GB655216A - Improvements in or relating to electric discharge tubes - Google Patents

Abstract

655,216. Thermionic valves. PHILIPS ELECTRICAL, Ltd. Aug. 23, 1948, No. 22182. Convention date, Aug. 26, 1947. [Class 39 (i)] An electric discharge tube having one or more flat electrodes and a cathode with a discshaped emissive surface is characterized in that the cathode is mounted on a cylindrical body which has a wall made at least in part of perforated or expanded metal and which is secured in a metal tube sealed in the envelope. In the thermionic valve shown in the Figure the cathode comprises an emissive disc 5 mounted on a tube 6 within which is positioned a heater 7. The leads 8 for the heater are sealed in a metal cylinder 10 by a glass bead 9. The tube 6 is supported by a cylindrical body 11 preferably made of " stretching material," i.e. metal sheet provided with very small cuts which by stretching the metal sheet are elongated to form apertures. The cylindrical body 11 is sealed to the cylinder 10 and also to the copper tube 13 sealed to the envelope 12. In assembly the cathode is sealed in the cylindrical body 11 and the cylinder 10 carrying the heater is introduced into the cylindrical body 11 until the heater is correctly positioned. The whole is then introduced into the tube 13, correct position between the cylindrical body 11 and the tube 13 being maintained by stretching or compressing the cylindrical body 11. The cathode 5 is then correctly positioned relative to the grid 3 by using a microscope. Sealing is accomplished by heating and thus melting solder or enamel previously inserted by rolling in the perforations of the cylindrical body 11. A thin foil 14 may be arranged at the top of the cylindrical body 11 to reduce heat radiation from the tube 6 and to reduce high-frequency resistance. The end of cylinder 10 may be closed by a ceramic member 16. One of the heater leads 8 may be connected to the cylinder 10.