Patent GB-666224-A (GB)
Title: Improvements in or relating to electron discharge devices
IPC: H01J31/06
Filed: 1948-08-18
Abstract: 666,224. Cathode-ray tubes. WESTERN ELECTRIC CO., Inc. Aug. 18,, 1948 [Sept. 6, 1947], No. 21771. Class 39 (i). [Also in Group XL (b)] A cathode-ray tube for use as a receiver in a multichannel or time division multiplex communication system comprises a plurality of circularly arranged targets 33A, 33B, Fig. 2, mounted on an insulating disc so that they are inclined to the radial, and means for sweeping the beam in a saw-tooth path over the targets so that it sweeps along each target at the inclination thereof. As shown, the mica disc 31 carries tapered rectangular shaped targets 33A, 33B and an equal number of metallic shields 39, 41 comprising base portions 39 attached to the disc 31 and upstanding zshaped portions 41, the intermediate parts of which extend between adjacent targets. The targets may or may not be secondary emissive, e.g. they may be of silver-magnesium alloy or may be coated with secondary emissive material. The shields 39, 41 collect the secondaries and are treated or coated to minimize secondary emission therefrom. The targets 33A, 33B are locked'to the disc 31 by tabs, Fig. 3 (not shown) and are provided with individual leads The cathode-ray tube, Fig. 1, comprises electron gun 13 ... 15 of which control electrode 14 and focusing anode 15 are held in spaced relation by discs 19, 20 and insulating bodies 21. Two pairs of deflecting plates 23, 24 in quadrature are supported from disc 20 by insulating bodies 22, and frusto-conical metal shield 25 is also carried by disc 20. Insulating rods 26 support and space frustoconical shields 25, 30 and frusto-conical deflecting electrode 29, being secured thereto by U-shaped brackets 27 and cement 28. The mica disc 31 is mounted in a shoulder 32 on the shield 30. Cylindrical deflector electrode 44 which co-operates with deflecting electrode 29 is supported from the disc 31 by flanged collars 45. The individual target leads 35 and lead 46 to deflecting electrode 44 are brought out to separate terminals 36 carried by insulating support 37 within dished shell 38 secured to the envelope 10. The shields 39, 41 are all connected together by tabs, Fig. 3 (not shown), and connected to a terminal 36 via lead 43. In operation the beam is deflected in a circular path by plates 23, 24 and is then subjected to a saw-tooth voltage applied between electrodes 29, 44 which produces the required saw-tooth trace. The output coupling to the individual target terminals may be of resistance-condenser form or of transformer type. The input signal which may be amplitude modulated or pulse length modulated is applied to control electrode 14; the input circuit is so arranged that the beam is suppressed during the normally radial transits between the targets. The width of the targets is greater than, and the length several times greater than, the beam diameter. Stray secondaries from shield members 41 are collected by the shield 30. In a modification the targets are not secondary emissive and a mask having apertures of the form and arrangement of the targets is placed between the gun and the targets. In another modification the parts of the trace between the targets are non-radial.