GB686093A - Image pick-up tube - Google Patents

Abstract

686,093. Cathode-ray tubes. RADIO CORPORATION OF AMERICA. Dec. 20, 1948 [Dec. 20, 1947], No. 32914/48. Class 39(i) in an image pick-up tube of the low velocity beam type, the target reflects varying portions of the beam and provides scattered electrons in proportion to those landing on the target and provision is made to increase the inherent spiral motion of the beam electrons to cause the reflected electrons to spiral outside the majority of the scattered electrons in the return beam, and means are provided for selecting'the scattered electrons for the output signal. Electrons from gun G are focused and deflected by coils 36, 37 or electrostatic means and pass through lifting plates 44, 45 to the double-sided target T consisting of a semi-conducting glass 27 closely adjacent signal screen 28 and tautly across the electrode cylinder. 29. An axially adjusting compensating coil 40 is provided. Other electrodes comprise a field anode 31, a wall coating or cylinder 33, an anode ring 34 with a fine mesh screen 35 for decelerating the beam. The electron gun G is the central part of a block 20 containing an electron multiplier M and the electrons emerging therefrom are given a extra lateral velocity component by means of two small deflection plates 42 close to the gun aperture. The lifter anodes 44, 45 displace the beam before and after the low velocity scanning of the target, and the extra spiralling velocity causes separation between the reflected electrons and those scattered electrons produced by the " light'' parts of the target. A separator disc 32a with either a straight or a circular edge and integral with the persuader 31 is so positioned at an antinode of the returning spiral beam as to receive the external part of the beam which contains the reflected electrons, and allows the inner portion of scattered electrons, which is modulated by the image, to proceed through to aperture and fall on the first dynode of the multiplier M. The spiralling of the beam may also be created by disalignment of the gun or by adjustment of the alignment coil 40. The target T is made slightly positive relatively to the cathode to allow for loss of electron speed due to spiralling. The screen 35 also prevents scanning of the first dynode. In a modification (Fig. 9, not shown), the gun is mounted above the axis of the tube, and the separator disc is part of the front end of the anode cylinder, an opening for the scattered electrons being pressed out the bent metal forming the first dynode of the multiplier. The target in the tube may be single sided.