Patent GB-221854-A (GB)
Title: Improvements in vacuum electric tubes
IPC: H01J19/34
Filed: 1923-06-14
Abstract: 221,854. Robinson, E. Y. June 14, 1923. Vacuum tubes. - A rigid cathode of sheet material or tubular, and adapted to be heated by electron bombardment, radiation from an auxiliary heater, or by high frequency induced current, is provided with several stems for the purpose of leading in the space current so as to reduce unequal heating. The stems may act as supports, and may be connected in parallel. They are preferably attached to the edges of the cathode sheet on more than one side, the stems on one side acting as leads and on the other side as supports. Main and auxiliary cathodes are preferably heated in the manner described in Specification 205,613. In the arrangement shown in Fig. 2, which is for use in a valve of the type described in Specification 195,691, having a small discharge gap, the main cathode 3 consists of a tube of tungsten, molybdenum, platinum, or nickel, with or without a coating of barium, calcium, or strontium, and is mounted on leading-in stems 17 brazed to a steel or other metal holder 21. Stems 18, secured to an inner tube 15 forming an auxiliary cathode, are brazed to a metallic tube 22, and stems 19, 20 carrying a starting filament 16 are brazed to nickel supports 23, 24. The supports are insulated by a steatite bush 25 and washer 26. A flange 27 on the bush is secured to the holder 21, which is mounted on a split tube 6 embracing a re-entrant tube. The bush and washer and secured by a head and washer on a steel rod 28 supporting the bight of the filament, and shields 4, 5 are provided for confining the discharge. The brazing operation is carried out by wrapping copper foil around the stems, which are then inserted in holes in the supports, and the whole placed in a vacuum or hydrogen furnace. The re-entrant tube extends from a tube forming a conical joint with an extension of the anode. The other end of the anode may be connected with a vacuum pump through a conical joint. In the arrangement shown in Fig. 4, a tubular cathode 3, heated by an internal filament 54, is mounted at one end on stems 57 brazed to a tubular support 58, which is secured by arms 60 to a clamp 59 embracing are-entrant tube 56. Stems 57 at the other end of the cathode are secured to a ring 61, slidably mounted on a flanged tube 62 secured by arms to a clamp. A spring 66 is interposed between the ring and flange so as to allow expansion of the cathode; or each stem may be free and provided with a separate spring. The filament is mounted on stems 68 provided with shields 71 confining the discharge, as described in Specification 214,721. The anode 1 consists of a copper tube sealed to two vitreous tubes 55. In the arrangement shown in Fig. 5, two main cathodes 72 of square or rectangular shape are mounted on each side of and parallel with an auxiliary cathode of similar shape. The cathodes 72 are supported by stems 80, which are held by strips within grooves 81 in a frame 74, and are placed in tension by bow springs 82. Stems 75, supporting the auxiliary electrode, pass through apertures in insulated brackets 76, and are held in tension by springs 78. The frame is attached to a tube 86 by a supporting-member 85. In the arrangement shown in Fig. 10, the main and auxiliary cathodes 3, 15 are in the form of tubes perforated near the ends, and mounted on steatite bushes 88, 89. The cathode 3 is secured to the bush 88, and slides at the other end over an enlarged part of the bush 89. The slotted portions form the leads and act as shield for confining the discharge from the main portions, which may be coated with barium and strontium oxides, as described in Specification 221,851. Specification 211,221 also is referred to.