GB637877A - Improvements in or relating to high frequency electronic valve amplifiers - Google Patents

Abstract

637,877. Modulating systems. SOC. INDEPENDANTE DE TELEGRAPHIE SANS FIL. June 17, 1947, No. 15974. Convention date, Aug. 12, 1946. [Class 40 (v)] In a modulated amplifier of the type in which two output valves operate in phase quadrature at carrier frequency, modulation is applied to the output valves and to a driver valve such that during the negative modulation half-cycle the driver valve only is modulated and one of the output valves is quiescent and during the positive half-cycle the output valves only are modulated, the quiescent valve becoming operative. As shown, a driver valve 10 fed with unmodulated carrier energy supplies two output valves 1, 2 whose grids are coupled through a 90 degree phase-changing network 7, 8, 9 and whose anodes are coupled through an impedance inverting network 3, 4, 5 and supply a load 17. A class B modulator valve 11 modulates the screen grid and anode potentials of the driver and two further class B cathode follower modulators 12, 13 fed from modulating source BF in antiphase to valve 11 modulate the suppressor potentials of valves 2 and 1 respectively. The biassing potentials from source 15, 16 are arranged such that in the absence of modulation, valves 10 and 1 act simply as amplifiers and valve 2 is quiescent. During the negative modulation half-cycle valve 11 modulates the output of valve 10 and since modulator valve 11 is substantially biassed to cut off, valve 1 still acts as an amplifier. On the positive half-cycle valve 10 acts as an amplifier and valves 1 and 2 receive the modulation. At modulation peaks valves 1 and 2 deliver equal power to the load. To avoid non- linearity at the junction of the two half-cycles impedances 18, 20 and 19, 21 are provided in the cathode and screen grid leads respectively of valve 1 to produce non-linear negative-feedback at modulation frequencies. Alternatively modulation of the driver may extend into the positive half-cycle.