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.
The circuit shown was found in a 1994 Linear Applications Handbook by National Semiconductor. The...
We found this circuit in documentation from the 1970s; The circuit uses Japanese transistors of...
This traditional crystal oscillator configuration with FET was found in the 1994 Linear...