This two-tube circuit, one being a double, was found in Radio Electronics magazine from July 1958. The distance to the microphone depends on noise and losses. The cable must be shielded.
This metal detector was found in a 2001 Poptronics, but it can still be easily assembled, as the...
We found this circuit in a 1980 documentation. The flasher uses 3 transistors in the configuration of an...
This current meter with many scales was found in a 80s American documentation. The operational amplifier...