Three-Beam Guns for Color Kinescopes

The three-beam gun assembly for the aperture-mask tri-color kinescope consists of three guns located so that their axes are mutually parallel, equidistant from, and spaced 120 degrees about the axis of the assembly. The No. 4 grids open into a large common cup. The three electron beams are converged to a point on the aperture mask by an electrostatic lens formed between the large cup and the conductive neck coating. The focus of the individual beams is controlled mainly by the voltage applied to grid No. 3. The potentials of grids Nos. 3 and 4 may be varied in synchronism with the scanning frequencies so as to maintain beam focus and convergence over the entire screen area. The individual guns, of glass-beaded construction, are held in position by support spacers welded to eyelets around the gun cylinders. Many standard-type gun parts and manufacturing procedures are used. The beam spacing and gun placement are related to the design dimensions of the screen assembly. The guns are positioned with accurately machined, three-fingered fixtures which use the gun apertures as reference positions. Separate leads for cathodes and grids Nos. 1 and 2 of the three guns permit adjustment of grid drive charactexistics so the ratios of three beam currents are constant with grid drive. Thus, correct color is maintained, independent of changes in brightness. A variation of the parallel-beam type of gun uses a single set of cylinders in which triple-aperture disks are placed in appropriate positions.