Suggested by General Electric in a 1965 publication this circuit uses a light bulb. Can be changed to use LED and capacitor can be 22 uF.
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...