Crystal Set in storage for the Summer

This last winter I built a simple crystal set radio receiver using oatmeal containers for the inductor forms and a cats whisker assembly along with a couple of variable capacitors. It has been setting on my bench taking up too much room so I thought I would document the build and then store it away. I should  create a chassis or base for it the next time I assemble it. This is the basic schematic.

The antenna was a simple slinky stretched in the attic of the garage, it of course would work better with a larger antenna but my outside dipole is in use for other radio activities. The antenna connection goes to a dual ganged 365 pf variable capacitor (C1) then through a 35 turn inductor wound on the first oatmeal container and then to a cold water pipe ground. The ground is very important for crystal sets. Next I have about 60 turns of wire on the second inductor with taps every 5 to 6 turns. The second inductor is another oat meal container. The two inductors are sitting on top of each other as you can see in this photo. No electrical connection between the two inductors.

Ideally if I set this up again, I will position the inductors horizontally on a wooden rod or something to be able to adjust  the air coupling between the two. The first inductor circuit is the antenna tuner and the second inductor forms the resonate tuning to the desired frequency with capacitor C2. The antenna tuner section could be with a series capacitance like I am using or it could be in parallel depending on the size of the antenna. Some crystal sets let you change all the connection which makes them very versatile. I was using clip leads so I could easily adjust the configuration. My diode detector is a modified MidnightScience unit. It came with a galena crystal, however I found that iron pyrite worked the best for me. I used a 1/2 inch copper pipe cap with adjustment screws to hold the pyrite crystal in place. The chunk I had was much larger than the galena sized holder so I needed to build my own holder.  The pyrite detector is typically twice as loud as the galena with the antenna I use. I have also tested germanium as well and in this set, the pyrite is the best.

With my simple indoor antenna and a good ground, I was able to receive several stations. The strongest were KFI (640 khz) and KNX (1070 khz). Fortunately  these stations had some separation. Two strong stations near each other on a crystal set can be a problem. KNX is actually near a weaker Spanish station that required delicate tuning but with the separate antenna tuning and frequency tuning it did pretty well. The other key to crystal sets are the headphones. I have two pairs of antique high impedance (2000 ohm) magnetic headphones. The ones I used on this set don't look that great but work well. I have also used the small piezo ear pieces but they fail if left connected to the radio for any length of time and in general are not very rugged. I have built many crystal sets over the years but they still bring great enjoyment and fun.