GB581419A - Selective amplifiers employing electron discharge tubes - Google Patents

Abstract

581,419. Square wave and sine wave generators ; frequency dividers. STANDARD TELEPHONES & CABLES, Ltd. April 7, 1944, No. 6580. Convention date, Sept. 18, 1942. [Class 40 (v)] In a thermionic valve circuit for producing an output wave different from the input, a resistance - capacity phase shifting network couples the output to the input, producing, with the valve, a 360 degree shift at a harmonically related frequency of the input, the circuit normally being maintained quiescent in the absence of an applied wave, and a high input impedance being provided over which the input is applied to the valve. The phase shift network 3, 4, 2, Fig. 1, coupling the anode to the grid of valve 1 is arranged to give a 180 degree phase shift at the fundamental or some harmonic of the applied square wave A, to produce an output sine wave B. To prevent oscillation in the absence of an incoming signal, the load 18 is made small and the screen grid potential adjusted. The high resistance 23 attenuates the input so that frequencies other than that required are not amplified to an appreciable extent. To produce sub-harmonics, as in a frequency divider, the phase shift network is adjusted for a submultiple frequency of the fundamental and the input driving voltage is increased. In a modification, Fig. 2 (not shown), the condensers and resistances in the phase shift network 2. 3, 4, are interchanged. In a further modification, Fig. 3, for producing a square wave output, the valve 40 is back coupled over a phase shift network to give 360 degrees shift at the fundamental or a sub-harmonic and feeds a triode 50 normally biassed off by the potential drop over the common cathode load 54. The positive half cycles cause valve 50 to conduct, in turn biasing off valve 40. Valve 50 continues to conduct until condenser 57 discharges sufficiently to reduce the anode current and allow valve 40 to pass current, valve 50 then being cut off by multivibrator action over the common coupling resistance 54.