GB801487A - Arrangement for connecting tangential and/or radial distortions in a cathode ray beam - Google Patents

Abstract

801,487. Electromagnets; permanent magnets. RADIO CORPORATION OF AMERICA. Aug. 15, 1955 [Sept. 14, 1954; Dec. 8, 1954 (2)], No. 23498/55. Class 35. [Also in Group XL (a)] A plurality of magnets and pole forming members are mounted adjacent to and around the periphery of the multi-element screen of a C.R.T. to provide an adjustable magnetic field for correcting distortion produced in the scanning deflection. Magnets or electromagnets 50 are arranged to control the electrons in their path from the shadow mask to the multi-dot screen of a colour television tube 14. In Fig. 1, the shadow mask 20 is concentric with the curved screen 18 carrying groups of red, green and blue phosphor dots and controls beams from three guns 24, 26, 28. Two split iron rings 52, 54 encircle the tube periphery and are held by brass or other non-magnetic spacers 56 and brackets. A cylinder of plastic material separates the rings 52, 54 from the tube. The bar magnet 50 (Fig. 6) is held in a clamp 66 which is pivotally movable on a bolt 72 in a soft iron shunt 74 and a plastic supporting block 76. A conical compression spring 82 surrounds the bolt and bears against a groove 84 in the block 76. Soft iron brackets 90, 92 extend between the rings 52, 54 and the block. Rotation of the magnet enables a varying amount of magnetic flux to pass to the rings and corrects rotational and tangential colour dilution of the multidot screen 18. Radial colour dilution is corrected by providing a sectionalized inner pole forming ring 55, 55a (Fig. 11) located between the other two rings 52, 54. The magnet 50 is held on a threaded bolt 66 in its support block 74 and can be moved to bridge either the sections 55, 55a of the inner ring, or the two outer rings 52, 54. It is retractable by screw motions within a keeper block. An alternative to the single permanent magnet is the provision of two ironcored electromagnets bridging the two outer rings and the segment inner ring respectively (Fig. 13, not shown). The two ends of the ring segments 55, 55a may be upturned. In another form the permanent magnets bridge sectionalized parts of two discontinuous pole-forming rings. They may be octagonal or cylindrical and retractable into a keeper ring by means of the screw-threaded engagement of the supporting bolt with a U-spring and hushing (Fig. 16, not shown). Each cylindrical magnet 50 acts in co-operation with segments 52, 52a, 54, 54a which have inturned ends spaced from each other to provide an air gap. When the magnet is fully retracted it is short-circuited by a surrounding ring of magnetic material, but when fully extended or intermediately, field strengths are induced in the sectionalized rings, the polarity of the sections depending on the position of the magnet either longitudinally of or transverse to the rings (Fig. 18).