GB293462A - Amplifier volume control for carrier signalling - Google Patents

Abstract

293,462. Hazeltine Corporation, (Assignees of Wheeler, H. A.). July 7, 1927, [Convention date]. Thermionic amplifiers and detectors.-Relates to amplifiers with automatic volume control. Fig. 4 shows high-frequency neutralized amplifiers 90, 91, a detector 94, and audio-frequency amplifiers 105, 108. The grid bias applied to the amplifier 90 is varied in accordance with the rectified current in the detector circuit to control the volume. A switch 115 is provided to cut out the volume control and resonance is indicated by a milliammeter in the plate circuit of the amplifier 90. The combination of resistance 101 and battery 100 is such that the point 112 is negative with respect to the filament in normal operation. A resistance -capacity coupling, Fig. 5 (not shown), may be substituted for the transformer 99. A rheostat 106 is provided to enable the volume to be manually adjusted, the transformer 107 being shunted by a resistance 110 to avoid loss of low frequencies when the impedance of the amplifier 105 is increased by dimming the filament. The automatic volume control may be applied to more than one of the high-frequency amplifiers and the detector may comprise a two-electrode valve to secure direct proportionality between the input and output. In a further modification, Fig. 6 (not shown), the batteries are dispensed with and the supply is taken from the mains. Fig. 7 shows a mains operated receiver employing a two-electrode valve 66 as a detector in which control is applied to the grids of amplifiers 84, 86. The valve filaments are series connected and tappings taken so that correct grid bias is obtained for all valves. Auxiliary volumecontrol is effected by rheostat 130 adapted to shunt variably the filament of the audio frequency amplifying valve 74, while resistance in the series circuit is varied to prevent current change in the remaining valve filaments. The difference in grid bias applied to amplifiers 84, 86 due to differences in filament potentials is corrected by supplying additional plate voltage to the amplifier 84. Specifications 222,895 and 223,181 are referred to.