This circuit that can be activated by light or heat was found in an old American documentation, but the components it uses are perfectly current. The power transistor shall be fitted with a heat sink.
This circuit is a traditional configuration with the 741 Operational Amplifier and its gain is...
This is a voltmeter with high input resistance. The transistor is germanium. We found it in an...
A Popular Electronics from the 90's suggests this circuit that is based on a low voltage...