This two-tube circuit, one being a double, was found in Radio Electronics magazine from July 1958. The distance to the microphone depends on noise and losses. The cable must be shielded.
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....