GB673604A - Improvements in or relating to circuit-arrangements for amplifying electric voltages or currents - Google Patents

Abstract

673,604. Amplifying circuits. PHILIPS ELECTRICAL INDUSTRIES, Ltd. Aug. 25, 1950 [Aug. 30, 1949], No. 21069/50. Class 40 (iv). [Also in Group XL (c)] An amplifier comprises a valve stage and a transistor stage fed from the same supply source, the input being applied to one stage and the output being derived from the other, a D.C. coupling being provided between the stages. As shown, N-type transistors are connected to the output of the valve stages shown in Figs. 1 and 2 and P-type in Fig. 3, the resistances being chosen such that in Figs. 1 and 2 with respect to the base electrode 6 the input electrode is slightly positive and the output electrode 8 considerably negative, whereas in Fig. 3 and Fig. 7 (not shown) the input electrode is slightly negative and the output electrode considerably positive. The D.C. level of the output voltages is suitable for direct connection to a similar succeeding stage (Figs. 4 and 5, not shown), and in such an arrangement positive feed-back may be applied by means of a resistor between electrode 8 and the preceding grid and overall feed-back may be provided to reduce the gain to the value produced without the positive feed-back. In Fig. 1 positive feed-back is provided by resistor 15 and negative feed-back by resistor 18 and the effect on the input impedance of the base electrode resistor 9 may be neutralized by a suitable choice of the output resistor 10. In the Fig. 2 circuit the cathode resistor 3 may be omitted (Fig. 4, not shown). Pushpull output potentials may be obtained from between the valve anode and base electrode of either circuit (Figs. 6 and 7, not shown), providing approximately equal D.C. biases for the succeeding valves. The transistor may be structionally combined with the valve and an internal connection provided between the two in order to save valve pins.