This circuit is from a 1969 RE Experimenters Handbook. The circuit is powered by the voltage of the circuit being tested. Integrated circuits are current.
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...