Patent GB-742776-A (GB)
Title: Improvements in or relating to television signal or image storage tubes
IPC: H01J31/32
Filed: 1953-11-25
Abstract: 742,776. Cathode-ray tubes. FERNSEH GES. Nov. 25, 1953 [Nov. 25, 1952; Nov. 28, 1952], No. 32663/53. Class 39 (1). A television or image storage tube having an electron optical image converting system and including electrodes in the form of several metallic coatings, e.g. of aluminium, to which may be applied different potentials, has the coatings 2, 3, which act as accelerating and collecting electrodes respectively, evaporated on to glass cylinders disposed coaxially with the wall 1 of the tube envelope and each fused to the well at a few, preferably at only two, points 6, 8. The fused points can be disposed diametrically. opposite each other and leads to the metallic coatings can penetrate the wall of the tube envelope at the fused points. A pump stem can be connected at a fused point. The envelope consists of a wider part for the storage electrode or mosaic 14 and a narrower part for the photocathode 5 generating the electron picture, the glass cylinders carrying the metallic coatings 2, 3 being spaced from the wall of the envelope except at the fused points. An auxiliary photocathode 4 for providing a flow of low viscosity electrons for discharging the storage electrode 14 is mounted at the junction of the narrower and wider envelope portions and is connected with a metallic coating on a tubular part 9 of the envelope containing the scanning beam generating gun. In order to produce the metallic coatings a movable evaporation source of aluminium or other metal is arranged in the interior of the tube and the interior, except the places for the photo-cathodes 4, 5 which are covered by screens held in position from the outside by magnets, is exposed to the metal vapour. The photo-cathodes are then produced by vaporization of a metal, e.g. antimony, and the carrier of the storage electrode or mosaic and the beam producing system are fused to the envelope, the latter being connected to a vacuum pump. The rims of the electrodes 2 and 3 facing the auxiliary photo-cathode 4 can be suitably shaped so as to transmit evenly the flow of electrons from the photo-cathodes on to the storage electrode. In the construction shown in Fig. 2 in order to prevent light from the incandescent lamp source 17 which illuminates the auxiliary photo-cathode 16 from falling on the main photo-cathode 12 through interior reflection on the mirror-like parts of the tube, the accelerating anode 13 is provided at the end facing the storage tube with such an expansion that a beam of light from the source 17 is reflected by the mirrored surface 13 on to the auxiliary cathode 16. Other mirrors can be used for this purpose. The auxiliary cathode 16 is made semi-transparent so that part of the light not absorbed passes out through the wall of the tube. The metallic coatings 13, 15 are coated with a light-absorbing film, e.g. a chromium film produced by atomization in a stream of inert gas, to prevent unintentioned reflections. The auxiliary photo-cathode 16 can be made sensitive to red and ultra-red light, e.g. by use of silver oxide-caesium films, and illuminated by a red-light source, e.g. by one or more neon lamps or caesium vapour lamps, and the main photo-cathode can be made of maximum sensitivity in the green or blue and insensitive to light of longer wavelengths.