Improvements relating to thermionic valve circuits of the type having one stable limiting condition of operation and one unstable limiting condition of operation

摘要

575,598. Thermionic valve circuits. FERRANTI, Ltd., and THOMAS, G. I. June 28, 1944, No. 12338. [Class 40 (v)] In a multi-vibrator having one stable state, a normally conducting control valve is capacitatively coupled to an output valve normally made non-conducting by a current in a cathode resistor. On triggering, the control valve is suppressed, the positive pulse from its anode causing the output valve to conduct. To prevent the output valve being biassed off by its own anode current through the common cathode resistor, the cathode is connected by condenser to a tapping on the anode resistor of the control valve, the rise of cathode voltage being thus transmitted through the capacitative coupling to the grid of the output valve. In the Figure, the values of resistances 7 and 9 are arranged so that the potential developed across 9 is not less than that developed across 7. An incoming negative pulse on its grid causes a positive pulse on the anode operating through coupling condenser 14 to render output valve 16 conducting, the resulting heavy current in the resistor 7 biassing off valve 1. The output is also taken from resistor 7. The rise in cathode potential transmitted to the grid of valve 16 through condenser 13, resistance 9 and condenser 14 enables valve 16 to continue to conduct. The charge on condenser 22 maintains the screen grid potential constant to keep the amplitude of the' output pulse constant. On the discharge of condenser 14 through resistance 17, condenser 3 having now partially discharged, the fall in cathode potential allows valve 1 to conduct again, thereby applying the voltage developed across resistance 9 to cut off the valve 16 so terminating the pulse. A triode may alternatively be used as control valve and triggering can be effected by means of a positive pulse on the cathode.