| 摘要 |
PURPOSE:To enable automatic regulation of cut-off without damaging the picture image by providing a beam shielding grid between second grid and acceleration grid of electron gun then applying negative voltage and detecting the beam current produced in second grid. CONSTITUTION:A beam shielding grid 7 is provided between second grid 4 and acceleration grid 5 of electron gun to be employed in color picture tube. Under normal operation, the grid 7 is applied with same voltage with that of second grid 4 from power source 8 to converge the electron beam 11 through an electron lens containing an acceleration electrode 5 thus to display a picture image. When detecting current for the purpose of bias control, negative voltage is applied from the power source 10 onto the grid 7 to detect the beam current produced by trapping the beam 11 in second grid 4 through a resistor 12 and feed back from an arythmetic unit 13. Since the beam current can be detected without emitting light from the fluorescent screen, influence of automatic regulation of cut-off onto the picture image can be eliminated.
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