GB1210089A - Colour kinescopes - Google Patents

Abstract

1,210,089. Colour television tubes. TOKYO SHIBAURA ELECTRIC CO. Ltd. 22 Dec., 1967 [27 Dec., 1966; 23 Jan., 1967], No.58497/67. Heading H1D. A colour television tube comprises an electron gun 8, Fig. 1, the beam from which is scanned over a secondary electron emitting screen 7 which emits electrons which are controlled by a colour switching grid 4 and directed towards a fluorescent screen 3 in the form of strips of different coloured phosphors. Since the colour switching grid 4 is acting on slow electrons it requires low switching voltages; for example the primary beam from gun 8 may be accelerated to 4KV, the grid 4 may be 240 volts positive with respect to the secondary emitting cathode 7, the screen 3 may be 12KV positive with respect to the cathode, and the colour switching voltage may be 18V. The cathode 7 may comprise an aluminium foil 6 having a thickness of 500 Š.U., and a secondary emitting layer 5 of the same thickness comprising lithium fluoride. The switching voltage may be reduced by placing the colour switching grid in contact with the secondary-emitting layer, Figs. 3 and 4 (not shown). In one example of a combined colour switching grid and secondary emitting cathode (Fig. 5, not shown, insulating layers (21) of calcium fluoride are deposited on the sides of the grid wires (20) facing the electron gun; an insulating film (22) of aluminium oxide is formed over the insulating layers and is coated on one side with secondary emissive material (LiF) and on the other side with a metallic film (22). In another construction, Fig. 6 (not shown), wires (31) coated with insulation (32) are coated with metal on one side to form the colour switching grid; the other side adjoins a secondary emitting layer (36) on a metal film (35) deposited on a metal mesh (34). A platinum layer 10 A.U. thick may be provided on the back plate of the secondaryemitting electrode to improve the secondary emission ratio by improving its conductivity.