| 摘要 |
PURPOSE:To reduce unnecessary electron emitting material so as to prevent the lowering of picture quality by forming an electron beam passing aperture in such a way that the curvature of the inlet on the side opposed to a higher voltage side grid electrode is made to be larger than that on the side opposed to a lower voltage side grid electrode, thereby reducing the field intensity at the aperture portion. CONSTITUTION:In electron passing apertures 28 formed on grid electrodes 11 to 13, which are subjected to unnecessary electron emitting sources by the evaporation of the electron emitting substance of a cathode 14, the curvature of the inlet on the side facing to a higher voltage side grid electrode 11 is made to be larger than that on the side facing to a lower voltage side grid electrode 13. Since the curvature of the electron beam passing apertures 28 are enlarged on the higher voltage side, the concentration of equipotential line is relaxed so as to reduce the field intensity. Therefore, even if evoparated sbustance from the cathode 14 is adhered in the vicinity of the electron beam passing aperture 28 of the second grid electrode 12, since the field intensity is reduced, the generation of unnecessary electrons from the second grid electrode is suppressed so that the preferable picture quality can be maintained.
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