GB645349A - Electron discharge devices - Google Patents

Abstract

645,349. Thermionic valves. STANDARD TELEPHONES & CABLES, Ltd. Feb. 21, 1947, No. 5136. Convention date, July 24, 1945. [Class 39 (i)] A filament cathode structure for a high frequency electron dis charge device comprises a helically wound filament with terminal connections at either end and a metallic cylinder 24, Fig. 1, preferably of tantalum, connected tc one end of and arranged coaxially inside the helix in such a way as tc increase the series resonance frequency of the structure as measured between the terminals. The cylinder 24 is placed as closely as possible to the turns of the helix. In the form shown a quadra-filar filament is used with the lower ends of the filaments connected individually to leads 12, 13, 18, 19, of which 12 and 13 pass through clearance holes in metal terminal plate 7 and are connected to a similar plate 9, and 18 and 19 are connected to plate 7. The upper ends of the filaments are connected via a castellated metal boss 11a and metal support-rod 11 to lead 10 passing through clearance holes in plates 7, 9 to terminal 3. Plates 7, 9 are connected via leads 6 and 8 to terminals 2 and 4 respectively. The resonant frequency of the structure is the same as the operating frequency of the tube. The cylinder 24 is preferably hollow and is closed at the upper end by a plug or disc, Fig. 2 (not shown), brazed to the boss 11a, but may be secured to lead 11. The various clearance holes in the plates 7, 9 provide blocking condensers so that the individual terminals are all at the same high-frequency potential. The filament structure may have six strands instead of four. The Specification as open to inspection under Sect. 91 states that the cylinder 24 may be welded to the boss 11a. This subject-matter does not appear in the Specification as accepted.