Quartz crystals
pa3fwm.nl
pa3fwm.nl
I used many similar techniques to the same end of removing quartz which raised its frequency. Grinding materials included abrasives such as jeweler's rouge, cerium oxide, commercial polishes such as Brasso and Silvo and even HF solution. I'd place the quartz on a small section of plate glass and slide it through a slurry of the abrasive periodically testing its frequency until I'd reached my target.
There's an art to this that's too long to mention here except to say abrasives were used strategically, course grinding would get me near the desired frequency and I'd finish off with a fine abrasive. Then there was the job of re-aging the crystal after its recent abuse to increase its stability. Other techniques were involved such as not lowering its Q factor, etc. which I'll not cover here.
The most desired crystal cut was from the XT-plane (being the most stable) but it was generally difficult to get as it's only a small section of the quartz crystal (also each cut oscillates only over a limited range of frequencies). I used to have a book that explained these cuts in detail, their frequency ranges and electronic properties along with the basic crystallography which I lost years ago. A quick glance at the book would have shown that a great deal of science, engineering and skill is involved in the selection of quartz and its manufacture into useful resonators.
BTW, the mentioning of HF will likely horrify chem-phobic readers. We were well aware of its dangers and took special precautions never to come in contact with it.
The other details are fascinating, though - the intersection of mechanical, crystallographic, and RF (?) properties of a crystal that you can adjust through abrasives and selection of the cut.
Teflon is not affected by HF, so if you use only vessels of Teflon to hold the HF solution and tweezers made of Teflon for handling anything that you submerge in the solution of HF, it works fine.
Besides using Teflon for anything that is in contact with the HF solution, you must do all work under a hood that evacuates the vapors of HF emitted by the solution, otherwise handling a HF solution would be very dangerous. It is good that gaseous HF is lighter than air, so after being evacuated it will continue to rise in the air, while becoming more and more diluted.
The bottle was flat on top from which protruded its 'neck' — more a threaded spigot of perhaps 8mm in dia. and about 10 to 12mm high with a small hole in it for the HF to exit. A red plastic cap screwed onto the thread to seal the bottle.
If the bottle were ever knocked over (which it never was) very little would have spilled out (picture the threaded top and screw cap on the small bottles of Tabasco sauce and you've pretty much got it).
So the HF only came out in drops which were poured directly into a small plastic beaker of about 50ml containing about 20ml of H2O and the crystal. The crystal rested on some finely corrugated plastic and not lying flat on the bottom to ensure the etching process was reasonably uniform.
The operation was done outside and if I recall the HF was neutralised with NaOH.
The soln was very dilute and the process could easily take over an hour and was used mainly to finish off crystals that had already been through the abrasive process.
I don't know what type of plastic the bottle was made of but it was jet black.
And, if you're sneaky, you can add solder.
I'm working on something much, _much_ smaller than that!
I've been trying to remember the name of a particular instrument for you for the last 24 hours but so far no success, if I recall it I will post it here.
The good thing about harmoniums is that they have clearly defined layers, and each layer can be approached left to right.
The things that worried me were the steps that are difficult to reverse without the risk of damage, like gluing and tuning. I've done some of both now!
Curious about that mystery instrument. Give me a clue.
They are fairly big compared to your typical harmonium.
https://www.reedsoc.org/index.php/rosdb/vieworgan?ascnd=1&ID...
They're a funny half breed, they have a blower motor, use reeds instead of pipes, and were popular with churches as practice instruments.
Oh, and this might interest you if you haven't found it yet:
https://www.reedsoc.org/index.php/information/reed-organ-rep...
Incidentally, I'm one of those mad people who'll put on a recording of Helmut Walcha playing Bach's Passacaglia and Fugue in C minor on a Silbermann and turn the volume up until the room shskes.
I'd assumed that with piezo crystals etc there was a mechanical connection rather than an electrode bonded to the crystal?
But if you can add solder presumably there is some kind of molecular connection with the metal?
The electrodes may consist of multiple layers, a base layer that adheres strongly to quartz and a top layer that is solderable, e.g. made of nickel or silver.
The pins of the package that hosts the crystal resonator are soldered on the electrodes, in places well chosen so that they will not damp much the oscillations of the crystal.
When the mass of the crystal must be increased to shift the resonance frequency, excess solder may be deposited on the electrodes.
Fun video of 'metallization' on a coarser scale! https://www.youtube.com/watch?v=e-QcseGvU5o
I grant you it's not in the same league as voicing a diapason though. :-)
I reckon adjusting and tweaking things goes with the territory. I'm pretty much at home tweaking crystals, fixing reeds, aligning IF stages in radio and TV equipment, there's much of a sameness in the way one tackles all of them.
BTW, I've actually repaired reeds by soldering them. Not a good fix though as the solder can fatigue with use. Throws out equal temperament a bit too but most can't hear the difference.
https://blog.afandian.com/tags/harmonium/
By 'repaired' you mean closing a fracture? I'm interested to hear your experiences! Electronics solder or silver solder?
This one is 60 cents sharp across the board (not uncommmon), but I wanted a social instrument. So I brought them down with solder. The bottom two octaves have worked out well. The next two... we'll see. I now have the fear that I've weakened the brass by heating it. But it still sounds nice and speaks well. Fingers crossed.
Right, I haven't had many fracture but it was more than I expected. I've had some come apart (completely—shear off). One I recall fixing (replacing the reed) with a piece cut from a phosphor bronze shim several thou thick (I had various thicknesses). Replacing the reed was easy but voicing was a problem because p-bronze has different properties to the original. It was a long while ago so I can't remember exactly what I did but it worked—sort of. I eventually got it roughly in tune but it was a different volume to the others.
About two weeks ago I was up at my old family home for the first time in years and there are two harmoniums dating from the the mid to late 19th C. which I meant to fix years ago. The woodwork on one is particulary ornate and in excellent condition. They both have dead keys when I played them. Reckon I've some wok cut out for me. .
The book was a harback with a bright yellow dust jacket and I think its title was printed in red. It was about 300 pages and was no lightweight, full of resonance equations, tables etc.—the sort of book you'd find in the lab of a commercial crystal manufacturer.
Can't remember the price but it was damned expensive. At times over the years I've had need to refer to it and I still get a bit peeved when I think about it.
Damn nuisance my memory isn't better. However, I'd recognize it instantly if I saw it. Must check those references out. There may be enough info online for me to figure it out. Thanks.
Ah, that has to be the book, just did a search and there's a photo of the cover on Amazon that I recognize. I said it was bright yellow with red writing and I was pretty close with its red lines and bits.
240 pages and not 300, but that's not too bad after close on 50 years. And I was correct about the price too, it is expensive, Amazon has it at $110 for the hardback.
Good one!
Some of you guys should have picked that up. ;-)
I've seen much more detailed diagrams of the crystal and cuts/cutting angles but I can't find one online. . Those precision diagrams are required by those who cut the quartz at the start of the manufacturing process.
https://xoprof.com/2023/09/unleashing-the-mystery-of-crystal...
New fear unlocked
The quartz crystals themselves were grown with carefully controlled levels of specific impurities (like scandium) in order to reduce their temperature sensitivity.
Galvanic deposition of silver has been frequently used for increasing the thickness of thin metal layers that had been deposited in vacuum, in order to adhere to the crystal.
For instance:
https://www.pa3fwm.nl/projects/sdr/
The longer you read, the more amazed you will be.
It's much easier to build/buy electrical rather than mechanical LC components to hit audio frequencies ~100Hz-10kHz.
For electronic circuits such as frequency reference markers where frequency stability is important the lowest practical frequency is 100kHz with 1Mhz preferred, and where frequency tolerances are tight 5 and 10MHz are much preferred with operation in a temperature stabilized oven to minimize frequency drift.
The most frequency-stable crystal cuts are at those frequencies, as frequencies increase (say >10MHz to 100MHz), which at the highest frequencies require the crystal to operate in overtone mode, frequency stability again tends to decrease.
In the past, audio RC oscillators or LC oscillators were used, with the former being preferred as the latter required too bulky inductors to reach so low frequencies.
Nowadays, it is usually simpler to not use any audio oscillator, but to use some microcontroller that divides the frequency of its clock until reaching the desired audio frequency.