This crystal or galena radio is one of the many versions available on this website. This is from a documentation from the 70s. The coil is formed by 50 + 50 turns of wire 28 in a ferrite rod.
This sample and hold circuit configuration was found in a manual from the 70s. The operational amplifiers...
In this 1990s circuit, found in a National Semiconductor manual, the output voltage is the square of...
This circuit of a publication from the 70's uses a different type of power that we had already...