GB726888A - Improvements in or relating to electric discharge devices - Google Patents

Abstract

726,888. Thermionic valves. STANDARD TELEPHONES & CABLES, Ltd. Dec. 30, 1953, No. 36133/53. Class 39 (1). An annular sheet of insulating material is interposed between the anode and grid of a thyratron to prevent backfire. In the tube shown the cathode is a helical tape 5, coated with electron-emissive material. wound edgewise-on about an insulating mandrel 6 and supported at the ends by leads 7 and at an intermediate tapping point by a lead 13 which is also used to assist in centring the cathode structure within the tube envelope. Surrounding the cathode 5 is an inner cylindrical heat shield 8 connected to lead 13 by a lead 14 and welded to a number of indentations 11 in the wall of an outer heat shield 9 supported from the base of the envelope by leads not shown. The lead wires 7 pass through insulating bushes 12 let into a plate 10 closing the lower end of the shield 9. The remaining electrodes of the tube are constructed as a unitary assembly mounted upon three support and lead wires 15 and comprising a screening member 16 in the form of an inverted cup whose base is centrally apertured at 17, a similarly shaped control grid 18 having a series of slots 19 situated over the aperture 17, an upper centrally apertured screen member 20, and an inverted cup-shaped anode 23 carrying a central lead 24 which is surrounded by a group of radial heat-radiating fins 25 and is connected to a top cap 4. An annular mica sheet 21 is located immediately above the top screen 20 and seats against a curved portion 22 of the envelope. The electrodes and mica sheet 21 are secured together by three insulator stacks 26 each provided in known manner with metal plates and cups to prevent leakage between the electrodes. The rods 15 are taken through the insulator stacks, one providing connection to the screens 16 and 20 and another to the grid 18. The tips of the rods 15 are shielded by fine gauge screens connected to the anode to prevent ionization of the gas and subsequent discharge to the rods 15. The gas filling may be xenon at a pressure of 0.1 mm. of mercury at a filling temperature of 20‹C.