CRT Focusing electrode structure

Claim 1

An improved beam focusing structure in a color CRT plural beam in-line electron gun assembly embodying a center and two side-related integrated gun structures from which said beams emanate on respective axes in a common in-line plane, said gun assembly being a construction of sequentially positioned in-line electrodes including a forwardly positioned main focusing electrode having rear and forward apertured ends and an adjacent terminally-related plural-apertured final accelerating electrode; said improved structure comprising means for beneficially modifying the lensing fields associated with the main focusing of each of the respective electron beams, said means comprising: a common elongated perimetrically configurated aperture formed in the forward portion of said main focusing electrode to provide three adjacently overlapping in-line non-symmetrical focusing lenses thereat associated with the respective in-line beams, said perimetrically configurated aperture being formed of peripherally in-turned projections extending substantially normal to the interior surface of said forward end, said configurated aperture being delineated by circular end portions each having termini merging with those of opposed side-related arc portions to produce a pair of equi-spaced opposing cusps pointing toward said in-line plane on either side of said configurated aperture, thereby forming three apertural regions of said common elongated aperture, said arcuate side and circular end portions being delineated substantially from the respective beam axes by substantially similar radii of values greater than the radii of the related individual apertures in said adjacent accelerating electrode; said means further comprising two like planar wall elements oriented in equi-spaced parallel position on either side of said center axis in a manner to effect jointure with opposed cusps of said aperture, each of said wall elements having a defined length extending into said focusing electrode and a width greater than the diameter of a single aperture in said adjacent accelerating electrode, said wall width being sufficient to bridge said opposed cusps but less than the diameter of a single apertural region of said common configurated aperture, with the forward edge thereof being a concave arcuate formation.