Patent GB-1003165-A (GB)
IPC: H01J29/70
Abstract: 1,003,165. Colour television tubes. RADIO CORPORATION OF AMERICA. Dec. 6, 1962 [Dec. 7, 1961], No. 46161/62. Heading H1D. A colour cathode-ray tube of the type in which electron guns 16, 17, 18 project beams at low, medium and high velocity on to a luminescent screen 20 comprising superimposed layers 22, 24, 26 of different-coloured phosphors (red, green and blue), has a magnetic deflection yoke 28 which produces two fields in the zone 19 to scan the beams over the screen 20 in two mutually perpendicular directions at different scan frequencies. The low and medium velocity beams are provided with tubular magnetic shields 76, 78 respectively mounted directly and indirectly on a convergence cage 40, the axial position of the shield 78 relative to the shield 76 being selected to obtain the least asymmetry of the high velocity beam raster. The theoretical basis for this selected position is given and the factors determining the length and diameter of each shield are discussed, Figs. 7 to 11 (not shown). The guns 16, 17, 18 are mounted in triangular array and symmetrically about the axis of the tube, the gun 18 being arranged in the plane through this axis which is perpendicular to the scan produced by the higher frequency deflection field (in the present case a vertical plane perpendicular to the X-X axis of the screen, Fig. 2 (not shown). The theoretical basis for this particular gun orientation is discussed (briefly it is to symmetrize the field distortion caused by the shields 76, 78) and a typical example of raster misregistry caused by incorrect gun orientation is given and explained, Figs. 12 and 13 (not shown). Enhancers 84-87 of magnetic material are provided for the high and medium velocity beams to effect shaping of the raster by altering its aspect ratio. The effect of the enhancers 84, 85 on the raster of the high velocity beam is explained, Figs. 14 and 15 (not shown), and the influence of such factors as enhancer length, cross-section, and spacing relative to the beam is discussed. The enhancers 85, 86 may be attached to each other or formed as a single integral member. The shield 78 is mounted on the cage 40 by means of non-magnetic members 80, 81, 82, but the last two may be omitted and member 80 is then mounted on the enhancers 86, 87. Each gun comprises a cathode 30, control grid 32, screen grid 34, focusing electrode 36 and anode 38, these members being mounted on straps 60, 61, 62 secured to glass rods 59, and the anodes 38 being also attached to the cage 40. Approximate beam convergence near the centre of the screen is achieved by mounting each gun at a small angle with respect to the tube axis. Dynamic convergence is obtained by providing each beam with a pair of polepieces 64 and an energizing electromagnet 66, the poles 64 being mounted in the cage 40 with a Y-shaped magnetic shield 68. Precise static convergence at the centre of the screen is effected by a permanent magnet assembly 69 which permits lateral adjustment of the position of the high velocity beam in a direction normal to the radial adjustment of this beam provided by the poles 64. Additionally, the poles of assembly 69 may be dynamically energized to assist in shaping the raster, and the mounting strap 60 may be of magnetic material to help shape the field of assembly 69. The screen 20 may include non-luminescent separator layers between the phosphors, and spring snubbers 54, conductive coating 56 and metal backing layer 27 complete the arrangement. Specifications 1,003,166 and 1,003,167 are referred to.