Electron gun for color picture tube with electrostatic focussing lens

Claim 1

An electron gun for a color picture tube comprising: means for generating three electron beams along a tube axis of said picture tube; a first electrode having three electron beam passing holes arranged in line in a direction orthogonal to said tube axis; and a second electrode arranged to oppose said first electrode with a predetermined distance therebetween and having three electron beam passing holes arranged to oppose said electron beam passing holes of said first electrode, said first and second electrodes forming main electrostatic focusing lenses between said respective opposed electron beam passing holes of said first and second electrodes when applied with predetermined potentials, respectively; wherein each of said first and second electrodes is formed of an oval thick plate; said in line electron beam passing holes of each electrode including two side or outer electron beam passing holes each having an outer half in the form of a semi-circle and a remaining half in the form of a semi-ellipse having a diameter of said semi-circle as its major axis, as viewed along said tube axis, and a central electron beam passing hole in the form of an ellipse having a major axis which is equal to the diameter of said semi-circle and which extends in a direction orthogonal to the direction of arrangement of said electron beam passing holes, as viewed along said tube axis; and at least one of opposed surfaces of said first and second electrodes is formed with a recess between the center of each of said outer electron beam passing holes and the center of said central electron beam passing hole except for a peripheral edge of said surface, said recess having a predetermined depth whereby the distance between said first and second electrodes at ends of the minor axis is wider that that distance at ends of the major axis of the elliptical portions of said electron beam passing holes.