Radio Broadcast (May 1929-Apr 1930)

" I replaced the tubes again and turned on the current. The tubes did not light, but a bright red spark showed up in the 281-type tube. I replaced this tube with a new one, and the set was back in working condition again. In examining the rectifier, I noticed that the filament had broken, and one of the broken ends was touching the plate, causing a short in the tube, which in turn heated the winding of the rheostat." C. Washbubn, Jr., of Jacksonville, Fla., suggests reversing antenna and ground posts on many receivers suffering from low sensitivity. The improvement in sensitivity is generally due to increased regeneration with the removal of the stabilizing effect of the ground. A Useful Voltmeter Formula: Boris S. Naimark, service engineer with the Riverside Radio Service Company of New York City, notes the formula in " Strays from The Laboratory" for August for determining the value of an unknown resistor with a voltmeter and a battery. panel and the panel is supported by angle strips along each side. "The spring contacts on one side are about an inch from the angle strip support, but I found that the lightning had burned the panel and left a smoke or carbon deposit thick enough to ground these spring contacts to the angle supports that held the panel in place. This is an ideal type of truck for radio service work. Note the ladder for making antenna installations. Mo., notes a cause of sensitivity drop in a Crosley. "Sometimes a Crosley Showbox set, model 706, loses its kick after a few months use and new tubes do not always remedy the trouble. "I have found that in some cases this loss of volume is caused by a sideway movement of the stator plates of the condenser in the first tuned r.f. stage. This can be remedied easily by loosening the two set screws holding the rotor plates to the shaft and slipping the plates to the center of the stator plates again. This puts the condenser in resonance with the other two and the set will tune as sharply as ever." How Ijmg Do A.C. Tubes Last?: George Lewis, of the Arcturus Radio Tube Company, thinks that the average set owner should get along for two years on one set of tubes. Offhand, service contacts tend to indicate that two sets of tubes a year is nearer the mark. We should appreciate first-hand data on this. R Where R is the unknown resistor Ei the voltage indicated on the meter E the voltage of the battery Rm the resistance of the meter Mr. Naimark points out that this same formula can be used to determine the correct value of a resistor to be used as a voltage multiplier to secure any desired range with any voltmeter. Let R equal the value of the resistor Ei full-scale voltage of the meter itself E the voltage desired at full scale Rm the resistance of the meter If, for instance, we have a meter reading up to 100 volts, having a resistance of 1000 ohms per volt, and we desire to place a resistor in series with it so that it will indicate full scale on 500 volts, what value of resistance should we use? The calculation is simple : The calculation is simple /500 \ VlOO — U ohi "After sanding off this deposit of carbon everything was OK." Blaine Martin, Cleveland, Ohio. Installation and Operation of Moving Coil Speakers: "Many times you will run across a customer who wants receptacles for a dynamic loud speaker of either the 6-volt field type or the 90-volt field type, in two rooms. "The easiest method to use for this purpose is to attach an old tube base on the speaker leads and wire a radio tube socket on the floor in the rooms desired, thus providing the necessary four contacts for the field and moving coils." C. H. Jenkins, Radio Service Audubon, New Jersey. Pepping up a Crosley: Eugene 0. Whitaker, in charge of service with the American Electric Company of St. Joseph, A Home-Made Tube and Set-Tester R = ( _ 1 ) X 100,0011 = 400,000 ohms A Grounded Transformer: "After an electrical storm last week I was called upon to service an Eveready set. I first discovered that the fuse was blown in the light line, and, in trying to replace it, I found that the line was grounded. After disconnecting the radio set the fuse stayed put. "Upon close inspection of the set I found the socket panel of the power pack was badly burned near the transformer, and, upon testing the transformer, found the primary to be grounded. Everything else OK. "After removing the transformer from the set I failed to test it, which was careless of me. Replacing it with a new transformer I was surprised to find that I still had the same ground. "The primary taps on an Eveready set run to spring contacts which are set in the rubber socket OPERATING AND SERVICE MANUALS AVAILABLE Tn response to a recent questionnaire submitted by Radio Broad■*■ cast, the radio manufacturers Listed below have indicated their willingness to supply operating and service data on their receivers to us for distribution to legitimate servicemen. In order to secure this material it is necessary to direct your request to Radio Broadcast on your business stationery, enclosing the correct amount in stamps or money-order when a charge is indicated. F. A. D. Andrea, Inc.: Wiring diagrams and special sheets covering current models. No charge. Ail-American Mohawk Corporation: Instructions and Service Manual (specify model). No charge. Bremer-Tully Manufacturing Company: Instruction Books and Service Manuals. No charge. Colonial Radio Corporation: Instruction Books, Service Sheets and Service Manual, at 50c, 25c, and 50c, respectively. Bulletins number 31A-C, 31D-C, 32A-C and 32D-C are also available. Continental Radio Corporation: (Slagle), Service Manual. No charge. Columbia Phonograph Company, Inc.: Service Manual. Nominal charge not yet determined. Crosley Radio Corporation: Instruction Sheets or Service Manuals (indicate receiver model numbers) No charge. Day-Fan Electric Company: Complete Service Manual. Price: fifty cents. Electrical Research Laboratories, Inc.: Instruction Bulletins and Service Bulletins. No charge. Charles Freshman Company, (Earl and Freed receivers) : General literature. No charge. Federal Radio Corporation: Instruction Books and Service Manuals (specify receiver model). No charge. A. H. Grebe and Company: Operating and Service Data (specify receiver models). Nominal charge. Grigsby-Grunow Company (Majestic Radio) : Operating and Service Sheets. No charge. Stewart-Warner Speedometer Corporation: Instruction Books, Service Manuals and Wiring Diagrams (specify receiver types). No charge. Steinite Radio Company: Service Manual in .standard binder, 50c, leather binder, $1.00. Silver Marshall, Inc.: Service Bulletin, Silver Badio Instruction Booklet. No charge. Data Sheets, two cents each. General catalog, no charge. Temple Corporation: Service Bulletins. No charge. United Reproducers Corporation: Operating Data, Service Data. No charge. U. S. Radio and Television Corporation: Service Manuals. No charge. e present the following service contribution from G. Wesley Taylor, of Berkeley, California, for the benefit of those servicemen who make their own test equipment, and who endeavor to incorporate, in single test devices, as large a number of functions as is effectively practical. While there are several commercial types of testing equipment that may effect individual tests more conveniently than Mr. Taylor's arrangement, the versatility and economy of this device will recommend it to many servicemen. "The average tester tests tubes with the current supplied by the receiving set. The tester described on this page tests tubes regardless of the condition of the batteries in the receiving set, and will rejuvenate them if necessary. An oscillator is built into the circuit to facilitate adjusting the receiver in case it is not possible to pick up a broadcasting station. "The d.c. voltmeter is a Weston with an 0-5 range. By removing the resistance, this instrument was converted into 0-8 milliameter. The proper resistances and shunts were determined by the use of Ohms Law to give the desired ranges. The a.c. voltmeter is a Jewell with a range of 0-15. Removing the resistance from this meter provided an instrument with a range of about an 0-8. The above meters were on hand — ■ therefore the extra work. If it is necessary to buy the meters an 0-1.5 d.c. milliameter and an 0-8 a.c. voltmeter should be selected. The ammeter was purchased from an auto wrecking house for the sum of fifty cents. The shunt and the coils were removed and replaced with new coils having more turns to lower the range below that desired. The range was then adjusted to suit by means of a new shunt. • OCTOBER 1929 • • 345