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Old 28th July 2011, 05:48 AM   #1
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Default What happened to my tube??

So I have an ART Pro MPA II Mic Pre, and I replaced the tubes with Sovtek 12AX7's. A couple weeks after replacing the tubes, the second channel died. Assuming it was a tube issue, I opened it back up and saw that the tube was in fact obviously dead. What could've caused it? I have a picture of the tube now, I have no idea what happened to it. The top of the tube is just this white stain looking thing.
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Old 28th July 2011, 08:16 AM   #2
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Welcome to the forum, but please mind your language.
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Old 28th July 2011, 08:22 AM   #3
Gilgy is offline Gilgy  United Kingdom
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Looks very much like the vacuum has leaked out
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Old 28th July 2011, 09:04 AM   #4
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Old 28th July 2011, 09:10 AM   #5
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Look for a puddle of vacuum, scoop it up and see if you can funnel it back in there.
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Old 28th July 2011, 09:11 AM   #6
gruni is offline gruni  Germany
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I would say that air leaked inside the tube as in my opinion vaccum can't flow.

but yes thats the point
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Old 28th July 2011, 05:28 PM   #7
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Quote:
Originally Posted by Sperrino View Post
What could've caused it? I have a picture of the tube now, I have no idea what happened to it. The top of the tube is just this white stain looking thing.
The vacuum escaped. This is a problem with those mini types that don't have bases. Bad sockets with misaligned pins/too tight pins can promote hairline cracks at the base, especially with a few incidents of thermal cycling.

Bent pins can also cause this, and tube shields are notorious for this as well.

There is also the possibility of factory defect: either a hairline crack that wasn't noticed, or glass that wasn't quite annealed properly.
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