Single Tuned Crystal Set — My #36 Crystal Radio
Hi there. Here is a pretty simple crystal set project that you and the kids can build before any of you lose your concentration. The tuned circuit is based on the Tuggle Tuner that is popular in high performance crystal sets. This set is like my #12 set too. Yes, I know this is starting to sound like a mutt crystal set, but it really works quite well.
The wood base is made from the top to the box that became my #8 Octoset. I hate to waste anything. The variable capacitor is a multi section unit. Just the two larger capacitors are used here. The coil is wound with 40/44 litz wire on an AOL cd spider coil. The set is quite attractive with the knurled brass thumb nuts.
This radio has the ease of tuning that my #13 has but works better. The ganged capacitor boosts this set to the medium performance set. Use the parts you have around. If you have an old radio tuning capacitor with a 365 pf antenna section and a 140 pf oscillator section, go ahead and use it. Put the smaller section directly across the coil.
The coil is not tapped on this radio. The best performance is achieved with an audio transformer with around a 100k ohm primary impedance. If you have one of these, take out the 47k resistor and replace it with a 100 - 200 pf fixed capacitor. Do the same if you want to use high impedance headphones without a transformer. You can, in this situation, move the diode to a tapped position on the coil. About ten turns down from the top would be around right. Leave the circuit as is for a crystal earphone.
I really like how this set looks and I hope you do too. Best wishes ~ Dave