GB820484A - Improvements in or relating to the manufacture of electrode structures - Google Patents

Abstract

820,484. Cathode ray tubes. ELECTRIC & MUSICAL INDUSTRIES Ltd. Feb. 27, 1956 [March 1, 1955], No. 5985/65. Class 39(1). A method of constructing an electrode structure, preferably an electron gun of a cathode ray tube, in which the electrodes are held in spaced relationship by insulators, preferably ceramic rods 5, Figs. 1, 2 comprises applying during an early stage of assembly a protective covering to the insulating material or rods 5 lying between the electrodes and keeping the covering on during subsequent stages of assembly to reduce contamination of the insulating rods 5 between the electrodes, especially between the second and third anodes 2, 3, the protective covering being finally removed just before insertion of the electrode structure into the tube envelope. The contamination is generally due to grease from handling by operators, during such operations as (a) securing the cathode tube to a ceramic rod 5 and inserted within modulator tube, (b) assembly of the electrode structure on base 8, (c) insertion of cathode heater and the welding of leads to the heater modulator, first and second anodes 6, 2 to contact elements 9, (d) better strips and spring contacts 11 welded to flange 4, (e) inspection, (f) insertion into oven and heating to 200‹C. The protective covering is therefore applied at an early stage, e.g. on completion of assembly of the electrodes and before removal thereof from a jig to the insulating rods, particularly to those parts of the rods which lie between the second and third anodes 2, 3 which have the highest potential difference during operation. The protective covering is preferably a band of paper held in position by adhesive tape or possibly by a springy band of metal or plastic so that it can withstand the temperature of up to 200‹C. required for curing the cement used for bonding the electrodes to the rods. There may be protective bands provided around the insulating rods in the spaces between all the gun electrodes. A preferred method of manufacture is (a) degrease rods and electrodes by firing in hydrogen, (b) position rods in a jig, handling the rods only at the ends, (c) thread the electrodes over the three ceramic rods, gauges holding the electrodes at the correct spacing, (d) secure electrode flanges to rods, e.g. by a quick drying cement or by clamps. The electrode flanges are triangular and have apertures for the rods at the corners, (e) the protective covering is applied as soon as possible after mounting the electrodes on and securing them to the insulating rods and is not removed until after removal of the electrode structure from the oven and just before sealing it into the tube envelope. The invention can be applied to the manufacture of any form of electrode structure where it is necessary to protect the insulation between electrodes from contamination. The first anode 6 is a triangular plate and the other electrodes each have one or more triangular flanges 4.