GB776351A - Improvements in or relating to cathode-ray tubes - Google Patents

Abstract

776,351. Cathode ray tubes. PHILIPS ELECTRICAL INDUSTRIES, Ltd. April 26, 1954 [April 29, 1953], No. 11987/54. Class 39(1). A cathode ray tube has a side tube for trapping loose particles and one or more funnel-shaped partitions separating the main and side tubes, each partition having one or more apertures through which loose particles can be shaken into the side tube, and the apertures being so placed in relation to the convexity of the partitions that the particles are prevented from returning into the main tube. This removes patches in the image on the screen of a cathode ray tube due to loose particles of solid material collecting on the screen, especially when the tube is operated with the screen facing downwards. The partition is conical or dished and has one or more small openings at the parts of the partition which are most remote from the screen. The tube is shaken (by a machine in manufacture or manually while in use) so that the particles pass through the small opening(s) in the partition, the conical shape of the latter preventing their return. The loose particles may be (a) emissive material detached from the cathode, or from glass or ceramic support rods during testing of the tube, (b) luminescent particles from the screen, (c) carbon or aluminium particles from the wall coating. The screen may be a luminescent or glow screen and the tube may be used for oscillography or television purposes, especially for projection television where operation of the tube with the screen facing downwards is stated to simplify the optical projection system and to reduce the total size of the apparatus. The partition is in a side tube adjacent to the screen and there may be a plurality of partitions one behind the other. Various forms and arrangements of partitions are described ; in one of them, Fig. 6, two oppositely facing partitions 17, 18 are disposed in a side tube 16. Partition 18 is clamped or sealed directly or with enamel to the side tube wall and has a central opening, while partition 17 has four arcuate openings at its outer edge and is secured to the side tube by four tags. Two inverted W-shaped partitions one behind the other and each having a set of four holes, the sets of holes being offset, may be used, Figs. 7, 8 (not shown). The partitions may be of Ni or Mo.