Improvements in or relating to charge storage pick-up tubes

摘要

798,628. Cathode-ray pick-up tubes. ELECTRIC & MUSICAL INDUSTRIES, Ltd. July 4, 1956 [July 13, 1955], No. 20213/55. Class 39(1). A charge storage pick-up tube having a target electrode including a mosaic of photoemissive elements and a source of electrons for generating a beam which can be scanned over the target with a low velocity to stabilize the elements of the target at or near cathode potential is provided with means permitting electrons with relatively large transverse velocities to approach the target with the scanning beam and set up a space charge barrier in the vicinity of the scanning beam whereby secondary electrons emitted by scanning the target elements with the beam are substantially all returned thereto by the barrier. Preferably the selection of electrons with relatively large transverse velocities is done by an apertured electrode 4, Fig. 2, located in front of the gun, with a central aperture 5 passing electrons with low transverse velocities, i.e., up to about 2 volts and apertures 6 passing electrons with transverse velocities of the order of 10-40 volts. Electrons with transverse velocities between 2 and 10 volts which cause spreading of the scanning spot are suppressed by the solid portion of the electrode 4. The apertures 6 may be replaced by arcuate slits concentric with the central aperture 5. The suppression of secondary electrons by the space charge surrounding the beam is said to stabilize the tube under conditions of intense illumination. The beam is magnetically focused and scanned. In operation the electrode 4 and the preceding limiter electrode are maintained at 300 volts positive with respect to the cathode, the wall anode being at 200 volts positive.