Color television screen and shadow mask assembly having increased

Abstract

This disclosure depicts a novel apparatus for use in a shadow mask type color television picture tube having a funnel and a faceplate attached to the mouth of the funnel. The faceplate has an electron excitable phosphor screen having triads of red, green and blue phosphor elements deposited thereon and an apertured shadow mask in spaced adjacency to the phosphor screen. The funnel has a neck containing an electron gun assembly for forming three electron beams. The apertures in the shadow mask form beam landing areas on the phosphor elements when the electrons pass through the apertures. This invention is a system for increasing color purity tolerance and leaving tolerance in at least a portion of a predetermined sector of the phosphor screen and shadow mask assembly to increase tolerance to radial registration errors between the electron beam landing areas and the phosphor elements due to shadow mask doming during operation of the tube. The geometry of the beam landing areas and the phosphor elements in the portion of the sector are characterized by having off the tube axis the smaller ones of the phosphor elements and the mask apertures radially compressed relative to the larger ones without a corresponding azimuthal compression. The radial compressing increases with increasing radius such that the tolerances in the radial direction increase off axis without a corresponding increase in azimuthal tolerance. This provides increased tolerance to the aforesaid doming-induced registration errors between the phosphor elements and the beam landing areas.