GB790427A - Improvements in or relating to cathode-ray tubes and circuits therefor - Google Patents

Abstract

790,427. Electron lenses. PHILIPS ELECTRICAL INDUSTRIES, Ltd. Feb. 9, 1955 [Feb. 9, 1954; June 28, 1954], No. 3854/55. Class 39(1). Reduction of astigmatism and coma in a cathode-ray tube comprising a plurality of electron guns producing a composite ribbon beam for colour or stereoscopic television viewing, is produced by making the width of the composite beam parallel to one direction of scanning deflection, and the meridional image surface of this direction of deflection and the sagittal image surface of the other direction both coincident with the surface of the screen. The theoretical bases for the correction two systems of deflection coils for the purpose are described. The C.R.T., Fig. 3, has three guns 22, 23, 24, the beams passing through a focusing coil 26 and a deflecting system comprising two half coils 27a, 27b for one direction and two half coils 28a, 28b, Fig. 4, for the other. The half coils are unsymmetrical as shown, the amount of the tube unembraced at the coil ends varying between limits calculated in the Specification. In Fig. 8, two ferromagnetic rings 33, 34 surround the neck of the tube, each carrying eight coils wound toroidally. The X and Y deflection systems each comprise four coils wound on ring 33 and four on ring 34, two of each set for the X system being shown at 35, 36 and 39, 40 respectively. The coils in dotted line 45, 46 and 49, 50 are part of the Y system. 'The angles subtended by the coil pairs are 25 degrees, 33 degrees, 43 degrees and 20 degrees respectively, Figs. 9a-10b (not shown). The eight coils in each set are connected as two parallel groups of four coils in series, each series connection including part of an inductance coil having an adjustable core, Fig. 11 (not shown) ; or as a series connection between the supply 61, 62, the asymmetrically variable impedance 59, 60 lying across the supply with its mid point connected to the point between the two groups of coils 45- 48 and 49-52 as in a bridge circuit.