摘要 |
A 90 percent electron gun aperture astigmatism is used in conjunction with a four-pole electromagnet (52a-52d) to make a CRT electron beam (54) just focus point and minimum beam width occur closer to the same focus voltage. A single grid (34) may have the 90 percent astigmatism, or astigmatisms in two or more grids may combine to produce an effective 90 percent astigmatism. A four-pole electromagnet (52a-52d) is positioned around the focusing grid and current driving the electromagnet is varied with beam position during normal operation.
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