GB1165002A - Improvements relating to Cathode Ray Tubes and Focusing and Deflecting Arrangements Therefor. - Google Patents

Abstract

1,165,002. Cathode-ray tubes. ELECTRIC & MUSICAL INDUSTRIES Ltd. 15 Sept., 1966 [25 Sept., 1965], No. 40904/65. Heading H1D. The electron-optical system of a cathode-ray tube includes a first cylindrical lens formed at the entrance end of a first pair of deflection plates by co-operation with a preceding pair of plate electrodes, for focusing the electrons in a line focus perpendicular to the plane of deflection, and a fine mesh grid positioned between the first and a second pair of deflection plates, to form with the second pair a second cylindrical lens for focusing the electrons in a line focus perpendicular to the second plane of deflection, whereby, by choice of the potential applied to the mesh grid, the curvature of the image field may be controlled to render the focus of the beam more uniform over the target area of the tube. In a videcon tube having a target 1, the plates 3 are held at a low potential relative to the mean potential of the deflection plates 4, to form a convergent cylindrical focusing lens therewith, while the fine mesh electrode 5, which may be held at the mean potential of plates 4, provides a lens action which varies with the deflection voltage and may be used to counteract curvature of the image plane introduced by the succeeding deflection plates 6. Electrode 5 forms with plate 6 a second converging cylindrical focusing lens, the variable component of which has little effect on image curvature due to its position at the pre-deflection end of plates 6. A second mesh grid may be positioned on the target side of the plate 6, and both the mesh grid or grids and the deflection plates may be curved. In modified arrangements the plates 6 may be of stepped form (Fig. 4, not shown), and plates 3 may overlap plates 4 (Figs. 5(a) and 5(b), not shown).