Convergence means for a plural beam color picture tube

Abstract

In a color cathode-ray tube of the plural-beam type wherein the beams originate on a horizontal or vertical straight line and are directed into fields produced by a horizontal-vertical electromagnetic deflection yoke at predetermined incident angles to each other so as to converge at a color screen, magnetic shielding means, for example, secured to electron beam convergence plates, are disposed for selectively shielding at least one of the beams from the leakage flux produced by the horizontal-vertical electromagnetic deflection yoke in deflecting the beams in the direction of the line of origination thereof, whereby such leakage flux acts selectively on only the unshielded beam or beams for correcting a deviation between the positions of rasters on the color screen produced by the plural beams.

What we claim is: 
     
       1. In a color cathode-ray tube having means generating plural beams .Iadd.including a central beam and opposite side beams which originate in a common horizontal plane and .Iaddend.which are directed, at predetermined incident angles to each other for convergence on a screen, through horizontal and vertical deflection fields produced by electromagnetic deflection means and by which said beams are made to scan said screen, the improvement comprising magnetic shielding means disposed .Iadd.in advance of said electromagnetic deflection means .Iaddend.adjacent the paths of said beams through said deflection fields and being operative to .[.selectively.]. .Iadd.equally .Iaddend.shield .[.at least one of.]. said .Iadd.opposite side .Iaddend.beams from leakage flux from said horizontal deflection field while permitting said leakage flux to act on .[.another of said beams.]. .Iadd.said central beam .Iaddend.for correcting deviations between the rasters of said plural beams on said screen. .[.2. A color cathode-ray tube according to claim 1, in which said plural beams originate in a common plane and include a central beam and opposite side beams, and in which said magnetic shielding means are positioned to permit only said central beam to be acted upon by 
     
     
        said leakage flux while shielding said side beams therefrom..]. 3. A color cathode-ray tube according to claim .[.2.]. .Iadd.1.Iaddend., in which said magnetic shielding means includes two spaced-apart shielding members disposed at outer sides of the paths of said side beams and being shaped to collect and to direct around said side beams the leakage flux that 
     
     
        would otherwise act on said side beams. 4. A color cathode-ray tube according to claim 3, in which each of said shielding members includes a substantially straight portion extending substantially parallel to and in spaced relation to the straight portion of the other shielding member, and end portions at the ends of said straight portion and being directed at substantial angles to the latter in the direction toward the corresponding 
     
     
        end portions of the other of said shielding members. 5. A color cathode-ray tube according to claim 4, in which .[.said common plane is horizontal and.]. said straight portions of the yoke members extend substantially vertically so that said shielding members collect and direct around said side beams the leakage flux from the horizontal deflection 
     
     
        field in the lateral regions through which said side beams pass. 6. In a single-gun, plural-beam color picture tube which includes a color screen having arrays of color phosphors and beam-selecting means provided with apertures corresponding to said arrays, beam-generating means for directing a central electron beam and two side electron beams in a common plane toward said screen for impingement on respective phosphors of each array through the corresponding aperture, lens means for focusing said electron beams on said screen and having an optical center at which said beams are made to cross each other with said side beams emerging from said lens means along paths lying in said plane and which are divergent with respect to the central beam, electron beam convergence deflecting means operative, upon the application of a convergence deflecting voltage thereto, to deflect said side beams emerging along said divergent paths for convergence of all of said beams at an aperture of said beam-selecting means, and deflection yoke means having sweep signals applied thereto to provide fields which deflect said beams in directions respectively parallel and at right angles to said plane for causing said beams to scan said screen; the improvement comprising magnetic shielding means disposed .Iadd.in advance of said deflection yoke means .Iaddend.adjacent the exit from said convergence deflecting means and shielding only said side beams from leakage flux from said field which deflects said beams in said direction parallel to said plane while permitting said leakage flux to pass unimpeded in a zone through which said central beam passes for correcting deviations in the direction of said plane between the positions of the rasters on the color screen produced by said beams in scanning said 
     
     
        screen. 7. A single-gun, plural-beam color picture tube according to claim 6, in which said magnetic shielding means includes spaced-apart shielding members arranged at the outer sides of said side beams and each having a substantially straight portion at right angles to said plane and end portions at the ends of said straight portion and being directed inwardly at substantial angles to the latter.