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.
We found this circuit in an English publication from the 1980s. The circuit uses current...
The circuit shown in the figure can be useful in cases where a common telephone extension is used....
We found this circuit in an American documentation from 1977. The circuit must not be powered by a...