Patent GB-377726-A (GB)
Title: Improvements in and relating to gaseous conduction electric lamps
IPC: H01J17/00
Filed: 1931-03-27
Abstract: 377,726. Discharge lamps. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Moore, D. M. ; 592, Park Avenue, East Orange, New Jersey, U.S.A.) March 27, 1931, No. 9405. Convention date, March 31, 1930. [Class 39 (i).] Lamps for producing light varying rapidly with the discharge current and applicable to facsimile receiving apparatus, television and signalling, comprise a solid cathode 23 having at one end a crater 24 of depth greater than its width, a concentric tubular anode 30 and a separate metal plate 34 mounted on and electrically connected to the anode and overlying the end of the cathode so that a negative glow appears solely in the crater 24 and is visible through an aperture 35 in the plate 34. Shoulders 28, 31 are provided on an insulator 26 and on the anode and the parts are clamped together by screws to form a self-contained structure mounted on the pinch by a stud 29. A narrow annular gap 33 is left at the ends of the electrodes. The bulb 18 may be exhausted by mercury condensation pumps and the electrodes heated by high-frequency induction. The bulb is filled at 30 mm. pressure with neon containing three-eighths per cent of argon. Residual gases may be cleaned up by reversing the polarity of the lamp to produce a glow discharge in a crater in a magnesium block in the anode. A motor-driven pole-changing switch may be used to give repeated reversals. With a neon filling, a nickel or tungsten cathode gives a red light, a magnesium or cold rolled steel cathode a less red light, a cathode of steel containing 17 per cent of tungsten a yellowish light and a cathode of cerium-iron alloy a purple light. With helium, a magnesium cathode gives white light. Alkali or alkaline earth metals such as caesium, sodium and barium may be incorporated in the cathode material, or the walls of the crater 24 may be coated with an azide or other compound decomposing during operation. In forming the cathode, tungsten powder may be sintered at 1700‹ C. to form a porous body or at 3000‹ C. to form a dense body. The cathode 23 may have a stem 25 of a good conductor of heat such as iron or copper. A ribbed cooling jacket 41 fits on the bulb 18. In a modification, the plate 34 is recessed above the window and abuts against a thin insulating layer on the end of the cathode. The Specification as open to inspection under Sect. 91 (3) (a) comprises also modifications, including a lamp similar to that shown in Fig. 7 of Specification 315,369, [Class 39 (i), Electric lamps, Arc, &c.], and filled with pure helium or argon or with neon containing 20-25 per cent or more of helium and À5 per cent or more of argon. In another modification, Fig. 5 (Cancelled), the plate 34 is omitted or is replaced by a sheet of insulation or of metal insulated from the electrodes 42, 47 or the top ends of the electrodes are coated with a layer of zirconium oxide and a binder such as water glass or colloidal graphite. In alternating current lamps, two semi-cylindrical electrodes, each with a crater, are mounted in an insulating cup or electrodes 48, 50, Fig. 6 (Cancelled), with craters 49, 52 and insulating layers 51, 53 are superposed. This subject-matter does not appear in the Specification as accepted.