Color cathode-ray tube with in-line plural electron sources and central section of common grid protruding toward central source

Claim 1

A color cathode-ray tube comprising a display screen, beamproducing means including a plurality of electron beam sources for respectively producing a central beam directed toward said screen along the axis of the tube and two side beams which originate at opposite sides of the central beam and are directed toward said screen along paths converged with respect to said axis for intersecting said central beam at a point in said tube between said beam-producing means and said screen, said beam sources including three individual cathodes having electron emitting surfaces and a first grid assembly disposed adjacent to said cathodes and having respective grid portions with three apertures therein corresponding to said cathodes, said grid assembly being shaped so that the distances from said cathodes to their respective grid portions are substantially identical, said screen being scanned by said beams and including arrays of different color phosphors for excitation by said central and side beams, respectively, and electron lens means common to all of said beams and including main focusing lens means for producing an electric focusing field which is substantially centered at said point where the beams intersect and auxiliary lens means positioned between said beam-producing means and said main focusing lens means for at least prefocusing all of said beams, said lens means having different focusing effects with respect to said central beam and said side beams, respectively, said beam source of the central beam being disposed at a greater distance from said main focusing lens means than on said beam sources of the side beams, to compensate for said different focusing effects and thereby cause all of said beams to be precisely focused upon said screen, said electron lens means comprising a second grid disposed adjacent to said first grid assembly and having three apertures corresponding to the three apertures of said first grid assembly, said second grid including a central cylindrical protruding portion having a flat face opposing the central grid portion of said first grid assembly and containing the central aperture of said apertures in the second grid, the distances from the apertures in saId first grid assembly to the respective apertures in said second grid being substantially identical, and a plurality of electrodes, said electrodes and said first and second grids being at different electrical potentials to establish the electrical fields constituting said main focusing lens means and said auxiliary lens means with said protruding portion of the second grid causing the field corresponding to said auxiliary lens means to enhance the prefocusing effect thereof on said central beam.