GB1275226A - A cathode ray tube and a method of fabrication - Google Patents

Abstract

1275226 Electron guns RCA CORPORATION 16 June 1970 [16 June 1969] 29134/70 Heading H1D A method of construction of an electron gun in the manufacture of a cathode-ray tube, e.g. a colour T.V. tube, comprises the steps of fixing the position of a control grid in the tube; movably mounting the cathode in alignment with the grid; evacuating the tube and applying operating voltages to the electrodes with a desired beam cut-off voltage between the cathode and grid; then adjusting the cathodegrid separation until beam cut-off is achieved when the cathode position is fixed. The screen grid 13 and control grid 15 are supported on insulating rods 17 which also support a flange 18 of a metal cathode support sleeve 19 within which a cathode cylinder 21 is slidably mounted. The upper end 22 of the cathode is closed and has an electron emissive coating 23 and the lower end is attached by welding to an expansion bellows 25 of nichrome or other material of high thermal expansion. The lower end of the bellows is supported by the insulating rods 17 so that heating of the bellows, e.g. by a pulsed ruby laser 37 reduces the cathode-grid separation. The cathode-grid separation is initially adjusted to be larger than the critical separation for beam cut-off and the bellows is heated until the cathode-grid separation is such that beam cut-off occurs when the cathode is spot welded to the support sleeve 19 by heating means, e.g. a ruby laser 45. In further embodiments, the cylindrical cathode abuts against a bowed strip of high thermal expansion or against a bimetallic strip in place of the expansion bellows.