Found in a PE Hobbyst Handbook, this circuit checks if there is voltage in a power outlet by emitting sound and lighting an LED.
The circuits shown below consist of diode protections against accidental polarity reversal in the supply...
Found in an Electronics World of 1968 this circuit has a 40 to 12 000 Hz bandwidth providing a 1.9 Vpp...
This circuit was found in an American documentation from 1968. The circuit uses transistors from that...