Radio Broadcast (May 1928-Apr 1929)

New Apparatus 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. Two-Stage Power Amplifier for A.C. or D.C. Operation X71 Device: National Push-Pull Amplifier. This is a complete two-stage transformer-coupled power amplifier. It does not contain any power supply, but it may be light-socket operated by the use of a 227-type tube in the first audio stage and two 210 or 250-type tubes in the output stage, which is push-pull. An extra socket is provided so that those who desire may use a Slow Continuously variable resistance Connect Color to Color FIG. I. Diagram shows method of connecting Baldor motor with condenser block and a.c. line 1 i2A-type tube in the first stage and operate the amplifier from a storage battery. Resistances are contained within the device so that the proper C-bias potential is supplied automatically to the tubes. The unit is wired completely. Manufacturer: National Company, Inc. Price: $40.00 completely wired but without tubes. Application: The amplifier may be used readily in conjunction with radio tuners or it may be used with a phonograph pick-up for the electrical reproduction of phonograph records. It may also be used to replace poor audio systems in old sets, thereby improving the quality of the reproduction. Improved Motor for Television X72 Device: Baldor Ball-bearing Motor. These motors are intended for use in television receivers for driving the scanning disc. Two types are available. Type YIV is a |-HP, uo-Volt, 60-cycle, single-phase, 1800-RPM motor designed for receiving sets using a 24-inch scanning disc. It is designed to maintain a constant speed between 750 and 1700 RPM with a 5 to 45-ohm variable resistance. Price: $30.00. Type M2V is a ts-HP, 1 m-Volt, 60-cycle, THE NATIONAL TWO-STAGE POWER AMPLIFIER single-phase, 1800-RPM motor for receiving sets employing 9 to 18-inch aluminum scanning discs. The motor revolves 1750 RPM at full load and a variable speed range of 750 to 1700 RPM is obtained with a 60-ohm rheostat. Price$23 .00. Machined flange for scanning disc for all motors. Price: $3.00. Rubber-cushioned base. Price: $2.50. Manufacturer: Interstate Electric Company. Application: This motor is of the induction type, not relying upon a commutator either for starting or running. Because of the fact that the motor is placed in close proximity to the television amplifier, tiny sparks, such as are produced by brushes sliding over the surface of a commutator while the motor is running, would create disturbing electrical waves, which if picked up by the amplifier may cause distortion or fogging to such a degree that the sought for picture would be a failure. This motor is silent in operation and free from hum, either of which affects the amplifier because of distortion and lack of clearness. The circuit is given in Fig. 1. The following excerpt from one of the engineering Test Department Reports of the Interstate Electric Co. is of interest: "The scanning discs as used to-day for television reception are anywhere from 9 to 24 inches in diameter, and tV or \ inch thick, usually of aluminum. These discs, may be driven by an M2V, tsHP; Baldor motor, which has ample power for this purpose. As a matter of NEW PORTABLE METER MADE BY WESTINGHOUSE fact, with a 15-inch disc the motor may run up to within 50 to 75 revolutions of synchronous speed which is 1800 RPM. In order to reduce this speed to what is required it is only necessary to place a series resistance in the circuit with a means of short circuiting about 1 5% of the total resistance in the form of a key. For example, for a disc 15 inches in diameter, \ inch thick with a required speed of 1080 RPM there is required a fixed resistance of 160 ohms with a key shunting around 25 to 30 ohms. "There is a means of obtaining somewhat more stable operation, which is to load the motor in some way (a flat disc is practically a frictionless load), as for example, by a fan. If we place six small blades, 1 by 2 inches on the side of the scanning disc, we will have accomplished the result we are looking for; namely, a slight load on the motor, enabling the operator to hold the speed of the disc more nearly constant. The motor now requires only a 30-ohm fixed resistance with approximately 5 ohms short circuited with a key, assuming a 15-inch diameter disc is used and a speed of 1080 RPM is desired." High Grade A.C. Meters X73 Device: Portable Alternating-Current Instruments for Laboratory Use. The Westinghouse Company have recently developed a new line of portable alternating-current instruments for laboratory use. These instruments are operated on the electric-dynamometer principle, containing two stationary coils and a moving coil. The unit shown on this page is a single-phase wattmeter. The unit illustrated has a case made of wood. However, they are now being manufactured with cases of built-up sheet micarta. This construction of case is novel and gives the units a great many advantages which wooden cases do not possess. The finish on the micarta case is that of burl walnut and is very hard, not easily scratched or marred like the finish on the wooden case instruments. The dials of the instruments are metal under which is a mirror so as to prevent parallax reading of the knife-edge pointer. The scale is 5§" long with quite uniform markings throughout. Although the design of these instruments is primarily for alternating current use they can be used on direct current and are just as accurate as on alternating current when the average of the direct and reverse readings are taken. The instrument element has an iron shield around it so as to make it immune from external stray magnetic fields. The accuracy of the instrument is f of 1 per cent., of full scale deflection. The terminals supplied on the instruments are non-removable, engraved with the scale value and have large contact surface. Ammeters are made in double-scale ranges from § to 30 amperes in capacities multiple of 2. The voltmeters are also made in double ranges of multiples of 2 capacities, from 3 volts to 600 volts. The double range 0-3 and 0-6 volts or 0-7^ and 0-15 volts are particularly desirable for measuring the filament voltages of the radio tubes in laboratory testing. The instruments are also provided in single-phase wattmeters with voltages as low as 30 volts up to 600 volts and currents from \ ampere up to 30 amperes. Manufacturer: Westinghouse Electric and Manufacturing Company. Application: The usefulness of such instruments in any electrical laboratory is obvious. The 52