Focusing means for cathode ray tubes

Abstract

A cathode ray tube comprising a cathode (K) for emitting a beam of electrons; a grid (G) for controlling the intensity of the beam; three or more anodes (A1, A3, A4); a control for varying the potential of at least one of the anodes (A3) for focusing the beam to form a spot on a screen; and an additional, dynamic focus electrode (A2) maintained generally at a potential close to the cathode/grid potential. Suitable structure may be included for applying to said dynamic focus electrode a high frequency signal to provide a rapid focus control. Said dynamic focus electrode may comprise a plurality of circumferentially disposed segments and including applying a separate high voltage to each segment thus allowing the possibility of creating a quadruple action in conjunction with at least one adjacent electrode, said segments covered with a deposited high-resistance conducting film to prevent charging effects. Preferably the potential of the first anode (A1) is substantially greater than the controlling voltage range of the grid (G), the potential of the static focus electrode (A3), interposed between the first and final anodes, is substantially equal to or lower than that of the first anode; and the potential of the final anode (A4) is substantially higher than that of the first anode (A1).

Dependencies are inferred from the claim text.