Building and testing the Trekster Crystal Radio.
Tuesday, April 14, 2026 at 12:22:56
The Trekster Crystal Radio is a small kit that was purchased from eBay. I did an unboxing not that long ago: https://wereboar.com … kster-crystal-radio/.
I was going to put this together in a couple weeks, but had some time in-between laundry and lunch this past weekend.
For this build, I used my 35W iron. You probably don’t want to go much lower than 30W, too small and you won’t get a good joint. Size your iron appropriately!
To start, there aren’t really any instructions, per se, with the kit. It’s pretty self explanatory where things go, and most only fit in their own spot. Easy enough…I started with the inductor and resistor:
Solder flow-through on the board is excellent, and I was able to get nice fillets on both sides.
Next was the diode. This kit had a smaller than required footprint, and the kit creator tells me that’s now corrected. However, that doesn’t stop us from installing the part. Simply (gently) grip one end of the diode with pliers or tweezers, and bend one lead over so you get a triangular shape. Then insert in the holes. I used a piece of old solder wick to lift the diode temporarily because I didn’t want the glass body in the fillet, and then just temporarily touched the opposite side with some solder and the iron to tack it in from the top.
After the one lead was tacked in, I turned the board over, soldered the opposite end, and finished the first side.
A note about these diodes, and Soviet diodes in particular:
Germanium diodes are more sensitive to heat than other parts. While not as bad as they were back in the olden times, it’s still good to get in and get out as quickly as possible. I wasn’t terribly worried about a good top fillet here, the bottom is fine and I was quick about it. So…be quick, and be gone. Don’t let your iron linger.
I’ve written a longer post on the differences between USA and Soviet diodes, you can read that here if you would like.
Second, the diode isn’t installed wrong. Soviet diodes put the band on the anode, not the cathode like USA diodes. It looks wrong, but it’s not - if you get a similar (or any other Soviet-era diode,) just remember - bands opposite the markings on the board!
I went ahead and installed the connectors and the headphone jack. If you want to completely wash the board with alcohol to remove flux, now is the time to do it. You don’t want that getting into the capacitors.
Last was the variable capacitors. Those were soldered in and gently cleaned on back so as not to get any flux in the capacitor itself. Note that you’ll need a very thin, small flatblade to turn these. It’s ideal for setting a station and forgetting it.
How’s it all look?
How’s it work?
Pretty good, I’m pleased. I mean…a crystal radio can only get you so far, but it performs better than the old Science Fair unit in the background of the image. The only other thing I need to test is a longwire, as my tuned loop well overrides any capacitance on the board itself.
In conclusion, this is a really cool little kit, and crystal radios are a great introduction to both kit building, and to radio itself. These have always fascinated me, and this one is no different.
These require no power, so they’re ideal for emergency preparedness. With standalone radio vanishing from modern homes in favor of phones and streams and computers, having an alternate source of information in the event of some adverse event is really something everyone needs. Pack this up with some long wire for an antenna, some clips to connect to a ground, and a small screwdriver - you have a nice little package to take wherever you want.
Mine is, as soon as I can get some small standoffs, going to be tuned to a station and slipped under the stand on my desk as an always on audio source that has no power connections to interfere with what I’m doing.
Thank you to trekster4tw7 for the excellent communication and feedback. Happy listening!
Link to the eBay store where you can purchase one in the previous post.
Previous part of this series: https://wereboar.com … kster-crystal-radio/