GB446497A - Improvements in or relating to thermionic valves and circuits therefor - Google Patents

Abstract

446,497. Thermionic valves; valve generating and amplifying circuits. PLESSEY CO., Ltd., and HODGSON, A. D'A., Vicarage Lane, Ilford, Essex. Sept. 25, 1934, No. 27485. [Classes 39 (i) and 40 (v)] A combined oscillation generator and amplifier comprises a thermionic valve having a plurality of anodes, a common control grid and a common cathode, one anode, together with the common grid and cathode, forming with a frequency determining circuit a generating circuit, and another anode, together with the common grid and cathode, forming with an output circuit an amplifier ; the two circuits are intercoupled through the common grid and the valve is so constructed that a common bias applied to the grid biasses the generating circuit only to the cut-off point while it biasses the, or each amplifier section substantially beyond the cut-off point. The amplifier thus works under " Class C " conditions, whereas the generator is arranged to give sinusoidal oscillations. The required difference in the characteristics of the generating and amplifying sections may be obtained by varying the pitch of the grid, or the spacing of the anodes, or both together. In a modification, the effect of a variation of mesh in the common grid 2, Fig. 3, may be obtained by interposing an auxiliary grid 5 between the cathode 1 and one portion of the grid 2, the turns of the grid 5 falling between those of the grid 2. The grid 5 may be connected to the grid 2, or to a source of different potential. The usual frequencydetermining circuit may be replaced by an electrical long line or the equivalent artificial line, or a filter network. In a modified circuit shown in Fig. 6, the auxiliary grid 5 is employed in the generating circuit, and the common grid 2, which is maintained more positive than the grid 5, collects a portion of the oscillator electron stream, the potential developed across the impedance 11 actuating the amplifier. The frequency-determining and output circuits are denoted by 10 and 9 respectively. A number of amplifying sections may be employed and these may be designed to give, in conjunction with suitably tuned output circuits, a series of harmonics of the oscillator frequency. For example, the anodes may be arranged with successively greater diameters as the order of the desired harmonic increases. Alternatively the grid mesh may be varied or a number of auxiliary grids similar in function to grid 5 may be employed. The dimensions and electrical characteristics of a design of two-anode valve are given. An electrostatic shield may be placed between the anodes and around the common grid to reduce interaction between the oscillator and amplifier sections.