GB617788A - Improvements relating to thermionic valve control circuits - Google Patents

Abstract

617,788. Valve circuits. SHAND, G., BAUGH, A., and METROPOLITANVICKERS ELECTRICAL CO., Ltd. July 9, 1946, No. 20504. [Class 40 (vi)] A chain switching arrangement in which a number of circuits are arranged in cascade so that when any circuit is actuated it initiates the actuation of the succeeding circuit after a predetermined time delay, comprises at least two cathode-coupled flip-flop circuits connected in cascade so that when the first flip-flop reverts to its initial stable state after having been tripped into its unstable state by an initiating pulse, the pulse produced across its cathode load resistor trips the succeeding flip-flop circuit. Fig. 1 shows an arrangement in which the valve VI of the first flip-flop is normally conducting and valve V2 cut-off by the bias across the common cathode resistor R4. A negative initiating pulse across the input resistor R1 cuts off valve V1 and the circuit flips over to its unstable state with valve V2 conducting and drawing considerably heavier current than V1. The voltage across the cathode resistor, Fig. 2 (not shown), rises, but has no effect on the first valve V3 of the second flip-flop which is already conducting. When the first circuit flops back to its normal stable state the voltage across its cathode resistor falls and the negative pulse thus applied to the valve V3 causes it to flip over to the unstable state. This sequence then continuing round the chain which may be a closed one. When a flip-flop is in the tripped position the time constant of the grid-cathode circuit is made large to ensure stability, but in the untripped position the time constant is considerably reduced by the diode D1 which conducts on the negative tripping pulses and shorts resistor by the lower value resistor R12. The flip-flops may be associated with gating valves which are thus rendered operative in sequence to pass signals applied to their inputs to a common load circuit. In a modification, Fig. 3 (not shown), the first valve of each flip-flop is normally non-conducting and action is initiated by a positive going pulse, a negative going pulse being produced across the common cathode resistor of each flip-flop circuit as each circuit is actuated, by returning the grid leak of the normally conducting valve to a positive potential so that this valve normally draws a much higher conducting current than does the other valve of the flip-flop when that also is conducting.