GB849664A - Improvements relating to polychromatic pattern-reproducing electrical beam tubes andto methods and means for designing screens for such tubes - Google Patents

Abstract

849,664. Colour television tubes. GENERAL ELECTRIC CO. Dec. 21, 1956 [Dec. 27, 1955], No. 38964/56. Class 39(1). In a colour receiving tube the phosphor pattern is modified to compensate for undesired beam deflection in the post acceleration between apertured mask and fluorescent screen ; to do this a master pattern for the fluorescent screen is prepared by subjecting a light sensitive surface 28, Figs. 4, 8, to a source of visible light 33 the light passing through a masking member 27 corresponding to the tube mask and means being provided for deflecting the light rays leaving the source at different angles to follow the same paths as the electrons follow in the post acceleration field. The invention also corrects for yoke imperfections and dynamic convergence imperfections. A photographic technique is then used for preparing the screens proper. The light rays may be differentially deflected by a plano-convex lens 32, Fig. 4, or by a layer of glass 38, Fig. 8, of suitable thickness and refractive index placed between the masking member 27 and the light sensitive member 28. In Fig. 8 there may be more than one glass plate 38, or a plurality of layers of air or water. A single layer of glass plus a single layer of air can be used. The mask used in the optical apparatus may be a gelative coating on a glass base, the coating being ruled scored or engraved, or can be replaced by a photographic copy thereof, or even by the tube mask. There may be two further electrodes between mask and screen for colour switching, the post acceleration field being set up between the mask and a conductive coating on the screen ; the mask can be a wire grill or possibly an apertured plate. The phosphor can be strips or dots arranged at the corners of equilateral triangles, each mask aperture covering one phosphor triad. The phosphor pattern at the centre of the screen corresponds to the grill pattern but becomes denser in any direction away from the centre, the outer phosphor lines being slightly moved. The optical mask and light sensitive plate can be adjusted longitudinally to obtain the correct starting conditions. To correct for the lens thickness in Fig. 4 the distance between the light source and mask is increased slightly. The fluorescent screen can be curved instead of flat. The design procedure is described mathematically and illustrated graphically, Figs. 3, 5, 7, 9 (not shown).