GB525402A - Electronic amplifier - Google Patents

Abstract

525,402. Electron multipliers. FARNSWORTH TELEVISION, Inc. Dec. 22, 1938, No. 37271. Convention date, Jan. 5. [Class 39 (i)] In an electron multiplier the electron stream is caused to undergo alternate multiplication and attenuation by absorption of part of the stream; the output current is of the same order as the primary electron current and the D.C. component is reduced in radio &c. signal amplification. A helical channel is formed, three cylinders 7, 8, 9, Figs. 1, 2 and 3 with vanes 11, these cylinders surrounding a central anode 2 ; the wall of cylinder 9 has grids 10 between alternate sections of the channel. A collector electrode 3 which may be a wall coating surrounds the cylinders and a screen 12 at anode 2 potential is interposed between the cylinders and the output electrode 13, the primary electrode for the multiplier may be thermionic, photo-electric, or an electron multiplier which may be of the kind described in Specification 471,199. The grids 10 have a slight negative bias and the cylinder 7 receives a driving A.C. ; the electrodes 2, 3, 13 receive positive potential in that order, an input signal being applied to the grids 10. An electromagnet 14 causes flow of the stream in the helix. The time of flight of the electrons round the three part cylinder is related to the impressed A.C. voltage so that electrons will be accelerated towards the secondary emitting surfaces on the cylinders 7 and 8 but will be slowed down as they approach the grids ; part of the stream will pass through these grids and be taken up by electrode 3. In a modification the longitudinal movement of the stream is effected electrostatically by means of grids 40, Fig. 6, on the anode 2, and grids 42 on the electrodes 7, 8 and 9. The A.C. potential on the cylinder 7 may be supplied by the primary multiplier described in the Specitication referred to above. The absorption of the electrons may be obtained by making the cylinder 9 slightly positive and without grid surfaces.. The signal can be applied to the multiplier cylinders 7, 8. The grids 10 may be omitted, attenuation being controlled by the potential of the edges of the openings in the electrodes. The Specification as open to inspection under Sect. 91 also describes (i) an arrangement consisting of a number of multiplier stages in cascade, a control grid being interposed in some of the stages; (ii) the use of a single stage of attenuation; and (iii) static potential control of the electrodes. This subject-matter does not appear in the Specification as accepted.