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.
An integrated circuit 741 (operational amplifier is the basis of this voltage indicator, which can also...
This circuit converts inductances on two scales into voltages. The circuit was obtained from a...
This field effect transistor amplifier circuit in common gate or common port configuration is from an old...