This circuit was obtained in an Electronic Design from the 80's. It has the adjustment of the gain through a simple potentiometer. The power supply must be symmetrical.
This circuit of a 1978 American publication monitors a telephone line by triggering a relay. The...
This interesting FET-tester circuit was obtained from an old American documentation. The bipolar...
This old VHF TV booster that also serves FM was found in Radio Electronics magazine from April...