GB534208A - Improvements in or relating to electric discharge devices - Google Patents

Abstract

534,208. Electron multipliers. BULL, C. S., and HILL, S. June 26, 1939, No. 18498. [Class 39 (i)] Electron multipliers comprise a series of secondary emissive electrodes 1...4 shaped as described in Specification 520,117, a thermionic cathode C which is the source of the electrons, disposed at the crown of a horse-shoe shaped electrode S, and an apertured electrode E of the same shape as the secondary emissive electrodes. The electrodes E, S are maintained at cathode potential whereby the trajectories of the electrons between the electrode e and the first multiplying electrode are the same as between the successive multiplying electrodes. End effects are reduced by an electrode El welded to the electrode and shaped to coincide with the zero equipotential surface, and by the anode A which is shaped to coincide with the output equipotential surface. The cathode is surrounded by a control grid G and screen grid SG. Part of the latter is removed to prevent escape of electrons from the face F<SP>1</SP> of the cathode. Vaporous or other undesired emission from the cathode is prevented from reaching the secondary emissive electrodes, by disposing the electrodes so that no rectilinear path is provided between them. Specification 507,448 also is referred to. The Provisional Specification describes a circuit comprising an electric discharge device which is so operated that the potentials of the electrodes are such that the cathode current is maintained below the value at which space-charge becomes effective to reduce the ratio of the slope of the characteristic of the device to the cathode current, and in which the spacing between successive windings on the grid are less than, and preferably less than half of, the spacing between the cathode and grid.