Radio Broadcast (May 1928-Apr 1929)

140 RADIO BROADCAST JULY, 1928 160 150 140 i 130 . 120 I 110 : 100 i 90 i 80 : 70. : 60 ; 50 : 40 I 30 20 10 0 1 -\Ep <Ec [Ef 90 Volts am 1 a von 1 > p 100 1000 FREQUENCY CYCLES PER SECOND AMPLIFICATION CURVE OF THE SAGAMO TYPE A AUDIO UNIT henries. Price: $5.00. Plate Impedance Type F. Designed for use in impedance-coupled amplifiers or as audio-frequency choke coils in the plate leads to prevent oscillation and motor boating in audio-frequency amplifiers. Inductance about 200 henries. Price: $5.00. Push-pull Input Transformer Type B. Ratio 4.5 to 1. Price: $12.00. Push-pull Output Transformer Type C 1 7 1 . For use in push-pull amplifiers using 171 type tubes. Impedance step down ratio 2:1. Total primary inductance 80 henries. Price: $12.00. Push-pull Output Transformer Type D-210. For use with push-pull amplifiers using 112 and 210 type tubes. Total primary inductance 100 henries. Price: $12.00. Manufacturer: Sangamo Electric Company. Application: The above apparatus may be used in constructing transformer impedance-coupled amplifiers. The Type A audio transformer, using a special alloy core, has the disadvantage that the ratio is somewhat low so that a two-stage affair will not have any too much gain. With two of these transformers and a 201-A type tube in the interstage the voltage gain from the output of the detector to the grid of the power tube will be about 6.3. To load up a 171 type tube the detector output will have to be about 0.7 peak volts. However, the frequency characteristic of the transformer, as announced by the manufacturer, and which we consider to be trustworthy, is very good and the excellent frequency transmission which the transformer will give compensates their rather low gain. The output impedance, Type F, is arranged with terminals so that it is possible to use it with different types of power tubes, and adapt their impedance to that or ordinary types of loud speakers. A condenser with a capacity of about 4 0 mfds. must be used in constructing a complete output device using this impedance. Center -Tapped A. C. Tube Resistors • X43 Device: Center-Tapped Resistors type CU-20. Small and convenient center-tapped resistors designed especially for use across the filament circuits of a.c. tubes. They measure about 2 inches long and about T3j inches wide. Available in resistances up to 100 ohms. Manufacturer: Carter Radio Company. Price: $0.25. Application: Circuits using a.c. tubes generally require one or more center-tapped resistances across the filament circuit. The 20ohm size in this type of resistance may also be put to very satisfac tory use in the filament circuits of screengrid tubes. Twenty ohms is just right to reduce the storage battery voltage of six to the 3.3 volts required by the screen-grid tube. The center tap in the resistance may be used for the grid circuit return as shown in the circuit diagram, and a C bias of 1.3 volts obtained in this way Antenna Tuning Unit X44 Device: Sickles Intensifies A unit to be attached to a receiver to obtain greater volume. It consists of a coil and a condenser mounted in a small box and functions to tune the antenna circuit to resonance. Manufacturer: F. W. Sickles Company. Price: $7.50 Application: If the antenna circuit of a receiver is tuned by means of a coil and a condenser it is generally possible to obtain somewhat greater volume than can be obtained if the circuit is untuned. Many modern single-control radio receivers CENTER-TAPPED RESISTOR In the grid circuit return SICKLES 1NTENSIFIER use untuned antenna circuits and if one does not mind adding another control to the set it will be possible to increase the volume considerably by tuning the antenna circuit. The lntensifier is such a device and may be easily added to most any type of receiver. The idea is not new — especially to radio experimenters — but in this device the idea has been put into workable form so that an average person, knowing little or nothing about radio circuits, may be able to use it to advantage. This is a good gadget for the radio service man to handle and to make use of in those cases where a customer complains of insufficient volume. A. C. Tube Filament Transformers X45 Device: A. C. Filament-Lighting Transformers. Ten different types of filament transformers are made with specifications as given below. No. 6512. Designed for one to four ux-226, one UY-227 and one ux-171 or two UX-171A. Transformer is mounted in crystallized lacquered case equipped with lamp cord and plug outlet, also tap for control switch. 15 V., 4.2 amp.; 25 V, 1.75 amp.; C. T., 5 V. \ amp. Price: $5.75. No. 6515. Same as above without plug outlet and control switch tap. Price: $4.75. No. 6570. Same as 65 12 but with terminals on secondary. Price: $6.50. No. 4586. Designed for one to eight ux-226, two UY-227 and two ux-171, \\ V. 8.4 amp., 2! V. 3.5 amp. C. T., 7! V. z\ amp. C. T. Price: $8.00. No. 4587. Designed for one to eight ux-226, two UY-227 and two ux210, \\ V. 8.4 amp., 2§ V. 3.5 amp. C. T., 75 V, 25 amp. C. T. Price; $8.00. No. 6513. Designed to operate one to six Arcturus a.c. tubes. Transformer is mounted in crystallized lacquered case equipped with lamp cord and plug outlet for B power unit, also tap for control switch. 15 V., 2.1. amp. Price: $5.25. No. 65 1 1. Same as above without plug outlet and control switch tap. Price: $4.25. No. 286. Designed for heating filament of one ux-210. q\ V., \\ amp. C. T. Price: $2.50. No. 287. Designed for heating filaments of two ux-171 or ux-112 power tubes, 5 V., 1 amp. C. T. Price: $2.50. No. 820. Designed for heating one to eight McCulIough (Kellogg) a. c. tubes, 3 V., 8 amp. C. T. Price: $6.00. Manufacturer: Dongan Electric Manufacturing Co. Application: These transformers are to be used as a source of filament current for a.c. tubes in the construction of light-socket-operated receivers making use of any of the well-known types of a.c tubes.' This line of transformers satisfies the demands of the valve combinations found in most receivers in use to-day. Choke-Condenser Unit x46 Device: Audichoke. A combination of a choke coil and a by-pass condenser, both contained in a single case. The chokes are rated at 100 henries with a d.c. resistance of 445 ohms and the condensers have a capacity of 1.0 mfd. Manufacturer: Leslie F. Muter Company. Price: $5.00. Application: The internal impedance of power units and old B batteries is frequently sufficiently high to cause an audio amplifier to begin to oscillate and, sometimes, to motorboat due to common coupling owing to the power unit's impedance. In the ideal case, the amplifier should be absolutely independent of its power supply so that it is entirely unaffected by the impedance of the source of power — but unfortunately in practice this is rarely the case. The receiver may be made practically independent of the power supply by properly filtering the plate by means of choke coils or resistances in conjunction with by-pass condensers. This Audichoke is a device of this sort making use of a choke coil and 1.0-mfd. by-pass condenser. The connection of the unit in a typical amplifier is shown in the circuit diagram. There is no reason for the use of this device in an amplifier that is giving satisfactory operation, but in cases where the amplifier oscillates or motorboats these choke-condenser units may be included in the circuit. In making use of these units it is generally not necessary to revise the amplifier; the chokes may simply be connected in series with the B-plus leads. Muter Clarifier Output Filter Muter Audichoke A A+ B B* Bt B* C C C* TRANSFORMER COUPLED AMPLIFIER MUTER CHOKES IN AN AUDIO SYSTEM