Multiband Crystal Radio Set Pulls Out All The Stops

Most crystal radio receivers have a decidedly “field expedient” look to them. Fashioned as they often are from a few turns of wire around an oatmeal container and a safety pin scratching the surface of a razor blade, the whole assembly often does a great impersonation of a pile of trash whose appearance gives little hope of actually working. And yet work they do, usually, pulling radio signals out of thin air as if by magic.

Not all crystal sets take this slapdash approach, of course, and some, like this homebrew multiband crystal receiver, aim for a feature set and fit and finish that goes way beyond the norm. The “Husky” crystal set, as it’s called by its creator [alvenh], looks like it fell through a time warp right from the 1920s. The electronics are based on the Australian “Mystery Set” circuit, with modifications to make the receiver tunable over multiple bands. Rather than the traditional galena crystal and cat’s whisker detector, a pair of1N34A germanium diodes are used as rectifiers — one for demodulating the audio signal, and the other to drive a microammeter to indicate signal strength. A cat’s whisker is included for looks, though, mounted to the black acrylic front panel along with nice chunky knobs and homebrew rotary switches for band selection and antenna.

As nice as the details on the electronics are, it’s the case that really sells this build. Using quarter-sawn oak salvaged from old floorboards. The joinery is beautiful and the hardware is period correct; we especially appreciate the work that went into transforming a common flat washer into a nickel-plated escutcheon for the lock — because every radio needs a lock.

Congratulations to [Alvenh] for pulling off such a wonderful build, and really celebrating the craftsmanship of the early days of radio. Need some crystal radio theory before tackling your build? Check out [Greg Charvat]’s crystal radio deep dive.

Turning Scrap Copper Into Beautiful Copper Acetate Crystals

Crystals, at least those hawked by new-age practitioners for their healing or restorative powers, will probably get a well-deserved eye roll from most of the folks around here. That said, there’s no denying that crystals do hold sway over us with the almost magical power of their beauty, as with these home-grown copper acetate crystals.

The recipe for these lovely giant crystals that [Chase Lean] shares is almost too simple — just scrap copper, vinegar, and a bit of hydrogen peroxide — and just the over-the-counter strength versions of those last two. The process begins with making a saturated solution of copper acetate by dissolving the scrap copper bits in the vinegar and peroxide for a couple of days. The solution is concentrated by evaporation until copper acetate crystals start to form. Suspend a seed crystal in the saturated solution, and patience will eventually reward you with a huge, shiny blue-black crystal. [Chase] also shares tips for growing crystal clusters, which have a beauty of their own, as do dehydrated copper acetate crystals, with their milky bluish appearance.

Is there any use for these crystals? Probably not, other than their beauty and the whole coolness factor of watching nature buck its own “no straight lines” rule. And you’ll no doubt remember [Chase]’s Zelda-esque potassium ferrioxalate crystals, or even when he turned common table salt into perfect crystal cubes.

Potassium ferrioxalate crystal

Growing Spectacular Gem-Like Crystals From Rust And Simple Ingredients

When we talk about crystals around here, we’re generally talking about the quartz variety used to make oscillators more stable, or perhaps ruby crystals used to make a laser. We hardly ever talk about homegrown crystals, though, and that’s a shame once you see how easy it is to make beautiful crystals from scratch.

We’ve got to say that we’re impressed by the size and aesthetics of the potassium ferrioxalate crystals [Chase Lean] makes with this recipe, and Zelda fans will no doubt appreciate their resemblance to green rupees. The process starts with rust, or ferric oxide, which can either be purchased or made. [Chase] chose to make his rust by soaking steel wool in a solution of saltwater and peroxide and heating the resulting sludge. A small amount of ferric oxide is added to a solution of oxalic acid, a commonly used cleaning and bleaching agent. Once the rust is dissolved, potassium carbonate is slowly added to the solution, turning it a bright green.

The rest of the process happens more or less naturally, as crystals begin to form in the saturated solution. And boy, did they grow — long, prismatic lime-green crystals, with a beautiful clarity and crisp edges and facets. The crystals don’t last long under light, though — they quickly lose their clarity and become a more opaque green.

[Chase]’s crystal-growing efforts have shown up here before, when he turned humble table salt into beautiful cubic crystals. We find the whole crystal-growing process fascinating, and we’re looking forward to more of this in the future.

Mining And Refining: Pure Silicon And The Incredible Effort It Takes To Get There

Were it not for the thin sheath of water and carbon-based life covering it, our home planet would perhaps be best known as the “Silicon World.” More than a quarter of the mass of the Earth’s crust is silicon, and together with oxygen, the silicate minerals form about 90% of the thin shell of rock that floats on the Earth’s mantle. Silicon is the bedrock of our world, and it’s literally as common as dirt.

But just because we have a lot of it doesn’t mean we have much of it in its pure form. And it’s only in its purest form that silicon becomes the stuff that brought our world into the Information Age. Elemental silicon is very rare, though, and so getting appreciable amounts of the metalloid that’s pure enough to be useful requires some pretty energy- and resource-intensive mining and refining operations. These operations use some pretty interesting chemistry and a few neat tricks, and when scaled up to industrial levels, they pose unique challenges that require some pretty clever engineering to deal with.

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Growing The World’s Largest Snowflake

Plenty of areas around the world don’t get any snowfall, so if you live in one of these places you’ll need to travel to experience the true joy of winter. If you’re not willing to travel, though, you could make some similar ice crystals yourself instead. While this build from [Brian] aka [AlphaPhoenix] doesn’t generate a flurry of small ice crystals, it does generate a single enormous one in a very specific way.

The ice that [Brian] is growing is created in a pressure chamber that has been set up specifically for this hexagonal crystal. Unlike common ice that is made up of randomly arranged and varying crystals frozen together, this enormous block of ice is actually one single crystal. When the air is pumped out of the pressure chamber, the only thing left in the vessel is the seed crystal and water vapor. A custom peltier cooler inside with an attached heat sink serves a double purpose, both to keep the ice crystal cold (and growing) and to heat up a small pool of water at the bottom of the vessel to increase the amount of water vapor in the chamber, which will eventually be deposited onto the crystal in the specific hexagonal shape.

The build is interesting to watch, and since the ice crystal growth had to be filmed inside of a freezer there’s perhaps a second hack here which involved getting the camera gear set up in that unusual environment. Either way, the giant snowball of an ice crystal eventually came out of the freezer after many tries, and isn’t the first time we’ve seen interesting applications for custom peltier coolers, either.

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Jan Czochralski And The Silicon Revolution

If you were to travel back in time to the turn of the previous century and try to convince the average person that the grains of sand on just about any beach would be the basis of an industry worth hundreds of billions of dollars within 100 years, they’d probably have thought you were crazy. Aside from being coarse, rough, and irritating, sand is everywhere, and convincing anyone of its value would be a hard sell, unless your interlocutor was a real estate visionary with an appreciation of the future value of seaside property and a lot of patience.

Fast forward to our time, and we all know the value of the material that comes from common quartz sand: silicon, specifically the ultra-purified crystals of silicon that end up as the wafers we depend on to build the circuitry of life. The trip from beach to chip foundry is a long and non-obvious one which would not have been possible without the insights of an undistinguished Polish student and one-time druggist who discovered the process that made the Information Age possible: Jan Czochralski.

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Pulling A Crystal By Grinding It

If you own a radio transmitter, from a $10 Baofeng handheld to a $1000 fancy all-band transceiver, setting the frequency is simply a case of dialing in where you want to go. A phase-locked-loop frequency synthesizer or a software-defined radio will generate your frequency, and away you go. There was a time though when synthesizers were impossibly complex and radio amateurs were faced with a simple choice. Use an LC oscillator and put up with drifting in frequency, or use a crystal oscillator, and be restricted to only the frequencies of the crystals you had. [Mark Erdle, AE2EA] modified a 1950s broadcast AM broadcast transmitter for the 1.8MHz amateur band, and his friend [Andy Flowers, K0SM] thought it needed its crystal back for originality rather than the external frequency source [Mark] had provided. He documents the process of modifying a crystal oven and moving a crystal frequency in the video below the break.

A crystal oven is a unit containing the crystal itself alongside a thermostatic heater, and in this one, the crystal was a 1970s-vintage hermetically sealed HC6 device. He modified the oven to take a socket for older FT243 crystals because the quartz element can easily be accessed. [Andy] picked a crystal as close as he could find below the required frequency. He then ground it down with very fine grit on a glass plate, reducing its mass and thus its resonant frequency. We’re taken through the process of getting it close to frequency, but sadly don’t see the etching that he uses for the very last stage. At the end of the video, we see a QSO on the transmitter itself, which is something of an oddity in an age when AM on amateur bands has been supplanted by other modes for decades.

If you’re curious about the transmitter there’s a video thread following its restoration, and if the guts of older radio gear interests you then take a look at this aircraft receiver lovingly brought back to life.

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