Radio Broadcast (May 1928-Apr 1929)

RADIO BROADCAST this cause is removed by bending the prongs to assure a tight contact. The Case of the Broken Vase: " A telephoned service call" writes D. F. Greer, Coatesville, Pennsylvania, "informed me that while the set tuned properly, it lacked volume. I assumed that it was probably a case of poor tubes, open transformer, or similar ailment. On testing the set, antenna and ground were o.k. and routine tests showed no opens, no shorts, tubes good, plate and filament voltages correct, proper C voltages, and still the set did not deliver a "kick." A new speaker was substituted with no change. I was on the point of removing the set to my shop for a bench test when I accidentally discovered the difficulty. In testing the B power unit, I had clipped the negative lead of the meter on the negative post and the positive lead at the time lay in my left hand. I gazed disgustedly at the set and toyed abstractedly with the extension cord of the loud speaker. There was a deflection in the voltmeter (the cord had been tested for continuity), and at the same time a tingling sensation in my hand. Then the truth dawned. The loud speaker was being shunted by moisture in the cord. I could not understand what caused the dampness until one of the maids confessed she had knocked over a vase containing cut flowers and the water had seeped into the cord. This experience illustrated to me the value of a high-resistance voltmeter. Antenna-Ground, connections: While there are several devices made for the purpose of bringing the antenna and ground wires into the house, the use of an ordinary convenience receptacle makes a neat job and one which is uniform with other receptacles and wiring in the house. I have found that the owners of higher-priced sets prefer this manner of entrance rather than the use of window strips and manufactured receptacles. A porcelain tube is used through the brickwork to insulate the antenna lead-in. The wires are then pulled through the knock-out in the rear of the receptacle and the ends clamped under the screws inside the box. A length of doubleconductor and receptacle plug then connects the set to the outlet. Be sure to cut the hole in the baseboard to fit the box and not the outlet plate. Fig. 4 shows this method. — D. L. Love, Greensboro, N. C. Items of Interest CONTRIBUTIONS on the routine of servicing, the general equipment, and tools employed are piling in on the service Brick _ Veneer .Plastered Wall Radio Set, editor's desk in response to our recent request for such material. Just what we are going to do with this — outside of the fact that // will be used — we don't know. It is possible that the material will prove of sufficient interest and length to justify a separate article — or perhaps we shall make a symposium of the various contributions — or, again perhaps, we shall pick the best points of all contributions and give them to you as a digest. At any rate we are still open for suggestions on the routine of servicing and the simplest, yet complete, equipment with which to do it. FRANCIS H. ENGEL, Radiotron Engine r, with the R. C. A., sends along the following suggestions in reference to tests on rectifiers and power tubes suspected of suffering from old age: (1) The loss of emission in a rectifier tube (which is the usual cause of failure) is quite often accompanied by an increase in alternating-current huni The most practical and simplest method of determining whether or not the rectifier tube is defective is to remove the tube in question and substitute in its place a new tube of known good quality. (2) The average life of the 281-type rectifier is greatly in excess of 1000 hours when operated under maximum rated conditions. Individual tubes may fall short of this figure but the large majority of them will exceed it. (3) Regarding a test for defective output tubes the same scheme as outlined above for the rectifier tube would seem best. Many servicemen have written us asking for suggeslionsas to thebest book available on the background of radio theory. We don't know any such book because each inquirer wants a book with some special emphasis to suit his particular needs. Most of our correspondents want a book on radio circuits, particularly dealing with receiving circuits, which does not devole major attention to the general theory of electrical circuits. There is such a book, indeed there are several. How Radio Receivers Work, by Walter Van B. Roberts and published by Radio Broadcast, Garden City, N. Y. at $1 net contains precisely the simple, clear analysis that is so welcome when it is found. Other useful books are listed on page 295 of this issue. Fig. 4 — A neat method for bringing antenna and ground wires in the house (4) Another test which a serviceman should make when looking for trouble in the rectifier unit of a receiving set is to test for d.c. voltage across the output terminals of the filter and voltage divider. Knowing, from experience, the normal value he can readily tell by his meter reading whether or not the rectifier tube is performing satisfactorily. Literature That Sells Service: The radio service business, for the greater part, concerns a commodity that sells itself. When a radio set actually goes wrong, the average person turns to the serviceman and it requires no salesmanship to convince him that his set needs repairing. But sales literature — circulars and cards describing the advantages of some particular serviceman or company — can go a long way toward building up a profitable service business. Such literature acts in several ways. It reminds the radio owner that it is foolish to wait until his set actually goes bad, — until he misses entertaining programs — before calling in the serviceman. It also impresses on his mind the name and address of a reliable serviceman available in case of trouble. Thirdly it may call his attention to subtle difficulties existing in his set of which he was only vaguely aware. Fig. 2 shows a card circulated by William V. Lowe, Certified Radiotrician, of Fitchburg, Fig. 3 — A simple antenna clamp which is easy to install. Mass., that gives a good idea of what can be done in the way of progressive servicing. The possibilities of drumming up trade in this manner are enormous. Special circulars could be prepared, prior to important broadcasts, suggesting the inspection services of an expert at a special price. The average set owner should be educated into having his equipment examined at regulate intervals — in the same way that the intelligent man goes to his dentist. Stock circulars can be prepared for distribution in the late summer suggesting that now is the time to have receivers gone over thoroughly in preparation for the coming radio season. Good radio service sales literature might turn the summertime into a profitable radio season. "The Serviceman's Corner" is particularly interested in circulars, letterhead and cards of this nature, and will pay a special price for those reproduced. Arthur Rogers, New York City serviceman, has been building up sales on electric phonograph pick-ups by following up his old customers. He circularizes the owners of receivers he made several years back, adding to this list all recent service jobs on old equipment. He suggests modernizing these receivers by the installation of power amplifier apparatus and new speakers. The phonograph pickup naturally follows. "The Serviceman's Corner" pays for live sales tips. What should the serviceman charge? What is an equitable price for an inspection? — for an hour's work? How should the serviceman figure his charges? Should the profit on parts lessen his charges for time? "The Serviceman's Corner" will welcome an exchange of ideas on this subject. tf]f An antenna clamp which makes installation quick, and much neater than is often possible has been brought out by the F. G. Manufacturing Company. 1117 Peoples Bank Building, Indianapolis, Indiana. This clamp requires no nails or braces to affix it to the root, or chimney. A sample has been examined in the Laboratory and found very satisfactory. The picture, Fig. 3, shows how the device looks. • march, 1929 page 321