Interdigital grids for dynamic astigmatism control in picture-tube guns

Astigmatism control of Coty-29 picture tubes has been achieved through the incorporation of interdigital grids in the gun-focus electrode. These grids produce quadrupolar fields so that the focusing induced in the beam's vertical ray by the self-convergent yoke is compensated, thus eliminating the vertical flare previously observed for deflecting spots. The utility of cross plots for studying astigmatic gun/yoke systems and for measuring gun and yoke astigmatism values has been demonstrated. Measurements on a number of tubes are described and the results are compared with formulas derived from paraxial equations.<
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