A transistor amplifier with AGC for telecommunications applications produces a constant amplitude alternating output signal regardless of the amplitude of the input signal. It uses a heat dependent resistance in feedback network to achieve this. - The circuit depends on amplifying the input signal (UE) by means of a single transistor (T) amplifier stage and applying the output in two anti-phase forms to a resistance (R7) so that if the output signal is of the defined amplitude, the current through this resistance is zero. The current is in fact monitored and rectified and fed back in direct current form to two heat dependent resistances (R8, R9) which affect the gain of the single stage amplifier.
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