This circuit was found in a 1965 General Electric manual. It is intended for cars that have negative ground. At the time there were vehicles with positive mass.
Using SCRs, this circuit from a 1967 General Electric manual allows full wave load control with SCRs....
This interesting circuit from a publication from the 1970s, measures the intensity of the sound...
This simple NPN and PNP transistor tester configuration can use the low current range of a common...