In this circuit the LED lights up when the voltage drops below the value set in the trimpot. The transistors can be the BC548. The circuit is from a 1999 American publication.
Found in a 90s Popular Electronics, this circuit uses common components. The power transistors can be...
Found in the documentation on PCs, this circuit excites LEDs whose current is determined by R3....
Found in a 1990s Motorola documentation, this high voltage circuit uses a PUT that is not a common...