ETCHING A CRYSTAL..?

[ve6pg]

...HI FROM TIM...I CANT FIND THE OLD ARTICLE,SO I'M ASKING HERE...WHAT ARE THE PROCEDURES FOR MOVING A CRYSTAL IN FREQ?...I'VE GOT SOME ROCKS,THAT I WANT TO MOVE FROM THEIR CURRENT FREQS...TNX...TIM...SK..

[Don, W2DL]

Hi Tim,  first I assume you have the older "FT-243" xtals that can be disassembled and the actual quartz xtals plate can be removed. The modern smaller crystals have the leads soldered to metallic coatings on each side, making grinding impossible as far as I know. I always used a fairly thick (1/4" as a minimum, 1/2" is better) piece of plate glass, maybe 8" x 8" or so  to do the grinding on. I used Bon-Ami cleaning powder, which although it was advertised as "hasn't scratched yet" actually was abrasive enough to move crystals a ways if you spent the time to do it. Use a thin coating of some  mildly abrasive powder sucha s this and a bit of water to make things go easier and put the xtal plate down on the powder/water, and grind it around in a figure eight motion. Be sure and keep constant pressure on the center of the xtal, don't do one edge more than another. Problem is, there is a limit as to how far anyone xtal can be moved, and this is pretty much a function of what "cut" it is. Some moved fairly easily, some died after just a bit of grinding and never came alive again. Can't tell before you try it. As I remember, on 75/80 m I could move most xtals about 10 KHz before they became less active  - do it slowly, use a freq counter to see how far a certain amount of grinding moves it.  Eventually, excessive grinding will kill almost any xtal if carried to extreme, be careful! 

73's
Don, W2DL

[KA8WTK]

Tim,
  One of my old handbooks talks about lowering the crystal frequency by rubbing it on both sides with cold soft solder. They reccomend about a 1/4" of an inch circular area in the center for rubbing. Additional applications go in the same spot. The book also says you can get a total of about 35 kc at 3500 kc "with a good active crystal".
  So, if you grind too far, you can bring it "back" just a little.
  Good Luck!

[Don, W2DL]

Good point Bill -

I also used to use a medium "lead" (graphite) pencil added to the middle, good thing about the "lead" pencil is the eraser will remove a lot of it if you drop the freq too far. Down side is, the graphite is not too stable on the crystal surface and over time the frequency goes up, and up, and up until you eventually get back somewhere near the original freq.

Don, W2DL

[W2JBL]

  i use "crystal grinding compound" my Dad left me with good results on FT234 crystals. i can go about 100-150 KC on 75, farther on 40. the stuff is (i think) silicon carbide in powder form, and i have two different grits- 800 and 1000. i use 70% rubbing alcohol for a lubricant while grinding. mix up a fairly wet paste of the two and apply it to the grinding plate. keep carefull count of the number of laps you have on each side of the blank, using a "fugure eight" motion. cut a few laps on one side, flip it over, cut the same number on the other, then clean the blank and check frequency. frequent replcement of the alcohol/compound mix is a good idea- after every two or three sides ground wash the blank and glass, then add fresh compound/alcohol mix. keep the work clean, and do not handle the blank with your bare fingers (use surgical gloves) to keep oil from your skin from conatminating the blank. activity drops off rapidly if you don't grind both sides perfectly flat and paralell. if you go too far the pencil lead trick works, but i also use an old buzzard trick of dipping the blank in liquid iodine to lower the frequency- it's more stable than pencil lead.

   the method used for chemically "etching" crystals is rather nasty, as you have to dunk them in a solution of water and amonium biflouride. not recommended for the hobbyist, unless you don't mind an occasional visit from your local "hazmat" cleanup squad. one can also build a very effective VFO in about the same time it takes to grind  three or four crystals (an afternoon's work). replicating a VF-1 or Johnson 122 is not rocket science.

[w3jn]

Good point, Chris, I don't know why hams are afraid of building oscillators.  That seems to be the stumbling point in building receivers as well.  It sure ain't rocket science - $20 and a handful of transistors makes a Fine Business VFO indeed.

Careful attention to parts layout, mechanical rigidity, and parts quality yields success 100% of the time.  The time spent f'ing around with crystals can be better spent building a VFO, IMHO.

And if you don't wanna build, most any hamfest will yield a mid-70's/early 80's Wavetek or HP "synthesizer oscillator" which usually cover .01 Hz thru 13 MHz = the HP 3330 is an example of one that sweeps, has keyboard programmable output levels, etc.  Paid $20 for mine...

[ve6pg]

...NO QUESTION THAT BUILDING A VFO IS SIMPLE,OR USE A SIG GEN,ETC...BUT A FRIEND IS BUILDING A CW RIG,AND HE WANTS CRYSTAL CONTROL..CONSIDERING THE ROCKS AVAILABLE ARE NOT THE FREQ HE WANTS,WE WERE DISCUSSING HOW TO MAKE A ROCK MOVE FREQ...TIM...SK..

[w3jn]

Hey, to each his own.... but for the time he spends messing with crystals he could include a nice VFO in the xmitter.

73 John

[The Slab Bacon]

       I reground a handfull just to say i did it. Took a bunch of somewhat worthless cw crystals and reground them to AM frequencies. It was somewhat a pain in the ass, but not that terribly difficult to do. I found another interesting way to do it. I used
"wet and dry" sandpaper like used for automothve refinishing and water on a piece of glass for a flat surface. Started with #220, then #400, then finished up with #600. It worked OK-FINE. but was time consuming.
       Building a vfo would definately have been time better spent, but like a right of passage, it was something I wanted to do just to say I did, and now i have a nice handful of rocks for the AM frequencies.
                                                            The Slab Bacon

[Bacon, WA3WDR]

A friend of mine told me that he ground my old 1620 KHz crystal up to the 160 meter band using toothpaste as the abrasive.

[WA1HZK]

I bought a bunch of crystals from Brian Carling, AF4K, all cut for the 75 AM freq's. They worked pissa.
af4k@af4k.com
He's in Sanford FL. 407-323-4178
$9.00 each
Can't beat that!
Keith

[k4kyv]

I have a good collection of the old buzzard "Bliley" and "Valpey" style xtals, with the round holder and pins that fit #2 and #4 of a 5-pin tube socket.  Also have a number of blank holders of that style (the original xtal was crapped out or missing, or was for a totally useless frequency). I have found that many of the large WW2 surplus xtals such as the ones designed for the BC-610, and even FT-243's will work in the old-style holder.  I just disassemble the original xtal and put the quartz plate in the round holder, reassemble, and it nearly always works, sometimes better than it did in the original holder.

That's one project I have had on the back burner for several years now, to try grinding some of the useless xtals I have to popular AM frequencies and putting them in the old style holders, which fit in the HF-300 rig.  I use two good VFO's, one a Collins type PTO from a T-368 and the other a DDS VFO, but I would like to be able to say I have successfully ground xtals, kind of a rite of passage for "real" amateur radio.

In the "old days" hams could buy "xtal blanks," plates of quartz that hadn't been ground for any specific frequency, and grind them to the frequency of choice.  If that was possible from a rough slab of quartz, I see no reason why a pre-ground xtal shouldn't be even easier to move a few tens of kc's.  Of course it does depend on the cut of the orginal xtal.  There is a  lot of info on the subject in the pre-WW2 ARRL and RADIO handbooks.

I have found many times that a xtal that appears inactive can be rejuvenated by cleaning the xtal and  holder.  Take the xtal apart and wash the quartz piece in denatured alcohol or acetone.  Wash the metal plates that sandwich the xtal.  If the metal plates are tarnished, etched or corroded, try polishing with Brasso or similar metal polish, until a mirror-like surface is achieved.  Then wash the metal plate in alcohol or acetone.  Carefully reassemble the xtal, and chances are it will work with good activity, if the quartz plate is not cracked.  Make sure the correct side of the metal plate, the one that is polished, is what touches the quartz plate.  Sometimes the sides of the metal plates that touch the xtal have little spacer pads at the corners.

I don't use surgical gloves, but I do wash my fingers with alcohol or acetone to "degrease" them before handling the xtal, and then handle the xtal only by the edges, as little as possible.