The indicator for this circuit is a 0 to 1 mA milliammeter. The operational is from the 70s, when the circuit was published. Modern equivalent can be used.
I found this circuit in a 1992 Electronics Experimenter Handbook. The circuit can be easily...
Found in the February 1990 Radio Electronics issue, this sophisticated 100 MHz probe uses a period...
Found in 90s Popular Electronics, this circuit fires a load through a MOSFET from an audio signal...