I bought a Crystal Radio Set. A Poldhu, its a kit on eBay. I wanted to compared a real crystal radio receiver with one that I had made. So I bought a DIY kit. It has a Valve / Tube as well as the ability to be just crystal. After I built it I did make a couple of changes, not because the set was bad, because I wanted an aesthetics change and to try a germanium detector diode with a lower forward voltage to see what if any difference it would make.