This circuit was found in a Popular Electronics from the 90s. The circuit uses a general purpose JFET. The coils depend on the signal range that must be amplified.
This simple transistor tester uses a common 3 mA analog instrument that has its scale changed as...
This Texas Instruments circuit is from the 80's. However, it can be implemented with modern...
This circuit shows how to trigger and shut down an SCR using common pressure switches. The circuit...