GB683061A - Improvements relating to thermionic valves utilising secondary electron emission amplification - Google Patents

Abstract

683,061. Electron discharge tubes. ELECTRIC & MUSICAL INDUSTRIES, Ltd. Jan. 1, 1949 [Jan. 24, 1948], 2190/48. Class 39(i) A valve comprises a thermionic cathode 1 and a secondaryelectron emitting cathode 7 and between them, a control electrode 3 and an electroncollecting electrode 8, the primary electrons being formed into a beam by a beam-forming means 6, 13 so that they flow on a rectilinear path 23 to bombard the cathode 7 and the cathode 7 is coated with a 10<SP>-4</SP> inch thick composition of 20 to 50 per cent alkaline earth oxide. The coating is a mixture with a refractory oxide of preferably barium oxide with magnesium oxide as described in Specifications 670,554 and 670,582. The electrodes 3, 8 are pervious to electrons, and accelerating and suppressor grids 4, 5 may also be provided between the cathodes 1, 7. The beam-forming plates 6 are curved and provided with inturned extensions 13; and the electron beam impinges on the secondary cathodes with a density of 5 mA per cm<SP>2</SP> of emitting surface 11. The valve may be used in an amplifier circuit (Fig. 2, not shown) the potential of the plates 6 being that of the cathode 1, and the input signal is applied to electrode 3, with an accelerating potential on the grid 4, the load being in the anode-to-secondarycathode circuit. During the manufacture of the valve the cathodes 1, 7 are raised together to the same final temperature for a short time to prevent matter from cathode 1 contaminating cathode 7 which may be heated by embedded heaters 25. Although the surfaces 11 of the cathodes 7 are planar they may be convex to the cathode 1. Specification 601,966 is referred to. According to the Provisional Specification the secondary cathodes 7 operate at a temperature between 400‹C and 500‹C, as described in Specification 682,153.