This 6W amplifier with 4 tubes was indicated in an American documentation from 1947 to operate with recorders. The circuit uses a source with a transformer.
This circuit for recognizing a frequency with a narrow range was found in Radio Electronics...
Any small sound amplifier from 200mW to 1W can be used in this simple circuit. Or circuit of two...
This Linear Technology circuit was found in a 1980s documentation. The circuit can swing up to a...