Found in an Electronics Now from the 90s this mixer has several inputs. The integrated circuit can still be found easy and the power supply need not be symmetrical.
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...