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 uses a digital module from the time. We found it in February 1984 Radio Electronics...
I found this circuit in a Popular Electronics from November 1999. The magazine is no longer...
Found in a 90s 303 Circuits, this circuit has an output power of 100 mW. L1 consists of 890 turns...