| 摘要 |
In a circuit for controlling beam current in an image pick-up tube, suitable bias potentials are applied to the photo-conversion layer and the control grid electrode of the image pick-up tube, and a periodical beam blanking bias is applied to the cathode electrode by means of first and second switching devices, such as transistors, connected in series between different reference potentials with a junction point between the switching devices being connected to the cathode electrode of the pick-up tube, and with a blanking pulse signal controlling the first and second switching devices so tha the latter act in a complemental manner. There is further provided an optimum beam current setting circuit for assuring discharge of the photo-conversion layer of the pick-up tube by the electron beam regardless of changes in brightness of the object image projected on the target electrode, and a circuit for maintaining a desired excess beam current between that at the target electrode and the beam current at the cathode electrode of the pick-up tube.
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