The story goes that many years ago an old radio repairman had a shop a few blocks away from a young boy in his neighborhood. He used to hang out there, as he was interested in TV, radio, and other electronic stuff. He became friends with this man and did odd jobs for him on Saturdays, while he listened to his tales of the war with the Nazis and England, and listened to the repairman's ham set that he always had going in the shop.
The boy was looking for a diode to build a crystal set from a Cub Scout book. When the repairman had a look at the schematic he said: "This is ok, but for a real good radio, you should build something like we used to build when I was a boy."
He sketched me out a layout and told the neighborhood boy to hook up the crystal radio this way and wind the coil that way. The boy got his diode and promised to try out the old timers plan.
Now, this was just humoring him, as the young boy thought the
old timer ought to be given a chance, even though the Cub Scout radio was the
one he was going to build to help get his bear patch. He went and built his
radio. Boy, was he in for a surprise. The thing worked too well! It was
sensitive and selective, with good volume and with using only the usual garden
antenna and water pipe ground.
Later, the repairman told the boy how everyone in his town knew about these sets, during the pre-depression years, when things were getting so tough. Radios were very expensive. This one had the reputation of being the one to build, as they were so good, simple, and cost-effective to make. Now, you can build the same crystal radio. I bought the plans back in November 2001 off from an eBay auction.
The coil is one of the unique things about it, as it is wound unlike any I've seen, including tapped and basket weave, tickler, slider and inductive types. Only three parts and wire are required. There are two ways to hook up the antenna, this is another factor in it's working so well. If you build this radio, and follow the plans exactly, you'll be very pleased.
The computer drawn schematic and coil shown here was copied from the original plans that I bought from eBay. It is the schematic that was shown to the young boy by the radio shop repairman many years ago. The plans that were sent to me have been retyped and edited by me for clarity. I am now using this design in my latest radiant energy prototype. I believe that this is the same type coil that T. H. Moray used in his device. The circuit that I am now using has been added to my Radiant Energy Power Generation special edition book release.
Constructing the set
Winding the coil is a bit unusual , I'll try to make it easy to follow. Wind twelve turns of 24 gauge wire on one end of a coil form. Stop winding the coil without cutting it.
Make two small holes in the form and push the end of 30 gauge wire through both these holes. Make sure that this wire is securely held in place by the two holes leaving a few inches of lead to connect to later.
Continue to wind with both the 24 gauge and 30 gauge wires together side by side. For the next twenty-five turns the coil will have a 30 gauge wire between each turn of 24 gauge wire for another thirteen turns. You should have wound thirty-six turns of 24 gauge wire and twenty-five turns of 30 gauge wire. Now, stop and do not cut the 24 gauge wire. Cut the 30 gauge wire and secure it as before with another two drilled out holes in the form.
Wind on with another thirteen turns of the 24 gauge wire. Finally, secure this wire with another drilled out pair of holes and your coil is finished.
Three simplified steps
1. Wind 12 turns of #24 gauge wire on the coil form;
2. Wind 25 turns of both 24 gauge and 30 gauge together side by side;
3. Wind 13 turns of 24 gauge wire to finish the coil.
I can't overstress that you build the radio closely following the instructions for the coil and schematic. Everything is placed in the circuit for a very good reason. Take your time and do a good job of winding the coil. Keep connection wires as short as possible. Make your connections secure. Everything that you can do to neatly complete this project will mean all the difference in performance, than if you are in a hurry. You might want to mount components on a plastic case.
Two ways to connect antenna
The broadband antenna connection makes the radio much broader in tuning. Some interference may occur. However, volume is greatly increased. Use this connection when you are attempting to tune a station that you can't quite "catch" on the sharp tuning connection.
The sharp antenna connection will be very selective and will tune without interference. Use this when trying to receive dx or low power locals. Don't hesitate to experiment with both, one may work better than the other.
Of course you will want to hook up a 1N34 diode or a catwhisker galena crystal. You might even be surprised that instead of galena that iron pyrite (fools gold) will work better. Try other types of mineral crystals as well. One might just work better than the 1N34 diode.
For the variable capacitor a 365pf is suggested. A tuner from an old AM transistor radio will work in a pinch, at least until you get a 365pf variable capacitor from an electronic parts supplier. It is suggested that you visit flea markets and yard sales for "junk" radios as a cheap, and plentiful source of electronic components. There is a certain satisfaction in actually building the radio with as little cost as it was designed to be built.
If you have built the set and are successfully listening to it you can see just how well the coil and circuit work. It's a definite solution to the selectivity problems that ordinary crystal sets have. You get both "umph" and selectivity. There is really no mystery in how this radio works. The coil steps down voltage and raises amperage which provides more output to the earphones.
There are two possible antenna coil connections without any ground. The crystal detector and output is untuned and is connected to the ground. This is not the usual setup is it? The coil and circuit receives local stations without overlap and with good volume. Its broadband will assist in tuning in the station that you want to capture. As always, this is a crystal set, results may vary due to local conditions and antenna/ground configurations. If you live on the doorstep of a radio transmitter you might get some overlap. Otherwise, you should be quite pleased with the performance of this set. Many people in pre-depression England built these sets as the best crystal receiver of the poor working class radio listening public. Regular sets at this time when radio was relatively new were expensive and the times were hard.
365 microfarad variable capacitor
2-3/4 inch by 5" cylinder for the coil form
1/4 pound of 24 gauge enameled insulated wire
2 oz. of 30 gauge wire plastic insulated wire
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