Cracked 12ax7's

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nick79nick79 Frets: 144
I've just replaced a Mesa branded 12ax7 valve in my Mini Rec after discovering a hairline crack that runs pretty much the whole way up. This was the second one that i've found like that (the first was also Mesa branded), the first one had 3 cracks in it and i noticed that after a while of it sitting on my desk that it lost it's vacuum and is now filled with a white powdery substance. 

As far as i know they are the original valves that were in it since new (2012), is this normal for valves that are past their best or do i need to start thinking about getting the amp checked over? 
The others all seem fine (they aren't original, a mix of Tung sol and JJ). 
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  • ChesterChester Frets: 35
    edited June 13
    Sounds like the amp has had a hard life, or been dropped to cause that type of issue

    If it was mine, I would totally re-valve it to be sure. I've had good results with JJ 12ax7s and Mesa biased TAD's
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  • ecc83ecc83 Frets: 820

    There was for a very short time a problem with  the 12BH7 in the original HT-5. In a few cases the valve was found to have cracked and filled with the white ***t. The problem was put down to overzealous tightening of a cable tie on the cableform exiting the valve base. I used to snip off any I saw.

    Both valves are now of course on the PCB.

    Dave.

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  • nick79nick79 Frets: 144
    3 months ago it was fine, i checked all of them when i replaced the first dodgy one. Since then the amp hasn't been dropped or banged about, so seeing as the other non Mesa ones are ok i'm erring towards it being something to do with the valve itself rather than a fault with the amp. 
    Just strange how it's happened to 2 (of the same make). 
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  • ICBMICBM Frets: 32827
    Were they in the same socket?
    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone."
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  • nick79nick79 Frets: 144
    No, as far as i can remember the first one was in v1, the one today was v3. I'm not 100% sure about the first one but i think that's where it was (Slept since then!) :)
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