GB515271A - Circuit arrangements and thermionic valves for amplifying electrical oscillations - Google Patents

Abstract

515,271. Valve amplifying circuits. STANDARD TELEPHONES & CABLES, Ltd., BLACK, D. H., and ROCHE, A. H. May 27, 1938, No. 15935. [Class 40 (v)] The negative feedback voltage of an amplifier is derived from an auxiliary positive electrode arranged between the control electrode and the output anode of the valve. The feedback voltage may be derived solely from an impedance R14, Fig. 2, in the circuit of the auxiliary electrode or partly therefrom and partly from voltage produced by the output current in impedance R13. The impedance in the circuit of the feedback electrode is preferably proportioned to the impedance in the output anode circuits in the ratio of the currents carried by the two electrodes, or so that the harmonics in the feedback circuit are greater than those developed in the anode circuit. The impedance in the circuit of the feedback electrode may be frequency dependant and be such as to reduce the output impedance of the amplifier. The output impedance may be controlled by adjusting the relative proportions of feedback derived from the auxiliary feedback, electrode and from the anode circuit. A threewinding output transformer may be used, Fig. 3 (not shown) the load for the auxiliary electrode being constituted by the third winding. Alternatively a small monitoring output may be obtained from the auxiliary electrode supplying the negative feedback voltage, Fig. 4 (not shown). The amplifier may comprise a push-pull stage in which case the feedback is adjusted to give optimum reduction in the odd order harmonics. The feedback may be applied to the control grid in series with the input voltage, Fig. 1 (not shown) or to the screen grid of the first amplifier stage, Fig. 5 (not shown). Fig. 6 shows an arrangement in which the output valve comprises a cathode, a control grid 3, an accelerating grid 4, a suppressor electrode 5, and a feedback electrode 6, and so arranged and constructed that the ratio of the electron currents flowing to the anode 7 and to the electrode 6 is constant for all working values of control grid voltage. The amplifier may operate over a range of 10 to 60 kc.