| 摘要 |
PROBLEM TO BE SOLVED: To satisfactorily control the luminance level of a video picture. SOLUTION: Video signals of three primary colors (R, G, B) formed in an video amplifying circuit 12 are supplied respectively to cathodes Kr, Kg, Kb through clamping circuits 13r, 13g, 13b. Moreover, a signal from the circuit 13 is supplied to a CPU 16 and, then, the format of the inputted color video signal is discriminated in the CPU 16 and prescribed variable (ADJ-VALUES) corresponding to this format are decided. Adjustments in a prescribed range are performed by a controlling input from a manual input terminal 17 with respect to these decided variables. Furthermore, values of cutoff voltages Ekcos of respective cathodes Kr, Kg, Kb and the voltage Vg of a second grid G2 are calculated by using these adjusted variables. Then, these calculated values are supplied to the clamping circuits 13r, 13g, 13b through a cathode voltage forming circuit 21 and, also, to the second grid G2 through a grid voltage forming circuit 22.
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