GB463896A - Improvements in or relating to oscillights or cathode ray tubes - Google Patents

Abstract

463,896. Cathode-ray tubes; television receivers. FARNSWORTH, P. T. Feb. 28, 1936, No. 6076. [Classes 39 (i) and 40 (iii)] The screen 14 on which the image is reproduced by means of a cathode-ray beam A is arranged obliquely to the beam and the beam is kept in focus in the plane of the screen, during its magnetic deflection to scan the screen, by an auxiliary magnetic focusing field which is produced by the current passing through the deflecting coils and which thus varies with the angle of deflection. The alternating current passing through the deflecting coils 23 may be passed through coils 17, 18 which also carry direct current and produce a longitudinal focusing field, or the deflecting coils may be inclined to the axis of the cathoderay tube 1 so as to produce a varying component in the longitudinal focusing field. As shown in Fig. 1, the coils 17, 18 are of different diameters with adjacent ends approximately in the same plane. Between the coils 17, 18 are arranged the coils 23 and also a lens 27 for projecting an enlarged picture on to a screen 28, perpendicularly from the side of the screen 14 bombarded by the beam A. The screen 14 has a metal backing connected to the anode 6. The plane of deflection by the coils 23 is rotated through 90‹ by the longitudinal focusing field. The high-voltage anode conductor 12 is insulated from a surrounding metal shield ,13 and passes into a metal container 48 to engage a spring contact 50. In a modification, the undeflected cathode ray strikes the top edge of the screen 14 and the coils 23 carry pulsating current to deflect the ray downwards. The focus of the beam is then varied by the component of the deflecting field in the deflected direction of the ray instead of, or in addition to, by fluctuations in the current through the coils 17, 18, or through focusing coils separate from the coils 17, 18. Specification 445,094 is referred to.