[ARC5] Etching Crystals and WHINK Revisited - contact resistance.

[Dennis Monticelli]

Ken: Thanks for the tip on buffing the plates.  I might try that the next
time I run into a sluggish crystal that just won't behave.

Dave: To accelerate Whink try putting a heat lamp over the solution or use
a hot plate.  The acceleration of etch will be pronounced.

Dennis AE6C

On Tue, Nov 4, 2014 at 1:49 PM, Kenneth G. Gordon <kgordon2006 at frontier.com>
wrote:

> On 4 Nov 2014 at 8:33, David Stinson wrote:
>
> > I started with a 3146 KC Marine crystal.   Put about an
> > ounce of WHINK in a sealed 2" square plastic container
> >  and in with the blank.
> > Ken had reported 70 cycles a minute.
>
> Yes, but that was a WWII FT-243 and quite old. I have been pretty certain
> for
> along time that these had been ground to frequency. Every one I have
> etched with Whink really "took off" at first. Then as the process
> proceeded, it
> slowed down....drastically. By this activity, I suspected that, as Dennis
> mentioned, the surfaces were just full of dirt or fragments of crystal
> "dust"
> which was dissolved first.
>
> I suspect your Marine crystal had been etched to frequency, not ground, and
> was therefore "clean" to begin with.
>
> In order to move those along a bit faster, you need a much stronger
> solution
> of HF. Although the Whink will move it, it will be very slow.
>
> Or, you could grind it "up" towards the frequency you want, THEN, when it
> is
> within, say, 5 Khz,  use Whink to thoroughly clean it and bring to your
> final
> frequency.
>
> One more thing concerning our old crystals which I learned from a recent
> article in Electric Radio Magazine: usually there are two plates, usually
> copper, which have "tails" which are soldered into the pins. These plates
> contact two other metal plates with raised edges which then sandwich the
> crystal between them.
>
> These other plates look like plain steel to me, but they MAY be stainless
> steel.
>
> What the author of the other article discovered is that there is a very
> thin
> layer of some sort of non-conductive oxide that has built up over the years
> on the surfaces of the steel plates which SEVERELY reduces the good
> contact between the two copper plates and those two steel plates, raising
> the
> crystal's " internal resistance" very high, and in some cases, absolutely
> preventing the crystal from working at all.
>
> He discovered that thoroughly cleaning the surfaces of the steel plates and
> of the copper plates, using a hard plastic "scrubby pad" and some sort of
> liquid, alcohol, maybe, vastly lowered the contact-resistance and crystals
> which wouldn't work at all before he used this procedure, became very
> active
> and worked just fine.
>
> It is certainly something to consider.
>
> Ken W7EKB
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