GB1118605A - Improvements in television and television cameras - Google Patents

Abstract

1,118,605. Cathode-ray tube circuits. COMPAGNIE FRANCAISE THOMSON-HOUSTON-HOTCHKISS BRANDT. 22 Dec., 1965 [8 Jan., 1965], No. 54425/65. Heading H4T. Residual magnetism in the screens associated with a colour television pick-up tube is eliminated by producing in the screens a periodically varying magnetic field the amplitude of which is progressively decreased to zero whilst simultaneously or successively the magnetic focusing field is progressively increased from zero to its nominal value. The periodically varying magnetic field is produced by supplying the focusing coil FC (Fig. 2a) from an A.C. generator Ga controlled by means Ca to progressively reduce the amplitude of its output to zero. Simultaneously or successively therewith, determined by a pulse generator P, further control means Cc operates a D.C. current regulator R 1 , comprising e.g. the anode impedance of a pentode or the collector impedance of a transistor, to progressively increase the current in coil Ec due to a D.C. source S from zero to its nominal focusing value. The focusing coils of a plurality of pick-up tubes forming a colour television camera may, together with appropriate balancing resistors, be grouped in series (Fig. 2b, not shown), or in parallel (Fig. 2c, not shown) and connected across terminals (a, c). The members P, Ca, Cc may be housed in a casing separate from the actual camera.