1,017,759. Transistor amplifying circuits. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. Dec. 3, 1962 [Dec. 6, 1961], No. 45613/62. Heading H3T. In a transistor amplifying circuit wherein the emitter collector path of a first transistor is connected in series with that of a second transistor from the collector of which the output is taken, gain control means are provided to vary the D.C. voltage difference between the bases of the two transistors and means are provided to maintain the D.C. emitter current of the first transistor substantially independent of the gain control means so that as a result of the control the D.C. collector current of the first transistor may decrease to a considerably smaller value than its emitter current. The circuit of the Figure shows an I.F. amplifier stage of a radio receiver in which input signals are applied over tuned circuit 2 and winding 3 to the base of transistor 4 the emitter collector path of which is connected in series with that of a second transistor 5 in the collector circuit of which is a tuned I.F. output circuit 6. The gain of transistor 4 is controlled in accordance with a voltage V proportional to the average amplitude of the signal oscillations and derived from the detector of the receiver and applied to the base of transistor 5. If the signal amplitude at the terminals increases, the control voltage at the base of transistor 5 decreases, i.e.. becomes less negative, with the result that the collector voltage of transistor 4 decreases so as to reduce the gain of the transistor. Due to resistor 10 in the emitter circuit of transistor 4 the D.C. emitter current of this transistor is fixed at a value determined by resistor 10 and potentiometer 12, 13 and if the collector voltage of transistor 4 decreases to a value such that the emitter-collector voltage difference is very small the D.C. collector current decreases further below the value of the emitter current and the gain is further decreased. The circuit may be used at high frequencies, e.g. 200 mc/s. and further gain control may also be obtained by applying V to the base of transistor 4 as well as to transistor 5. A diode 16 operating in the reverse direction may be connected as shown to a point of constant potential so as to extend the range of control further.