This 80's Exar circuit has a carrier detector for frequencies up to 500 kHz. The circuit uses a company 567 which is still a common component.
This audio generator that produces both rectangular and sinusoidal signals was found in a...
This simple circuit for a high impedance magnetic phone (500 ohms or more) has been found in a...
Found in an American publication from 1968, this circuit can be made based on a TIP42 that must be...