GB407398A - Improvements in or connected with amplifying circuits employing thermionic valves - Google Patents

Abstract

407,398. Thermionic valves and amplifying circuits. DEHN, F. B., 103, Kingsway, London.-(Elwell, C. F. ; and Terman, F. E. ; Stanford University, California, U.S.A.) Sept. 19, 1932, No. 26058. Drawings to Specification. [Classes 39 (i) and 40 (v).] In thermionic amplifiers, the control electrode to which the input signals are applied is coated with a laver of barium or other electronemitting material and is biassed positively so that the rate of change in the number of electrons reaching it pursuant to changes in its potential is substantially equal to the rate of change in the number of secondary electrons drawn from it to the anode. The output impedance is low and the dynamic input impedance high. The control electrode may be a grid of a large number of fine nickel wires and is coated with a thin layer of barium. evaporated from the filament or with a layer of thorium. The filamentary cathode is short and heavy and the cathode-grid and grid-anode spacing is larger than usual. A space-charge results about the filament and secondary electrons from the grid wires are easily drawn to the anode. Amplifiers are described in which the valve is of the triode or screen-grid type, the screen serving in the latter case as the positive control electrode and the inner grid being at positive, zero or negative potential with respect to the cathode. Specifications 187,233 and 302,307, [both in Class 39 (i)], are referred to.