Radio Broadcast (May 1928-Apr 1929)

OCTOBER, 1928 NEW APPARATUS 373 r _ \ r SAMSON CHOKE of B-power units. It is capable of carrying direct currents up to and somewhat in excess of 120 milliamperes. At 120 mA. its inductance is 30 henrys. The d.c. resistance of the choke is, approximately 290 ohms. Manufacturer: Samson Electric Manufacturing Company. Price: $12.00. Application: The choke coil is applicable to various filter circuits in which it is necessary that the circuit handle currents of about 120 mA. If the value of current does not reach values higher than about 80 mA. then the' Samson choke type 380 ($1 1.00) may be used; for currents not in excess of 30 mA. the type 30 ($5.00) is satisfactory. The low-r esistance characteristic of these choke coils makes them very satisfactory for use in filter systems, for with low-resistance circuits the voltage regulation of the power unit will be better than with high-resistance circuits; the resistance of the filter choke coils should be low enough so as not to have any great effect on the regulation of the system. These requirements are fulfilled very satisfactorily by Samson chokes. Radio-Frequency Choke Coils X66 Device: Radio-Frequency Choke Coils. Two types are available. Code No. RFC-85, with an inductance of 85 millihenrys, a distributed capacity of 3 mmfds. and a resistance of 215 ohms. Price: $2.00. . Code No. RFC-250, with an inductance of 250 millihenrys, a distributed capacity of 2 mmfds. and a resistance of 420 ohms. Price: $2.25 Manufacturer: Hammarlund Manufacturing Company. Application: These r.f. chokes are for use in the r.f. B-plus leads and in the detector plate lead to keep the r.f. currents out of the plate supply unit and out of the audio amplifier. Although two types are available it is likely that in broadcast receivers the cheaper 85-millihenry choke may be satisfactorily used in all cases. The impedance of these coils at broadcast frequencies will be determined by the distributed capacity of the coil. At 1 500 kc. the impedance of the 85-millihenry coil will be about 30,000 ohms and the impedance of the 250 millihenry coil about 45.000 ohms. The 85-millihenry coil, however, will give at broadcast frequencies a sufficiently high impedance so that satisfactory filtering action can be obtained. It is interesting that the coil with the higher inductance has less distributed capacity than the smaller coil. R. f. choke coils of this type can also be used in constructing an intermediate-frequency amplifier for a super-heterodyne. An example of such a use can be seen by referring to the article by L. T. Goldsmith in the May, 1928, issue describing the construction of a superheterodyne. A Neon Lamp for Television X67 Device: Kino Lamp. A neon tube designed for use in television receiving apparatus. The tube measures about 65" high and about 2" in diameter and is fitted with a ux type base so that it can be plugged into a standard tube socket. The a.c. resistance of the tube is about 1200 ohms and the current through the tube should not exceed about 20 milliamperes d.c. This corresponds roughly to about 200 volts across the tube. The three circuit diagrams in Fig. 4 show circuits in which the tube may be used in television receivers. All three circuits are quite satisfactory, circuit A probably being the simplest in construction and operation. Manufacturer: Raytheon Manufacturing Company. Price: $12.50. Application: The principal use for this tube is in the output circuits of television receivers, although it may be used in any place where a gas discharge tube is required, and probably other applications for it will suggest themselves to our readers. Since the plate of the tube is about \\" square the received television picture will be of the same size. A word of caution — never overload the tube. Don't put it across a d.c. source of voltage without a current limiting resistance in series with it. Keep the current as low as possible, for the lower the current used, the longer the life of the tube will be. ~> St wit To next *m Tube An A.C. ScreenGrid Tube fig. 3 THE A. C. 22 TUBE X68 Device: A. C. Screen-Grid Tube, Type A. C. 22. The tube is of the same general construction asd.c. screengrid tubes with the exception that the electron emitting member has a heater similar to that used in type 227 tubes. The heater requires 2.5 volts to operate it. This lube may therefore be connected in parallel with 227 type tubes, since they also require 2.5 volts. The a.c. 22 tube fits into a standard 5-prong socket. Manufacturer: CeCo Manufacturing Company. Price, $8.00. Application: This tube is for use in the construction of a.c. operated receivers requiring the use of a screengrid tube. The connections of a single r.f. stage using this tube are given in Fig. 3. Filler and Bypass Condensers X69 Device: Acme Parvolt Condensers. These condensers are available in all standard capacities and voltage ratings. Both bypass condensers designed for comparatively low voltage and filter condensers designed for 200, 400, 600, 800, 1000, and 1500 volts can be ob ACME CONDENSERS tained. The condensers are tested and fully meet the standards of the R. M. A. Complete block condensers can also be obtained designed for use in the various types of well-known power units, such as the Samson, Amertran, Silver-Marshall, Thordarson, etc. Manufacturer: Acme Wire Company. Prices: Vary depending upon capacity and voltage rating of the condensers. Application: These condensers are designed to fulfill every need for condensers in radio receivers and power units. The condensers are equipped with mounting feet and screw terminals. Loud Speaker Extension Cords X70 Device: Loud Speaker Extension Cord. A 50foot extension cord equipped with pin terminals on each end. Supplied with a bakelite connector for easy connection between the extension cord and the loud speaker. The cord consists of two rubber insulated wires covered with a brown cotton braid. Manufacturer: Belden Manufacturing Company. Price: $2.25 Application: This extension cord will prove useful in cases where the loud speaker is to be operated at a point distant from the radio receiver. In the good old summer time the loud speaker might be placed outside on the lawn, under a shady chestnut tree. To control the volume, use can be made of a variable resistor such as a Table Type Clarostat (mentioned in this department in the May issue) connected across the loud speaker terminals. FOR TELEVISION