| 摘要 |
PURPOSE:To attain a just focus corresponding to illuminance even if it varies by varying a prescribed grid voltage, and adjusting the illuminance of an image or a pattern displayed in a cathode-ray tube. CONSTITUTION:A G4 voltage control circuit 7 functions as a focus voltage control mans, and lowers the fourth grid voltage G4 of an electron gun 2 when the illuminance is at a high level at the time of receiving a first grid voltage sk, but rise the voltage G4 when the illuminance is at a low level. This means that if the movable terminal of an illuminance volume 6a is moved to pulse-side, the first grid voltage becomes higher, and the illuminance of the image in the cathode-ray tube is increased. The rise of the first grid voltage sk causes a collector current flowing through a NPN-type transistor Q2 is increased, both collector voltages of the transistors Q1, Q2 drop, and are impressed to the fourth grid G4 as a fourth grid voltage to provide a just focus corresponding to the illuminance.
|
