Electromagnetic deflection type picture tube device

Abstract

An electromagnetic deflection type picture tube has (a) a first field-control element which is disposed between the electron-beam emission end of an electron gun and a deflection yoke, comprising a pair of magnetic pieces disposed on the opposite sides of the path of an electron beam and being adapted to produce or introduce a barrel- or pincushion-like local field distortion which is opposite to a pincushion- or barrel-like deflection field distortion produced by the deflection yoke by introducing the rise portion of the deflection field; and (b) a second field-control element which is disposed between the electron-beam emission end of the electron gun and the first field-control element, comprising a pair of magnetic pieces disposed on the opposite sides of the path of the electron beam and being adapted to produce or introduce a pincushion- or barrel-like local field distortion which is opposite to the barrel- or pincushion-like local field distortion produced by the first field-control element. A positive or negative comma aberration imparted to the electron beam by the second field-control element is compensated for by a negative or positive comma aberration imparted to the electron beam by the first field-control element so that on leaving the latter, the electron beam sustains only an astigmatism, positive or negative, which is compensated for or corrected by an astigmatism, negative or positive, imparted to the electron beam passing through the deflection field. Thus, distortions of beam spots at the edges of a screen can be substantially eliminated.

Dependencies are inferred from the claim text.