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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.
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!;)
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.
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.
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.;)
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.
Gold Pins? Got Gold Sockets?

I work daily with control circuits of incredible sensitivity, in automotive applications. These are engine management ("fly by wire") systems that have no room for error; hence, the control circuits are redundant and constantly monitored.

When there is a "glitch", I'm the lucky propellerhead that gets the problem situations after others are befuddled.

The control systems are sensitive to glitches (signal voltage loss) of short duration, often below 1ms. Others are carrying an AC waveform, be it a sawtooth, sine, or square wave signal; any corruption of these signals (an engine bay is a nasty source of interference) either directly, or inductively, finds its way to me. Thus, I am the workshop "guru" for the "weird stuff". I won't delve into the interesting things that happen with the serial data lines that are twisted into the mix...or how about 14 (or more) seperate control modules talking?

Well, back to contacts. If your contact is gold, be sure that both sides of the equation are similar metals. I've seen resistive problems and interesting diodic effects here as well. Most audio applications here aren't subjected to the environmental conditions and vibrations that automotive applications provide. As a rule, when I have a gold pin connector, the socket end must also be gold.

Electroplated contacts are, as a rule, soft gold (24K). Be careful with abrasives, as the benefits of the plating can be ground away! Chemical reduction is a wonderful alternative, provided that the acid is neutralized afterwards, lest one have an electrolyte remaining! Most of the damage I see with contacts is "fretting" corrosion caused by subtle movement of the contact assembly. Often, making and breaking the contact a few times will rub a fresh contact junction.
Check out these tips..

More of the same really (And a little of the top) but here they are nevertheless...


Cleaning tube pins - I

Most tube pins on the all-glass 7 & 9 & 12-pin types are made from something called Kovar, one of those space-age nickel alloys that are quite impervious to just about anything, like the high heat and contamination they would be exposed to whilst being melted into a blob of glass under a gas flame... The metal does oxidize slightly, typically to an oil-slick like bluish or brownish tinge. Using the right abrasive and/or technique, it can be removed quite thoroughly. I use a #60 drill bit in a Dremel-type rotary moto-tool, which I GENTLY graze across the pin surfaces. It takes less than 5 minutes per tube, and the result is a pure-silver satin finish, not unlike what you see on the more premium Russian and Chinese tubes. The sound is improved quite noticeably, and with some types you can even see improved reading in your tube tester! With some NOS 7199's, I was getting 5-10% higher transconductance readings on the pentode section after doing this! Once cleaned, the tube pins stay clean, end-stop. Unless you put semi-conducting tropical-oil based toe-jam on it, that is...

"Source : Joe Rosen"

Cleaning tube pins - II

Here's John Camille's recipe for clean tube pins (from CyberVALVE issue 1)
1 Select a new tube that checks way over good.
2 Wire brush pins until shiny with a gun bore brush chucked up in a drill motor or Dremel tool. Practice on an old tube until you figure it out.
3 Wash tube thoroughly with tooth brush and 409. Rinse and blow dry. Do not touch pins with fingers again. We’re talking clean room plastic gloves here (food handler gloves are cheaper)
4 Chuck one half of a Q-tip in a drill motor and add a small drop of Caig Pro-Gold to the cotton. Use this rotary buffer to polish tube pins. Repeat process with clean Q-tips until pins produce no more black deposits on cotton. Surprise, surprise, you thought they were clean.

"Source : John Camille in CyberVALVE issue 1, posted by Doc B. at the Audio Asylum"


diyAudio Senior Member
2002-08-21 1:20 am

A lot of helpful answers there.From what I can tell from experience,the simplest trick is the most effective.
Your tube somehow lost its plating on one pin,(most probably due to some greasy contamination during nickel plating ) I've seen this before and when I was professionally working with tubes I had a simple flat eraser on hand for cleaning pins on noval and pico 7 tubes.Use the type of eraser used for ink erasing not the more common pencil eraser which is far less effective.The blueish type , not the white ones.
Gently push the tube in the rubber as not to bend the pins.
All the other tips given will help to an extend but I found this one to be less time consuming and most off all most effective of all.
If all else fails try applying (brush on) Cramolin (Caig Industries) sparingly.This is a nonconductive fluid used in the computer industry.In high end circles it used to be sold as Tweak.
If you still get trouble after that it is most likely that your tube has develoved a fault due to the erratic contact...replace!
And on a final note it is indeed not good practice to mix disparate metals since this would be prone to what is known as a Peltier effect.
It is common knowledge in the computer industry especially where high speed memory modules with gold plated contacts get sometimes replaced with tinned ones in gold plated memory holders.This can and often does result in seemingly unexpicable system crashes.

Good luck,