METHOD FOR PRODUCING A MULTIPOLAR PERMANENT MAGNETIC FIELD CONFIGURATION WHEN MANUFACTURING A CATHODE RAY TUBE AND DEVICE FOR CARRYING OUT THIS METHOD

摘要

A method of manufacturing a cathode ray tube in which magnetic poles are provided in or around the neck (4) of the envelope (1) and around the paths of the electron beams extending substantially parallel to the axis (8) of the tube, said poles generating a permanent multipole magnetic field to correct the occurring errors of convergence and color purity and frame defects of the color display tube, which magnetic poles are formed by magnetizing a configuration (17) of magnetizable material which is provided around the paths of the electron beams, which configuration is magnetized by energizing a multipole coil unit (15) by means of a combination of currents with which a static multipole magnetic field is generated and the magnetization is produced by means of a decaying alternating magnetic field which is generated by means of an alternating field coil (16) and which initially drives the magnetizable material on both sides of the hysteresis curve into saturation. When the decaying alternating magnetic field is an axial magnetic field which is substantially parallel to the paths of the electron beams, much less crosstalk occurs in the radial coils (21 to 28) of the multipole coil unit (15) than when a radial alternating field is used and the effect of the stray field components is reduced. The driving of an axial alternating field coil (16) is much simpler than of a number of radial alternating field coils.