This sensitive circuit was found in an Electronics Hobbyists Handbook from the 1990s. The circuit can use common general-purpose transistors in place of the original ones.
This sensor was published in Radio Electronics magazine in April 1962. The two-transistor circuit...
Another of the many similar configurations we have in this section. This one is from a Radio...
This circuit like the previous one is intended for 24V x 3W solenoids being connected from the...