GB801841A - Improvements in or relating to cathode ray tubes - Google Patents

Abstract

801,841. Cathode-ray tubes. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Nov. 24, 1954 [Dec. 4, 1953], No. 34058/54. Addition to 794,257. Class 39(1). The " flat television cathode-ray tube of the parent Specification is used with grid controlled valves or with diodes to control the deflection systems. The tubes may be inside or outside the main evacuated envelope. Control valves and deflection systems. In Fig. 3 the vertical deflection plates 70 are controlled by the beam switch 73 as in the parent Specification, but the horizontal deflection U-shaped elements 45 are controlled by a pentode 50 with two control grids 53, 54 in which the spacings between wires progressively increase from end to end. The spacings increase in opposite directions in the two grids. The control valve may also be e.g. a triode with one only variably spaced grid or a hexode with screen and suppressor grids. The valve may be linear or cylindrical. Deflection elements 45 and 70 in Fig. 3 may be replaced by wires. In Fig. 6 the deflection systems consist of single plates 185, 208 inclined to the screen 180 and connected respectively to a conventional pentode 192 and a conventional triode 211. An accelerating screen 206 is in front of the screen 181. In Fig. 5 the horizontal deflection system consists of a series of electromagnets 135 connected to a series of conventional pentodes 142 connected along a potential divider 145 to which the sweep voltage 151 is applied. Diodes or triodes may be used instead. Deflection elements and magnets. The deflection elements 45, Fig. 3, may have curved or slanted ends or tails to improve linearity of sweep. The single deflection plates of Fig. 6 may also be curved. The electromagnets 135, Fig. 5, may have pole faces inclined towards one another and may increase in strength away from the gun 133. Other deflection systems. In Fig. 19 the horizontal deflection system consists of a single electromagnet 275 and the beam 280 is delivered perpendicularly to the pole faces, or at an angle thereto. The field strength is varied or the beam velocity modulated to effect the scan. The field strength may increase away from the gun 279. The field strength may be extra strong at the far end to ensure the beam leaves normally to the screen 281. In one deflection system of Fig. 6 the plate may be at constant voltage and the beam velocity modulated. Correcting picture distortion and focusing. In Fig. 3 the beam 44 may be delivered at an angle to the plates 46, 47 to correct keystone distortion ; elements 45 may also be at an angle. The spacing between focusing plates 59, 60 or between deflection plates 70 and the screen 40 may be varied to improve focusing. Dynamic focusing may be employed, an increment of the vertical deflection voltage being applied to the horizontal deflection system, or increments of both deflection voltages may be applied to plates 59, 60 or to an electrode of the gun 43. Other dispositions of gun. The electron gun may be at the edge of the screen 342, Fig. 24, at 340, or behind the deflection elements 352, Fig. 25, at 350. A colour television receiver tube may include two, three or four transparent screens bearing different colour phosphors and each with its own beam and deflection systems, or a single beam may be switched to each screen in turn. The screens are of suitable thicknesses and spacings to reduce parallax errors. One screen may have a phosphor on each face. The phosphors may be uniform transparent coatings or multi-dot. An additive or subtractive colour system may be used. A three-dimensional tube may have a concave or convex screen with correspondingly curved deflection systems, Figs. 46, 47 and 48 (not shown), or a number of transparent screens in depth, Fig. 49 (not shown), or two screens 710, 711, Fig. 50, with polarizing filters 712, 713, mirrors 717, 718 and a viewing screen 716. The screens may be disposed back to back or perpendicularly to one another. Again a single beam may be used, switched to each screen in turn. A radar display tube, Figs. 54, 55 (not shown) has a transparent screen with different colour phosphors on its two faces. A single beam is switched between the two faces. In Figs. 56, 57 (not shown) the beam is directed along different base lines. A colour television camera tube has three transparent storage targets 801, 802, 803, Fig. 58, with colour filters 822, 824 disposed between them. Transparent electrostatic shields are provided between the deflection systems 814, 815 and the signal coatings 807, 808. The deflection elements may consist of thin conductive glass or transparent printed circuit, e.g. or of fine wires. In Fig. 58 the deflection systems may be coatings on the colour filters 822, 824.