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A new electron gun has been designed by developing an asymmetrical main lens with horizontally large and vertically small lens diameters. The electron gun provides a good focus performance improving the spot distortion at the screen periphery with an available dynamic voltage in 29.1mm neck diameter for 76cm 120-degree 16:9 color TV tubes.

The spot distortion at the screen periphery of an in-line self-converging CRT is formulated by considering four factors; (a) oblique incidence of the beam at the screen periphery, (b) increased path length of the beam, (c) beam compression due to the deflection, and (d) the astigmatism due to the deflection field. The analytic spot size calculated with the formulas agrees well with measurement, though the effects of a particular gun system, spherical aberration, and space-charge repulsion are not taken into consideration in the formulas while assuming an ideal deflection field. The analytic formulas enable easy evaluation of spot distortion at the screen periphery because they give an intuitive understanding of beam behavior in the in-line self-converging system. In addition to the derivation of the formulas, "transposed scanning" is analyzed with the use of the formulas for one of the ways to optimize the spot distortion at the screen periphery.

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