Back in the 1960s during my Novice days I operated on the 40-meter band only with 4 different quartz crystals that determined my transmitting frequency with my Eico 720 CW transmitter. I had heard about other old-timers who would shave (or something, not sure of the actual act) the crystals to shift the frequency by small amounts, maybe up to 10 KHz (or, back then it was 10 KC).

Has anyone done this and if so do you know how it was done. Did they change the dimensions merely by sanding or something or did they actually cut the crystal. At that time, most of the quartz crystals were in a packaging known as FT243 and this packaging allowed the crystal to be taken apart by unscrewing the package sides and removing them.

Today, I have a number of old-style FT243 quartz crystals that I would like to experiment with just for the fun of it but I would like to know more about the process before I start.

[Note: none of the tags are specifically fitting that I can tell so I picked two that might hint].

  • $\begingroup$ Scouring powder and water on a glass plate using a very light figure 8 motion will raise the frequency by thinning the crystal. A light stroke of solder lowers the frequency by adding mass to the crystal. Cleanliness is essential. A trimming capacitor will also allow fine tuning. $\endgroup$ Apr 26, 2016 at 1:30
  • $\begingroup$ If you want to get fancy, you can try to find a Q-switched laser nearby, and try to ablate the material from the crystal edge. This should induce less defects to the surface. This is something which was not available in the prime age of the crystals. $\endgroup$ Apr 26, 2016 at 22:56

4 Answers 4


didn't do it, but back in the day stumbled across this, and thought it might be on-topic.

EDIT: inserted original text below.

To: Multiple recipients of list From: [email protected] (Paul Carreiro) Subject: Help in FT-243 Grinding

Greetings fellow boatanchorites!

I need help from all the BA gurus out there practiced in the mysterious art of grinding FT-243 type surplus crystals to operate in the ham bands.

I have had some success bringing crystals down in the 6.8 to 6.9 MHz range up into the 40 meter band using dry "ultra fine" grade sandpaper. Some have resulted in fine CW tones, others seem to be chirpy and have rather lousy short term stability as the transmitter is keyed ( <1/2 second of instability). I realize this instability is a characteristic sound of the era, but some of these crystals seem to be overly unstable and are just about unusable for CW work.

So, I'd like to call on the collective experience of all you OTs out there, to help pass on this magical, little understood, and quite possibly lost art of grinding surplus FT-243 type crystals into the ham bands. What were all the tricks of the trade back then? Are there any new fangled products on the market that would make this task easier or more accurate?

I also have some general questions on the subject: Is there a limit in how far you can change the frequency of a crystal? Seems my attempts at bringing crystals up from 6.7 MHz and below up into the 7.0 MHz range have all resulted in very chirpy output signals.

I've heard that you can alter the frequency slightly up or down by
changing the spring tension inside the crystal. If so, does more tension lower or increase the frequency?

What's the best trick to keep from overshooting your desired frequency?

Also, is there a frequency or section in the 40 meter band that is the hang out for Vintage/Classic gear?

Incase you're curious, I'm using these crystals in Johnson Viking Valiant, WRL Globe Chief 90A and Allied Knight T60 transmitters.

Thanks in advance for any and all help! 73 from a young pup trying to get the old dogs to teach me some new tricks.

Paul, N6HCS [email protected]


From: "Hal R. Waite" Subject: Re: Help in FT-243 Grinding

Try tooth paste or better yet tooth powder in a heavy water slurry on a glass plate. Using light pressure from the second finger (the one that is used for signaling) and a circular motion, grind each of the straight outer edges lightly. Then clean off and dry. If you overshoot, a small amount of pencil lead rubbed on the center of the crystal face will either lower the frequency or cause it to fail to oscillate.

This takes a light touch and a bit of practice. Avoid grinding the center of the crystal face.

Hal K4GFI/7 [email protected]


From: "Roberta J. Barmore" Subject: Re: Help in FT-243 Grinding

Hi! [Fair warning--most of what I'm going to say is hearsay, culled from old magazines rather than actual experience. At least one fellow who posts to the list has ground his own xtals from scratch, and I'm hoping he'll have additional comment--oh, Gordon???]

On Fri, 4 Aug 1995, Paul Carreiro wrote:

I have had some success bringing crystals down in the 6.8 to 6.9 MHz range up into the 40 meter band using dry "ultra fine" grade sandpaper. Some have resulted in fine CW tones, others seem to be chirpy. [...etc. ...]

Based on what I've read, any grade of sandpaper is too rough--scouring power for big jumps, toothpaste for small ones & final grinding on the larger changes. You can also get grinding paste in various grades at hardware stores, though most of what I see is in a waxy base for buffing-wheel work. You've got to keep both of the large surfaces parallel and flat! Work on a slab of plate glass (try junk shops, glass stores, and/or any telescope hobbyists you know--don't take a used lens grinding glass, though, it's not flat any more), and for small rocks, consider grinding a bit of thick brass flat and using it to push on the crystal with. If it goes inactive, grind gently at the corners. Cleanliness is vital. before putting it back in the holder, wash your hands, rinse the crystal; set it down on a clean and soft surface, wash your hands again, put on gloves and clean it with something that'll zap any oil, like 1,1,1 trichlorethane ("Carbo-clor") or possibly denatured alchol. (With older rocks, "cleaning the crystal" was a regular thing). Wash your hands before you start, too, and don't touch your face or hair while thinking what to do. (A dab of denatuared or trichlor will de-oil your hands, though it doesn't do the skin any good [yessiree, that's why I'm a hand model now, ha!] and may be hazardous--EPA and kin aren't very keen about trichlor). B

I've heard that you can alter the frequency slightly up or down by changing the spring tension inside the crystal. If so, does more tension lower or increase the frequency?

More tension, higher freq--within limits! Saw mention of this and other tricks, like adding a shunt trimmer condenser, in an old CQ just the other day. (Naturally I can't find it now). The article mostly concerned making 'em tweakable--the best trick was an FT-243 version of the old vari-gap "rubber crystals," for which purpose it was suggested the best type of tension spring was made of a retangular plate with a half-circle bend in the center and the long sides bent flat with a 1/8" radius half-circle cut-out in the center of the long sides (end view like an omega, looking at the short sides; top view, a sort of fat H, wider than it is tall). Drill and tap the cover plate in the center, run a screw into the tapped hole, and you have a tweakable xtal. Tweak too far and it may break; that's at your risk and no liability on the part of the writer is implied or assumed. Offer void where prohibited. :)

What's the best trick to keep from overshooting your desired frequency?

Go slow, check often. Most GDOs will work for xtal checking--tune it in on your receiver to check freq. If you run up the meter sensitivity, a good crystal will give a lot of deflection. A five-prong or octal tube socket and some plugs that'll fit the coil jacks on the GDO make a nice test fixture. (A five-prong socket can be wired to fit both "doorknob" and FT-243 rocks, a trick I saw for the first time last week and am now finding in a lot of places--tie pins 3 & 4 together, and use pin two for the other connection). If you like fiddlin' measurements, buy a cheap micrometer; measure the thickness, check freq; grind a bit and check & measure again. By the third iteration, you'll be able to plot a fair curve correlating thickness and freq, which will hold pretty close for other crystals of the same type and range. Still need to fire it up and see in the last stages, especially if you're trying to hit a specific freq. (There are ways to fake up a micrometer, with a well-calibrated dial and fine-theaded hardware, a Depression-era trick; using a real mike is probably just as cheap nowadays).

Hope that's of some use. 73, --Bobbi


From: "Ray L. Mote" Subject: Re: Xtal Grinding

  1. Bon Ami powdered cleanser makes a good grinding paste. Been using that for over 30 years now.

  2. The plate glass out of the front of an old (BA-era) TV set makes a good grinding surface. Just spread the paste on the glass and have at it very gently with a circular motion.

  3. N E V E R try to grind both sides of a crystal using this technique! Put a bit of permanent ink or whatever on one side before starting, to show you which side not to grind on each attempt. (Translation: always grind the same side.)

  4. Never tried grinding the edges. Will have to let those with experience talk about it.

  5. I've never had decent results more than 5-7 Kc away, if I remember correctly. (Yeah, I've got Crumbling Mind Syndrome like a lot of other folks.)

  6. There were a number of articles written on this topic in QST, CQ, 73, etc. If you can get next to a CD-ROM version of "From Beverages Through Oscar", you might do a search on XTAL and grinding.


From: "nuusers" Date: Sat, 5 Aug 1995 21:56:37 EST Subject: Re: Help in FT-243 Grinding

Back in 1969 I was interested in making a xtal filter for 455 Kc (oh,oh, I mean 455 Khz) and an old timer showed me how to "edge grind" old military xtals. The ones I used had a lead fused to the each side of the thin material. It worked great...in fact an other old timer gave me about 100 of the xtals...I think they worked in the SCR-522 sets but there fundamental freq. was 400-500 Kc range...to build him a I.F. filter...

On the presure type (FT453 I think) xtals, the secret is to take your time...use 100, 200, 300, and 400 grit NON EMBEDDING grinding compound (Clover brand). The only place I have ever seen it for sale is machine tool and gun smith supplies. Do not use valve grinding compound as it is an imbedding type!! You take it down fast with 100 then go to 200 and finish polish with 300 and 400. You use a flat plate glass piece to grind on. Once you are finished you let the xtal soak in for about a week in old developing solution that has been used a lot...this silver plates it. Take the xtal out of solution with cotton gloves so as not toget grease or rub off the coating. Take a clean piece of plate glass and put white tooth paste on the glass and rub the coating off the edges. There is also a trick for measuring activity and frequency with a sig gen, vtvm and a freq meter...but I can't remember off hand...good luck!!! 73, Steve, KD1DT


From: [email protected] (John Wendler) Subject: Crystal Grinding

In re: Crystal Grinding... Bobbi's summary looked pretty good, from what I remember reading. I remember also seeing something about using Hydroflouric Acid as an etchant, but would discourage anyone from pursuing this option unless they are a trained chemist operating in a proper lab with proper garb. HF is absorbed through the skin and goes to the bone. All reports indicate that this is extremely painful.

I looked into crystals at one point from a professional perspective; checked into the books and talked with some colleagues who make the world's lowest phase noise SAW devices. Suffice to say that cleanliness, proper processing, and good materials are all necessary to go for "world class." For well made crystals, the differences in performance between nitrogen atmosphere, ambient atmosphere, vacuum, in a cold weld or resistance weld or a glass package are all very noticeable. The presence of a gas will dampen the vibrations, decreasing the Q. Contaminents will settle on a crystal, lowering the frequency and the Q; this can be part of the aging characteristics or a deliberate tuning strategy. Pencil lead, anyone? How about water vapor from the atmosphere, and dust in the package?

You can guess where WWII crystals end up in the general scheme of things, as well as crystals for microprocessors, etc that are cranked out by the million. We are fortunate that we do not require world class for amateur application!

One book had a calculation of the acceleration that an atom on the surface of the crystal suffers... I seem to remember ~1,000,000 G. Deflections were on the order of an atomic diameter, if the memory hasn't completed faded this morning. I would certainly expect the lead to move around over the long term, thus changing the frequency slightly.

I hope this background gives a little insight into why tuning with a pencil can sometimes cause problems, both long and short term, as well as why some of the old style crystals might require periodic cleaning as Bobbi mentioned.

A common cleaning process in many semiconductor fabs (for grease removal) is (was? EPA?) some kind of Trichloro for grease removal, followed by methanol for Trico removal, followed by de-ionized water for methanol residue removal. The DI water is then baked off. I used something similar to this while preparing samples (electronic, not insectile) for a scanning electron microscope. (There! I got mention of a hollow state device into this post, so it's partially legitimized!)

You may want to consider distilled water from the supermarket for the final clean up of your crystal. I know that I would not use the water from my faucet to clean it; it's loaded with iron!

BTW, you may want to check your can of Tuner Cleaner/Degreaser ingredients; my can will double for the Trichloro and alcohol steps above, even though the ingredients are not exact.

73 es GL John


From: "Roberta J. Barmore" Subject: Re: Xtal Grinding

Hi! I'd like to expand on the following, for the benefit of the younger folks. (It's just a good thing my rheumatiz' isn't actin' up, Sonny! )

On Sat, 5 Aug 1995, Ray L. Mote wrote:

  1. N E V E R try to grind both sides of a crystal using this technique!

Occurs to me it's might not be clear why this is so--you see, if we want our xtal to be a good one, both sides need to be parallel (if not, you can end up with a dead'un--or worse) and remain at the original angle to the crystalline structure of the quartz. In particular, the AT-cut is a bit fussy; you can think of this common cut as a way to combine the frequency vs. temperature characteristics of the ol' X and Y-cut rocks, which are opposite in sign but of differing slopes. [Real Engineering and Science types among us will know I'm glossing over a lot in that assertion, but it covers the gross effects]. Get too far off, you've got a drifty rock, and the poor feller with a super-solid-state-Whizbang Wonder xcvr will not be able to follow you; he doesn't know from drift. A hardware-store micrometer might be very useful for checking parallelism, especially if you plan to do a lot of crystals. (At what they're getting for 'em new, moving the surplus ones is pretty attractive!) There's also some things having to do with surface smoothness that come into play, and saving at least one of the original surfaces helps keep the rock active--might be wise to put the side you've been grinding against the plate that's got a spring right back of it; last time I opened up a junk FT-243-type holder, there was only a spring on one side. (Dunno if they're all that way).

Oh, the flattish metal spring I mentioned in an earlier post can be found in some types of mil-surplus crystal holders. (I found the article). Interested parties can e-mail me for details & such. Think it was the March '62 CQ.

A source tells me Petersen is looking to get back into crystals for ham gear. Anyone know for sure? Can't seem to find their number....

73, --Bobbi


From: [email protected] (Sheldon Wheaton) Subject: Re: Help in FT-243 Grinding

I've ground quite a few xtals for my use in the Antique Wireless Association's annual CW QSO contests (Rig is 1939 vintage reproduction 6L6-809). A couple of my comments on the subject:

For a given type of "cut" (direction of XTAL lattice molecular alignment), the fundamental frequency is inversely proportional to the thickness. Most FT-243 xtals are "AT" cut. The formula is listed in many early (1930's) ARRL handbooks. Using this formula, and a good micrometer, you can make some rough cuts without having to assemble the crystal every time.

Keep your eye out for old xtal grinding kits at hamfests. I have some with different "grits" of grinding powder. Not sure what it is, but looks & feels about like talcum powder, except gray in color.

If the xtal is not ground with both sides parrallel, you may end up with two or more different "fundamental" frequencies! Not good.

Sometimes an otherwise good xtal that worked fine, but won't oscillate or does so erratically after the last grind that moved it only 5 kc or so, can be made to work correctly by slightly "beveling" all four edges on both sides (8 edges total). This procedure is documented in many books of the 30's. It usually doesn't need to be a visible bevel, just a few "strokes" with the compound.

I have best luck with a figure 8 motion for grinding. Some grinding kits have a flat piece with a pentagon shaped, shallow cut-out, with inwardly curved edges, which will make the quartz piece move around in an impressive "Spiro-graph" type motion, but I haven't had much luck with this item.

gud luck & 73, Sheldon KC0CW [email protected]


From: [email protected] (Roy Morgan) Subject: Re: Help in FT-243 Grinding

Greetings fellow boatanchorites!

I need help from all the BA gurus out there practiced in the mysterious art of grinding FT-243 type surplus crystals to operate in the ham bands.

Here are some short notes on your questions:

-use wet finest possible wet-dry emery paper, or fine carborundum or even toothpaste on a piece of glass.

-activity goes up and down as you grind the frequency upwards. You may have just gotten to a poor spot on most of your crystals because of the distance you moved the frequency.

-activity at/near a frequency depends on thickness/width ratio so activity can sometimes be restored by grinding the edge(s) of the crystal. Frequency will likely got up as you grind the edge. Do a LITTLE at at time.

-a crystal in a holder with some dust will act strange, if it oscillates at all, so be CLEAN when assembling. Handy things to have are: acetone or alchohol, clean - the kind you might get at the paint store may not be too clean (and ventilation!), little soft brush from the art store, blower like a bulb-type solder sucker or baby nose syringe ...

-increasing spring pressure in the holder will usually increase frequency, I think. beware of cracking the thing.

-a bit of pencil lead or solder rubbed on the flat surface will lower the frequency by making it heavier, and doing this may help you predict what will happen if you grind the edges.

-capacitance of the oscillator circuit may affect the activity of a crytal you've ground.

I'm intersted in making up a "standard" oscillator circuit - I have a handbook giving lots of tube circuits. I'd be glad to cooperate on this project if you'd like.

-- Roy -- Roy Morgan / Tech A-266 / NIST / Gaithersburg MD 20899 (National Institute of Standards and Technology, formerly NBS) 301-975-3254 Fax: 301-948-6213 Internet: [email protected]


From: Andy Wallace Subject: xtal grinding monitor -- someone TRY THIS.

Also in the '49 Hints and Kinks book is a method (page 88) of monitoring the frequency of a quartz crystal DURING GRINDING.

Take a flat piece of aluminum or copper about 6" square, and connect it to your receiver antenna post using a short lead. Place the plate glass on which the grinding is being done on this sheet. You can tune in the crystal frequency on the receiver by the scratches you hear as the crystal is being ground.

This is the first time I've ever heard of something like this, but I assume the laws of physics and piezoelectricity allow this to work. 'scuse me, I have to go take apart a picture frame and find some PC board material! But seriously, would someone on the List volunteer to try this? Fascinating...

--Andy [email protected]

P.S. The H+K book also recommends automotive valve grinding compound for speedy xtal grinding. Hmm...I smell some new Novice xtals coming on, maybe even for 80m.

  • $\begingroup$ thanks for the post and the link. I think that is exactly the kind of information I was looking for. Definitely something to get started with. $\endgroup$
    – K7PEH
    Jan 14, 2015 at 17:17
  • 2
    $\begingroup$ Can you quote or describe the relevant material from your link? Link-only answers become useless if the linked site goes away. $\endgroup$
    – Kevin Reid AG6YO
    Jan 14, 2015 at 19:21
  • $\begingroup$ I had read long ago of using "figure 8 motion" for grinding, as mentioned in one of the articles. To avoid barreling the xtl. $\endgroup$ Jan 15, 2015 at 0:23
  • $\begingroup$ @KevinReidAG6YO: better ? :) $\endgroup$ Jan 15, 2015 at 14:18
  • 2
    $\begingroup$ It would better if you quoted just the relevant parts, and even better if you added additional information of your own. $\endgroup$ Jan 15, 2015 at 19:32

It is the thickness of the crystal that primarily determines its operating frequency.

When crystals are manufactured, they are gradually ground down in a special fixture. The operator monitors the process by keeping a shortwave radio nearby, which picks up the electrical noise created by the stress of the grinding action on the crystals, which is relatively narrowband noise centered on the resonant frequency. When this gets to be slightly above the target frequency, the grinding process is halted.

The next step is to plate electrical contacts on the newly-ground faces of the crystal so that it can be mounted in a holder. The thickness of this plating affects the final frequency (thicker plating reduces the frequency), and this is how the final calibration of each crystal is accomplished.

If you want to adjust (lower) the crystal frequency after it has been completed, you can try adding additional mass to the contact areas. I don't know any easy way to raise the frequency.

  • $\begingroup$ Yes, with the FT243 crystals it was the thickness that determined the operating frequency. But, during my recent research on this question, I learned that thickness is no longer the only parameter. Some crystals are very complex with geometric shapes in addition to thickness determining the more sophisticated operating with multiple operating frequencies and also (others) stronger harmonic overtone frequencies. Which means I probably would not be attempting this act on newer crystals besides the fact that they are often in sealed packages. $\endgroup$
    – K7PEH
    Jan 14, 2015 at 17:11

I only scanned that whole quote. I have my father's W9EHS SK, FT crystal grinding equipment. It has two special grinding compounds and the two plates. One of the plates has a rosette-like shaped indent that helps guide the blank in the figure 8 pattern. There is a special FT holder that allowed easy insertion and removal.

At times, the edges had to be ground, usually to stop unwanted modes. An acid was also used, IIR to finish it off and, I think< help prevent some spurious modes or possible start-up problems. I've forgotten much about those crystals...

Modern crystals are quite a bit different, though operating to the same principles. I didn't know these FT crystals were AT cut and I only have some design using modern, mostly AT cut crystals, but some other cuts as well as the tuning fork (Statek) types.

I believe I am the first to have a synthesized 2 meter hand held back in the 70's and had to learn about crystals for a work project that led to that PLL synthesizer.


I can second the comments about bon-ami. Way back 2/3 of the way through the last century, we also used some of the super fine abrasives used for the later stages of grinding amateur telescope mirrors. Try Googling "Amateur Telescope Making Supplies" and "Telescope Mirror Blanks" for suppliers. - W6HPA


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