GB326617A - Improvements in thermionic tubes - Google Patents

Abstract

326,617. Wedel, C. J. R. H. von. Jan. 25, 1929. Vacuum tubes.-A tubular cathode C, closed at one end, contains a heater in the form of a doublv-wound conductor H mounted on an insulator B, which is supported by an axial conducting rod 0, the cathode, the rod, and optionally the heater being connected at or near the centre of the closed end of the cathode, and preferably with the neutral point of an A.C. supply. The cathode may be of platinum, molybdenum, nickel, or cobalt or alloys of these with each other or with aluminium, and is coated with electron emitting oxides oramphoteric compounds. The insulator consists. of a mixture of oxides of beryllium, thorium and .aluminium with sintering materials such as barium and calcium fluoride. The heater may .be a helical wire coated with insulating material, tor example amphoteric compounds such as beryllium oxide, and aluminium mixed with sintering materials such as strontium fluoride. A nickel or tungsten wire may be plated with metal before the insulating compound is applied. In order to compensate for the loss of heat from the end of the cathode near the stem E, additional heating may be provided at that end as by (a) varying the spacing of the turns of the helix (b) varying the slope of the grooves on the insulator or (c) providing an electron emitting compound such as strontium nickelate on the wire so as to produce a discharge between the parts of the heater. In a modification in which the valve contains gas, ionic discharge between the parts of the heater are prevented by filling the space between the insulator and the cathode with a powder of the insulating materials previously mentioned; the cathode is mounted on a flanged support. Two stems S may be provided, the grid and anode leads being taken through one stem and the heater wire through the other.