GB1352217A - Cathode-ray tube for producing an elongate spot - Google Patents

Abstract

1352217 Cathode-ray display tubes PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 29 July 1971 [1 Aug 1970] 35655/71 Heading H1D A cathode-ray tube includes cathode 8, grid 9, anode 10, acceleration electrode 11, focusing electrode 12 and target, the grid having elongate opening (e.g. elliptical opening 15, Fig 3, not shown) so that the gun forms an astigmatic lens such that in the plane containing the longitudinal axis of the aperture and the gun axis the electrons may be focused at a point spaced from and on the gun side of the target while in an orthogonal plane the electrons may be focused on the target, the anode having an elongate opening the length direction of which is at right angles to the length direction of the grid aperture. The acceleration electrode may form part of the focusing lens 31. The anode opening may widen stepwise and may develop into a rectangular opening towards the target as at (16), (17), (Fig. 2). Application to index type 110 degree deflection colour TV tubes is described wherein the target comprises parallel phosphor strips separated by guard bands and with index bands, wherein the beam spot is elongate in the strip direction to attain adequate brightness without saturation. The construction enables beam current to be increased without increase of beam width. The above construction inhibits effects due to deflection astigmatism and the longer distance travelled by electrons emitted further from the gun axis, the latter effect accentuated by spherical aberration due to the sharp equipotential surface bend on the target side of the anode opening unless the latter is widened. Fig. 1 (not shown) includes strip layer (4), metal light reflective layer (5), and index strips (6) emitting u.v. on electron incidence and further accelerator (13) may be included. Beam shapes are considered in relation to Figs. 5 to 12 (not shown). Constructional dimensions and electrode potentials are given. The cathode may be an osmium plated "L-type" and the inclination of the spot (Fig. 12) may be reduced by separate connecting means.