Cathode ray tube

Abstract

At least one of the focusing electrodes stages disposed between an acceleration electrodes stage and a rear focusing electrodes stage is constituted by first and second grid electrodes, confronting portions thereof having asymmetrical construction with respect to an electron beam axis. A constant focusing voltage is applied to the first grid electrode, and a dynamic focusing voltage gradually increasing or decreasing from the constant focusing voltage as the degree of beam deflection increases is applied to the second grid electrode.

What is claimed is: 
     
       1. A cathode ray tube comprising: .[.a plurality of electron guns.]. .Iadd.an electron gun assembly .Iaddend.disposed in a neck portion of a glass envelope of said cathode ray tube, .[.each of.]. said electron .[.guns.]. .Iadd.gun assembly .Iaddend.including a cathode electrodes stage,   a front focusing electrodes stage, and   a rear focusing electrodes stage, said stages being sequentially disposed in a direction of an axis of said cathode ray tube,   said .[.first.]. .Iadd.front .Iaddend.focusing electrodes stage including   a first focusing electrode,   a second focusing electrode .[.comprising.]. .Iadd.comprised .Iaddend.of a first grid electrode and a second grid electrode, and   a third grid electrode disposed between said first and second focusing electrodes;   means for applying a constant focusing voltage to said first focusing electrode and said first grid electrode;   means for applying to said second grid electrode a dynamic .Iadd.focusing .Iaddend.voltage superimposed on .[.said.]. .Iadd.a .Iaddend.constant voltage which dynamic focusing voltage gradually varies as a function of the deflection of an electron beam so as to asymmetrically converge the electron beam to produce substantially the same beam spot configuration on said tube for any deflection of said beam; and   means for applying a high voltage to said third grid electrode and said rear focusing electrodes stage.     
     
     
       2. A cathode ray tube according to claim 1 wherein said first grid electrode is provided on a surface thereof confronting to said second grid electrode with plate shaped projections disposed on both sides of apertures for passing the electron beams, and said second grid electrode is provided on a surface thereof confronting to said first grid electrode with upper and lower plate shaped projections such that said plate shaped projections of said first and second grid electrodes are superposed perpendicularly to each other but not in contact with each other. 
     
     
       3. A cathode ray tube according to claim 1 wherein each of said first and second grid electrodes is formed of a plate provided with vertically elongated apertures arranged horizontally. .Iadd. 
     
     
       4.  A cathode ray tube according to claim 1, wherein said constant voltage on which said dynamic focusing voltage is superimposed is said constant focusing voltage. .Iaddend. .Iadd.5. An in-line type cathode ray tube comprising: an electron gun assembly disposed in a neck portion of a glass envelope of said cathode ray tube, said electron gun assembly including   a cathode electrodes stage,   a front focusing electrodes stage having at least a first grid electrode and a second grid electrode, one of said first and second grid electrodes having a surface confronting the other of said first and second grid electrodes and provided thereon with first plate shaped projections for a plurality of aligned first apertures formed in said one of said first and second grid electrodes, said aligned first apertures passing electron beams emitted by said cathode electrodes stage, said first plate shaped projections extending in a direction substantially parallel with a direction of alignment of said plurality of aligned first apertures so as to sandwich said aligned first apertures, and   a rear focusing electrodes stage, said front and rear focusing electrodes stages being sequentially disposed in a direction of an axis of said cathode ray tube;   means for applying a constant focusing voltage to said first grid electrode;   means for applying to said second grid electrode a dynamic focusing voltage superimposed on a constant focusing voltage which dynamic focusing voltage gradually varies as a function of the deflection of an electron beam so as to asymmetrically converge the electron beam to produce substantially the same beam spot configuration on said tube for any deflection of said beam; and   means for applying a high voltage to said rear focusing electrodes stage.   
     
     
        .Iaddend. .Iadd.6.  An in-line type cathode ray tube according to claim 5, wherein the other of said first and second grid electrodes has a surface thereof confronting said one of said first and second grid electrodes and provided thereon with second plate shaped projections for second apertures formed in said other of said first and second grid electrodes, said second apertures passing the electron beams, said second plate shaped projections extending in a direction substantially perpendicular to said direction of alignment of said plurality of aligned first apertures, each of said second plate shaped projections having a width smaller than a spacing between said one and said other of said first and second grid electrodes, an adjacent two of said second plate shaped projections being disposed so as to sandwich an associated second aperture. .Iaddend. .Iadd.7. An in-line type cathode ray tube according to claim 6, wherein said second plate shaped projections have a length of extension larger than the diameter of said second apertures formed in said other of said first and second grid electrodes. .Iaddend. .Iadd.8. An in-line type cathode ray tube according to claim 5, wherein said constant focusing voltage on which said dynamic focusing voltage is superimposed is said constant focusing voltage applied to said first grid electrode. .Iaddend. .Iadd.9. An in-line type cathode ray tube comprising: an electron gun assembly disposed in a neck portion of a glass envelope of said cathode ray tube, said electron gun assembly including   a cathode electrodes stage,   a front focusing electrodes stage, and   a rear focusing electrodes stage, said front and rear focusing electrodes stages being sequentially disposed in a direction of an axis of said cathode ray tube,   said front focusing electrodes stage having at least a first grid electrode and a second grid electrode, at least one of said first and second grid electrodes having a surface thereof confronting the other of said first and second grid electrodes and provided thereon with plate shaped projections for apertures formed in said at least one of said first and second grid electrodes, said apertures being arranged for passing electron beams emitted by said cathode electrodes stage;   means for applying a constant focusing voltage to said first grid electrode;   means for applying to said second grid electrode a dynamic focusing voltage superimposed on a constant focusing voltage which dynamic focusing voltage gradually varies as a function of the deflection of an electron beam so as to asymmetrically converge the electron beam to produce substantially the same beam spot configuration on said tube for any deflection of said beam; and   means for applying a high voltage to said rear focusing electrodes stage. .Iaddend. .Iadd.10. An in-line type cathode ray tube according to claim 9, wherein said constant focusing voltage on which said dynamic focusing voltage is superimposed is said constant focusing voltage applied to said first grid electrode. .Iaddend.