Patent GB-567011-A (GB)
Title: Improvements in or relating to electrical switching circuits incorporating electron discharge valves
IPC: H03K17/54
Filed: 1943-06-22
Abstract: 567,011. Thermionic valve circuits. WHITE, E. L. C., SCANTLEBURY, G. S. P., and CLAYDEN, R. T. June 22, 1943, No. 10093. [Classes 40 (iii) and 40 (v)] An electrical switching circuit comprises an electron discharge valve having a cathode, control grid and anode, a uni-directionally conducting device, an impedance included in the cathode circuit of the valve and in circuit with said device, a first source of signals connected between said control electrode and the end of said impedance remote from said cathode, a second source of signals connected in series with said impedance and said device, and an output impedance connected in circuit with said electrode, so as to repeat signals from said first source when said valve is in the conducting state, the arrangement being such that by adjustment of one or both of said signals said device can be switched from a non-conducting to a conducting state so as to cause the potential difference across said impedance to be substantially determined by said second source of signals, whereby said valve may be switched from the conducting to the non-conducting state or vice versa. Fig. 1 shows the arrangement in its simplest form, in which a triode 1, having a cathode impedance 8 and load impedance 9, has its cathode 2 connected to the cathode 6 of a diode 5 having an anode 7. Terminal 11 is normally held at a potential sufficiently negative relative to terminal 10 connected to grid 3 to ensure that diode 5 is non-conducting and signals applied at 10 are repeated by valve 1 and appear across load 9. If a positive switching signal is applied at terminal 11 so as to make diode 5 conducting, cathode 2 will assume substantially the potential of terminal 11. This may be made high enough to cut off' valve 1 and interrupt the repetition of the signals applied at terminal 10. With this arrangement, spurious signals applied at 11 with the switching signals are not repeated across load 9. Alternatively, a negative switching signal may be applied at 10, terminal 11 being kept at a suitable fixed potential. Fig. 2 shows an arrangement in which a switching signal is automatically generated a predetermined time after the application of the signal to be switched. In this case the triode 1 and diode 5 are arranged as before and the diode anode 7 is connected through a delay network 13, 14 and terminating impedance 17 to a tapping 15 on the supply potentiometer 16. The grid of the triode 1 is connected through a leak 20 to a second tapping 21 on potentiometer 16. Tappings 15, 21 are adjusted so that in the absence of a pulse at 10, valve 1 is conducting and diode 5 is non- conducting. When a negative pulse is applied at 10, the potential of cathode 2 falls and hence that of cathode 6 until diode 5 conducts to generate a negative voltage wave along network 13, 14. Also valve 1 cuts-off. After a predetermined interval, the reflected wave in network 13, 14 returns to make anode 7 very negative and diode 5 is again rendered non- conducting. This makes valve 1 conducting and the anode 4 returns to substantially its original value. This enables a pulse applied at 10 to reappear across 9 cut to a predetermined duration. The circuit may be used by applying to terminal 10 a train of signals from a television camera and these may be interrupted by switching signals applied to the diode 5 to allow the insertion of synchronising signals. Specification 497,637 is referred to.