Patent GB-295904-A (GB)
Title: Improvements in or relating to vacuum electric tube devices
IPC: H01J1/18
Filed: 1927-08-05
Abstract: 295,904. Robinson, E. Y., and Metropolitan-Vickers Electrical Co., Ltd. Aug. 5, 1927. Divided on 285,537. Vacuum tubes. - Filament cathodes are supported, registered or restrained at one or more predetermined points between the ends of straight lengths of the filament by means of insulating material directly engaging the filament and carried on an electrode or on an additional rigid member which is secured directly to an electrode or is tied with an electrode at both ends. The insulating material avoids cooling of the filament at the points of support and may insulate the supported points from another electrode. Microphony may be avoided by dispensing with filament springs and providing several intermediate supports. The bights of the filament may be supported by insulating members as in Specification 285,537, the construction of Figs. 11 and 12 of this prior Specification being described. The filament may have a preliminary metal sheath and may receive an oxide coating as in Specification 285,538. The insulating material may be a uniform covering on a wire or strip care of U, V or indented shape near the filament. For oxide-coated, platinum-iridium filaments, ceramic insulation or quartz is used; for caesiated tungsten filaments, the insulation may be mica. A straight wire may be placed in a quartz tube and the whole bent in a flame, or a formed core may be repeatedly dipped in a kaolin or porcelain slip such as a suspension in water of 3 parts of porcelain to 1 part of kaolin, the coating being dried in a flame after each dipping and finally fused in a blow-pipe flame. A straight filament 40, Fig. 1, may be registered at its centre by a perforated insulator 46 held by a rigid frame 45 constituting one lead to the filament. The frame may comprise two bars passing through the insulator 46 or three bars with the insulator retained between them, the bars being crimped at 47 to retain the insulator in place. A cross-bar of the frame is cut through after mounting on the pinch, as described in Specification 285,536. A grid 20 and an anode 19 are supported from the pinch 15 and tied to the framework 45 by a glass bead 49. In a modification, the bars of the framework are insulated from the filament and each extends into the bead 49. The bars, with or without welded-on rings, then constitute an additional control electrode or space-charge grid or form the sole control electrode. In further modifications a straight filament of molybdenum sheathed in platinum and oxide coated is registered by porcelain beads secured to it or to turns of a grid, two grids being preferably provided and the filament being registered by a plate spring as described in Specification 222,176. In a further modification, a hairpin filament 65, Fig. 12, is registered by molybdenum wires 67 shaped as in Fig. 16 and coated with insulation 68, the, ends of the wires 67 being welded to supports 63 of the control grid or of either grid if two grids are used and the electrodes being tied together by a bead 64. Specifications 1694/15, 115,700, and 204,237 also are referred to. Reference has been directed by the Comptroller to Specification 193,525.