GB979369A - Improvements in or relating to amplitude modulated transmitters - Google Patents

Abstract

979,369. Valve amplifying circuits. CONTINENTAL ELECTRONICS MANUFACTURING CO. June 8, 1962 [June 13, 1961], No. 22214/62. Heading H3W. The radio frequency output of a transmitter subject to unwanted changes of output, due e.g. to reduction of H.T. supply on the application of modulation, variations in line voltage, or valve ageing, is fed via a capacitor to divide rectifier 10 and the R.F. components removed from its output by means of low-pass filter 12, A portion of the filter output is selected by means of potentiometer 18 and all except very low frequency variations removed by capacitor 13. The residual voltage is amplified in a direct-coupled amplifier comprising a first stage 14 with its cathode stabilized at a negative potential by means of a gas discharge tube 16 which forms a voltage reference source. The anode of this valve is direct-coupled to a second stage, D.C. and A.C. negative being applied between the two anodes by means of a resistor/capacitor combination. The second stage 20 is direct coupled to a cathode follower stage 22 comprising the two elements of a double triode in parallel, the load of which comprises the screen grid of an R.F. amplifier 24 in the R.F. signal path, the gain of which is thus controlled so as to counteract low frequency variations. A switch 26 permits of the screen grid potential being controlled manually instead.