GB736987A - Improvements to or relating to cathode ray pick-up tubes or the like - Google Patents

Abstract

736,987. Television pick-up tubes. L'OUTILLAGE, R. B. V. Jan. 6, 1953 [Jan. 8, 1952], No. 390/53. Class 39 (1). In a pick-up or like tube with a plane photocathode spaced from a curved storage target, the photo-cathode and scanning gun both face the concave side of the target, the photoelectrons are focused and accelerated by an electron lens and the centre of deflection of the scanning beam coincides with the centre of curvature of the target. In a low velocity beam scanning arrangement the optical image is projected on to photo-cathode 4 and the resulting electron image focused and accelerated by immersion lens 20, 21, 22 sets up a charge image on target 5 which is scanned by the low velocity beam from gun 10, 11, 12. The output can be taken from signal plate 7 or by passing the returning electrons to a multistage multiplier 27. Target 5 is shaped as a spherical cap and may be of glass which charges by secondary emission or of electron bombardment induced conductivity material such as CdS. Second anode 13 is a wall coating interrupted near the target 5 to form two or more ring electrodes 17, 18, 19 at decreasing positive potentials to decelerate the beam and ensure its normal approach to the target. Electron lens 20, 21, 22, electrode 22 which is connected to wall coating 13 and has diaphragm 30 at the cross-over point, is designed to correct the field curvature to compensate for the fact that the optical image and photo-cathode are plane while target 5 is curved. The construction of rings 17-19 is such as to minimize interaction between the two sections of the tube. If a high velocity scanning beam is used, interaction minimizing design is unnecessary and rings 17-19 may be omitted or kept at the potential of second anode 13.