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

[WA5CAB--- via ARC5]

Over the last 30-40 years, I've sold a lot of crystals in FT-243 holders, 
mostly for either BC-611 or BC-659.  My experience has been that about 85% 
work OK.  5% work but have noticably lower activity than most.  These may 
be/have been candidates for plate cleaning.  The remaining 10% are dead.  100% 
of these dead ones have one or sometimes both pigtails broken off of the 
brass contact plate.  These are all repairable with a matching plate from a 
donor holder.  Unfortunately, the different manufacturers used various 
size/shape plates and for the most part, only the same size/shape of plate with work 
in the crystal you are attempting to repair.

FT-241's are exhibiting a different problem.

In a message dated 11/04/2014 16:49:18 PM Central Standard Time, 
dennis.monticelli at gmail.com writes: 
> 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
> >

Robert & Susan Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480