Collinear electron gun system including accelerating grid having greater effective thickness for off axis beams

Claim 1

A cathode ray tube comprising: a screen; and electron gun means comprising beam producing means including a first set of cathode and control grid means providing a central beam source located on the axis of the tube for directing a central electron beam along said axis toward said screen and second and third sets of cathode and control grid means providing said beam sources spaced from said central beam source at opposite sides of the latter for directing respective side beams toward said screen in a common plane containing said axis of the tube, accelerating grid means spaced from said control grid means in the direction toward said screen and having a central aperture and two side apertures respectively aligned with said central and side beams, and a main focusing lens comprising a plurality of electrode means arranged in sequence along said axis between said accelerating grid means and said screen, said accelerating grid means cooperating with said beam producing means to establish electric fields for narrowing said beams to minimum crosssections at respective crossover points adjacent said accelerating grid means, means for directing said side beams to intersect said central beam at a location in the main focusing lens whereby said side beams pass through the main focusing lens at angles to said axis and the focusing effect thereon is different from that on said central beam, said cathode and control grid means being substantially equidistant from each other in said first, second and third sets thereof and said control grid means of said first, second and third sets being substantially equidistant from said location in said main focusing lens where said side beams intersect said central beam, said accelerating grid means having greater effective thickness at said portions thereof containing said side apertures than at the portion thereof containing said central aperture, whereby an electric field established between said accelerating grid means and said electrode means of said main focusing lens panetrates said central and side apertures of the accelerating grid means to different extents and thereby disposes said crossover points of said side beams and said central beam, respectively, at different distances from said main focusing lens to compensate for said different focusing effects.