Patent GB-632917-A (GB)
Title: Improvements in and relating to electric discharge devices such as discharge lamps
IPC: H01J5/50
Filed: 1945-06-19
Abstract: 632,917. Discharge lamps. BRITISH THOMSON-HOUSTON CO., Ltd. June 19, 1945, No. 15543. Convention date, June 19, 1944. [Class 39 (i)] The filamentary cathode 13, Fig. 1, of . a cold starting lowpressure fluorescent discharge lamp has two leads 15, 16 which are mechanically but electrically insulatively connected by a glass bead 23, one lead 15 is electrically connected to the metal disc 11 to which the glass envelope 10 is sealed and the other lead 16 is brought out insulatively near the edge of the disc 11 but cut off outside the envelope and is not provided with a terminal contact. A similar construction may be employed at both ends of the lamp. The cathode 13 is a coil or coiled coil and is provided with anodes 14, 14, and the disc 11 may be of the chrome-iron alloy " Allegheny 55." The lead 15 terminates in a split-ring 25 which elastically grips the boss 19 which also serves to house the exhaust tube 31. The ring 25 may be welded to the boss 19. The wire 16 or at least the thinned portion 24 thereof, may also be of chrome-iron alloy.' In the sealing process, the disc 11 with the electrode assembly mounted on it is sealed to the envelope 10 by fusion of the envelope end, the lead 24 being placed in a notch 26 in the edge of the disc 11 and being forced away from the disc into the softened glass of the envelope by suitably applied pressure. The extra conductor 16 enables the electrode 13 to be resistanceheated to degas it during the course of manufacture, and after degassing the free end is cut off and any short protruding wire end is bent up against the envelope wall so that it cannot give any trouble in a lamp socket. In a modification, Fig. 5 (not shown), the end disc has no notch and the lead wire 16 is pressed into the softened glass of the envelope during sealing by the resilience of the other lead wire 15. The lead 16 is of the same thickness throughout. In another modification, Fig. 6 (not shown), the lead 24 is brought out through a hole near the periphery of the disc and is insulated from the disc by part of the glass of envelope 10 which is sealed up round it. Specification 452,191, [Group XI], is referred to. The Specification as open to inspection under Sect. 91 describes a form, Fig. 6 (Cancelled), in which the cathode 13b extends axially and is carried by short leads 33, 34 supported by leads 15b, 24b respectively. The disc anode 14b of molybdenum or iron is carried by lead 16b, a glass bead 23b being interposed between leads 15b, 16b. To prevent disc 11 acting as an anode it may be covered wholly or almost wholly with insulation. This is accomplished by the provision of a mica disc 35 rather than by an insulating coating on the disc 11 or by a complete vitreous end wall inside the disc 11. The lead 24b is of finer wire than the other supports and leads. The lamp is operated on A.C. and the electrodes are heated to emission mainly by the heat from the discharge though there is some consequential resistance heating. Dimensions of an example are given; the coiled or coiled coil cathode is wound on one or two mandrels which after heat-setting of the coils are subsequently removed by dissolving them out. This subject-matter does not appear in the Specification as accepted.