GB725525A - Beam-controlling systems for tri-colour kinescopes - Google Patents

Abstract

725,525. Colour television tubes. RADIO CORPORATION OF AMERICA. Sept. 7, 1953 [Sept. 17, 1952], No. 24677/53. Class 39 (1) [Also in Group XL (b)]. Relates to an electron beam controlling arrangement for a shadow-mask tri-colour cathode-ray tube 15, such as the tube described in the Proceedings of the LR.E. Vol. 39, No. 10 at page 1194, in which the beam from a single gun 22-24 is subject to a rotating field so as to produce the equivalent of a number of component beams 18, 19 and 20 approaching the mask 17 from different angles. The invention concerns the problem of maintaining the beams convergent at a point in the plane of the mask over the whole of a scanned raster. The rotating field is produced by deflecting means 26 from which the beams emerge divergent and are converged to the plane of the mask by coaxial cylindrical electrodes 27 and 28 energized statically by the potential across resistor 32 in the tube E.H.T. supply. According to the invention the energization of deflecting means 26 is varied as a function of the horizontal and vertical deflection signals so as to vary the beam divergence and thereby the convergence according to the angle of deflection. The deflection means 26 is energized by 90 degrees phase-displaced waves at the system sub-carrier frequency which are obtained from a local synchronized oscillator 28 applying its output through 90 degerees phase shifter 42 to amplifiers 43 and 44. Included between the oscillator and phase shifter is an amplitude modulator 41 to which are applied signals at the vertical and horizontal scan frequencies. A first pair of signals comprise parabolic waves 47 and 48 applied from generators 45 and 46 and in addition a second pair of signals 49 and 50 may be applied in the form of sawtooth waves. Generators 47 and 48 may be of the type described in the Proceedings of the I.R.E. Vol. 39, No. 10 at page 1249.