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Old 22nd October 2013, 11:04 PM   #1
piano3 is offline piano3  United Kingdom
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Default Corroded valve pins

There doesn't seem to be much on this subject; I have recently purchased a fairly big lot of noval valves in boxes which have at some stage in storage become wet. The circular cutout in the cardboard which retains the pins has caused the pins to corrode right against the glass envelope. The green corrosion can be removed with a brush but 20% of the valves are ruined-the getter has turned completely white. The remaining 80% look ok with the getter still looking pristine. Can I have any confidence at all that they actually are ok and will not fail early in use? Has anyone else encountered this problem?
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Old 22nd October 2013, 11:22 PM   #2
AJT is offline AJT  Philippines
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as long as the getter flash is intact, then you can use the tube,
i use fine grit sandpaper to clean the pins...
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Old 22nd October 2013, 11:51 PM   #3
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The non-abrasive method for cleaning corroded steel pins is to soak them in lemon juice for a few hours. Lemon juice contains citric and ascorbic acids, neither of which is particularly strong, to quickly attack the metal. Ascorbic acid is a reducing agent and will convert the Fe+3 species into Fe+2. The citrate ion is a good complexing agent. Between ascorbate and citrate, corrosion products enter solution.

After the soak, rinse with water and wipe dry, with a paper towel. Ensure moisture is eliminated by a final flush with anhydrous isopropanol.
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Old 23rd October 2013, 12:50 AM   #4
piano3 is offline piano3  United Kingdom
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Thank you for your replies. Actually, the corrosion is nothing like normal iron rust, it is globules of a bright green colour (a nickel ion, if I remember correctly my high school chemistry? ) A non abrasive brush removes most of it. My main concern is the likely health of the valves once they are put to use given that the getter has been already totally destroyed in a fifth of them.
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Old 23rd October 2013, 01:06 AM   #5
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Yes, Ni+2 is green. However, basic copper carbonate is also green. Lemon juice will get rid of those crud forms too.

I think you are OK, where the vacuum is still intact. Stop the corrosion process in its tracks and get some use out of those "fire bottles".
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Old 23rd October 2013, 01:31 AM   #6
davym is offline davym  Scotland
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I used to use P1200 grit wet and dry sandpaper in a small strip wrapped around the pin and gently rotated, it's the best method I tried and worked perfectly every time. Coke (of the cola kind) or even vinegar can also work but not so well and you have to clean the pins with rubbing alcohol afterwards.
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Old 23rd October 2013, 01:51 AM   #7
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Vinegar = acetic acid. Colas contain phosphoric acid. It's the weak acid theme, again. However, the reducing agent is not present.
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Old 23rd October 2013, 02:18 AM   #8
davym is offline davym  Scotland
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I never used a wet solution to clean larger power valve pins in case it seeped inside the cap where it can't be cleaned out. You can of course leave small capless signal valves or EL84's etc with their pins standing in a dish full of a solution for a few hours.

I found the very fine grit sandpaper approach worked best with all of them, just remember to clean off the dust afterwards though.
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Old 23rd October 2013, 03:25 AM   #9
AJT is offline AJT  Philippines
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a toothbrush is handy in those cases, after fine sanding...
will try citric acid next time...
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Old 23rd October 2013, 07:38 AM   #10
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Plunging the pins into a Schotchbrite pad helps to clean them up if they are just oxidized (mostly, they are). I never tried the lemon juice dodge, but then I don't have any really corroded tubes except for some NOS 1625s whose boxes obviously got really wet. Scotchbrite and a fine wire brush worked in that case (different pin material).
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