Re: FT243 crystal grinding.
If only I had known this 59 years ago when I was KN5LZJ. All I knew was that a
xtal could be ground up in frequency.
I did use, either Bon-Ami or Ajax abrasive cleanser, mixing it with water on
the smoothest concrete sidewalk I could find and grind awhile, drying the
crystal, keeping skin oil off of it, reassembling the xtal, and testing it in
the rig and usually after about 3 or 4 tries, I was near where I wanted to be.
Anything to get off of Radio Moscow on 7183!
When I went past my target frequency, I would mark both sides on the xtal with
a #2 leal pencil to lower it.
Thanks for the radio history.
Sam Neal N5AF
Subject: [4sqrp] FT243 crystal grinding.
The crystal grinding workshop at Ozarkcon was given by Daorrel Brehm,
WA3OPY, Ron Hale, AC5UR, and me, W1REX. My friends Darrel and Ron both
work at International Crystal Manufacturingin Oklahoma City and I, of
course, 'work' at QRPme. The boys at ICM provided some frequency
counting equipment while I supplied the FT243 crystals and my special
crystal oscillators. My unique contribution to the art of crystal
grinding was the crystal oscillators. They were based on the ubiquitous
universal crystal oscillator circuit with a twist. I built the
oscillators inside tuna cans with a bare copper pcb on the top of the
can. The entire copper pcb was a grounding plate where you placed the
crystal for frequency measurement. The second electrode for the FT243
crystal was a copper plumbing cap attached to a wire going a Manhattan
pad whichis also connected to the pcb to the oscillator inside.
The procedure was to FIRST measure the unmodified FT243 crystal holding
the FT243 to the Manhattan pad and ground plate.
Then you take apart the FT243 and measure the frequency of the blank by
placing it on the pcb ground plate and placing the plumbing cap
electrode on top.
Now you can slowly add lead shot, BBs or any other uniform small weights
into the plumbing cap until the frequency reads sufficiently CLOSE to
the original unmodified frequency. Now you have the cap fixture 'tuned'
to the spring & pressure plates inside the FT243 holder.
You can do some grinding... we used Bon Ami on 1/2" plate glass grinding
surfaces. Clean the blanks thoroughly with distilled water, dry with hot
air and test in the cap fixture.
Once you get a reading you are happy with, you reassemble the FT243
using your new blank and you should then be fairly spot on to the
desired frequency. I scored on a big batch of 6975 FT243s and we
successfully moved them all to 7030 which was a hard to find crystal in
those days...I wrote up the whole process and did a kit run of the
oscillator at FDIM... It was my first attempt at a NO Solder Buildathon.
We did itlive over the Internet and it was billed as the FDIM Build-A-Long.