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 normally open, two-terminal, high-sensitivity circuit was found in General Electric's...
This circuit was obtained in a 1977 Radio Handbook. The transistor is from the era and the coils...
Based on an LM36000 OTA this circuit was found in the July 1988 issue of Radio Electronics...