GB297966A - Improvements in vacuum electric tube devices - Google Patents

Abstract

297,966. Robinson, E. Y., and Metropolitan-Vickers Electrical Co., Ltd. Sept. 23, 1927. Vacuum tubes.-Indirectly-heated cathodes comprise a heater filament helically wound around and in contact with a rod or tube of refractory insulating material, an enclosing cathode tube spaced away from the heater and any associated insulating material at least for the major portion of the hot or active portion of the cathode, the return lead for the heater being brought outside the cathode tube, and means co-operating with one or both ends of the heater rod or tube and of the cathode tube to register and space them. In the construction shown in Fig. 1, the cathode comprises a metal tube 9 coated with oxides only along the part that lies within the grid 4, and a heater comprising a helical filament of tungsten, molybdenum or carbon wound on a rod 12 of porcelain or quartz. The tube 9 is supported by wires 10 sealed into the pinch and by wires 11 fused into a glass bead 7, 'and the rod 12 is supported by a tube 15 sealed into the pinch, while porcelain washers 14 space the tube from the rod, which is slidable in the washers. These may be secured by crimping the tube 9 as at 20, Fig. 3, and gaps 22 are formed in the tube to lessen conduction of heat to its ends and to provide an exit for one end 17 of the heating-filament. Instead of providing washers 14, the ends of the cathode tube may be flanged over to engage the rod 12 loosely. Further modifications consist in expanding the upper end of the tube 9 at 26, Fig; 5, to embrace a larger washer 14<a>, and in threading metal clips 29, Fig. 6, over the rod 12 to embrace the tube 9, to which they may be welded. The ends of the filament may be secured at 16 to the support tube 15 and to a wire fused in the bead 7, Fig. 1, or to clamping-rings 30, Fig. 8, placed on the rod 12. The anode and the grid may each be supported by a single wire 2 or 5, Fig 1, or by two such wires as shown in Fig. 8. In the latter construction a lead 33 for the heating current is welded to a wire 32 which supports the rod 12. In the construction shown in Fig. 10, all the vertical support wires are spaced by being threaded into perforations in a mica or like plate 35 which may be secured to the anode support wires 2 by welded wires 37. In the construction shown in Fig. 12, the tube 9 is supported by discs 39 carried by support wires 40 fused into the pinch. Fuse wires may be inserted between the ends of the heating-filament and the leading- in wires. Carbon-filament heaters may be made by winding a cellulose thread on an insulating rod and decarbonizing it, e.g. by heating to a red heat in powdered charcoal. Guard rings may be inserted in the rod as described in Specification 292,707 to prevent electrolysis occuring through the rod baneath the filament clamps.