Patent GB-841832-A (GB)
Title: "improvements relating to cathode ray tubes"
IPC: H01J19/00
Filed: 1956-10-08
Abstract: 841,832. Cathode ray tubes. GENERAL ELECTRIC CO. Oct. 8, 1956 [Oct. 6, 1955], No. 30634/56. Class 39(1). The end wall of a cathode ray receiving tube preferably for colour reproduction is formed with marginal internally extending ledges which support directly or indirectly an electrode such as a colour switching or focusing grid or a shadow mask permeable to the cathode rays. The transparent face plate 15, Fig. 6, of leadglass is arcuate, substantially plane, a cylindrical segment, spherical segment or a segment of irregular configuration, and may or may not have a flange 17 ; if it has a flange 17 it is sealed to the cone also of lead glass by two metal annuli 20 welded together. The red, blue and green phosphors 21, Fig. 3, are horizontal or vertical strips or dots or squares arranged in triangular arrays, and are coated with an aluminium layer 22 (first electrode). The grid wires 24 (2nd electrode) which are all at the same potential are parallel to the phosphor strips. The ends of the grid wires are secured to ledges 26. The ledges can be metallised to give a metal to metal bond or the wires are secured to the ledges by a conductive cement e.g. a mixture of powdered aluminium silicate and aluminium phosphate in a dilute water solution of phosphoric acid as set-out in Specification 793,764 or a non-conductuive cement obtained by mixing two parts powdered glass frit, two parts powdered ferro-silicon alloy powder, three parts flint with sodium silicate diluted 1 : 1 in water. In the latter case the ends of the wires must be electrically interconnected as by bunching the wire ends as by twisting them into bunches and connecting them by a wire or by painting the wires down on the ledge by a conductive lacquer obtained by mixing silver powder with sodium silicate in water to a suitable consistency for brushing; after application balsing is used to drive off the volatile constituents. The ledge surface can be ground to conform to the shape of the face plate 15 to give uniform spacing between the wires and screen. The grid wires exercise a focusing action and 'the aluminium layer as a post-acceleration electrode. The grid wires are secured in place before the phosphor screen and its conductive layer are formed. In manufacture the plate 15 is placed flange side up beneath an array of grid wires 24, Fig. 4, held in anchoring device 30 and run over two pulleys 31 the wires being fed from a reel tensioned by a weight, Fig. 5 (not shown). The frame comprises cross bars 36 and two combs 37, the combs being received in the channels 27 formed between the ledges and flange 17 of the face plate 15. The frame 35 is moved into engagement with the wires so that the grid wires are received between the comb serrations and is then moved down to move the combs into the channels 27; the wires can now be secured to the ledges 26. Three adjustment screws or legs 39 are threaded through the cross pieces 36 and engage the face plate or some other reference surface e.g. metal annulus 20. The grid wire-face plate spacing can be uniform or vary in any desired manner depending on the configuration of the ledges and comb-teeth. In Fig. 6, the wires do not touch the ledge and are kept at a slight spacing therefrom by turning down lock nuts 40 on to cross pieces 36. The cement 25 is applied and cured or dried with the frame 35 still present so that the cement acts as a shim or filler between the wires and ledges ; accurate grinding of the ledge is therefore not necessary. The frame 35 is now removed and the projecting ends of the wires trimmed off. Finally the phosphor screen is applied to face plate 15. A light source shining through the grid wires may be used to print the phosphors parallel to the wires by a photochemical process or the light source can be replaced by an electron beam In another process the phosphor screen and conductive layer 22 are laid down before the wires are secured to the ledges. In the latter case the frame screws 39 are used to get the desired wire-screen separation before the wires are bonded to the ledges. The light source is used to throw shadows of the wires on to the screen so the wires can be fixed parallel to the phosphor strips. In a modification, Fig. 7, the groove between the ledge and side wall of the face plate has an inclined edge and a dovetailed groove or channel 43 in the ledge containing an elongated metal or glass member 45 which has an accurately ground uppersurface and is grooved, e.g. by etching, to receive grid wires 24. The frame is used to move the wires into the grooves of 45 and against the inclined edge of the ledge. The wires are now secured in place at 46 by conductive or non- conductive cement as before ; in the latter case member 45 can serve as a connection between the free ends of the wires. The face plate 15 can be marked or grooved, e.g. by etching as 45, to locate and align the phosphors correctly with respect to the grooves in 45, so the phosphor strips and grid wires are parallel. The grooves in 45 determine the grid wire-base plate spacing so screws 39 are not required. The tubes have an interior coating of high resistivity to dissipate wall charges and have three guns. The invention is not limited to colour reproducing tubes but can be applied to monochrome tubes.