GB803225A - Improvements in or relating to electron tubes having ceramic envelopes - Google Patents

Abstract

803,225. Thermionic valves. EITELMcCULLOUGH, Inc. Aug. 30, 1955 [Feb. 4, 1955], No. 24850/55. Class 39(1). A double-diode, -triode, -tetrode or -pentode comprises a generally cylindrical envelope having side and end walls, the side wall comprising metallised ceramic rings 1-5, 22 and 23 with a metal ring 6-9, 19 and 21 sandwiched between each adjacent pair of ceramic rings, metallic bonds uniting the ceramic and metal rings, a double cathode and heater structure comprising a pair of electron emitting cathode discs 13 and a common heater 16, opposite ends of the heater being connected to different ones of a first pair 7 and 8 of the metal rings, and a pair of conductive supports 14, one for each of the cathode discs 13, which supports extend inwardly from a second pair 6 and 9 of the metal rings, the first pair 7 and 8 of metal rings having terminal tabs H<SP>2</SP> and H<SP>1</SP> for the heater 16 and the second pair 6 and 9 of metal rings having terminal tabs K<SP>2</SP> and K<SP>1</SP> for the cathode discs 13, and the end walls 11, 12 of the envelope being of stamped-out dish-shaped copper discs forming anodes and having terminal tabs P<SP>2</SP> and P<SP>1</SP>. In the double-triode construction shown in Figs. 7 and 9 a pair of conductive supports 18 for the disc-shaped grids 17 extend inwardly from a third pair 19 and 21 of the metal rings, the grid supports being of conical shape and having nested in them the anodes 11, which are dished to form conical surfaces. The metal rings 19 and 21 have terminal tabs G<SP>2</SP> and G<SP>1</SP> for the grids 17. All the electrodes can be of slightly domed formation. The ceramic rings can be of alumina metallised by a molybdenum-manganese sintering process and the metal rings are about À020. inch thick or less and can be of copper. The ceramic and metal rings are brazed together using high temperature brazing alloys such as copper-gold, some of the parts preferably being first brazed together in subassemblies. The brazing material can be in the form of thin flat rings À005 in. thick. Flanges 24 and up-turned lips 26 are provided on the metal rings to facilitate assembly. The structure can be evacuated through an exhaust tubulation or the parts, held apart, can be placed in a vacuum furnace and outgassed, the cathode activated, and finally the parts brought together and the final brazing, e.g., with copper-silver alloy, effected in the vacuum furnace by radiant or induction heating methods. The cathode discs 13 can be of oxide-coated nickel and each cathode support 14 can comprise a number of, e.g., three, spaced wire rods. The heater 16 can be a coil of insulated wire of toroidal formation.