Patent GB-797047-A (GB)
Title: Improvements in or relating to gas-filled electric discharge devices
IPC: H01J17/56
Filed: 1955-02-08
Abstract: 797,047. Thermionic valves. M-O VALVE CO., Ltd., COOK, K. G., and ISAACS, G. G. May 8, 1956 [Feb. 8, 1955; Feb. 15, 1956], Nos. 3705/55 and 4798/56. Class 39(1). A gas filled electric discharge device such as a hydrogen filled thyratron comprises a control grid made up of a plurality of radial resistive rods 6, Fig. 1, or a plurality of separate cathodes 19, 20, 21. Fig. 3, and a further electrode, namely the cathode or control grid, a like plurality of impedance elements being integral with the rods 6 or such as inductances 30, 31, 32, Fig. 3, outside the tube envelope, so that when triggering pulses from source 16 are applied between a common lead to the plurality of separate members and the further electrode an auxiliary discharge is initiated between at least one of the members and the further electrode and after such initiation the impedance elements are such that discharges can occur between the other electrode and each of the remaining members, the discharge being finally transferred to the main anode 4. The anode 4, Fig. 1, is made positive by high voltage pulses from source 15 in phase with the triggering pulses. The filamentary thermionic cathode 2 is connected at one end to and surrounded by a heat shield 3 and is almost completely screened from control grid 6 by baffle 5. A resistance 18 is connected to the baffle lead and a condenser 17 between the baffle lead and the glass sheathed control grid lead 5, and the cathode is heated by a filament transformer 14. The control grid may have eight radially extending resistive rods connected to a central boss to which the lead is secured. In Fig. 3 there are three separate directly heated cathodes 19, 20, 21 forming three symmetrically disposed circular arcs respectively connected at one end to three inductances 30, 31, 32 and at the other end to a common lead 29. Trigger pulses from source 16 are applied to the control grid 24 in phase with the anode pulses to initiate the discharge between one of the cathodes 19, 20, 21 and the control grid 24, the anode 23 taking over the discharge when sufficient current is passing to the control grid 24. A condenser 17 is connected to the control grid lead and a resistance 18 between this lead and the common cathode lead 33. When the anode takes over the discharge due to the inductances 30, 31, 32, the anode-cathode potential in Fig. 3 does not fall to the potential across the discharge to one cathode but remains high enough for discharges to be struck between the anode and remaining cathodes. In Fig. 1 the integral resistances produce similar effect. The invention can be applied to electrodes other than to the cathode or control grid, to gas filled diodes, triodes or to valves with a plurality of control electrodes. If the current through the impedance elements does not rise rapidly as the discharge spreads the rise of resistors to form at least part of the impedance elements may be necessary. Resistors may entirely replace the inductances of Fig. 3, but inductors are preferable for rapid current rise conditions. The initial discharge may in general be struck between any number of parts less than the total number and the further electrode.