This very low frequency amplifier has a gain of 1,000 and was found in a 1967 documentation. The circuit is suitable for detecting explosions, distant echoes and seismic vibrations.
This circuit appears in several versions in publications of the time and can be modified by...
This interesting circuit of the American publication Electronics Handbook Volume XIII 1993 shows a...
This simple SCR alarm circuit was found in an old Poptronics, but can be easily assembled as all...