[600MRG] restoring old crystals ??

[Kenneth G. Gordon]

On 5 Feb 2013 at 16:23, Neil Klagge wrote:

> Thanks Ken. Ur comment "*It would be an excellent cleaner for the
> crystals*" is just what I want to use it for. It might just activate
> the crystal enough to oscillate.
> 
> Neil

Neil, I am assuming you are trying to reactivate FT-243 crystals: if so, there 
are a couple of other things besides CRYSTAL cleanliness you should think 
about.

First, the two metal plates between which the crystal is held have raised bits 
at the four corners: those corners should contact the crystal in such a way 
that there is a small air-gap between the two metal plates and either surface 
of the crystal. Sometimes, folks have put those back in backwards, not 
realizing there are "lands" at each corner.

Secondly, those metal plates must be totally clean. I use alcohol to clean 
those and handle them with clean tweezers.

Thirdly, the entire interior of the holder must be as clean as a whistle. Alcohol 
works well here too.

Fourthly, there should be two small thin copper plates which are connected 
to the pins. These usually are clamped when the crystal holder is closed up 
to the two metal plates mentioned above.

Lastly, there should be a piece of flat rubber between the crystal holder's 
cover (the part with the three screws in it) and the spring that is supposed to 
press against the top connector and metal plate. There should be no 
electrical contact between either metal plate and the outside of the crystal.

I have also seen some FT-243 holders in which the copper connectors are 
actually not making contact inside the pins. Sometimes, these can be 
resoldered.

However, the most important factor is that the crystal itself must be 
scrupulously clean. You can use an old toothbrush and dishwashing 
detergent to scrub the heck out of it without hurting it. Get all the dirt, 
finger-grease, solder, flux, or anything else that is not "crystal" off and out of 
there.

Good luck.

Ken W7EkB