Patent GB-723268-A (GB)
Title: Improvements in or relating to cathode ray tubes
Inventor: BOSWELL DAVID
IPC: H01J29/48
Filed: 1952-07-08
Abstract: 723,268. Cathode-ray tubes. GENERAL ELECTRIC CO., Ltd. July 6, 1953 [July 8, 1952], No. 17213/52. Class 39 (1) An electron gun in a cathode-ray tube comprises an anode in the form of a hollow nickel cylinder 7 which is pushed through an aperture 2 in a cylindrical steatite block 1 until a radially extending collar 8 formed on the anode abuts against the block and an annular disc 9 is then welded to the anode cylinder to prevent axial movement. A tongue 10 formed in the disc 9 is bent into a recess 11 in the block 1 to prevent relative rotation of the anode cylinder and the block. The cathode assembly, which is constructed substantially as described in Specification 722,345, includes a cathode consisting of a rectangular tube 12 containing a heater 34 and a cylindrical modulator electrode 13 having a closed end 35 with a central circular aperture 14. The ends of the cathode tube 12 project through apertures in two rectangular mica sheets 15 which rest against a flange 16 extending radially outwards from the open end of the modulator cylinder 13, the surface of the cathode tube near the aperture 14 being coated with electron emissive material. The outer part of the radial flange 16 is continued as a cylindrical flange 17 which fits within a skirt formed on the block 1 and is welded to a cylindrical sleeve 18 formed of two semi-cylindrical portions welded together by means of flanges (not shown), provided with six symmetrically spaced radial lugs 20 which are welded to a flange on a circular collar 21 fitting over a projecting shoulder 6 on the block 1 and having a part 23 pressed into a recess 22 in the block to prevent rotation of the collar 21. The mica sheets 15 are kept in abutment with the flange 16 by a retaining spring 24 having lugs which fit within depressions in the edges of the sheets and spring fingers 26, the ends of which fit within slots 27 in the sleeve 18. The electron gun is supported within the glass neck 28 of the tube envelope by two projections (not shown) on the disc 9 and two corresponding projections (not shown) on the collar 21 which are kept in abutment with the neck 28 by a spring finger 33 attached to the tongue 10 and also bearing against the neck 28, the arrangement being such that the assembly. is supported at points separated by 120 degrees intervals around the neck. Axial movement of the assembly is prevented by means of the electrode lead-in wires (not shown) which may conveniently be connected to terminal tags attached to one or both of the mica sheets 15. Cut-away portions 31 in the sleeve 18 allow the cathode and heater terminals to extend beyond the sleeve for attachment of the cathode and heater leads. One or more additional blocks 1 carrying additional anode or other electrodes may be provided. The extension of the anode cylinder 7 beyond the aperture 2 towards the cathode is designed to prevent distortion of the path or shape of the electron beam due to wall charges on the surface of the block 1, and the length of the extending part of the anode necessary to attain this end is reduced by providing an annular recess 3 in the surface of the block. The cylinder 17 provides a shield for the space into which the anode projects..