GB314811A - Improvements in and relating to electric gaseous discharge devices - Google Patents

Abstract

314,811. British Thomson-Houston Co., Ltd., (Assignees of Found, C. G.). July 2, 1928, [Convention date]. Vacuum tubes; low-pressure metallicvapour apparatus.- Electric discharge lamps in the form of a long tube are provided with a filling of gas, such as neon, helium or mercury vapour, at a pressure of one to five millimetres of mercury, and at each end with a thermionic electrode acting alternately as cathode and anode and having a large continuous surface. When started, the lamp operates steadily on alternating current of ordinary mains voltage. A quartz or glass tube 1 is provided at each end with a cylindrical electrode 10 of nickel, iron or platinum enclosing a heating coil 11 of tungsten or molybdenum. The coil 11 is connected at one end to the cylinder 10 while at the other it is joined to a lead-in wire 4, the circuit for the heater being completed by a second lead 5 which is also connected to a metal shield 12 surrounding the electrode. The cylinder 10 may be coated with a mixture of barium carbonate and a cellulose binder and heated to 1300‹ C. in a maintained vacuum. In operation, the heating coils of the electrodes 8, 9 are connected to secondaries 20, 21 of the supply autotransformer 14. A starting device may consist of a mercury switch 22 connected to an intermediate point of the transformer through a resistance 23, and to an end terminal through an electromagnet 25. The closing of the main supply circuit 15 energizes the magnet 25 and causes the armature 26 to interrupt the current in the switch circuit, the resulting high voltage impulse serving to put the lamp into operation.