| 摘要 |
PURPOSE:To make characters of teletext more visible by raising a collector potential of a transistor for amplifying each original color output when there is a YM signal of teletext and lowering the luminance on a CRT. CONSTITUTION:Original color signals processed in a video processing circuit 1 are supplied to bases of respective output amplification transistors (TR) TR1- TR3, amplified and impressed to respective cathodes of color cathode-ray tubes 2 of their collectors. Emitter resistances R4-R6 of respective TRs are grounded through an emitter follower TR4, and adjusted in terms of bias. Where teletext is not broadcasted, a base bias of the TR4 is decided by resistances R7 and R8, while at the time of teletext, teletext synchronizing signals YM are outputted from a signal switching circuit 3. Then an A point potential rises, and a current of the TR4 is decreased. Finally a cathode potential is up, and the luminance on a CRT is lowered.
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