GB641428A - Improvements in or relating to cathode ray tubes of the signal storing type - Google Patents

Abstract

641,428. Electric discharge tubes. RADIO CORPORATION OF AMERICA. April 10, 1947, No. 9605. Convention date, April 12, 1946. [Class 39 (i)] A cathode-ray tube for use in radar comprises means for focusing and deflecting a beam from an electron gun over a target, a screen adjacent and on the gun side of the target and adapted to control the flow of secondary electrons bombarded from the target, electron multipliers on the other side of the target and extending radially beyond it and means for directing the electrons escaping from the target into the multipliers. The cathode-ray tube shown in Fig. 1 contains a wall coating 12 and a persuader cylinder 13 having an opening 15 to permit entry of the deflected electron scanning beam and into which projects a flanged end 17 on a metal pedestal 16, the flanged end 17 supporting a flanged aluminium disc 18 having a slightly convex surface anodized to form a thin coating 19 of aluminium oxide constituting the target. A fine woven mesh screen 20 conductively joined to the pedestal 16 is stretched over the coating 19. Dynodes 21, 22, 23 and 24 forming part of an electron multiplier are placed around the pedestal 16, each dynode having a plurality of slanting vanes with fine mesh screens 25 spaced from but conductively attached to the metal support of the vanes, as described in Specification 634,639. The last dynode 27 of the multiplier is a metal disc without an attached screen and a collecting screen electrode 28 is placed between the dynodes 27 and 24. A metal shield 29 is welded to the pedestal 16 and a signal wire 30 is connected to the inner unoxidized surface of the disc 18. In the construction shown in Fig. 2 an asymmetrical field is produced in front of the target to prevent return of the secondary electrons to the target by cutting out about one half of the persuader cylinder 31 and replacing it by a semi-cylindrical fine-mesh screen 32. Another semi-cylindrical screen 33 is located outside the screen 32 and makes contact with the first dynode comprising a semi-cylindrical cup 34 having an inside surface of good secondary emission properties. One half of each of the other electrodes of the electron multiplier is inactive and may be cut away.