Patent GB-780959-A (GB)
Title: Improvements in gas filled thyratron
IPC: H01J17/06
Filed: 1952-06-03
Abstract: 780,959. Thermionic valves. MACHLETT LABORATORIES, Inc. June 3, 1952 [June 15, 1951], No. 13962/52. Class 39(1). An electron tube for use as a thyratron comprises a vacuum envelope filled with low pressure gas and having therein a cylindrical anode, a thermionic cathode and a grid cylinder lying between cathode and anode which is continuous except for perforations therein opposing the anode and both ends of which terminate at the vacuum envelope. In the embodiment shown in Fig. 1, the anode 10 is mounted relative to a metal envelope by a flange 11 clamped between flanges 12, 13 on the metal envelope part and which provides a low impedance heat flow path. The active grid member 17 comprises a ring, which is preferably provided with a single row of elongated slots, and the ring may be integral with or may be sealed to two cylinders 19, 20, the cylinder 20 being sealed to the glass envelope portion 15 by a collar 21 and the cylinder 19 contacting a cylindrical metal wall portion 23 by means of spring fingers 22 which allow for thermal expansion and contraction. The end wall 24 is adjacent the active grid member 17 and the inner surface of the cylinder 20 is thus available for convective cooling. The cathode comprises a cylinder 27 which may be coated internally with emissive material and provided with a baffle 28 secured to it by tabs 29. A high inductance heater is secured to a tab 30 on the baffle 28 and is provided with an axial lead 35 passing through the envelope. The cathode is secured to an insulator 39 by a sleeve 40, and the insulator is in turn secured to the metal envelope portion 23 by a sleeve 41 ; the cylinder 27 passes through the envelope to form a low inductance cathode lead, and the disposition of the insulator 38 is such that ions are unlikely to deposit on it. If the cathode has an oxide coating the cathode assembly may be inserted in a temporary envelope to which the sleeve 41 is sealed either by a gasket or by a low melting point solder ; after processing the cathode, the assembly is removed from the temporary envelope and inserted in the tube. This prevents gas evolved during the cathode processing from being adsorbed or absorbed by the grid and anode. The tube may be provided with a baffle comprising an annulus 45 having vanes 46, Fig. 3, attached on both sides; there may also be a deionizing electrode comprising a ring 43 arranged inside the grid 17 and provided with similar vanes. In a modification, Fig. 4 (not shown) designed for use at higher anode voltages, a voltage dividing anode is provided between the grid and anode and is preferably held at about half the anode potential. The electrode is sealed to the envelope by a flange similar to the anode flange, is provided with elongated slots similar to those in the grid and staggered with respect to them, and its lower edge is rounded towards the envelope to reduce electrical stresses. Further voltage-dividing electrodes of similar construction may be provided between the grid and anode, Instead of using a deionizing electrode with straight vanes the grid may be provided with tortuous vanes, Fig. 5 (not shown), and with smaller tortuous vanes covering each aperture; alternatively vanes 59 may be arranged within grid 551 as shown in Figs. 6 and 8 and have the shape illustrated in Fig. 7 which prevents direct paths between the cathode and the grid apertures.