This primitive solar radio was found in a Gernsback publication from 1960. The transistor is made of germanium of the time and the earphone is magnetic with high impedance.
This circuit found in a European publication from the 1980s, is based on PLL 566. The frequencies...
The circuit shown, with the printed circuit board, was found in an article in the June 1990 issue...
In the figure we have a simple timer with two voltage comparators of the four of an LM339. The...