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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!
Best wishes from -- Dave N2DS
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