Way back, during the Second World War, prisoners of war learned how to build radios from whatever they could find.
The “classic” way of building a rectifier was to use a pencil lead and a Gillette blue razor blade. By touching the blade with the tip of the pencil a very basic PN junction was created. This was used to rectify the AM signal so that an earphone could resolve it.
They would also use the barbed wire fence around the camp as an antenna – until the Germans discovered this and replaced all the metal fence wire with plastic.
[Are you sure about that? -Ed]
I managed to track down an original blue razor blade from the 50′s – so I’ll be giving this a go with the crystal radio set I’ve been tinkering with – to see what happens.
These radios were often called “Foxhole” radios as they were also used in the trenches. It was important not to use a radio receiver with an oscillator as the Germans were able to detect these and use them for targeting. For more information on “Foxhole Radios” check out this link.
If you want to try this yourself, you can “blue” a standard razor blade by heating it with a torch till it glows, or you can track down one of the original blades right here.