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.
One of the problems with common 3-terminal regulators is that the internal reference, normally 1.25 V,...
This windshield wiper interval was found in old documentation. The NPN transistor is general...
This circuit was found in a Radio Escuela Gráfica magazine from Argentina published in the 70's....