GB1384908A - Cathode-ray tube comprising and electron gun system for producing two or more electron beams - Google Patents

Abstract

1384908 Cathode-ray tubes PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 13 March 1972 [16 March 1971] 11614/72 Heading H1D The focus and convergence of a multi-beam tube may be affected by charges on the glass neck portion of the tube between electrodes of the gun which take some time to reach equilibrium; the approach to equilibrium is speeded up by diverting part of the beam. In Fig. 2 the final anode 12 of an electron gun opens into a tube 13 associated with the internal convergence device, and the opening is closed by a gauze. When first operated, the beam burns a hole in the centre of the gauze, but the peripheral portions remain and serve to reflect some electrons so that they escape at the gap between electrodes 11 and 12 to charge the area 15 of the neck to its equilibrium potential within 10 seconds. The gauze comprises intersecting tungsten wires 20 microns thick stretched over the opening at a pitch of 200 microns and welded or soldered by means of gold. Alternatives mentioned comprise a wire or one or more pro. jections across the opening, an aperture smaller than the beam diameter, or an aperture equal to the beam diameter but displaced from the beam axis. The tube may be of the three-gun shadow mask type.