Cathode-ray tube having a screen grid with asymmetric beam focusing

Abstract

The asymmetric beam focusing slot provides a two-part crossover of the electron beams. The slot has a length greater than the spacing between the outer apertures and a width greater than the diameter of the apertures. The screen grid also has an improved refraction lens which comprises a transversely disposed recessed portion including a substantially rectangularly-shaped central portion and substantially triangularly-shaped end parts. The refraction lens provides a compensating field between the screen grid and the main electron lens to offset any changes in the main electron lens caused by variations in the focus voltage in the main electron lens. The recessed portion has a length, extending in the plane of the electron beams, at least coextensive with the length of the slot, and a width, extending substantially orthogonal to the plane of the electron beams, substantially greater than the width of the slot. The recessed portion is surrounded by a peripheral rim which conforms to the shape of the recessed portion. The central part of the peripheral rim is remote from the center aperture, and the triangularly-shaped end parts of the rim are in proximity to the outer apertures, thereby affecting the electrostatic field in the vicinity of the outer apertures by tilting the field lines within the recessed portion.