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 was found in a 1968 General Electric documentation. It has an input impedance of 2 M ohms...
This circuit shuts off and locks the power to a load in the event of a failure. The circuit is from...
This circuit is from 1995 documentation, but can be easily assembled today, as the components used are...