GB683491A - Improvements in or relating to electron beam electric discharge tubes wherein an electron current is formed into a beam - Google Patents

Abstract

683,491. Cathode-ray tubes. PHILIPS ELECTRICAL INDUSTRIES, Ltd. May 11, 1950 [May 14, 1949], No. 11772/50. Class 39(i) In a cathode ray tube of the kind in which an axial potential gradient is set up along one or more concentrating electrodes of high resistance material by current flow therethrough, at least 30 per cent of this current consists of electrons from the beam. If the concentrating electrode voltages vary slightly the number of electrons collected thereby also vary in such a manner as to maintain the focusing constant. The concentrating electrodes may be of semiconducting material or of insulating substance coated with such material and the effective resistance in the direction of the beam is 1-5 megohms. In one form, Fig. 1, two flat concentrating electrodes 3, 4 are used with a flat electron beam, and both ends of each of the concentrating electrodes 3. 4 are connected to an external battery. Under the action of deflecting plates 5, 6 the beam falls on anode 7 or 8. In a modification, Fig. 2 (not shown) the ends of the concentrating electrodes adjacent to the cathode are connected to the cathode instead of having separate external leads. In this case the current from the beam is about half the current through the concentrating electrodes, and the Wehnelt cylinder 2 may be dispensed with. In another modification, Fig. 3 (not shown) the concentrating electrodes are left entirely free at their ends adjacent the cathode so that only current from the beam can flow through them. In another form, Fig. 4, the beam is convergent and the concentrating electrodes 14, 15 converge correspondingly. In all forms the beam may be of circular section in which case a single cylindrical concentrating electrode is used, and the electrodes 7, 8 'may be replaced by a fluorescent screen or by a single collecting electrode. Further deflecting plates, accelerating electrodes, diaphragms may be provided. The beam may be divergent instead of parallel or convergent. Since the collected electrons do not all traverse the concentrating electrodes through their entire length the potential may be made to vary as x <SP>4</SP>/ 3 where x is the distance from the cathode while keeping a constant resistance per unit length, which is the condition required for maintaining a parallel beam. A prior art arrangement is described in which the current through the focusing electrode is produced solely by an external battery and in which the desired x <SP>4</SP>/ 3 variation is obtained by making the electrode conical or by compressing it more at the end adjacent the cathode so as to make the resistance per unit length increase with distance from the cathode.