This circuit was found in the October 1987 Radio Electronics magazine. The circuit is a PWM control with a 555. It appears that the 555 is missing a connection that would be pin 4.
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...