[ARC5] Can old crystals be restored ?

[Kenneth G. Gordon]

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