Radio Broadcast (May 1928-Apr 1929)

New Apparatus T) RODUCTS of radio manufacturers whether -L 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. Power Apparatus for the 250 Type Tube Device: Power Supply Apparatus for use with the type 250 tube. In constructing a power unit to use the type 250 tube it is essential that apparatus be used that will be capable of supplying to the tube sufficient current and voltage. There is given below a resume of power apparatus, old and new, made by several manufacturers which may be used satisfactorily to operate a power amplifier using a type 250 tube. Amertran Power Transformer, Type PF 250. Price: $30.00. Gives a d.c. output of 400 to 450 volts, 200 mA., with two type 281 rectifying tubes, full-wave; either one or two power tubes, type 250, single or push-pull, can be used. Filter Choke Coil, type 709. Price: $6.00 each. Inductance: 50 henries at 120 milliamperes. Dongan Power Transformer, Type 7568. Price: $13.00. Designed for full-wave rectification using two type 281 rectifiers. Double Filter Choke Coil, type 5554. Price: $1 1.00. National Power Transformer, type R. Price: $14.50. Designed for full-wave rectification using type 281 rectifiers. Filter Choke Coil, type 80. Price: $10.00. Samson Power Transformer, type 162. Price: $18.00. Designed for half-wave rectification using type 281 rectifier. Filter Choke Coil, type 312, 30 henries, 120 mA. Price: $12.00. Silver-Marshall Power Transformer, type 328. Price: $18.00. Designed for full-wave FIG. I One use of the Duplex Clarostat is, as shown in this diagram, to control the plate voltage applied to either tube of a two stage radio frequency amplifier THE DUPLEX CLAROSTAT rectification using type 281 rectifiers. Type 327 {Price: $12.00) may be used in half-wave circuits. Filter Choke Coil, type 331. 27 henries, 120 mA. Price: $8.00. Thordarson Power Transformer, type T 2900. Price: $20.00. For full-wave circuit using two type 281 tubes. Double Filter Choke Coil, type T-20-99. Price: $14.00. Application: The above apparatus is for use in constructing power amplifiers using the type 250 tube. The General Radio Company also manufacture apparatus for this purpose and their units were described in this section in the June issue. Further information including circuit diagrams, can be obtained from the above manufacturers through Radio Broadcast. A Dual Resistance with Many Uses X53 Device: Duplex Clarostat Resistance. A novel form of resistance consisting essentially of two Clarostat resistances in a single metal case. Each section can be independently adjusted to any value of resistance within the range of the Clarostat, which is from a low resistance to a high resistance of about five million ohms. Resistance is varied by tuning a slotted screw with an ordinary screw driver. May be mounted on panel, sub-panel or baseboard. Furnished with mounting bracket. Manufacturer: Clarostat Manufacturing Company. Price: $2.25. Application: The instruction sheet supplied with each Duplex Clarostat points out many uses for the device. These include its use in resistancecoupled amplifiers, in push-pull amplifiers, as a plate voltage control, as a center-tap resistance, etc. In Fig. 1 and 3, which illustrate two of these uses, the Duplex Clarostats have been enclosed in dotted lines. Aluminum Shields X54 Device: Aluminum Box Shields. Designed for use in constructing shielded receivers. Two sizes are available; the Junior size measuring 45 x \\ x 5 inches high and the large size measuring 5x9x6 inches high. The Junior shield has room for a coil and a tube; this shield is for use with a metal sub-panel and is not supplied with a bottom the large shield can be used to house the coil, tube, and tuning condenser. The shields are made of 0.08 inch thick aluminum, and they consist of four sides, top, bottom, and two slotted corner posts into which the sides are fitted. Manufacturer: Aluminum Company of America. Price: $8.00 for set of four Junior shields, $3.50 each for large shields. Application: Shielding is of importance to radio amateurs who wish to improve their present outfits or who have decided to incorporate shielding in new equipment of their own design. Reviewing the circuits generally used, a singletube receiver with regenerative detector usually is not improved by shielding, unless it happens 284 to be located very close to a broadcasting station. In this case the entire detector circuit, including the coil, the tube socket, and the tuning condenser, may be mounted advantageously inside a standard aluminum box shield. In a receiver employing one stage of radiofrequency amplification and a regenerative detector, the detector circuit may be shielded completely. If this is done there is little additional advantage in shielding the radio-frequency stage. A circuit using two stages of radio-frequency amplification may be improved slightly by using shields of the partition type. Where selectivity and stabilization are especially necessary, the coils, tube sockets, and condensers may be mounted in shields. The apparatus of one stage only should be placed inside a single box, separate boxes being used for additional stages. An alternative is to place the coils and tube sockets of each stage in Junior Shields with the tuning condensers outside of the shields. For circuits employing three stages of radiofrequency amplification, it is recommended that each stage, including the condensers, be housed in a standard box shield, or the Junior size shields may be used for covering the coils and tube sockets only. For super-heterodyne circuits, in which the maximum of selectivity is desired, it is advisable to shield the entire first detector circuit in a boxtype shield and the entire oscillator circuit in a similar unit. Bat. [$~Q FIG. 2 Automatic Control for A and B Power X55 Device: Multiple Type 445 Automatic Power Control. Designed especially for use with radio receivers drawing a filament current of less than about 0.36 amperes (corresponding to the current required for six 199 type tubes). The Yaxley type 444 control should be used if the receiver has a total current drain of more than 0.36 amperes. This type 445 control automatically turns off the trickle charger and turns on the B-power unit when the filament switch on the FIG. 3 A second use for the double resistance described above in X^j lies in controlling the plate voltage to two tubes in a two or three stage audio amplifier. Another Duplex Clarostat may be used to control the grid leak resistance of the two tubes