This circuit is suitable for the calibration of old analog oscilloscopes. It was found in documentation from the 1970s and could be useful if someone is recovering an oscilloscope of the time.
This simple SCR alarm circuit was found in an old Poptronics, but can be easily assembled as all...
This circuit, for its simplicity and the fact of using a super-regenerative detector only works...
We found this circuit in a European publication from the 1990s. Transistors are still common types...