Tetrode section for a unitized, three-beam electron gun having an

Abstract

This disclosure depicts an electron gun especially for use in a color cathode ray tube of the small-neck, shadow-mask type. The gun design is also applicable to other television cathode ray tube displays that require a gun that provides small, symmetrical spots of uniform cross-section, such as guns used in monochrome television and beam index tubes. The gun is comprised essentially of a four-element tetrode section and a main focus lens section. The tetrode section generates at least one electron beam and a cross-over that is imaged on the screen of the tube focused by the main focus lens. The tetrode section is characterized by having a strong prefocus; that is, a prefocus in which the electron trajectories are substantially refracted, or bent, before exiting the tetrode section. The tetrode section has two associated grid means whose dimensions, configurations, and relative spacings, in combination with a strong electrostatic prefocusing field produced between said grids, forms in the grid interspace an electrostatic field which includes in the region of the beam strongly bent, preferably substantially hyperboloidal equipotential lines which help to suppress spherical aberration commonly associated with a highly refractive tetrode section design.