| 摘要 |
At the onset of ageing or in the further course of their service life, color picture tubes relatively frequently exhibit a rise in the field strength between the cathode (K) and the Wehnelt electrode (G1) of the respective beam system on account of a blooming effect of the cathodes (K) which is known per se and reduces the spacing between cathode (K) and Wehnelt electrode (G1). The cut-off regulation reacts to an effect of this type in a manner such that the reverse voltage acting between cathode (K) and Wehnelt electrode (G1) is correspondingly reduced in order to be able to drive the same reference cathode current. However, the reaction of the cut-off regulation must be taken into account for the circuit design since this would otherwise result in an unacceptable reduction in the modulation range, which would, in turn, have an adverse effect on the maximum contrast setting.The invention provides a regulating device (10) which makes it possible to automatically compensate for an ageing-related change in the field strength between the cathode (K) and the Wehnelt electrode (G1) of the respective tube system of a color picture tube (1), the cut-off regulating voltage produced in the respective RGB color channel on account of the cut-off regulation being used as the controlled variable for the regulating device (10).
|
