| 摘要 |
A 90 percent electron gun aperture astigmatism is used in conjunction with a four-pole electromagnet to make a CRT electron beam just focus point and minimum beam width occur closer to the same focus voltage. A single grid 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 is positioned around the focusing grid and current driving the electromagnet is varied with beam position during normal operation. |
