This amplifier with old germanium transistors is from a 1957 documentation. The power is a few hundred milliwatts and the transformers are common types of driver and output of the time.
Found in Radio Electronics this circuit uses a fotodiac to drive a triac. The circuit can use...
This circuit is from an old English documentation. It is intended for coupling a microphone to the...
Here is an interesting circuit to be used in physics demonstrations involving energy...