This circuit, with printed circuit board, is from an article in Radio Electronics magazine from May 1971. The circuit uses the C106 which was already a common component at the time.
The integrated circuit used in this project is not common today, but it can be implemented with more...
Found in an American publication from 1969, this circuit can be adapted to be used as a shield....
This current meter with many scales was found in a 80s American documentation. The operational amplifier...