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Old 29th July 2002, 06:00 PM   #1
JoeBob is offline JoeBob  Canada
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Default Cleaning oxidised tube pins.

I built two tube voltage gain stages to drive a mofet power follower, and initial testing with them driving headphones is fantastic, I'm perfectly content with their sound. Unfortunately one of the tubes I have has an oxidised (I do believe, it's dark and dull, not silvery and shiny) pin, and when I use that tube I get some crackling and hissing noises in the channel with the dirty pin (use the other tube and it's fine). So I'd like to clean that pin, I read somewhere to clean it with isopropyl alcohol and a q-tip, but that did absolutely nothing. If anyone knows a good way to clean it I'd love to hear, because it really is a great sounding tube, and I'd hate to have to go replace it just for a dirty pin.
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Old 29th July 2002, 08:22 PM   #2
Duo is offline Duo  Canada
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I have the exact answer to your question! When any type of metal oxidizes, you need to polish it to bring back the sheen and cleanliness. Think of gold and silver, they ozidize quite fast and need polishing often to keep their initial shine. In the case of any metal that has oxidized badly, it takes lots of force to polish it out.
For a tube pin you have to be extremely careful not to bend it or subject it to any sort of pressure. If you had dentistry polishing equipment then you'd have a very easy time polishing it but that's likely not the case. However, a rotating tool such as a dremel or similar device that rotates at 30000 rpm is good. Then just get a polishing bit for it and use a good metal polish. The best polish I have ever used is brasso, it works on almost anything and you can even remove cd scratches completely with it. It will do nicely for a tube pin if you have a toll to polish it. You could use a Q-tip but that would take a long time and you'd need a good way to support the pin so as not to bend it. Also, are you using an large octal or a miniature noval or 7 pin base tube, cause the octal ones have fat pins and are really much easier to polish??

Anyway, I hope this helps, I have done it and it works great!
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Old 29th July 2002, 08:54 PM   #3
JoeBob is offline JoeBob  Canada
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I will try that. Unfortunately it's a little noval tube (6922). I just tried steel wool on it and it cleaned it up a bit, so that the sound is back to normal, but I want to do it right so I don't have to clean it again in a month or two. I'll try the dremel polishing idea (unfortunately I'm not a dentist), thanks.
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Old 29th July 2002, 10:37 PM   #4
Duo is offline Duo  Canada
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Okay, then, good luck. Good to see lots of people are still into tubes!
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Old 30th July 2002, 01:35 AM   #5
SHiFTY is offline SHiFTY  New Zealand
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I used fine sandpaper on the pins, it seemed to do the trick. Have you checked your socket? Mine were pretty cruddy, I got an old worn out valve, filed the pins quite roughly and then inserted and removed the valve a few times - cheap and cheerful way to clean up the sockets!!!
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Old 30th July 2002, 02:08 AM   #6
JoeBob is offline JoeBob  Canada
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Actually these were brand new tubes and gold plated sockets. It only happened after listening for a while.

I tried sand paper, but 600 grit and 400 grit didn't seem to have much effect, the next lower grit I had was 120 so I didn't bother trying that. But the steel wool seems to have fixed it for now.
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Old 30th July 2002, 02:08 AM   #7
Duo is offline Duo  Canada
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Yes, sanding works well too, but you'll mar the pins and probably remove any sort of coating or plating such as gold or silver. This is okay for cheap tube like you said for cleaning out stubborn sockets, but it's usually better for the longevity of sound and quality to replace the defective socket if you can afford it. A socket with scrapes or dirt or shavings in it can also damage the plating on high end gold pin tubes or moderate ones with other coatings, so you have to be careful. Anyhow, good to see if there are any suggestions on this that are easier, since polishing is extremely time consuming and difficult for miniature tubes and it's easy to wreck the pins with the pressure needed to achieve an acceptable even polish.
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Old 30th July 2002, 09:30 AM   #8
SHiFTY is offline SHiFTY  New Zealand
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I am surprised that brand new "gold plated" sockets are having trouble making contact: I have never had any trouble with my 30 yr old slightly corroded ceramic ones!! Maybe you should do what they used to do and bend the tube legs slightly outwards... If you do this carefully with needle nose pliers its no great drama.
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Old 30th July 2002, 01:27 PM   #9
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Hi JoeBob,
Using wet and dry paper is a nono because of carborundum particles embedding into the surfaces.
The Dremel treatment should work.
I usually use a snap-off type knife and use the newly exposed snapped off end to scrape oxides from the tube pins.
Pipe cleaners are good for polishing the sockets.

Regards, Eric.
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Old 30th July 2002, 05:41 PM   #10
Duo is offline Duo  Canada
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ShiFtY: I think JoeBob meant that one of his new tubes had an oxidized pin that was causing the problem...

JoeBob: Is this right, or was it an old tube with the bad pin, or did new tubes with perfect pins have problems??
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