will become necessary to employ more intricate means of synchronizing. A synchronizing tone, let us say 720 cycles (which is the scanning frequency of a 48-line picture at 15 pictures per second), is transmitted to the receiving point. g-JO z (Continued from page 357) RADIO BROADCAST Information Sheet No. 340 Laboratory April, 1930 ning disc is placed backwards on the shaft or that the shaft is rotating in the wrong direction. The cure is obvious. Because of the 180-degree phase shift encountered in Calculating Detector Output each vacuum tube stage, it is necessary to employ an even number of stages in the amplifier, otherwise the will be "LABOFATORY SHEET" No. 339 is given the will be 0.46 If the i ./. is modulated picture IN milliamperes. "transrectification" diagram of a 20lA-type 43 per cent, it means that the r.f. voltage varies "negative" with the light and dark por- tube at a of 90 volts about its mean 7 43 operated battery potential value, volts, by per cent. There- tions transposed. Hence, a negative with a 110,000-ohm load in its plate circuit. This fore, it reaches maximum values of 7 pic- + (7 X 0.43) ture indicates that we are the diagram shows the relation between d.c. plate cur- or 10 volts and minimum values of 7 (7 X 0.43) employing rent and r.f. input voltage with various values of C or 4 volts. The plate current corresponding to 10 wrong number of stages or that a stage is bias. The method of the curve and brief volts is 0.63 obtaining a input milliamperes and the plate cur- inoperative. explanation of what it means will be found on the rent corresponding to 4 volts is 0.27. The a.c. plate If the travels across same Sheet. In the following notes we explain how current will therefore be one having an absolulo picture the field of it is possible from this simple diagram to determine peak of 0.63 milliamperes and a minimum of 0.27, vision from left to right, the receiver me- the from a detector the difference between these audio-frequency output voltage two being equal to chanism is leading that at the transmitter; with a given r.f. input signal. twice the peak value of the a.c. current. This differ- if from to left it is In either To explain how this is done let us take for exam- ence is 0.36 and dividing by 2 we get 0.18 as the right lagging. ple the center curve corresponding to a grid bias of peak value of the audio-frequency current in the case the motor speed should be adjusted minus 8 volts. This curve then shows the circuit. particular plate Dividing this peak value of 0.18 by the accordingly. current obtained with various r.f. root of 2 to r.m.s. values we have 0.128 plate voltages square get The be seen "out of frame" applied to the input. With zero r.f. input the plate as tlje effective a.c. plate current. This current in picture may current is approximately 0.12 milliamperes, and, as amperes multiplied by the load resistance gives the either vertically or horizontally. If this the r.f. is input increased, the plate current grad- a.c. voltage. In this case it is 0.000128 X 110,000 occurs in the vertical direction, the trouble ually rises and then flattens out. It reaches a maxi- ohms which 14.1 as the gives audio-frequency be rectified and mum of 0.8 milliamperes. Let us assume that an r.f. voltage. This value of audio-frequency output ob- may by starting stopping input of 7 volts modulated at say 43 per cent, is tained by calculation agrees very closely with the the receiving motor until the motors start to the What will be the a.f. measured value. This method of applied grid. voltage calculating detector off with the two scanning spirals in their appearing across the load resistance? The is therefore effective and steady output very compara- correct relation. plate current obtained with an r.f. signal of 7 volu tively simple. Should the picture be out of frame hori- zontally, the neon lamp may be moved laterally or the disc may be shifted on the shaft. This may be due to phase displace- ment in the supply voltage causing one motor to lag behind or lead the other. This factor is variable and it is desirable H No. 341 IDKI BBOADCAST Laboratory Information Sheet April, 1930 to construct the mechanism so that the adjustment may be readily made. This be done the neon Reflection of Sound may by having lamp mounted in a fashion allowing lateral movement at will or by arranging the INTENSITY of the sound we hear a! REFLECTED The phase relation between the two stator of the synchronous motor so that it THEany point in a room when listening to RAY A waves at the where the listener is point may be rotated during operation. the output of a loud speaker is a function located determines the intensity of the It is to of the intensity of the direct sound ray, sound (neglecting reverberation), and if impossible give a comprehensive the reflected ray, standing waves, and the the two waves are exactly opposite in resume of television because of limited amount of reverberation. The diagram on phase tittle sound will be heard. very space and because of the rapid strides I his sheet together with the following On the other hand, some sound will notes gives a simple idea of the effect of always be audible because reflections being made. It is hoped that these few the direct and reflected rays. are also taking place from all other parts words may assist in visualizing the basic The shows a cone loud of the room. The effects of this of diagram speaker tyj>e problems encountered. placed a snort distance in front of a wall. reflections are prevented somewhat by During operation of the loud speaker the use of a bunle (although this is not sound waves will be radiated in all dir ] No. 345 RADIO BROADCAST Laboratory Information Sheet April, 1930 Regarding Grounds for A. C. Sets THE INSTALLATION and use of a.c. radio receivers ground or a comparatively poor ground may cause INit is frequently found that more volume is ob- an otherwise perfectly stable receiver to regenerate tained without any wire connected to the ground slightly. terminal than is obtained with a ground connection This is the effect which is responsible for the to the binding post. This effect has evidently given peculiar operation of a.c. receivers with and without quite a few servicemen the impression that there proper ground connections. With a proper ground was something wrong with the receiver. The fact .iTi- set has a gain approximating that which its is, however, that this quite common effect does makers intended it should have. If, however, no not necessarily indicate that the receiver is defec- ground is used some regeneration will exist which tive. will generally tend to increase the gain and, as a The volume obtained from a receiver depends result, more volume is obtained. The disadvantage upon the ability of the antenna system to pick up of not using a ground, however, is that this in- signals and upon the gain of the radio receiver. creased gain may only be obtained over a small part Modern high-gain receivers have to be very care- of the dial and at other points the set may tend to fully designed from the standpoint of shielding, oscillate or the first tuned circuit may be thrown filtering, and grounding to make them absolutely out of alignment so that the selectivity is impaired. stable and if any one of these points is neglected For these reasons it is always advisable to operate the set will have some regeneration. On the other a receiver with a ground if it is intended that it hand, if the set depends for some of its amplifica- should have one. If for some reason the receiver tion on regeneration its performance will depend must be operated without a ground it is worth somewhat upon the conditions under which it is while to try reversing the plug in the light socket operated. Proper grounding is an important point in order to determine the position which gives the in the prevention of regeneration and the lack of a most satisfactory operation. >,*r,,,,,. n*^<,,,. -^fm*,,,,. ~r*,(. -^ffj^f. ^Ky^ ^gjjx-^,- yry Trade ISfiow J In Connection with the 6th Annual R.M.A. Convention and the Federated Radio Trade Assn. Convention The fourth annual R.M.A. trade show will be held this The June trade show marks the beginning of radio's June in Atlantic City, the of the playground America, new year. The most responsible manufacturers exhibit country's pre-eminent convention city. It will be the and demonstrate their latest models and accessories on largest trade show in the history of the radio industry, this occasion. It behooves connected with the twice as large as last year's Chicago show. everyone radio to visit the trade show this Atlantic City offers more hotels, better accommodations, industry year, which will be the most more to see, hear and do this is the one trade show you interesting and important radio gather- cannot afford to miss. ing ever convened. The Atlantic City Auditorium, facing the boardwalk and Hotel reservations should be made through the Atlantic cooled by the breezes of the Atlantic Ocean, is the largest City Convention Bureau, Atlantic City, New Jersey. convention hall in the country. All exhibition booths and Invitation credentials for the trade show will be mailed demonstration rooms will be under one roof, on one floor, to the trade about 1st. making it easy to get a comprehensive view of the entire May trade show. Reduced round trip rates on all railroads. Radio Manufacturers' Association Trade Show, Room 1904, Times Bldg., New York Under Direction of U. J. Herrmann and G. Clayton Irwin, Jr. FIRST MINUTE Let your customer hold a watch on any set equipped with Arcturus Tubes. Snap the switch and check the starting time. . . thepro- gram is there in 7 seconds! THII MINUTE DEMONSTRATION PROVES ARCTURUS SUPERIORITY TO ANY TUBE BUYER SECOND MINUTE Let your customer listen to the clear, pure tone that is characteristic of Arcturus Tubes. There's no annoy- ing hum, no trace ofom- side noises, to mar the beauty of any program. self-evident superiority ofArcturus THEBlue Tubes means increased sales and extra profits. If you have not checked Arcturus quality yourself, ask your jobber for a demonstration. Provedperformance, not sales talk, has made Arcturus the fastest growing tube in the radio industry today. ARCTURUS RADIO TUBE COMPANY Newark, N. J. THIRD MINUTE Show your customer, on the meter, that Arcturus Tubes easily withstand exceptional overloads. Thisunusualstaminaex- plainsArcturus 'long life. T Quick Acting RADIO TUBES TY, NEW YORK 100J6MOD of two stages as it is too difficult to into one tube and its circuit all Fig. 2 pack the gain required. The problem of cal- in a receiver tubes. Thus, if the input to the de- came two stages of transformer-coupled culating the voltage gain or has been illustrated this tector is 100 per cent, modulated, the a.f. amplification with an overall gain amplifier by Review Sheet" and r.f. voltage to deliver 20 volts a.f. of about 72. What was the total volt- "Engineering that was the in view. need be only 4 volts. age amplification? object Now suppose you use a pentode A Practical Case Problems power tube requiring only 12 volts to We need, therefore, an input r.f. deliver 2000 milliwatts. If worked 1. Four milliamperes of current at potential to the detector of 4 volts. from a detector with a four-to-one 1000 cycles are fed through a 10,000- Now suppose we are situated in the transformer the detector output need ohm input resistor. The voltage across field of a transmitter such that across be only 3.0 volts, and at 100 per cent, this resistance is applied to a 245-type the antenna appear 40 microvolts. modulation the r.f. input to this de- power tube whose amplification factor How much amplification must there tector need be only 0.6 volt instead of is 3.8 and whose plate resistance is be between the input to the set and 4 volts; thus we can get along with 2000 ohms. The output load is 2000 the input to the detector? Obviously one-seventh (1/6.7) as much amplifica- ohms. Calculate the input and output the amplification is 4 volts divided by tion in the r.f. amplifier. power and the power amplification. 40 microvolts or a total voltage ampli- Suppose you want to use a screen- 2. The power obtained from a tube fication of 100,000. Now between the grid detector which has a conversion is a maximum when the output resist- antenna and the input to the first r.f. factor of about 40 to 1, i.e., a 100 per ance is equal to the tube resistance, as tube there is usually a gain of 10, so cent, modulated r.f. signal of one volt in Problem 1, but the maximum un- between the first r.f. grid and the de- will deliver 40 volts a.f. It must be distorted power is secured when the tector grid there must be a voltage coupled to the power tube through a load has twice the tube resistance. gain of 10,000. resistance (because of the tube's high Calculate the power into a 4000-ohm Suppose it is possible to obtain a resistance) and so the gain in the load and notice how little power is lost voltage gain of 30 per stage from a transformer will not be secured. We in not exactly "matching" the tube screen-grid tube and its accompanying need 12 volts output and so the r.f. and load.