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 egg timer has been found in an English magazine that no longer exists in 1982. The...
This circuit was obtained in the publication 101 Electronics Projects of 1979. The circuit can be...
Found in Popular Electronics from the 1980s, this circuit uses two operational amplifiers from...