Using the 2N2646 this circuit was found in a Radio Electronics magazine from July 1968. The transistors are from the time and the lamp can be replaced by a high-power LED in a current version.
This is the basic configuration of many LM339 manuals, as a comparator with hysteresis. The font...
We found this circuit in a Popular Electronics of the 80's. The circuit can be used to drive...
This simple power supply for transistors was found in documentation from the 1940s. The...