GB235141A - Improvements in or relating to electric discharge tubes - Google Patents

Abstract

235,141. Naamlooze Vennootschap Philips' Gloeilampenfabrieken. June 4,1924, [Convention date]. R÷ntgen-ray tubes; vacuum tubes. - Parts between which there is a very high potential difference are connected to each other by a wall consisting of insulating sections alternating with one or more conducting sections. The potential difference may be equally divided between the insulating sections. In an X-ray tube for, say, 200,000 volts or more, the container may consist of glass tubes 1, 7 sealed to an intermediate chrome-iron cylinder 6 and carrying re-entrant tubes 2, 8 sealed respectively to the water-cooled anti-cathode 3 and to a metal shield 10 surrounding a filament cathode 11. These electrodes are situated within the metal portion 6 of the container. The anti-cathode 3 is of chrome-iron, with an inlaid tungsten plate 4. It is surrounded by a metal bell 18 to protect the joints of the envelope. An aperture 17 in the shield 10 allows passage of electrons and of the X-rays, which pass out through a window 9 closing the interior of the re-entrant tube 8. Connections 12 to the filament pass through silica beads in the metal shield 10 and are sealed through the glass tube 7. A separate leading-in wire 16 allows of impressing on the shield 10 a potential equal to the average cathode potential, or slightly lower than that of any part of the cathode. The metallic part 6 of the container is connected to earth and to the mid-point of the secondary of a transformer 23 supplying the electrodes. Variable resistances 21, 26 are provided in the primary circuits of the supply transformers. In modifications, a dome-shaped window for X-rays is sealed to an aperture in the side of the metal section of the envelope. The active surface of the anti-cathode, and the axis of the metal shield, may then be at right-angles to the positions shown, or the anticathode may have a bevelled end, the cathode being provided with a Coolidge focusing-ring. X-ray tubes of the kind described may be very highly exhausted, or may contain hydrogen or helium at a pressure such that harmful positive ionization does not occur. Such pressure may be about 0.0006 mm. of mercury, and in the case of helium may be 0.01 mm. Specifications 207,262, 208,108, and 209,833 are referred to.