GB888955A - Improvements in electron discharge devices - Google Patents

Abstract

888,955. Discharge tubes. STANDARD TELEPHONES & CABLES Ltd. May 14, 1958, No. 15408/58. Class 39(1) An electric discharge device comprises two ceramic insulators having surfaces placed closely adjacent each other, an anode formed on and extending over part of one of said surfaces, a cathode formed on and extending over part of the other of the surfaces and a control electrode on and extending over one of the surfaces and spaced from the other electrode on the same surface. In one form an insulator 1, Fig. 1, has a strip 4 defining the cathode which is separated by grooves 2, 3 from areas 5 which form a control electrode. The second insulator 15, Fig. 3, has projections which carry metallic strips 17 comprising the anode. In the arrangement of Fig. 6 two insulators 20, 25 are placed in close juxtaposition to one another. Insulator 20 carries a cathode comprising molybdenum, nickel and emissive material strips 23, 24, 31 respectively which are preferably separated from the control electrode by grooves, the control electrode comprising a molybdenum coating which may in turn be coated with a layer 32 of secondary emissive material to increase the mutual conductance of the device. A cathode heater 22 is provided in grooves 21, or the strip 23 may be used as the heater, or alternatively the cathode may be coated with a self-sustained emissive material. The second insulator, 25 which carries a metal coating 29 forming the anode, also has projections 26 carrying layers of molybdenum 27 and gold 28 forming a second control electrode. The two insulators may form part of the envelope, or the arrangement may be placed in a separate glass envelope. The insulators may be of forsterite. The molybdenum strips may be deposited by a printing process and the nickel and gold layers by electroplating, each deposition being followed by baking in hydrogen to improve adhesion and leads for the electrode may be sealed through the insulators at this stage. The strip defining the cathode may be coated with mixed carbonates of barium, calcium and strontium by electrophoresis, this layer later being heated to reduce the carbonates to oxides by applying a potential difference across the ends of the cathode strip. The cathode and control electrode on insulator 1 need not be in the same plane and may be domed or otherwise shaped to produce the required field configuration. In a further embodiment the insulators comprise two cylinders 38, 39, Fig. 8, not necessarily coaxial, on which cathode 42, control electrode 41 and anode 43 are formed. The ends may be hermetically sealed by ceramic discs. A gas filling may be present.