Deflection and Convergence in Color Kinescopes

This paper discusses the magnetic deflection of a number of closely spaced convergent electron beams as used in the three-gun shadow-mask color kinescope, or in the one-gun shadow-mask tube. The entirely different deflection problem of a line-screen color tube, which uses a raster of precisely straight lines, is also considered, but in less detail. The shadow-mask color kinescope requires the beams to strike the same spot on the raster, regardless of which part of the deflecting field region is being traversed. A uniform magnetic deflecting field yields only approximately the desired result since large deflection angles and a plane screen complicate the problem. An experimental arrangement, for yoke design-timming, utilized a single-beam black-and-white or color kinescope with the electron-optics of the one-gun shadow-mask color tube. A rotating magnetic field near the gun produced a conical scan. The rotating beam was next passed through a convergence lens. With adjustable dc currents through the yoke, it was possible to study the convergence at each beam position as a closed pattern on the phosphor screen; a small spot was desired at all deflection positions. Test yokes were built with distributed winding sections, each shunted by a variable resistance to adjust its contributions to the deflecting field. The dc in the coil of the convergence lens was varied as a function of the radial deflection angle to yield best convergence over the entire raster. Adjustable magnetic "compensating tabs" at the forward end of the yoke aided in achieving a final best result.