GB1223584A - Plural beam electron gun for a color picture tube - Google Patents

Abstract

1,223,584. Colour television tubes. SONY CORP. 18 Sept., 1968 [20 Sept., 1967], No. 44316/68. Heading HID. In a colour television tube using red, blue and green phosphors the blue phosphor saturates at a lower beam current density than the other two phosphors and thereby limits the brightness of the picture if the white balance is to be preserved; this difficulty is avoided by defocusing the blue beam so that the maximum beam density gives greater apparent brightness for each blue spot. In Fig. 3 the triple electron gun has a common control grid G wherein the aperture glB for the blue beam is of greater diameter than the other two apertures. The cathode K B for the blue beam is spaced from the grid by a distance d 1 substantially greater than the spacing d 2 of the other cathodes; this has the effect that the cross-over for the blue beam lies outside the object plane of an electrostatic focusing lens common to the three beams. Alternative arrangements use separate cathodes with separate control grids (Figs. 5 and 6, not shown) or a common cathode with separate control grids (Figs. 7 and 8, not shown). As described the gun is applied to a tube using coplanar beams, the outer beams being converged at the plane of a beam selecting grid or mask by a fixed deflecting system (Fig. 1, not shown).