What happened to my tube??

Sperrino · 28th July 2011, 05:48 AM

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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pinkmouse · 28th July 2011, 08:16 AM

Welcome to the forum, but please mind your language.

Gilgy · 28th July 2011, 08:22 AM

Looks very much like the vacuum has leaked out

DigitalJunkie · 28th July 2011, 09:04 AM

^ +1

chris661 · 28th July 2011, 09:10 AM

Look for a puddle of vacuum, scoop it up and see if you can funnel it back in there.

gruni · 28th July 2011, 09:11 AM

I would say that air leaked inside the tube as in my opinion vaccum can't flow.

but yes thats the point

Miles Prower · 28th July 2011, 05:28 PM

Quote:

Originally Posted by Sperrino

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.

28th July 2011, 05:48 AM	#1
Sperrino diyAudio Member Join Date: Jul 2011	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. ImageShack® - Online Photo and Video Hosting

28th July 2011, 08:16 AM	#2
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	Welcome to the forum, but please mind your language. __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

28th July 2011, 09:10 AM	#5
chris661 diyAudio Member Join Date: Feb 2008 Location: Lancashire Blog Entries: 7	Look for a puddle of vacuum, scoop it up and see if you can funnel it back in there. __________________ "Throwing parts at a failure is like throwing sponges at a rainstorm." - Enzo My setup: http://www.diyaudio.com/forums/multi...tang-band.html

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28th July 2011, 08:22 AM	#3
Gilgy diyAudio Member Join Date: Oct 2009	Looks very much like the vacuum has leaked out

28th July 2011, 09:04 AM	#4
DigitalJunkie diyAudio Member Join Date: Apr 2003 Location: Portland,Oregon Blog Entries: 4	^ +1

28th July 2011, 09:11 AM	#6
gruni diyAudio Member Join Date: Feb 2008	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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