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.
This circuit is from a Radio Electronics magazine from July 1984. The transistor determines the...
This circuit was found at Electronics Now. It can be used as a shield detector for dial signals in an...
This circuit was obtained from an English circuit manual. Components are common and LEDs can be 3...