Electron gun having an extended field beam focusing and converging lens

For use in a color cathode ray tube of the small neck, shadow mask-type having an electron gun including an extended field lens for generating in the tube neck an in-line or delta-cluster of red-associated, blue-associated and green-associated electron beams converged and individually focused at the screen of the tube, said gun comprising:

• electron source means comprising associated cathode means and grid means for producing three separate beam crossovers, one for each electron beam;
• and
• three main focus lens means situated on lens axes which are mutually parallel and parallel to a gun central axis, at least two of which lens axes are off-axis with respect to the gun axis, said three main focus lens means respectively receiving electrons from said three beam crossovers and converging said beams and individually focusing said crossovers at a common location at the tube screen, said focus lens means having for each beam at least three electrodes including a focus electrode for receiving a variable potential for electrically adjusting the focus of said beam, and in succession down-beam, at least two associated electrodes having potentials thereon which focus in the gaps between adjacent electrodes significant main focus field components, the strength of a first of which components is controlled by adjustment of the voltage received by said focus electrode, the strength of a second of which field components spaced down-beam from said first component being relatively less than that of said first component;
• each of said lens means being characterized by having addressing faces of said associated electrodes which define said second field component being so structured and disposed as to cause said second field component to be asymmetrical and effective to significantly divert said beam from its path, whereby due to the relative weakness of said second field component and the separation of said second field component from said first field component, said diverting of each of said beams results in convergence of said beams without any significant distortion of the beam and substantially independently of any beam-focusing adjustments of said first field component.

For use in a color cathode ray tube of the small neck, shadow mask-type having an extended field three-beam, inline, unitized gun;

• i.e., a gun generating three coplanar beams (two outer beams and an inner beam) and having common field-forming electrodes for the three beams, said electron gun producing in the tube neck an in-line cluster of red-associated, blue-associated and green-associated electron beams converged and individually focused at the screen of the tube, said gun comprising:
• electron source means comprising associated cathode means and grid means for producing three separate beam crossovers, one for each electron beam;
• and
• three main focus lens means (two outer focus lens means and an inner focus lens means) situated on lens axes which are coplanar and mutually parallel and parallel to a gun center axis, said three main focus lens means respectively receiving electrons from said three beam crossovers and converging said beams and individually focusing said crossovers at a common location on the tube screen, said three focus lens means being in unitized form and having at least three unitized electrodes including a focus electrode for receiving a variable potential for electrically adjusting the focus of said beams, and in succession down-beam, at least two associated electrodes having potentials thereon which form in the gaps between adjacent electrodes significant main focus field components, the strength of a first of which components is controlled by adjustment of the voltage received by said focus electrode, the strength of a second of which field components spaced down-beam from said first components being relatively less than that of said first components;
• each of said outer focus lens means being characterized by having addressing faces on said associated electrodes which define said second field component being plano-parallel and defining a gap which is angled forwardly and outwardly to cause said second field component to be asymmetrical and effective to significantly divert said beams from their paths to converge at a common point on said screen, whereby due to the relative weakness of said second field component and the separation of said second field component from said first field component, said convergence of said beams is accomplished without any significant distortion of the off-axis beams and substantially independently of any beam-focusing adjustments of said first field components of said outer focus lens means.