Degaussing device for colour cathode ray tubes

Claim 1

A degaussing device for a colour television picture tube which comprises a generally funnel shaped envelope portion having a faceplate at one end thereof, said faceplate having outer side peripheral portions, and a neck section at the other end thereof, the axial direction of the picture tube being defined as a direction extending substantially centrally through the funnel shaped envelope portion from the neck section to the faceplate, and electron beam deflection means (7) provided around the outer periphery of the neck section of the picture tube, and having a forward end portion which is located closer to the faceplate than the remaining portions of the deflection means (7), comprising: a frustum-shaped magnetic shield (6) received in the colour television picture tube and formed of a forward end portion (6a) magnetically connected to a shadow mask disposed adjacent to the faceplate of the colour television picture tube, a rear end portion (6b) set apart in the axial direction of the picture tube from the forward end portion of the electron beam deflection means (7) and an intermediate portion (6c) extending substantially along an inner wall of the generally funnel shaped envelope portion of the television picture tube; degaussing coil means (11,12) including a pair of outer coil portions (11a,12a) extending oppOsing each other along the outer side periphery of the faceplate and a pair of inner coil portions (11b,12b) extending opposing each other toward the neck section which passes between said inner coil portions, said inner coil portions (11b,12b) being on the outside of, and adjacent to, the funnel shaped envelope portion of said tube and said inner and outer coil portions being coupled with each other to form at least one loop, parts of the inner coil portions (11b,12b) being disposed substantially above the edge (6b) of the rear opening of the magnetic shield (6) and being between the rear end portion (6b) of the magnetic shield (6) and the forward endc portion (6a) of the deflection means (7), said outer coil portions (11a,12a) being positioned near the forward end portion (6a) of the magnetic shield (6) ; and a degaussing current source (14) connected to the degaussing coil means (11,12) to supply at least one graduately attentuating alternating current to the degaussing coil means so as to produce current flow in the outer coil portions (11a, 12a) in a predetermined direction relative to the tube and to produce current flow in the inner coil portions (11b,12b) in a direction opposite to said predetermined direction to thereby prodcuce degaussing flux flow which passes through both the magnetic shield and the shadow mask.