[600MRG] restoring old crystals ??

[Kenneth G. Gordon]

On 5 Feb 2013 at 14:11, Merv Schweigert wrote:

> Ken is correct on all counts,  I have activated many old xtals
> by cleaning the blanks and careful reassembly, all that was
> need was good alcohol bath,   not rubbing alcohol but the
> potent stuff from the pharmacy usually.

Right! Rubbing alcohol has been "denatured" by adding something like 
gasoline or worse to it. Use full-strength pharmacy-grade alcohol.

>  Do not touch the xtal
> after cleaning, use "tongs" or something hold the edges and
> put it back in the clean case.   Have had almost all bad ones
> come back to life.   You will change the freq if you use acid
> or any other "grinding" method.  I assume you want them to
> stay on freq.

Yes. I thought so too. Isn't that true, Neil?

> If grinding buffing compound mixed with water to a paste
> works well,  comes in many grits,  a piece of flat plate
> glass works as a bed.  the surface has to be perfectly flat
> or the xtal is ruined as you grind.

Yes. You should use as perfectly flat piece of heavy plate glass as you can 
obtain. It doesn't need to be much bigger than 6 inches square though.

Having a glass "button", i.e. a circular piece of very thick plate glass to  
manipulate with your hand to use to hold the crystal down on the grinding 
"table" would be very valuable too.

You grind in a figure eight pattern, manually turning the crystal 1/4 turn after 
every 5 or so "eights", then turning it completely over every complete 
revolution (every 4 5's). 

You have to do everything you possibly can to make certain the crystal sides 
STAY perfectly parallel.

And you can only grind crystals UP in frequency, never down.

Let's say you have done both sides for one complete revolution each: then 
you have to scrupulously clean the crystal, put it back into a clean holder, 
and test to see if 1) it is still active, and 2) how much you have moved it.

Sometimes, if you have a calibrated receiver, you can lay the antenna very 
close to the crystal as you are grinding it, and "hear" the crystal chirping as it 
is ground. If you are careful, you can then follow its movement toward the 
frequency you want. But you have to stop well short, clean the crystal, and 
test as above to make sure you don't overshoot.

Sometimes, if activity falls off, you can very carefully edge-grind all 4 edges 
and MAY bring it back....of course you could also ruin it too.

At least we aren't still at the stage for making crystals shown in an old 
handbook: "First, buy a chunk of Brazilian quartz, as clean and inclusion free 
as possible. Then clamp it in a vice and begin vigrously cutting out a square 
with a hacksaw. A piece 1" X 1" X 1/4" will be suitable. This will take several 
days." Etc. Sounds like great fun, doesn't it? ;-)

Ken W7EKB