Patent GB-494145-A (GB)
Title: Methods of and arrangements for producing television images with persistent light impression
IPC: H01J31/12
Filed: 1937-01-18
Abstract: 494,145. Cathode-ray tubes. RADIOAKT.-GES. D. S. LOEWE. Jan. 18, 1937, Nos. 1471, 1472, 1473, 1474, and 1475. Convention dates, Jan. 21, 1936, Jan. 27, 1936, March 19, 1936, March 31, 1936, and April 24, 1936. [Classes 39 (i) and 40 (iii)] A cathode-ray tube for television reception has a grid electrode, the insulated elements of which are scanned by a modulated cathode- or light-ray, and controls an electron beam which is focused on to a light-giving screen. The grid comprises wires 2, Fig. 1, which surround a cathode 1, and are supported on insulating members 3. The cathode is reproduced on a screen 7 through a diaphragm 4 by a system which consists of a box-like member 5 and the slit anode 6. The grid is scanned in one direction only by an electron beam formed by cathode 16, control grid 14, anode 12 and tubular member 13. The grid elements are discharged through a resistance, or by heating them to emit electrons by heating elements housed within the members 3. The potential on the diaphragm 4 is adjusted so that maximum light intensity is obtained when the grid elements are slightly negative. The controlled beam is deflected across the screen by plates 8, 9. In a modification, the scanning electron beam is modulated by the anode 12, Fig. 4, which is connected to the receiver 15 ; the control grid 14 is connected through a resistance to the cathode 16. The grid elements are coated with caesium or barium so that they can be discharged by the emission of secondary electrons. During the fly-back period, the beam is suppressed by a negative potential on the control grid. The grid elements may be light sensitive. In another form, an electron beam is deflected, preferably by magnetic fields, to scan a grid 35, Fig. 5, which comprises metal rods embedded in an insulator. The grid controls the emission from an incandescent mesh cathode 1, and may be formed by filling the apertures in a mica plate with silver by using a stream of silver vapour ; the grid is mounted between two perforated mica sheets. The cathode 1 may consist of a silver net, which is made light sensitive by coating with caesium and is activated by radiating with infra-red rays, or may consist of a fabric of filaments connected in parallel; it may be spherical, the centre of curvature being located at the anode 6. Electrodes 5, 6, or a coil, may focus the electrons on to the screen 7. To remove high-frequency currents, potentials for the electron-optical system 12, 13 are taken from a potentiometer 22a, the series resistance 39 is large compared with the internal resistance of the receiver 40 and condensers 43, 44 are connected as shown. An earthed coating 45 is provided. Modulating potentials are applied from the receiver 40 to the anode 12. In a modification, to avoid halo, the electronoptical system comprises electrodes 5, 6, 6a, 6b, Fig. 6, connected up as shown. The cathode 1 comprises two nets through which the current flows in opposite directions and coated on their adjacent faces only with oxide ; the nets are inclined at angles of 45 degrees, and may be mounted in frames. An accelerating net 49, which is similarly curved, may be provided, and the side of the control grid scanned by the beam from gun 16 is flat. Bifilar leads secured by insulating rivets are provided for the cathode. In another form, the cathode 1, Fig. 8, consists of an atomized coating, or of wires, preferably rolled flat, on a mica or quartz glass plate 62. The control grid 2 consists of a mosaic on the other side of the plate 62. The cathode is activated by caesium and is energized by infra-red rays from a lamp 63 through a filter ; the rays may be reflected onto the cathode by an internal mirror or may be projected thereon from the rear side. Alternatively, a double-mesh incandescent cathode may be used, and the requisite bias between the nets may be obtained by an internal resistance, Fig. 10 (not shown), connected therebetween. The scanning beam may be accelerated by short rings 68, Fig. 11, and the modulating potentials are applied to the final anode 69a. Deflecting plates may consist of iron to form pole shoes of an electromagnetic deflecting system.