Patent GB-853070-A (GB)
Title: Improvements in or relating to the manufacture of electron discharge tubes having a photo-conductive target
Inventor: TURNBULL ANDREW ALFRED
Filed: 1958-05-15
Abstract: 853,070. Television pick-up tubes. MULLARD Ltd. Dec. 11, 1958 [May 15, 1958], No. 15652/58. Class 39(1). A method of manufacturing a discharge device, such as a Vidicon television camera, which comprises an envelope terminating at one end in a window 4, Fig. 2, which carries a photoconductive target 52 and at the other end in a foot 27 from which the electrode structure is supported, includes the steps of providing an elongated tube 1 having an end portion 2 which is to constitute the envelope of the device and a further portion having a side arm 10 ; inserting the electrode structure 23 secured to the foot 27 within the tube with the foot remote from the window 4 ; and providing within the tube between the electrode structure and the window an evaporator 43 containing a supply of photo-conductive material such as antimony trisulphide. After evaporating this material to form the target layer the evaporator is withdrawn into the side arm, the electrode assembly is moved into its final position, the foot is sealed to the envelope 2 and the remainder of the elongated tube is separated from the envelope. As shown, the electrode assembly is supported by a socket 31 cemented to iron block 37 which is moved by means of annular magnet 45. During formation of the target layer in argon at low pressure, the evaporator 43 is supported 4À5 cms. from window 4 by a wire 42 having its end located in a socket 41 formed on the collector anode 23 and is heated by coil 50, the upper part of the tube being surrounded by a cooling jacket 46 and a ring 49 being provided to protect the fernicoring seal 3 from overheating. The evaporator and wire support may be lifted out of socket 41 by means of fork 15 secured to steel block 13 which is moved along the side arm by magnet 16. Prior to the formation of the target layer the electrode assembly may be moved into the end portion 2 of the tube, the evaporator being located in the side arm, and degassed by means of a cylindrical oven located about the tube. A liquid air trap 5 is provided to prevent grease vapour from the cone seal 7, connecting tube 1 to vacuum pump 9, from reaching the electrodes. When the electrode assembly has been moved into its final position, with collector mesh 25 2À5 mms. from the target spring contacts 34 press against platinum contacts to which voltages may be applied for activating the cathode of electron gun 24. After separating the envelope 2 from the remainder of tube 1, exhaust tube 28 may be connected to a vacuum pump via a tube containing a metal ball and the seal 29 broken by moving this ball by external magnetic means to enable the device to be finally evacuated. The evaporator may be of a kind described in Specification 853,101 and may alternatively, be supported on a disc 81, Fig. 12, lying across the end of anode 23. The lower portion of tube 1 may be of larger cr oss-section than portion 2 and the electrode terminals 30 may be connected to insulated segments of block 83, this block sliding on supply wires 84 so that electrical contact with the electrodes is possible for any position of the electrode assembly.