GB1254064A - Electron beam correction apparatus for a color picture tube - Google Patents

Abstract

1,254,064. Colour television tubes. SONY CORP. 11 March, 1969 [11 March, 1968 (2)], No. 12690/69. Heading H1D. A plural beam, single guncolour cathode-ray tube, of the type having a central and two side electron beams which lie in a common plane passing through the tube axis and in which the side electron beams converge with the central beam at a beam selection means in front of the screen, has provided, as part of the beam convergence system, magnetic field generating means arranged on opposite sides of the central beam; at a location where the side beams are spaced from the central beam, which are operative to produce oppositely directed magnetic fields which are generally perpendicular tothe common beam plane. The arrangement is such that it produces lesser flux density in the region of the central beam than in the region of at least one of the side beams to correct for misconvergence of the beams due to misalignment of, for example, the beam gun electrodes. The magnetic fields may be generated by permanent .magnets 22R, 22B, Fig. 3, which are held in plastics sleeves 34R, 34B that are adjustably housed in plastics casing 31. Alternatively, electromagnets 22<SP>1</SP>R, 22<SP>1</SP>B, Fig. 6, may be used, which, ifeach is energized from separate supplies 25R, 25B, may be permanently secured to a fixed non- magnetic holder, Fig. 7 (not shown), thus obviating the need for mechanical adjustment. The permanent magnets or electromagnets may, as shown, be convex towards each other to reduce any unwanted magnetic fields between the oppositely-polarized corresponding ends of the magnets. Alternatively, Fig. 9 (not shown), the magnets may be concave towards each other, following the profile of the tube neck and the unwanted fields reduced by providing weak. auxiliary permanent- or electromagnets between the adjacent oppositely-polarized ends of the main magnets. A dynamic convergence correction current, derived from the horizontal and vertical sweeps, maybe superimposed on the current through each electromagnet 22<SP>1</SP>R, 22<SP>1</SP>B. As shown in Fig. 1, the three beams are derived from the single cathode of a single electrongun which. incorporates a main lens system L at the centre of which is a beam convergence point. The resultant divergent beams then pass through a beam convergencedeflecting means F, a deflection yoke 20 and a beam selection grill Gp before reaching the screen. Preferably, the magnetic field generating means 22R, 22B are disposed between the convergence deflecting means and the deflection yoke.