Preamp tubes order messed up

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Mark I
Posts: 33
Joined: Wed Apr 27, 2016 4:03 am

Preamp tubes order messed up

Post by kenneho » Fri Jul 09, 2021 11:51 am


I noticed a while back that the drive channel on my Mesa Express 5:25+ amp had lost some drive/power. All the other channels seemed fine, so I assumed it was a preamp tube problem. So bought a few new tubes (for backup) and started swapping tubes today. Long story short, now all my preamp tubes are in some random order. Didn't think this would cause any problems, as I figured a tube is a tube as long as it is the same type (12ax7).

I just saw in the manual that the order of the tubes is very important. Had I known this I would never have done what I did. Plus. my amp doesn't sound as good as it used to, so I'm thinking a) somehow one of the tubes in there is not working correctly, and/or b) the new ordering of the tubes causes the sound quality to degrade drastically. When I push the gain now, the amp sound kind of weak and boxy.

So, a couple of questions:
  • Is there anything I can do to get the amp back to normal now that the tubes are on some random order? And is it really so that the order of (to me) identical 12ax7 tubes actually matters?
  • May it be that the issue actually is a power tube one, i,e. can a faulty power tube cause loss of the drive and power on a single channel?
EDIT: I moved this question over to another forum.

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