Dave Goes Postal With His #13 Crystal Set!!!
My apologies to our fine workers in the post office, but I couldn't help myself. Give Dave a day off from work and you see what happens. Well, this is my lucky set #13. As you might see, this lovely set is made from a section of a postal mailing tube. I got the idea from a set that Mike Peebles built.
This radio is quite simple but maybe these few hints might help you. First you need a 3 inch mailing tube. Make sure you save the plastic ends that come with the tubes. If you plan to build a bunch of these, you can make some extra ends or purchase them. Next, cut the tube to the length that you wish. I made mine 4 inches, but you may want to cut the tube a little longer. Then paint the tube with your favorite color. I use black lacquer paint.
After the paint has dried (duh!!) then wind the coils. I used my 40 strand, 44 gauge litz wire for this project. You can also use 26 gauge magnet wire and use the same coil dimensions. If you use larger wire you need more turns, smaller wire, less turns. Each place where the wire starts or ends, I poked 3 holes in the mailing tube, each about a quarter inch apart. I made 3 holes so the wire would be securely held and also the end would be on the inside of the tube. The main coil is 48 turns, tapped at 35 for the diode. The antenna coupling coil is 20 turns of the same wire. I try to use two coils as the capacitance added to the top of the first coil severely detunes it. You could even make several taps on the antenna coil and put a lot of fahnestock clips around the edge. It is up to you. This is America! (Well here it is).
I used fahnestock clips for the antenna, ground and earphone terminals. Screws with thumb nuts would also look nice. It is desirable to have the clips evenly spaced. It is kind of difficult measuring around that mailing tube. Here is how I did mine: I took a piece of masking tape and stuck it to the edge of a table. I measured in 3/4 inch and drew a line lengthwise along the tape. I then measured and put a mark in 4 places along the tape. For mine, I spaced at 1 inch, 1-1/2 inches, and 1 inch intervals. I then placed the tape carefully around the tube and poked holes in the 4 spots. Since I was using #6 screws, I used a 9/64 inch drilled and made the holes larger, twisting the drill by hand.
I then drilled a 1/2 inch hole in the end cap for the tuning capacitor shaft. I also drilled the two other holes that mount the capacitor. There is a 3 point solder terminal strip mounted on the bottom of the capacitor. This is used for the 3 components in this set. After wiring, I put a knob on the capacitor shaft and then stuck the ends on the mailing tube.
A local cub scout pack elected to build some of these crystal sets. You can download the plans. This is a 4mb file size, so give it of time.
As you might guess, the most expensive part in this set is the tuning capacitor. Going to cost you a little over ten bucks for that little piece. I guess that isn't too bad as those were about 4 dollars 30 years ago. This might make a nice school or scout project. It was fun to build and only took me less than 2 hours to put it together. Have fun, and as they say in the old country: Viel Spaß beim Nachbau!
Here is another simple crystal radio for you to look at.
Best wishes from -- Dave N2DS