| 摘要 |
PURPOSE:To prevent satisfactorily the oscillations without causing complicatedness of a circuit system by setting a pair of deflecting plates at the place near an electronic gun of an image pickup tube and fixing the potential of one of both deflecting plates with the potential of the other plate set at the same level as the potential of the 1st grid. CONSTITUTION:A pair of deflecting plates 20a and 20b are set at the place near an electronic gun K of an image pickup tube 1 with inclinations given toward the scanned direction of an electronic beam. The potential of the plate 20a is set at a fixed level, and the potential of the plate 20b is set equal to that of the 1st grid G1. A signal current extracted out of a target 2 is applied to an output terminal 4 and also added 6 with the DC voltage E0 through a feed back circuit. Thus the voltage Eg1 is obtained and impressed to the griod G1. The voltage Eg1 is increased and then an electronic beam current are increased. At the same time, the diameter of a beam spot is increased. Thus the scan position of the electronic beam is biased toward an area which is already scanned. Therefore the coincidence is obtained between the scan front ends of both horizontal and vertical directions despite the increase of the diameter of the beam spot. This prevents the oscillations due to the change of the beam spot diameter.
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