Cathode-ray tube having end electrodes of three electrodes connected by helical coil coaxial with tube axis

Claim 1

A cathode-ray tube having beam producing means generating a plurality of electron beams and a phosphor screen positioned to have the beams impinge thereon said beams being made to intersect each other at a location in the tube between said beam producing means and said screen; electron focusing lens means for focusing the beam on the screen having an optical center substantially at said location where the beams intersect each other and comprising: first annular electrode means coaxial with the longitudinal axis of the tube and having one end facing the same way as the direction of movement of the electrons, second annular electrode means coaxial with said axis of the tube and having an end facing said one end of said first annular electrode means and axially spaced therefrom, third annular electrode means coaxial with said axis of the tube and extending over the space between said ends of said first and second electrode means and partly over said first and second electrode means, said third electrode means being at a potential different from the potential of said first and second electrode means to provide an electric focusing field therebetween, and auxiliary electrode means including a helical coil with spaced turns extending conductively between said first and second electrode means and coaxially with the longitudinal axis of the tube within said third electrode means and operative to reduce the potential gradient of said field.