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.
Found in an EEE this circuit uses FETs of the time and a bipolar one. Current equivalent...
This capacitive switch or approximation relay was found in a 1980s US publication. Power should...
Although it is a common configuration today, this circuit was taken from an old publication. The...