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 a Radio Electronics magazine from November 1976. The clock frequency is...
This circuit was obtained in a manual for radio amateurs from 1975. It is a circuit that allows the...
The LEDs act as diodes, so if good they will show the same characteristic curve. Arrangment shown...