This Motorola circuit uses only one transistor. The circuit is from 1965 documentation. The transistor must have a collector current rated at least to 12 A.
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...