Ferromagnetic screening caps and demagnetizing coils for color picture tubes having rectangular display screens

摘要

1,171,138. Demagnetizing cathode-ray tubes. PHILIPS ELECTRIC & ASSOCIATED INDUSTRIES Ltd. 17 Nov., 1966 [20 Nov., 1965], No. 51552/66. Heading H4T. [Also in Division H1] A ferromagnetic substantially conical screening cap for a rectangular screen colour television picture tube having recesses 2 (Fig. 1) to accommodate the tube support lugs is provided with two demagnetizing coils 5, 5 wound with portions 6, 6 (see also Figs. 3 and 4) outside the edges 3 of the cap so that the latter form cores for the coils and the invention is characterized that the coils, before following a generating line of the conical portion, extend along the edges as shown at 7 over a distance which is at least 1/6 and at most 1/3 of the length of the longer sides of the tube screen. The arrangement provides an even horizontal magnetic field (Fig. 2, not shown), when an alternating current of decreasing amplitude is supplied to the coils at each switching-on of the apparatus utilizing known techniques, which is stated to remove magnetization of the ferromagnetic components of the tube, due e.g. to the switching on-and-off of electrical apparatus in the proximity of the tube and to changes in the direction of the latter with respect to the horizontal component of the terrestrial magnetic field. In the arrangement of Figs. 3 and 4 the anti-implosion band 11 of soft ferromagnetic material forms a pole shoe for the cap 10.