[ARC5] Can old crystals be restored ?

[Scott Johnson]

(With cotton or latex gloves on) try removing the quartz plate, wiping it
with ethanol, and re-inserting it 180 degrees from its original orientation.
I have found this to restore activity more often than not.

Scott V. Johnson W7SVJ
5111 E. Sharon Dr.
Scottsdale, AZ 85254-3636
H (602) 953-5779
C (480) 550-2358
scottjohnson1 at cox.net
scott.johnson at ieee.org

-----Original Message-----
From: ARC5 [mailto:arc5-bounces at mailman.qth.net] On Behalf Of Kenneth G.
Gordon
Sent: Saturday, June 11, 2016 9:46 AM
To: J Mcvey via ARC5 <arc5 at mailman.qth.net>
Subject: Re: [ARC5] Can old crystals be restored ?

On 11 Jun 2016 at 13:38, J Mcvey via ARC5 wrote:

> Got his box full of xtals for the BC-659, but wouldn't ya know that 
> only one of the
> 10 meter simplex ones are good!
> I suspect that the problem is internal contact oxidation, but I wonder 
> if anyone here has restored one and how they did it.
> Otherwise I'll just have to open one up and see what I can do with it.

I've accumulated a couple of hundred FT-243s from various sources and have
worked with them for some time.

Robert Downs has given you excellent advice on working with them, and I also
concur with his statement about the copper plates being broken off or
corroded off internally. Replacing or fixing those is relatively easily
done.

Where I could not find an exact replacement from a totally defunct crystal,
I have made my own from that very thin copper sheet used by artists for a
kind of art-work in which the thin copper is pressed into a mold by a wooden
stick. I forget the term, but the copper is easily available from art supply
stores. I use scissors to cut the replacement out, then unsolder the
remaining bits of the old plate, and solder in the new one.

Secondly, it was proven in an article in Electric Radio Magazine that many
FT-243s suffer from very poor electrical contact between the copper
connectors and the (usually) stainless steel "clamps". Sanding the two
surfaces with very fine sandpaper did not always reduce that contact
resistance, and some other method was used to fix that. But, in every case
in which that contact resistance was reduced to the absolute minimum, the
crystal activity increased many-fold. I'll try to find the reference article
for you to read as soon as I can.

Also, many crystals from the WW-II era were ground to frequency, rather than
etched with HF  (hydroflouric acid, pioneered by Bliley) and grinding leaves
minute bits of crystal and "dirt" embedded in the surface of the crystal,
and this not only reduces activity, but also lowers the oscillation
frequency.

CAREFULLY, using "Whink" Rust Remover to both dissolve the crystal "bits"
and to thoroughly clean the crystal will vastly improve activity. HOWEVER,
this also raises the frequency, so be very careful here. I have covered the
precautions about using "Whink" 
here in the past.

Lastly, unless the edges of a crystal are almost perfectly perpendicular to
the faces of the crystal, activity can suffer. One can hold the blank as
perfectly perpendicular to some perfectly flat surface, like a sheet of
thick window glass,  as possible, and give all four edges a swipe or two and
this can, often, restore activity.

Lots to consider here, but most crystals I have worked with have been
restored to activity by careful use of the ideas I mention above.

Ken W7EKB


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