We found this circuit in a 1996 publication. Equivalent components can be tried, especially in the case of the photodiode. The circuit is powered by a 12 V source.
This different configuration for a crystal galena radio or modernized since a diode is used, has a...
This circuit is from 1990 documentation. When we press D1 the lamp remains on for a time interval that...
This version of the test lights a lamp when the ring touches the tortuous wire. The SCR can be the...