|MadSci Network: Engineering|
Hi Josh, Your question brings back some fond memories of my youth, and some not-so- fond memories of the Viet Nam war. As a kid, I made many crystal radios; most using a Galena crystal and cats whisker, and later with 1n34 diodes or transistors. Transistors work well because they are basically back-to-back diodes - the base being common to the emitter and the collector, so you could use either base/collector or base/emitter. The first transistor readily available to the experimenter was the Raytheon CK-722, and could be had for 99 cents back in the early 50's. That would be the equivalant of about $15 in todays money! In the jungles of Viet Nam, you carried in only what you needed to survive. That meant no portable radios, no electric razors, etc. Our crystal radios were much the same as the foxhole radios of the WWII, in that we used razor blades for the detector, AND for the headset. Uncle Sam was kind enough to provide us with C-rations and K-rations left over from the WWII and Korean wars - er, excuse me - police action. In both you would have cans of crackers and jelly. The jelly was in a smaller can, about 2" dia., and 3/4" tall, and was packed inside a somewhat larger can with the crackers on top of it. The jelly can is what we used because your ear would fit inside it and would be very close to the bottom. Construction was as follows: 1. Open the can with your ever-present can opener. (Uncle Sam designed a little folding can opener that was about 1" long and was hinged and had a hole in it so you could keep it on your dogtag chain. With a little practice, you could open a can faster than any electric can opener ever made!) 2. Eat the contents, or throw it away - your choice. After untold numbers of cans of grape jelly, you really got tired of it. 3. Punch a rectangular hole in the bottom, slightly smaller than the razor blade. 4. Smooth off the rough edges of the hole, leaving only one or two SMALL sharp points sticking up into the can. 5. Lay the razor blade (NOT stainless steel - it's non-magnetic) over the hole, inside the can, with one end of it resting on one of the remaining sharp points. Secure the other end to the can by dripping candle wax on it. Two or three drops is sufficient. 6. Drive an iron or steel nail (not stainless) through a 1 1/2" long, 1/2" dia. piece of bamboo, leaving the head flush against the surface. 7. Wrap your magnet wire around the end of the nail that's sticking thru the bamboo, and connect it to your radio. Use very fine wire if possible, and put on as many turns as you can. We always carried a quantity of #36 wrapped around a regular thread spool from our sewing kit. If caught, the V.C. would think it was just thread! To use it, put the can around your ear and place the nail/wire/bamboo voice coil against the bottom of the can so the nail head is in close proximity to the razor blade. Viola! We either held the contraption in place by tying a piece of string around our head, or jammed it between our helmet liner and head - not very comfortable. You could make it more efficient by magnetizing the razor blade, prior to sticking it inside the can, by stroking it with a magnet or, if you didn't have a magnet, strike one end of a heated blade vertically on a rock a few times. The earth's magnetic field would give it a slight magnetism. We could usually pick up 3 stations - Voice of America, AFRS, and the BBC. Here's a link you might find interesting. http://freeweb.pdq.net /headstrong/foxhole.htm Good luck! Your Not-So-Mad Scientist Karl KarlKolbus@ameritech.net
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