Color picture tube having an inline electron gun with built-in stigmator

Claim 1

In a color picture tube having an inline electron gun for generating and directing three electron beams, a center beam and two side beams, along initial coplanar paths toward a screen of said tube, said gun including a main focus lens for focusing said electron beams, the main focus lens being formed by two spaced electrodes each having three separate inline apertures therein, a center aperture and two side apertures, each focus lens electrode also including a peripheral rim, the peripheral rims of the two electrodes facing each other, and the apertured portion of each electrode being within a recess set back from the rim, the improvement comprising each of the apertures in each of said focus lens electrodes having a shape that distorts a portion of the focus lens thereat to at least partially compensate for an astigmatic effect within said tube that acts on an associated electron beam, the side apertures in both of said electrodes being nonsymmetrical about axes that pass through the centers of the respective side apertures and are perpendicular to the initial coplanar paths of the electron beams, the apertures in one of the focus lens electrodes being of different shapes than the corresponding facing apertures in the other focus lens electrode, and the shapes of the apertures in one of the focus lens electrodes providing a similar compensation on the respective electron beams in a converging portion of the main focus lens that is provided by the different aperture shapes of the other focus lens electrode in a diverging portion of the main focus lens.