| 摘要 |
An apparatus is described that can prevent the variations of luminance and color by vibration of a shadow mask in a cathode ray tube(CRT). An invadid surface 4 which is a circumference of a shodow mask 1 and a fold 5 extruded or engraved at the curved edge of a skirt part 2 are repeatedly formed. In case that the shadow mask 1 is fixed inside a frame, the fold 5 is formed inside the curved edge thereof, whereas the fold 5 is formed outside the curved edge thereof in case that the shadow mask 1 is fixed outside the frame. When an elasticity coefficient R is increased due to the fold 5, the number of characteristic vibration is proportioned to a square root of the elasticity coefficient R and thus the band of the number of the characteristic vibration is moved to that of a high frequency. Thereby, it is possible to reduce the howling of the shadow mask.
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