GB1250408A - - Google Patents

Abstract

1,250,408. Colour television tubes. RCA CORPORATION. 12 Dec., 1969 [12 Dec., 1968], No. 60689/69. Heading HID. A colour picture tube comprises an envelope with rectangular faceplate and mosaic phosphor screen, an electron gun for projecting at least one electron beam, and a rectangular shadow mask comprising a rectangular frame 21 and rectangular masking member comprising multiapertured curved metal sheet 15 and peripheral skirt 19. The frame is of endless strip L crosssection, one flange 23 attached to skirt 19, the other flange 25 extending inwardly to serve as an electron shield during overscan of the beam. The sides of the frame are curved and flange 25 has a substantially smaller curvature along its long sides than the curvature along the corresponding long sides of the metal sheet and also substantially smaller than the curvature of the corresponding flange along the short sides of the frame ( Figs. 5 and 6, not shown). The flanges may be of equal width and conform to a barrel-shaped surface. Frame 21 may be detachably mounted by four studs (27) (Figs. 2 to 4, not shown) and four leaf springs (29), each within a triangular hole (31) and welded to temperature compensating bimetallic plates (34). The latter may be omitted and springs (29) welded directly to the frame (21). The curvatures may be such that the distance F (Figs. 5 and 6) between the common plane of the four corners of flange 25 and the central portions of the four sides are equal and lie in a common plane parallel to the plane of the studs. Alternatively, attachment may be by three spring clips attached near the mid-points of three sides. Preferably, the faceplate and mask 15 are. both spherical with different centres of curvature. Fig. 7 (not shown) indicates the shielding effect at each corner for a maximum deflection angle of 90 degrees and Figs. 8 and 9 (not shown) the shielding effect at the mid-point of the long and short sides with deflection angles of 63 and 79 degrees respectively. Beam apertures (17) are preferably in hexagonal array.