GB355978A - - Google Patents

Abstract

355,978. R÷ntgen-ray tubes. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Kearsley, W. K. ; 1606, Randolph Road, Schenectady, New York, U.S.A.) Sept. 19, 1930, No. 28091. Convention date, Sept. 19, 1929. [Class 39 (i).] The area of the focal spot in R÷ntgen-ray tubes is automatically increased with increase of the space current in the tube, by a coil 54 external to the tube magnetically focusing the space current. The coil may be supplied wich current from the mains by a transformer 55. As the space current is increased by varying a rheostat 24 in the filament heating circuit, the current through the coil 54 is decreased by a transformer 58 the secondary of which is in opposition to the secondary of the transformer 55 and the primary of which carries the space current. The Specification as open to inspection under Sect. 91 (3) (a) comprises also tubes in which the area of the focal spot is controlled by an electrostatic focussing device 11, Fig. 3 (Cancelled), surrounding the cathode and supported by a glass tube 14. As the space current supplied through a mechanical, thermionic or electrolytic rectifier 21, Fig. 1 (Cancelled), increases, the negative bias of the device 11 relatively to the cathode 6 is decreased by a vacuum tube 27 carrying the space current of the R÷ntgen-ray tube 1 and connected between the device 11 and the cathode 6 of the tube 1. As the current through the filament 6 is increased, the current through the filament 30 of the tube 27 increases and the voltage across the tube 27 decreases. In a modification, the tube 27 is replaced by a double rheostat with one-half in the circuit of the filament 6 so that as the current in the filament 6 is increased, the voltage across the double rheostat, and so the bias on the device 11, is decreased. In another modification, Fig. 2 (Cancelled), using a self-rectifying R÷ntgen-ray tube, the tube 27 is replaced by a transformer 35 supplied from the mains 22. An adjustable winding 40 carries the space current and a winding 38 is connected between the device 11 and the cathode 6, in parallel to a high resistance 39 smoothing out voltage fluctuations. This subject-matter does not appear in the Specification as accepted.