GB418435A - Improvements in or relating to thermionic valve circuits - Google Patents

Abstract

418,435. Valve amplifying circuits; thermionic valves. SIEMENS & HALSKE AKT.-GES., Siemensstadt, Berlin. March 17, 1933, Nos. 8213, 8214, 8215, and 8216. Convention dates, March 18, 1932, Oct. 27, 1932, Oct. 29, 1932, and Oct. 31, 1932. [Classes 39 (i) and 40 (v).] In an amplifier for use in multiplex or other telegraph or telephone systems, distortion due to curvature of the anode-current, grid-voltage characteristic or to iron-cored coils or other causes is counteracted by equal and opposite distortion due to negative gradient of the characteristic connecting the amplification factor Á with the grid volts Vg ; i.e. by employing such conditions that dÁ-<1>/d(-Vg) is negative. For a very limited range of conditions this result can be achieved with known valves ; but preferably "countercontrol" valves, which exhibit the peculiarity in question over an extended range of conditions, are employed. The range of variation of external load over which compensation is attainable is limited, but can be extended by combination with reaction circuits in which the anode circuit of the counter-control valve is coupled to the grid circuit by a resistance inside or outside the valve and in series with the load (Figs. 12, 15, not shown), or a tapped resistance in shunt therewith (Fig. 13, not shown), or a transformer in the output circuit connected to a differential transformer in the input circuit (Fig. 15, not shown). Thermionic valves. In order that dÁ/dVg, and therefore dÁ-<1>/d(-Vg), may be negative over an extended range of conditions, the cathode is located between the anode and the control electrode, which may be a plate or cylinder while the cathode is a flat or spiral wire, (Figs. 3, 4, not shown). The control electrode G, Fig. 6 may be corrugated in relation to the grid-like cathode K, to secure a large measure of the effect described and to secure at the same time a high mutual conductance. In a further modification the control electrode G, Fig. 10, is a cylinder embedded in insulation J. Inside the insulation is a heating-coil H and outside it is a spiral tape of emissive material forming the cathode K, the whole being surrounded by the cylindrical anode A. The result aimed at may be enhanced by the addition of a suitable screening-grid. The heater and control electrode may be enclosed in insulating material which has an emissive layer on its surface to act as cathode.