This circuit was found in American documentation from the 1960s. The operational amplifier is from that time, but the configuration applies to modern equivalents.
This circuit is from a 1995 technical documentation. The transistor can be a BC558 and the sensor...
Found in a Popular Electronics from the 90s, this circuit checks the presence of voltage on a...
The critical component of this amplifier is the output transformer. We found the circuit in an old...