Radio Broadcast (May 1928-Apr 1929)

Record Details:

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38 RADIO BROADCAST MAY, 1928 uses the same parts, is laid out on the panel and baseboard similarly, and its operation differs not at all. As stated before, to get 3.3 volts for the first tube's filament it is necessary to connect in series the 2.5-volt and the 1.5-volt windings of the standard filament transformer. If these windings are not connected together properly, the screen-grid tube will not light. No harm can be done, however, by such a connection, and, therefore, the builder can easily determine which connection is proper. The voltage on the filament of the screen-grid tube TU C is not critical as to hum; the variation in voltages occurring in practice, due to line fluctuations etc., are not great enough to cause hum. While the arrangement used .or t.ie operation of the 222 tube in the four-tube set has not been tried with two or three r. f. stages yet, there appears no reason why it should not function satisfactorily, and the application of a. c. operation to two and three-stage screen-grid r. f. amplifiers should prove a most fertile field of experiment. The parts used for constructing the four-tube a. c. screen-grid receiver are listed below. While the parts specified are recommended, the experimenter may substitute other makes of parts electrically equivalent with safety: Li — S-M 1 1 1 A Antenna Coil $ 2.50 U— S-M 114SG R. F. Coil 2.50 Two S-M 515 Universal Interchangeable Coil Sockets 2.00 L3 — Two S-M 275 R. F. Chokes 1.80 T — Two S-M 240 Audio Transformers 12.00 Ci — Two S-M 320 0.00035-Mfd. Variable Condensers 6.50 C2 — S-M 342 0.000075-Mfd. Midget Condenser 1.50 C3 — Sangamo 0.0001 5-Mfd. Condenser with Leak Clips .50 C4 — Two Fast i-Mfd. Condensers . . 1.80 Cs — Two Sprague o. i-Mfd. Bypass Condensers 1.70 Ri, R4 — Yaxley 1500-Ohm Grid Resistors 1 .00 R2, Rf, — Two Frost FT64 Balancing Resistors 1.00 R3 — Carter 4-Ohm Resistor .25 CONTROLS ARE GROUPED CLOSELY TOGETHER ON THE FRONT PANEL R5 — Yaxley 2000-Ohm Grid Resistor. . . .50 R7 — Durham 5-Megohm Grid Leak. ... .25 Rs — Carter 500,000-Ohm Volume Control Potentiometer 2.00 Thirteen Fahnestock Connection Clips .65 Two S-M 511 Tube Sockets 1 .00 Two S-M 512 Tube Sockets 1.50 Two S-M 805 Vernier Drum Dials. . . . 6.00 7x17x5" Wood Baseboard, with Hardware 1.50 1 Van Doom 7x18" Decorated Metal Panel 3.00 AND THE FOLLOWING ACCESSORIES UX-112-A (cx-312-A) Power Tube ux-222 (cx-322) Screened Grid Tube Two UY-227 (c-327) Heater Tubes Cone Loud Speaker Filament-Lighting Transformer with \\-, 2jand 5-Volt Secondaries, such as the S-M 247 Illustrated. Three 45-Volt Heavy-Duty B Batteries, or Any Standard Socket Power Unit Capable of Accurate Voltage Adjustment. The coils listed above are suitable to cover the broadcasting frequencies. Other coils from the same manufacturer make the receiver truly universal insofar as wavelength range is concerned. To hook this set up, it is simply necessary to connect the B batteries (or the socket power supply), loud speaker, antenna and ground, to the clips marked in the illustration, and to insert the tubes. The filament transformer must be r0.0000?5 mfd connected to its appropriate clips by means of carefully twisted wires. Preferably, it should be situated a foot or so from the audio transformers in the receiver. The receiver operates exactly as any other set of its type, the two station selector dials serving to tune-in the different stations in the broadcast band of 200 to 550 meters, the midget regeneration condenser controlling sensitivity (regenerative amplification) and the volume knob controlling loud speaker volume. No "On-Off" switch has been provided in the set for it is assumed that the socket-power unit or filament transformer used will be provided with a switch either in the instrument itself, or in the connecting cord, or if in neither, the set may easily be turned on or off at the lamp socket to which the power unit supply cord is attached. Using the standard 111-A and 114-SG coils the set tunes from 200 to 550 meters, while by dropping the r. f. stage and connecting the antenna to point 3 of the detector coil socket through a small 0.00002 5-mfd. midget condenser the set will cover the shorter wavelength ranges from 30 to 75 meters with 114-C coil, or 70 to 210 meters with a 1 14-B coil. Waves above 550 meters may be received with a 1 1 i-D and 1 14-D coils (500 to 1500 meters) or a 1 1 i-E and 1 14-E coil (1400 to 3000 meters). Although there are no American broadcasting stations operating above 550 meters there is great sport for those who know the code on these lower frequency bands. Ships at sea, compass stations, air*, mail stations, time signals, and navy vessels — all have wavelengths covered by this receiver. It will be necessary to shunt the regeneration condenser with a fixed capacity of 0.0001-mfd. to get good oscillation control when the D and E range coils are used. 4Vnlts FIG. 2 Circuit diagram of the a.c. screen grid receiver