This amplifier with the EL84 tube is a European commercial type from Corpim mounted on a printed circuit board. The diagram appeared in a September 1958 Radio Electronics magazine.
This circuit was found in a 1967 US documentation. The FET is general purpose and the 6V zener....
This High Side Current Sensor was found in a 2005 Linear Technology manual. The current sensing...
Found in American documentation from the 90's, this circuit is very current and can be implemented with...