GB320849A - Improvements in vacuum electric tube devices - Google Patents

Abstract

320,849. Robinson, E. Y., and Associated Electrical industries, Ltd. June 19, 1928. Vacuum tubes. - A heater for an equipotential cathode, genode, or other electrode consists of a wire core, preferably tungsten or molybdenum, surrounded by a refractory insulating sheath whereon is wound a conducting helix of tungsten, molybdenum, carbon &c. The insulating body may consist of kaolin, either alone or with other material, quartz, magnesium oxide, zirconia or thoria, and may be applied as a slip in successive coats by dipping, painting or spraying, the coated wire then being dried and sintered or vitrified while under tension. Alternatively, the kaolin may be pressed in a mould round the core before or after the application of the first coats, the kaolin being dried to the biscuit condition and removed at the required points. The coating may then be vitrified and the whole cut into lengths. An alternative method of applying a continuous coating is to pass the wire one or more times through a V- groove in a rotary wheel dipping into kaolin slip. Where other refractory materials, such as magnesia, steatiate, zirconia or thoria, are employed agglutinants, such as starch, sugar or gum arabic, may be mixed therewith. In the case of quartz, a tube of this material is drawn down while hot, placed on the wire core and heated. A sheath of magnesium oxide is formed by coating the core with magnesium and heating this in an atmosphere of steam. After the core is coated, the helix is wound thereon either in short lengths or continuously and in a non-inductive manner if desired. Where carbon is employed, a squirted cellulose thread is wound on the sheath and afterwards carbonized. As shown in Fig. 1, a tungsten or molybdenum wire core 4 is provided with an insulating coating <g> on which is wound, whilst the core is under tension, a heater wire 5 in a single or double spiral, the ends being secured by nickel clips 6 and connected to lead-in wires. If desired, the core 4 may act as a return lead for the wire 5. Fig. 2 shows a valve in which such a heating unit is mounted, the anode 16 being carried by wires 12 secured by a clip 13 to the reentrant tube 14 of the pinch 15. Carried by the wires 12 is a glass cross-piece 11 bearing wires 10 by which the grid 17 and cathode 18 are supported, the cathode consisting of a nickel tube coated with a mixture of barium and strontium oxides. Wires 20 are provided at each end of the cathode for supporting and spacing purposes in conjunction with the wires 10 and an insulating plate 19. The wire, core 4 of the heater is supported at its upper end by a wire 22 carried by a glass bead 21 supported from the wires 12, a spring tensioning-support 23 being situated between the core 4 and the wire 22. The wire 5 is connected at its lower end to a lead-in by a wire 25 and at its upper end to a wire 22a connected to a lead-in wire 26. Specifications 243,868 and 297,966 are referred to.