This circuit triggers an LED when the input signal exceeds the peak, or the value set in RV1. The transistors can be the modern equivalents BC549.
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...