This 3-tube receiver is from a 1924 publication. The circuit has 3 supply voltages and a high-impedance headphone output.
The circuit shown is from an old European publication. In it we have the way to activate a relay...
We found this circuit in a European publication from the 1990s. Transistors are still common types...
This circuit was found in an American documentation and can be added to common amplifiers of any...