GB307378A - Improvements in and relating to thermionic devices - Google Patents

Abstract

307,378. Graham Amplion, Ltd., and Freedman, P. Dec. 5, 1927. Vacuum tubes.-A four electrode valve is provided with an anode, an equipotential cathode, a control grid, a screening grid adapted to screen the control grid from the anode, and an auxiliary electrical heater for the cathode, the leads of the anode and the control grid passing through separate stems. To serve as a screen for the other electrodes, the cathode may surround the heater or be formed as a plate situated between the heater and the other electrodes, or it may be provided with a surface having a very high thermionic work function. Alternatively, the heater may be enclosed in an envelope of refractory insulating material, such as silica, and may be of the form described in Specifications 291,531 or 307,325, or it may be a filament of refractory material such as tungsten. The space between the heater and the cathode may be vacuous or filled with some such substance as zirconia or silica, or the heater may be connected to the cathode at the mid-potential point. The cathode may consist of a sheet or wire of tungsten, molybdenum, platinum or nickel and may be coated with alkaline-earth oxides. In the form shown diagrammatically in Fig. 1, the cathode 2 is a hollow body surrounding the heater 3, the space between being either vacuous or filled with an insulator which is a conductor of heat. The anode 5 is screened from the control grid 7 by a shielding grid 6 and the heater leads 8, 9 pass out of the envelope at the same end as the lead 10 of the anode, the leads 11, 12, 13 of the cathode, shielding grid, and control grid passing out at the other end. In a modified arrangement, the leads 10, 12 pass out at one end and the remainder at the other.