GB444050A - Improvements in or relating to thermionic valve amplifiers - Google Patents

Abstract

444,050. Wireless transmitting systems; valve amplifying circuits. LORENZ AKT.-GES., C., 1, Lorenzweg, Tempelhof, Berlin. May 1, 1935, Nos. 12962 and 12963. Convention dates, May 2, 1934 and July 20, 1934. [Class 40 (v)] With the object of increasing the ratio of power output to power supplied in a radiotransmitting amplifier, or in a push-pull audiofrequency amplifier, the anode supply voltage and the grid bias are automatically regulated according to the momentary strength of the audio signal. The transmitting-amplifier E, Fig. 7, is fed with modulated carrier from the preceding stages T, and its anode circuit is supplied from mains N through a grid-controlled rectifier G and smoothing-circuit S. The microphone M, which effects modulation of the carrier by means not shown, is connected on the one hand to a device A which regulates the gridexcitation of the supply rectifier G, and on the other hand through a full-wave rectifier B and smoother K to a resistance 1, 2 in the grid circuit of the valve E. The result is that the anode supply voltage rises as the signal strength rises, and at the same time the negative grid bias is increased so that the valve E continues to operate at the bottom of the rising part of its characteristic. It is arranged that the anode voltage rises from one half to its full value as the modulation rises from zero to 100 per cent. The supply rectifier G may be replaced by a dynamo or other regulatable source. When the invention is applied to a floating-carrier system of the kind described in Specification 363,480, the variable grid-biassing device B, K may be so modified that the carrier amplitude is reduced when the signals are weak and the anode supply voltage is low. Fig. 12 shows a push-pull Class B audio-frequency amplifier utilizing the same principle as the transmitting amplifier of Fig. 7. Part of the input to the valves R is diverted to an amplifier V and on the one hand regulates the anode voltage by operating through a rectifier G2 on a gridcontrolled supply rectifier GL, and on the other hand regulates the grid bias through a rectifier G1. A non-linear amplifier N compensates for the curvature of the valve characteristics.