Ever been working on a project and get stuck on one of those last little details? That’s what happened to [Empire of Scrap]. He’s building an Ohio Scientific (OSI) superboard II replica. He wants it to be accurate down to the dates on the chips. It is quite an impressive build. The problem is the crystal. OSI used large crystals, even by early 1980s standards. The crystal is in a large can with thick pins, like something you’d expect to find in old radio equipment. The problem is that this crystal package isn’t made anymore.
The crystal had to be exactly 3.932160 MHz, and while [Empire] has a huge collection of vintage crystals, he didn’t have the right one from the 70s. He did, however, have that value in a modern crystal.
The solution? Hide the new crystal in the can of an older one. The only problem is that crystals are sealed. The bottom appeared to be some sort of plastic or resin. Gong after it with a side cutter, [Empire] realized it was glass! Thankfully, none of it got in his eyes, though his hands may have taken a bit of a beating.
With the old crystal’s shell hollowed out, [Empire] installed the modern device and potted everything in resin. The transplant worked. Now, all that’s left is to fire up the OSI and start hacking.
Want to build a replica computer but don’t want to hunt down the parts? Check out [Taylor] and [Amy’s] build of this minipet. Regardless of the size of the case, crystals all work in the same way.
I suffer from CDO….. that’s OCD with the letters in the right order😂
“Gong after it with a side cutter,”
Sometimes I let typos pass without comment.
But the visual this one presented was worth the effort.
COD is the right order because all curves are outward.
I prefer DOC because it has curves touching each other and because it also shows up in common dictionary.
With those older HC6U crystals, the can is soldered to the base around the bottom edge.
Just needed some careful work with a hot air soldering tool to remove the can.
I did desolder the can bottom, but since the glass is molded into the bottom part of the cans and the old pins are surrounded by the glass, it was impossible to put the new crystal in.
The donor-crystal had solid , thick and short pins. It was not possible to reuse the original pins, since it was made for use in a socket, not for soldering, probably for radio related tuning.
Hmm, those big crystal cans….
You could hide a RP2040 inside it and emulate the whole thing.
Why not use a 555?
At nearly 4 MHz?
That too!
cough QRP Labs ProgRock2 programmable crystal. cough
https://qrp-labs.com/progrock2.html
Fits in an HC6 crystal holder. Up to 3 outputs. 3.5 KHz to 300 MHz. $18.
That’s tricky, I think. A “passive” quarz crystal (2 pin) is not same as an “active” crystal oscillator (4 pin).
The quarz crystal is being part of an oscillator circuit, which operates on clean sine waves.
At first, at least. It may turn the signal into square waves later on, to be processed by TTL hardware.
An crystal oscillator by contrast does output ready-to-use TTL signals right from the start.
That’s why it’s not easy to simply use an microcontroller in place of an quarz crystal. They oscillator pins are actively generating a frequency, already. In order to use that, the oscillator circuit on the computer board has to be bypassed.
I remember when you could send away to International Crystal and get back a crystal custom made to your frequency.
CSB: Valpey (now CTS Valpey Fisher) Crystals was founded right down the street from where I live. The founder’s house is next door and the founder’s son dug the foundation for my house. I have a couple of large WWII vintage crystals made by them.
Ah yes, those dinosaurs! I remember old hams talking about how they changed the crystal frequency by carefully applying thin layers of graphite to the resonating disc.
I’ve always admired their skill until I realized the crystals were so big and unhandy.
Being of a younger generation I assumed they’ve meant crystals in normal form factor. I thought they had used a microscope and fine tools to do the mod.
I didn’t think of those big, clunky crystals. I was so naive. 🥲
They’re talking about really big crystals: DC-35 and FT-243, used for higher current tube oscillators. You unscrew the lid, pull out the quartz wafer, and lower the frequency with graphite or raise it by grinding it with toothpaste or jeweller’s rouge.
Hah! Comet cleanser was my dad’s preferred grinding paste. Used a figure-8 motion to keep the thickness constant. Using pencil was more precarious. It had a tendency to reduce the activity of the crystal. But it all worked. Made my 40m crystals that way…
I have on my desk, two Valpey crystals: one CM1 (DC-35) for 1750 (kHz?) (s/n 5143) and one CM5 (FT-43) for 14096 kHz (s/n 61). Inherited from my f-i-l.
I confess that I’ve done a similar fix replacing capacitors in those large metal jacketed multi caps which are hard to find.
There are those that consider this sort of thing OCDish, but, IMO, it takes OCD types to make the world work at its best. You wouldn’t have original appearing tube radios and TVs and quality museums (for anything!) without this type of numbing attention to detail.
There is a big difference between people with OCD and people who are passionate and try to do things as well as they can.
This was actually what inspired me to do this. Vintage TV and radio restoration guys have been stuffing old capacitor shells for years!
They’ve also substituted historic anode batteries by a bunch of 9v batteries (10x).
The outer shell of the original anode battery was kept, however.
It was just cardboard more or less. Worked very well. It’s same technology in principle, after all.
Doing this occurred to me when I was wrapping a few Intel 4004 SBC’s recently. Incredibly, I found the proper frequency crystal for the 4004 on eBay and I got a bag of 100 for about $10 (but in HC-49/U) Unfortunately, all of the old school crystals that I have are in themselves valuable (like, 1.0 Mhz)!
Isn’t The Hidden Crystal Method on the soundtrack for Wipeout XL?