This 5.1 MHz circuit was found in a 1980s documentation. The frequency is given by the crystal and general purpose transistors can be used.
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...