Found in a 1924 publication, this 2-valve receiver has a speaker output. Power comes from several batteries. Information about the coils is given.
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...