Patent GB-842168-A (GB)
Title: Electron discharge tube
IPC: H01J21/36
Filed: 1957-06-28
Abstract: 842,168. Electric discharge tubes. EITELMcCULLOUGH Inc. June 28, 1957 [July 10, 1956], No. 20491/57. Class 39(1). [Also in Group XXXVI] A cylindrical electric discharge tube, particularly a triode or pentode, has a first section comprising a metal end plate 11, a heater 16, a supporting rod 12 connected to one end of the heater and attached to the end plate 11, a first ceramic ring 5 having one end seated on the end plate, a first metal ring 13 attached to the other end of the heater and seated on the other end of the ceramic ring 5, a second ceramic ring 6 having one end seated on the metal ring 13, a second metal ring 18 seated on the other end of the ceramic ring 6, a cathode cylinder 19 attached to the metal ring 18, a cathode disc 20 attached to the end of the cylinder 19, a third ceramic ring 7 having one end seated on the metal ring 18, and metallic bonds 10 joining the ends of the three ceramic rings to the end plate and the two metal rings. The cylinder 19 can be of " Kovar " (Registered Trade Mark) and has a heat shield 21 brazed or welded thereto. The tube also has a second section, one end of which is adjacent the ceramic ring 7 of the first section, and comprising at least one ceramic ring 8 and an anode 29 attached to the other end of the section, and sealing means forming a vacuum-tight joint between the second section and the ceramic ring 7, the sealing means including two sealing rings 25, 23 bonded respectively to the ceramic ring 8 and the ceramic ring 7 and a metallic bond 39 joining the sealing rings together externally of the tube. The tube has a second metal end plate 31 which is centrally apertured and the anode is formed by a copper exhaust tube 27 metallically bonded in the aperture, and having an end disc 29 and exhaust apertures 28. The metal ring 13 has a central aperture in which is positioned an alumina ceramic sleeve 14 surrounding the heater support rod 12, a metal band 15 being crimped inwardly against the rod 12 or the sleeve 14 being metallised and brazed in the aperture in the ring 13. A planar type control grid 35 has a supporting ring 34 sandwiched between the sealing rings 23 and 25 by nickel spacers 33 and 38. The ceramic rings are of a high alumina type, the metal rings are preferably of copper or nickel and the metallic bonds 10 preferably comprise a 80-20% mixture of powdered molybdenum and manganese in a liquid vehicle which is fired in a reducing atmosphere at about 1500‹C. A metal ring 26 is brazed to ring 25 and provided with a terminal tab 26a for the grid 35 and the metal rings 11, 13, 18 and 31 are provided with terminal tabs 11a 13a, 18a and 31a for the heater 16, cathode 20 and anode 29, respectively. In a pentode construction the second section of the tube comprises three ceramic rings, two planar type screen and suppressor grids and two metallic supporting rings, one for each of the grids, the two supporting rings being generally cup-shaped and surrounding the anode, an annular rim on each of the supporting rings being sandwiched between the three ceramic rings, and metallic bonds joining the rims to the adjacent ceramic rings. A shield ring is brazed to the supporting ring for the suppressor grid to prevent volatilisation materials from the oxide-coated cathode being deposited on the inner wall of the ceramic ring adjacent the end-plate supporting the anode. Specification 804,572 is referred to.