This circuit was found in the April 1971 Radio Electronics magazine. It uses common transistors and can be adapted to use an LED or audible indicator instead of a light bulb.
Found in Popular Electronics from the 90s, this circuit uses a 2N2646 and a general-purpose transistor...
The crystal frequency of this circuit found in an American documentation is limited only by the...
These two circuits were found in Radio Electronics magazine from February 1960. The transistor is a power...