Radio Broadcast (May 1928-Apr 1929)

New Apparatus To Help Cure Interference X39 Device; Davis Trouble Finder, Model T. F. 2. A compact portable radio receiving set for use in locating sources of radio interference. The set uses five cx-299 (ux-199) tubes in a circuit consisting of two stages of r.f. amplification, detector and two stages of a.f. amplification. A single dial is used to tune the receiver. The other controls are a volume control, a rheostat and an "audio-radio" switch. The set is designed for use with headphones, which are furnished with the receiver. An external loop of larger dimensions than the regular internal loop is provided. There is also provided a small exploring coil to be used as a loop where minimum sensitivity is required. Size: 14 x io| x 5f inches. Weight: 20 lbs. Manufacturer: Davis Emergency Equipment Company. Price: $225.00 complete. Application: This excellent receiver, an earlier model of which proved exceedingly useful in the Laboratory some months ago, is the only one of its kind — that we know of — being manufactured for the specific purpose of locating sources of interference. With the receiver is supplied a small booklet giving data on the use of the device. The "audio-radio" switch is a valuable feature. It functions, when thrown to the "audio" side, to cut out of the circuit the r.f. stages, so that only the audio amplifier is operating. The manufacturer's pamphlet describing the receiver states that, "No case has yet been observed where interference was audible, on the audio side, beyond a limited area, usually within 150 feet of the source of interference." After the source of interference has been located, it must be repaired and in this connection the series of articles in Radio Broadcast, by A. T. Lawton, on how to eliminate interference, will be useful. These articles appeared in the following issues: November, 1927, January, 1928, and March, 1928. A. C. Tube and Set Tester X4o Device: Sterling A.C. Tube and Set Tester. Universal Model No. R-512. Contains an a.c. voltmeter with two ranges, 0-3 volts and 0-15 volts and a volt-milliammeter reading voltages up to 200 and milliamperes up to 30. It is possible with the tester to check the plate current STERLING A.C. TUBE AND SET TESTER DAVIS TROUBLE FINDER of all types of tubes in an a.c. -operated receiver, test for open circuits, shorts, defective transformers, defective sockets, etc. The tests possible with this tester are divided into two general classes, so called "service tests" and "tube tests." The "service tests" check the characteristics of the receiver; determine whether or not the tube is being supplied with its rated filament and plate voltages, etc. The "tube tests" check the performance of the tube, determine if it has sufficient emission, whether it is amplifying, etc. The tester can be used with receivers using R. C. A. and Cunningham, Ceco, Arcturus, Marathon, McCullough, Sonatron, Van Home and any other a.c. tubes requiring filament voltage not in excess of 1 5 volts (the maximum voltage which can be read on the filament voltmeter). Manufacturer: The Sterling Manufacturing Company. Price: $35.00 Application: Radio service men, dealers, set builders, experimenters, will all find this tester useful. It is comparatively inexpensive and is accurate enough for all ordinary testing. To use the device a tube is removed from the receiver under test and the plug from the tester inserted in the tube socket. The tube itself is plugged into a tube socket on the tester. By pressing the button on the tester it is possible to read plate voltage, plate current and filament voltage. All of the readings are taken under operating conditions and are therefore exact indications of the voltages applied to the tube when it is actually in operation. Either fourprong or five-prong tubes can be tested by means of adapters supplied with the tester. PRODUCTS of radio manufacturers whether new or old are always interesting to our readers. These pages, a feature of Radio Broadcast explain and illustrate products which have been selected for publication because of their special interest to our readers. This information is prepared by the Technical Staff and is in a form which we believe will be most useful. We have, wherever possible, suggested special uses for the device mentioned. It is of course not possible to include all the information about each device which is available. Each description bears a serial number and if you desire additional information direct from the manufacturer concerned, please address a letter to the Service Department. Radio Broadcast, Garden City, New York, referring to the serial numbers of the devices which interest you and we shall see that your request is promptly handled. — The Editor. «j« Ufa ■39 Phonograph Pick-Up X4i Device: Erla Phonograph Pick-up Unit. This device, illustrated in the photograph, is sold complete with the tone arm and volume control. The small movable arm carrying the actual pickup is counterbalanced so that the needle will not press too heavily on the record. To install the device, it is mounted on the phonograph in such a position that when the arm is moved to the center the needle is directly over the center of the record. The base of the tone arm is then fastened in this position with three wood screws. Manufacturer: Electrical Research Laboratories. Price: $19.50 Application: Designed for use in conjunction with a phonograph turn table and an audio amplifier (contained in a radio receiver or separately) to enable one to reproduce phonograph records electrically. The counterbalancing arrangement used in this device to offset some of the weight in the pick-up is to be recommended. Some of the pick-ups which have been tested in the laboratory press altogether too heavily on the record. A member of the Laboratory's staff, witnessing a ERLA PICK-UP demonstration a short while ago of a Hewlett loud speaker located at the Schenectady plant of the General Electric Company, noted that the pick-up unit used in the demonstration was arranged with a counterbalance, similar to that used in the Erla pick-up. The Erla unit gave a quality of reproduction apparently about equal to that of other pickups the Laboratory has received for test, but the volume output was somewhat less. However, the Erla unit gave all the volume needed for ordinary home reproduction. Five New Audio Coils X42 Device: Sangamo Audio Apparatus. The following units are available: Audio Transformer Type A. Turns ratio 3, primary resistance i960 ohms, secondary resistance 7100 ohms, primary inductance 200 henries with no direct current, with 2 mA. direct current, 145 henries. Price: $10.00. Output Impedance Type E. With 25 to 28 mA. of d.c. flowing through the coil the inductance is 30 SANGAMO OUTPUT TRANSFORMER