Patent GB-770893-A (GB)
Title: Improvements in and relating to electrodes for gaseous electric discharge devices
IPC: H01J17/04
Filed: 1953-09-30
Abstract: 770,893. Discharge apparatus. SYLVANIA ELECTRIC PRODUCTS, Inc. Sept. 30, 1953 [Oct. 1, 1952 ; March 17, 1953], No. 26893/53. Class 39(1). A discharge device, for use as an attenuator or T.R. switch, has an envelope containing an ionizable gas and two electrodes, one of the electrodes constituting a keep-alive electrode having at the discharge end thereof a metal shell carrying within it a body of a semi-conductor which projects from the shell, an insulating sheath being provided upon the outside of the shell and of the semi-conductor body. In the construction shown in Fig. 2 the keep-alive electrode 30 is formed with a metal rod 32 of a glass-sealing alloy including a tapered portion 32<1> which is provided with an axial bore 34 forming the tapered portion into a shell 36. Within the bore there is an insert 40 of a semiconducting ceramic, which may be partially reduced titanium monoxide or dioxide. The insert 40 has a metal plating 42 on its cylindrical surface, the end face 40<1> being exposed. A glass sheath 38 is sealed on the outer surface of the shell 36 and along a portion of the rod 32 that extends beyond the shell 36. Method of assembling the electrode is described. The keep-alive electrode 30 is hermetically sealed by a glass button 44 to a sleeve 46 which is brazed hermetically to a waveguide 10, Fig. 3, and rod 32 is fixed coaxially with respect to cone 20 in a critically determined spacing relation thereto. The sleeve 46 is of glass-to-metal sealing alloy such as one of the iron-nickelcobalt alloys known under the Registered Trade "Mark Kovar". The keep-alive electrode cooperates with an electrode 22 of closed deformable construction for adjustment by engagement from outside the waveguide with the member 24 fixed to the electrode 22. The assembly of the keep-alive and cooperating electrode can be carried out as described in U.S.A. Specification 2,740,186. Associated with the discharge gap 26 is a laterally disposed pair of plates which provide an iris. One or more pairs of opposing discharge electrodes 20, 22 form a series of discharge gaps along the waveguide 10. The respective gaps and irises are at intervals which can be made equal to effective quarter wave length at the centre frequency of the band for which the device is designed. The wave-guide 10 is provided with resonant windows 14, 14<1> each of which includes a centre glass or ceramic body 16 and a metal frame 18. The wave-guide 10 is filled with a rare gas such as argon mixed with a quenching gas such as water vapour at a total pressure of about 25 mms. In the construction of keep-alive electrode shown in Fig. 4 the rod 32 of a glasssealing metal having a tapered portion 321 is provided with a cylindrical tip 50 on which is axially supported a thin-walled sleeve 51 of glass-sealing metal to form an axial passage 52. The sleeve 51 is welded at 53 to the rod 32. Within the bore 52 is an insert 40 of a semiconducting ceramic which may be partially reduced titanium oxide and which has an end face 40<1> exposed and projecting outwardly beyond the sleeve 51. An insulating sheath of glass 38 is sealed on the outer surface of the rod 32, along the sleeve 51 and along the lateral surface 40<11> of the insert 40. The electrode is assembled in the wave-guide as described with reference to Fig. 3.