GB1324565A - Cathode-ray tubes - Google Patents

Abstract

1324565 Cathode-ray tubes and image pick-up tubes SIEMENS AG 5 May 1971 [14 May 1970] 13269/71 Heading H1D A cathode-ray tube includes a post-deflection accelerating lens comprising electrically conductive hollow member 2, with open exit and entry apertures, the edge of the member adjacent the screen electrode being shaped so that the perpendicular distance from the plane of the screen electrode is less at the corners than at the middle of any edge of the screen electrode 1. Preferably the edge of the hollow member adjacent the screen electrode is matched to the symmetry of the screen electrode. The hollow member may be shaped as a cone or pyramid, or may be cone-shaped adjacent the deflection system and merge into a pyramidal shape adjacent the screen electrode. Also the member may be a lining or coating on the tube envelope. Reference is made to pin cushion distortion and lack of definition and elimination of errors formed by employing an open exit aperture instead of a metal gauze exit aperture. The potential differences between the screen electrode and hollow member will be larger, the greater the angle between the central beam path and the wall of the hollow member. With tubes incorporating a mask before the screen, the accelerating field is applied to take effect before impingement of the electrons on the mask, and in multi-gun tubes this may lead to a reduction in convergence difficulties and increase in brightness. Applicability to tubes having central deflection systems such as oscilloscope tubes, monochrome or colour picture tubes and camera tubes employing high velocity electron beams is exemplified.