GB595673A - Thermionic valve circuit - Google Patents

Abstract

595,673. Valve amplifying circuits photo-electric photometers. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. May 11, 1944, No. 9031. Convention date, May 11, 1943. [Classes 40 (iii) and 40 (v)] [Also in Group XXXVI] In an amplifier in which the anodes of the valves are fed with A.C., successive valves are energized in opposite polarity, the output of each valve being fed to a condenser, the potential of which controls the operation of the succeeding valves. The frequencies employed may vary from those of the mains to ultrahigh. During one half cycle of the supply, Fig. 2, valve 1 conducts, charging condenser 3 which determines the bias on valve 2 during the.succeeding half cycle, the time constant of condenser 3 and resistor 4 being long compared with a cycle of the supply. The process is continued through the amplifier to a final indicator 65. The bias on valve 1 is varied by potentiometer 30 and is adjusted to make the currents of all the valves equal with no input signal. To avoid grid current in valve 1 when the anode is negative with respect to the grid, the bias may be provided by means of a cathode resistor and decoupling condenser, Fig. 19 (not shown), the condenser being charged from line 12 through a variable resistor and diode. A curve, Fig. 4c (not shown), shows the variation in the response of the amplifier with variations of input frequency. To amplify speech frequencies, Fig. 11, the supply frequency is made higher than the highest audio-frequency to be amplified and the time constant of condenser 3 and resistor 4 is reduced. To maintain the response of the amplifier at the higher frequency a resonant circuit comprising inductance 131 and condenser 133 is included between valves 1 and 2. Valve 1 may be biassed by condenser network 128, 129, inductance 130 being included. Modulated radio-frequency currents may be applied to the amplifier, the valve 1 acting as a demodulator, the speech currents only passing through to the loud-speaker. For measuring the intensity of light, Fig. (i, a photo-electric tube 69 is connected to the input of the amplifier, the current through the tube causing a corresponding indication on meter 65. Specification 595,674 is referred to.