This circuit can detect static charges or extremely low voltages. The circuit was found in ancient American documentation and makes use of a JFET. A BF245 which is a more modern transistor can be used.
Found in a 1964 Electronic Design, this circuit shows how to modulate a signal with a dynamic low...
This circuit is from an 80's documentation, firing when the input voltage exceeds 5 V. The SCR can...
The transistor used is one of the first power Darlingtons with a collector current of 3 A. The...