My First Crystal Set — Built As An Adult
Hello crystal set fans. Thanks for stopping by. I am proud to present my first crystal set. Here's the story:
First, a little research had to be done. I went to Google search engine to find out what the rest of the world was doing with crystal set design. The best crystal radio site is Gollum's Crystal Receiver World. This is where I found the design for my first crystal set. I did make some changes to the circuit as the box didn't allow for easy construction with two variable capacitors. I left the capacitor that connected to the antenna out, and instead using two fixed capacitors that attached to two antenna binding posts. The circuit is similar to the antenna circuit design here.
Since a crystal set isn't a big performer as a radio, it should at least look nifty. This is where the translucent blue box comes in. Hammond Manufacturing in Canada made this box. Hammond plastic boxes have always been easy to work with. The binding posts are an all-metal type made by H.H. Smith. The H.H Smith part number is 1835 and are around seven dollars each. Two are needed for the headphones, three for the coil and 3 for the antenna and ground. I had some laying around in my surplus stuff. I don't think I would pay that much for binding posts, but I have to say that they sure add that "sizzle" to this set.
The coil for this crystal set deserves special attention. I decided to use a spider web coil in my design. After looking around home improvement centers and arts and crafts store, I found some red oak wood veneer. The manufacturer is The Cloverdale Company. The package contains 3 pieces of 8x12 inch veneer. This is enough to make 18 crystal sets. I cut the veneer with scissors and made the slots with a coping saw. The coil can be mounted inside or outside the box. I chose to put the coil on the outside using binding posts with banana plugs (Grayhill 02-1). (update - Instead of doing the veneer thing, you can build the coil as I did in my #8 set.)
The coil is wound with litz wire. This is a special wire that offers the best in radio reception. At the bottom of this page there is a table that shows the comparison in reception between a solid wire and litz wire coil. The drawback to using litz wire is it is hard to come by and usually has to be purchased in pound spool increments. Since I had more money than brains, I decided to purchase a pound spool of litz wire. I purchased it from MWS Wire. Each coil requires less than 50 feet of litz wire. The wire I bought has 40 strands of #44 wire. Each wire has a coating, and the whole wire has a nylon covering.
The litz that I have can be easily tinned by using a hot soldering iron and solder. I set my iron at 900 degrees when I am preparing my litz.
The headphone or earphone has to be a "high impedance" (2000 ohms or so) type. They are made as electromagnetic or a crystal earphone. If you use a crystal earphone, make sure to put a 33k ohm resistor across where the earphone connects. Otherwise a DC electric circuit is not made and there will be no reception.
The tuning capacitor I used is a single gang 365 pf. I added a
switch with a 250 pf capacitor in parallel with the variable capacitor
to allow for tuning the bottom of the broadcast band.
This receiver requires an antenna and ground. The ground connection can be made to a water pipe (NOT a gas pipe!). The antenna can be a 50 foot length of wire stretched outdoors between two objects. Please keep away from any power lines and use common sense when setting up this antenna. Remember that antennas can attract lightning strikes.