GB687261A - Improvements relating to electric discharge devices - Google Patents

Abstract

687,261. Cathode-ray tubes. BRITISH THOMSON-HOUSTON CO., Ltd. July 22, 1946 [July 24, 1945], No. 21844/46. Class 39(i). An electron discharge device of the type having a fluorescent anode and two deflecting members each connectable to a separate voltage source so that the fluorescent pattern formed on the anode indicates a voltage difference between the two sources, has two coaxial deflecting members positioned substantially parallel to a rectilinear cathode and in end-to-end relationship with their end faces parallel to and at a short distance from each other to form a gap between them, and a space charge control member interposed at least partly between the cathode and anode to retard the electrons. In the construction shown in Figs. 1 and 2 the electrode assembly comprises an indirectly heated cylindrical cathode sleeve 14, a control electrode 19 and, on the opposite side of the cathode and preferably in the plane of the cathode and the control electrode and nearer to the cathode 14 than the control electrode 19, elongated deflecting electrodes 22, 23 provided with reversely extending portions 24, 25 extending through spacers 7 and 8 and connected with conductors 26 and 27 sealed to lead-in conductors. A wire helix or grid-like space charge control member 30 is supported by the rods 28, 29, the latter of which is connected by a conductor 31 with a lead-in conductor. The cathode 14 and space charge control member 30 may be connected by a conductor 32. The fluorescent screen anode is provided by a circular glass disc 33 sprayed with willemite after the glass has been rendered conducting by treatment with tin oxide and mounted in a metal frame 34.including an inwardly directed flange portion 34<SP>1</SP> masking the edge of the disc 33 to define a rectangular display opening. A conductor 36 is connected to the frame 34 and to a lead-in conductor. A metal strip 38 extends diametrically across the face of the screen and is joined at its opposite ends to the frame 34 to lie directly over the gap between the deflecting electrodes 22, 23 to collect electrons which would otherwise blur the display at the centre of the screen. In a modification the electrode assembly is mounted vertically instead of horizontally and the fluorescent screen is supported at an angle of about 45 degrees with respect to the axis of the envelope and is viewed directly. A cylindrical shield extends around the screen to exclude extraneous light. In another modification the deflecting members are formed by two space charge control members formed by wire cages or helices of different diameters in end-to-end relationship around the cathode. In another modification the space charge control member comprises a plurality of wires attached to side rods and extending in a curved path between the cathode and anode but not extending to the other side of the cathode and the deflecting members are formed by a pair of angularly bent sheet metal members in end-to-end relation, extended portions of the deflecting members providing a shield collecting electrons tending to escape from the region of the cathode to the region outside the space charge control member. A sheet metal shield extends from the control electrode to collect electrons tending to escape from the region below the cathode. The device can be used as an indicator for a combination frequency modulation-amplitude modulation radio receiver. Specification 675,261 is referred to.