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 circuit was found in a 1968 General Electric documentation. It has an input impedance of 2 M ohms...
This protection circuit was obtained in a 1969 Electronic Design. The SCR can be the current...
This circuit was found on an old EDN and can be used as a shield. Optical couplers are from the...