[h. p. friedrichs] (AC7ZL) has some great plans for building a crystal radio. The stator coil and output coil are wrapped around the outside of a CDR sleeve. The tuning capacitor is constructed by sandwich two clear CDs between metal and attaching this inside the top of the sleeve. The rotor shaft is mounted using the bushings from a pair of disassembled potentiometers. A hot needle is used to tap the stator coil through the housing every fifth turn. Even though the parts aren’t very traditional it looks like a really solid radio. He’s got instructions for building a matching ear piece out of tea tins too.