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.
We found this circuit in a Radio Electronics from October 1960. The circuit uses just one...
Using components from the era, this 90's EDN circuit is used in analog to digital conversion...
Found in National Semiconductor documentation from the 1980s, this oscillator is used for...