GB668161A - Improvements in cathode ray tubes - Google Patents

Abstract

668,161. Cathode-ray tubes. BRITISH THOMSON-HOUSTON CO., Ltd. June 30, 1947 [July, 2, 1946], No. 17197/47. Class 39 (i). in a cathode-ray tube, the accelerating electrode 5, Fig. 1, and anode 6 are separated by a gap oblique to the axis so as to provide an electrostatic field with a transverse component, a permanently magnetized ring 7 is arranged around the tube neck to provide a transverse magnetic field, and the arrangement is such that the electric and magnetic deflections are in opposite sense so that the device serves as an ion trap. Preferably a second permanentlymagnetized ring 8 giving a weaker field than the first ring 7 is provided to give any desired final degree of centring of the beam; it may give a deflection in the same sense as or oppositely to that of the first ring 7. The rings 7 and 8 are mounted on a rubber tube 9 and are independently rotatable about the axis to give the desired adjustments. The magnets 7, 8 are split spring rings of copper-nickel-iron alloy and are magnetized to give north and south poles at restricted circumferential regions thereof. To assist in concentrating the field of ring 7 a pair of L-shaped polepieces are provided inside the tube and secured to accelerating electrode 5 by tabs, Fig. 2 (not shown). Thus by [rotating ring 7 the field strength is varied. The cathode 2 is mounted within a cupshaped control electrode 3, and the device has a fluorescent viewing screen. The Specification as open to inspection under Sect. 91 shows further tube details. An indirectly heated cathode 4, Fig. 2 (Cancelled), is supported by insulating disc 7 and is positioned and retained by washers 8, 9, 10 within control electrode 5. The latter is carried by flanged collar 11 attached to leads 3. The gun electrodes 5, 14, 15 are held in spaced relation by lugs 13, 16 sealed to four glass supports 12 and the gun as a whole is positioned in the neck by spring fingers 19 contacting wall coating 20 of " graphite solution." Coating 20 extends almost to the fluorescent screen of the device and has a terminal in the bulbous portion of the tube, Fig. 1 (Cancelled, not shown). An external coating is applied to the bulb and is capacitatively coupled to the internal coating. The fluorescent screen may comprise " medium persistent phosphors." The anode cylinder 15 is closed at one end by disc 17 with a central aperture for the ion-free electron beam. A cap 21<SP>1</SP> with pins 22 is secured to the tube by cement 23. It is suggested that one of the magnet rings may be axially adjustable as well as rotatably adjustable. This subject-matter does not appear in the Specification as accepted.