The operational amplifier used is not common today, but the circuit can be implemented with modern operational ones. The gain is 1000 and the source must be symmetrical.
The circuit shown is from an old European publication. In it we have the way to activate a relay...
We found this circuit in a European publication from the 1990s. Transistors are still common types...
This circuit was found in an American documentation and can be added to common amplifiers of any...