Electron gun device for color tube

Claim 1

An electron gun device for a color picture tube comprising two side cathodes and a central cathode therebetween having beam generating surfaces arranged substantially in a row for emitting electrons generally in parallel directions, first and second grids spaced successively in the axial direction away from said beam generating surfaces and having apertures respectively aligned with the beam generating surfaces and through which the emitted electrons are collimated into respective electron beams, and a plurality of electrodes maintained at different potentials and arranged axially following said second grid to provide an electric field defining a main lens means by which said beams are focused and cooperating with said second grid to provide another electric field defining an auxiliary lens means by which the beams from said side cathodes are converged with respect to the beam from said central cathode for passage of all of the beams through the center of said main lens means, the angle of a cone that can be projected to the center of said beam generating surface of said central cathode from the peripheries of the respective aligned apertures of said grids being smaller than the angles of the corresponding cones for said side cathodes for equlizing the effects of said other electric field at said beam generating surfaces of said cathodes so that the latter will have equal cutoff voltages.