This interesting circuit uses a sodion valve that we have already described in an article on the website. The circuit uses several batteries for power. The phone is of high impedance.
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...