Variable magnetically biased linearity control

A variable magnetically biased linearity coil assembly for use such as with a cathode ray tube display device, comprising, in combination, an essentially I-shaped core, a coil wound on said core, a first permanent magnet stationarily mounted adjacent one end of said I-shaped core, a second permanent magnet mounted adjacent the opposite end of said core, said first and second magnets providing a magnetic field having flux lines extending through said core, a non-magnetizable support mounted adjacent said one end of said core, a cylindrically shaped element having a magnetized substantially flat surface thereon mounted on said support in spaced relation to said core and said magnets with said magnetized flat surface facing said core and said magnet, a mounting shaft extending outwardly from said support in a direction transverse to the axis of said I-shaped core for mounting said element in rotatable relation to said core and said magnets, and rotatable adjustment of said element selectively adjusting the magnetic strength of said second magnet to thereby provide an adjustable linearity coil.