Metal Mold


2010-11-05 11:48 pm
I Have a Heathkit TT1 tube tester. All the wafer switches [approx 18] have a considerable amount of metal mold buildup. I have tried deoxit but will not breakdown the mold. Thinking of using oven cleaner but not sure. Any suggestions much appreciated.




2006-09-08 2:04 pm
Vinegar, citric acid are options, but they are far from ideal. Tartric acid is in the same league.
Phosphoric acid (diluted) is stronger, but gentle on most metals. It can attack various other materials, including organic ones.
They all need to be carefully rinsed multiple times with demineralized water, and possibly neutralized with a light buffer solution of sodium bicarbonate, as the acid can soak the surface of phenolic composites and other impregnated cardboard types, reducing their insulating quality.
Diluted lye is also gentle on metals, but it can be ferocious for some organic materials
BIG problem with corrosion is that maybe you can dissolve it away, as in using acids, but then, what do you replace it with?
Exposed bare metal corrodes in days-months afterwards.

Those tiny little contacts were stamped first but then they were "pickled" (washed in dilute acid to remove any rust and corrosion), perfectly washed and then metal plated/galvanized with some atmosphere resistant metal, : tin, rhodium, silver, zinc,some chromate treatment.

Done in a rolling perforated drum, submerged in a nasty electrolyte (most contain cyanide, go figure) with an electrode touching the thousand little parts bulk inside and another connected to a "brick" of the desired covering metal.

As you see, impossible to redo on an already assembled switch.

With a hand on my heart, "clean" it with deoxit to check whether tube tester works at all, but then replace all corroded switches with fresh ones.
Even NOS if kept for 50 years in a clean dry dark place, emphasis on dry.
Deoxit cleaning works on a microns thick surface of grime, but can´t do magic on flaking corroded plating as you see, specially because base metal under it is also corroded.

Cool Amp powder will actually replate surfaces you can get to. Such as the switch wiper. Won’t really work inside the fixed contacts but you probably don’t need to replate those.

What may have started the problem is cleaning the switches with spray cleaner only and not following with a lubricant. Normal exposure to air will tarnish silver, but silver oxide is actually a better conductor than silver!

Sulphur in the air as an oxide is the really bad problem. It is not corrosion rather crystal growth of a nonconducting type.

I often repair audio gear made in the 50’s and 60’s that requires pretty much just cleaning the switches. In some cases the lubricant causes the failure. Those switches get removed, soaked in alcohol, properly lubricated and then reinstalled.

The Deoxit folks also sell some excellent lubricant. A drop will do it. However their lubricant is packaged in a bottle that tips over easily and will spill half of the contents! Try not to lose the cap.

The two ounce jar will for many last a lifetime.
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