| 摘要 |
An electron gun for a color cathode ray tube includes a cathode, control and screen electrodes forming a triode, 1st to 3rd focus electrodes forming a first unipotential prefocus lens, 4th and 5th focus electrodes forming a second unipotential prefocus lens with the 3rd focus electrode, a 6th focus electrode forming a bipotential prefocus lens with the 5th electrode adjacent thereto, and an accelerating electrode for forming a bipotential main focus lens with the 6th focus electrode. Vertically-elongated electron beam passing holes are respectively formed in the outgoing planes of the 1st, 3rd and 5th electrodes and horizontally-elongated electron beam passing holes are respectively formed in the incoming planes of the 3rd, 5th and 6th focus electrodes. The 2nd and 4th focus electrodes are supplied with a predetermined first static focus voltage, the 3rd and 5th focus electrodes are supplied with a second static focus voltage higher than the first static focus voltage, and the 1st and 6th focus electrodes are supplied with a dynamic focus voltage which is synchronized with a deflection signal and whose negative peak equals the second static focus voltage. The astigmatism of an electron beam spot on the periphery of the screen is improved using a dynamic quadrupole lens, thereby forming an almost circular beam spot with a small halo. Also, the focusing distance is adjusted by the dynamic variation of the intensity of a main lens, so that the spot size formed on the periphery approaches that on the center of the screen.
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