This high-impedance headphone circuit was found in a 1990s William Sheets. The power is low, but the high input impedance makes it useful for radio applications.
This circuit is from an American publication of the 80's. It makes use of components of the time....
The integrated circuit used in this Electronics Now amplifier is not very common today. However,...
This PA or Public Address amplifier with a few watts of power was found in the March 1986 Radio...