GB1281750A - Cathode ray tube - Google Patents

Abstract

1281750 Colour television tubes SONY CORP 22 Dec 1969 [23 April 1969 26 April 1969] 62495/69 Heading HID A colour television tube of the type wherein three electron beams intersect at the centre of a common focusing system, is characterized in that the focusing system comprises a plurality of lenses. In the arrangement shown in Fig. 1 the main focusnig system comprises two equal lenses L m1 and L m2 formed respectively by electrodes G3-G5 and G5-G7. Since the power of the lenses is less than in a single lens system, the aberrations are reduced and also aberrations produced by the first lens L m1 are compensated by equal and opposite aberrations produced by the second lens L m2 . Electrode G5 may be replaced by a diaphragm with a central aperture which limits the sizes of the beams (Fig. 2,. not shown). In another modification (Fig. 3, not shown) the electrode G3 is extended inside electrode G2 by a cup-shaped portion provided with apertures which form individual stops for the beams. The lens system may be extended to include three or four lens components arranged either symmetrically or asymmetrically with respect to the lens centre O (Figs. 4-6, not shown). When the beams are converged at O by an auxiliary lens (Fig. 7, not shown) shown) instead of by the inclination of the cathodes, aberrations caused by the auxiliary lens may be compensated either by making the two lens components of the main focusing lens asymmetrical or by using two symmetrica components but displacing the centre of the system slightly from the point of intersection of the beams.