GB505500A - Improvements in or relating to non-linear thermionic valve stages - Google Patents

Abstract

505,500. Valve circuits. HADFIELD, B. M. Nov. 11,1937, No. 30919. [Class 40 (v)] A valve repeater comprises a pentode valve V1 biassed to cut off which has a high impedance in its anode circuit so that when a signal is received, current flow through a directly coupled valve V2 which is normally passing current is stopped, and a relay R in the circuit of a subsequent valve V3 is operated to repeat the signal. Alternatively the relay may be polarized and have windings in the anode circuits of both slave valves so that both makes and breaks are positively repeated. In the former embodiment valve V1 is biassed to cut off by the tapping on resistance R6, the resistance being of the order of 5,000-10,000 ohms to prevent grid current. Valve V2 is arranged to be normally passing grid current and valve V3 is biassed to cut off. When a signal is received valve V1 passes current and, in view of the high impedance of R1 the voltage on the plate of VI will drop almost to zero. This voltage drop will be communicated to the grid of valve V2 but its effect will be delayed until the grid current of V2 is overcome. Then the anode flow of V2 ceases so that the potential on the grid of V3 rises and the relay R is operated to repeat the signal. If the signal is alternating a condenser as C1 or C2 is required to prevent the relay R releasing on the negative half cycles. The relay R can be replaced by a polarized relay 1R (Fig. 2) having windings in the anode circuits of both second and third valves V5, V6 which in this embodiment are low impedance pentodes, the relay repeating both makes (when winding b is energized) and breaks (when winding a is operative) of the signal. As the combined anode and screen currents of valve V5, V6 is. constant, the valves can be provided with automatic bias by resistance B10. Condenser C4 enables an A.C. signal to be repeated and condenser C5 prevents the generation of low frequency oscillations. The invention can be used as a valve voltmeter of the slide back type. The relay 1R, Fig..2, may be made to operate at a rate determined by the constant of R7 and C4 if the potentiometer R12/14 is dispensed with and the cathode of V4 is taken back to a sliding contact on R10. This is due to hysteresis effects caused by small differences in the anode currents of V5 and V6. Specirication 472,728 is referred to.