GB1246198A - Cathode ray tube - Google Patents

Abstract

1,246,198. Electron lenses. SONY CORP. 19 Dec., 1969 [19 Dec., 1968], No. 62129/69. Heading HID. A focusing lens for a cathode-ray display tube comprising outer cylindrical electrodes 17a and 18a, Fig. 2, operated at a high potential and an intermediate cylindrical lens 19a surrounding the ends of the outer electrodes and operated at a lower potential, is characterized in that an auxiliary apertured electrode 30 extends between the outer electrodes to reduce the potential gradient of the lens field thereby reducing spherical aberration. In one example the electrodes 17a and 18a are operated at 20kV whilst electrode 19a is earthed. Because the electrodes 17a and 18a are connected through electrode 30 there is no need for a connecting lead between them passing round the outside of electrode 19a, so the diameter of this electrode may be increased, thereby further reducing spherical aberration. In Fig. 2 the electrode 30 is a helical wire; alternative forms comprise axial wires (Fig. 4A, not shown), an apertured cylinder (Fig. 4B, not shown), and wire rings joined by axially-extending wires (Fig. 4C, not shown). The lens may be used in a colour display tube of the type wherein three coplanar beams are directed through the centre of the lens and are subsequently converged on a shadow mask or grill by means of electrostatic deflection plates (Fig. 5, not shown).