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

Kenneth G. Gordon kgordon2006 at frontier.com
Tue Nov 4 16:49:32 EST 2014


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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