Finally got my hands on a point contact diode from a crystal radio, it seems to be (well tarnished) galena with a silver cat's whisker. It's 100 years old and a much better designed setup than my attempts at this.
The first electrons passing over this 1920s galena diode for maybe a century, and I'm getting some great curves moving the point contact around. Top left is a fairly respectable (but leaky) approximation of a germanium diode.
They are similar to my diy results with galena, it's more stable, but still easily disrupted by knocks. I can see how using it in the radio must have been frustrating.
Next I'll see how this sounds in the resonant ladder filter. More info and photos here: https://cornish-semiconductor.com/index.php/Semiconductor_history
New release & free download!
Live at Pattern Club Sheffield
The live rig included the 1920s galena point contact diode in the circuit, probably quite close to where it was mined, so a sort of local guest collaborator along with all the Cornish minerals. I've also swapped to sterling silver cats whiskers, I *think* it works better than steel or copper, but I need to do some proper tests.
bandcamp: https://cornish-semiconductor.bandcamp.com/track/live-at-pattern-club-sheffield
archive.org: https://archive.org/details/cornish-semiconductor-corp-live-at-pattern-club-sheffield
soundcloud: https://soundcloud.com/cornish_semiconductor/live-at-pattern-club-sheffield
Thanks to all at @patternclubsheffield
Photo credit Nik Nenov (cc-by-sa)
@nebogeo @IrrationalMethod However did they go about getting the glass blown parts just so, and the machined ends precise. And then someone supplied just the right type and size of spring. All with a precise bit of galena that doesn’t shake away? So many tech and craftsmen involved. Must have been big money back then to make such components.
@cobalt123 @IrrationalMethod here it is disassembled, the end caps are made of plastic (I think 'ebonite' probably) along with the handle. The crystal is usually fixed using wood's metal, which melts at 70 degrees (and is pretty toxic) but doesn't affect the galena. I can't imagine how futuristic this stuff must have been in 1920...
Oh i see now, that's quite a bit bigger than I was picturing from the first image.
I'm sure it seemed like magic in the 1920s, but honestly, it still seems quite a bit like _magic_, or alchemy, to me today.
"Oh yeah, just use this toxic amalgamation to stick a rock on side and just barely touch it with a spring connected to the other side, then you'll be able to pull whispers out of thin air!"
@IrrationalMethod @nebogeo HA-ha! Exactly!
Jun 7, 2026, 2:56 PM@nebogeo Love this alt text!
@nebogeo that is a beautiful artifact from a time when radio was pure magic. :)
Jun 9, 2026, 9:34 AM@nebogeo my father, who was born in 1935 (he would have been 90 last year...) I remember him telling me he would play with a galena radio in his childhood. My grandfather, who I didn't get to know, was into all sorts of experiments.