GB843340A - Improvements in or relating to circuit arrangements for the image-deflection and line-deflection coils of at least two cathode-ray tubes - Google Patents

Abstract

843,340. Cathode-ray tube circuits. PHILIPS ELECTRICAL INDUSTRIES Ltd. Feb. 5, 1959 [Feb. 8, 1958], No. 4114/59. Class 40(7). In a bridge circuit for the deflection coils of a system of cathode-ray tubes whose axes intersect at one point and some of whose axes are in the same plane, the distortion due to the non- parallelism of the axes is corrected by feeding one of the bridge diagonals with a correcting signal. For a system of three projection tubes, 1, 2, 3, Fig. 1, the image appearing on a screen perpendicular to the axis b and situated at P will be formed of three images 4, 5, 6, Fig. 2, and contains linear and trapezoid distortion. If, in Fig. 2, the line deflection is horizontal and the frame deflection vertical, linear correction may be obtained by feeding a parabolic current, Fig. 4 (not shown), to the line deflection coils, and trapezoid correction by feeding a current as in Fig. 5 (not shown) to the frame deflection coils. In a bridge circuit according to the invention for trapezoid correction the frame coils 11, 22, 33 of the tubes 1, 2, 3, are connected as shown in Fig. 6, impedances 7, 8, 9 being equal in value and the coils 11, 22, 33 being assumed to be equal in impedance. Frame deflection currents from a source 30 feed all three coils equally. The trapezoid correction signal source 31 is connected to the other diagonal and feeds current to coils 11 and 33 but not to coil 22. As the circuit is a bridge the sources 30 and 31 have no effect on each other. A similar circuit is used in connection with the line coils to correct for linear distortion. In a practical arrangement of Fig. 6, Fig. 8 (not shown) the sources 30, 31 are coupled to the bridge through transformers. Where four tubes are used, any two being in the plane of symmetry of the other two, the circuit of Fig. 10 (not shown) may be used. In this circuit the diagonal 23-10, Fig. 6, is formed by a second bridge circuit having two of its interconnected arms made up of the frame coils of the two tubes not used in the main bridge circuit. A linear correction signal source is connected in the remaining diagonal of the second bridge.