I wonder if you can still buy them.

http://home.earthlink.net/%7Ewb5rex/xtalman/detectors.html

Another thing to use for a detector was an old fashioned double edge razor blade, in particular, the (Gilette?) "blue blade". Touching the tip of the safety pin (or pencil lead) to the blue area, right next to the silver area would supposedly act as a detector. Those old blades no longer exist.

http://www.geocities.com/safetyrazors/blades/DEBladePage.htm

Makes you wonder who first got the idea... "Hey, let's take a razor blade and a pencil lead and..."

You think I jest?

http://bizarrelabs.com/foxhole6.htm (as a kid I had the book on this page "All About Radio and Television")

http://www.bizarrelabs.com/foxhole8.htm

And you had to have an oatmeal box to wind your coil... hah!

Here's the classic Quaker Oats crystal radio.

This site has lots of links, kits, plans, etc:

http://www.midnightscience.com/

http://www.midnightscience.com/catalog5.html

You can literally build this loop antenna, add an earplug and diode across the variable capacitor connections, and make a crystal radio from it:

http://www.mtmscientific.com/loop.html

Here is the correct diode, a 1N34A. You used to be able to buy a bag of these at Radio Shack for a buck or so.

http://www.mtmscientific.com/diodes.html

Just google "crystal radio" and you can find plenty of sites.

This one, Dave Schmarder's site, has both AM loop antennas and crystal radios:

http://www.schmarder.com/radios/misc-stuff/loops.htm

http://www.schmarder.com/radios/crystal/30.htm

Dave's crystal radios are very sophisticated. In fact, they are the most sophisticated crystal sets I have ever seen. Amazing!

http://www.schmarder.com/radios/index.htm

Yes - I am tempted to build my own crystal radio from scratch - just for the fun of it.

It's a pity they're not making the germanium crystal diodes any more... I guess they're just too expensive to produce, and there is not the demand.

Amazing that the POW's built crystal radios - I suppose it made perfect sense, then they could find out what was going on.

It's amazing that you can knock a radio together with just a few simple bits and pieces.

Playing cards could be split and inside a portion of a map. All 52 plus jokers could be laid out to make a map of Germany.

There were brothers that before the war were HAMs. They had designed a transmitter/receiver that used the same parts for both, just a switch was thrown to alter the circuit from transmit to receive. It used a single miniature tube. They had made up a model name for it.

The brother in the prison camp wrote to his Uncle Samuel in Washington and that his brother be contacted to get him what he needed. Somehow someone in the Post Office caught on to the address, and routed the letter to the War Department, and it eventually ended up at Mis-X. They contacted the brother who knew exactly what was wanted. He showed them how to make up a kit of parts and schematic.

The kits were put in hollow aluminum spheres that screwed together, and top company people at Spaulding stayed after hours and stitched coverings on them to look like baseballs. These were slipped into the prison camp as recreational goods.

And that is how 2-way radio was established with the prison camps.

Have you done a lot of research into this kind of stuff?