Quick question about a couple of bright red glowing 6L6's

[ibanezrocker720]

Well I was at practice the other day and my drummer was like..."why are 2 of your tubes glowing bright red?" I looked through the grill of my Dual Rec and noticed that the two power tubes farthest right if you are looking at the front of the amp were glowing super bright red and the other 2 were normal. I immediately turned the amp to stand by and the tubes went back to normal. I then waited a few minutes and turned it back to on and the tubes stayed normal for the rest of practice. Does this mean I have a couple of tubes going bad or is it something else? It seems fine now but I don't want to damage the amp. I do have a brand new set of power tubes, should I just go ahead and put them in now or should I wait until one actually blows. The amp still sounds great and I don't have any hissing or lower volume troubles. Thanks

 

[94Tremoverb]

You have a tube going bad. It has an intermittent short from grid to cathode so it's not only shorting out its own bias voltage, it's taking down that for the other tube on the same side as well. Sometimes this sort of thing comes and goes, but it's certainly not gone away for good even if it appears to be OK now. If you're not brave enough to test them both to see which is the faulty one, throw out both, keep the two from the other side as spares (a pair is always useful) and fit a full set of new ones.

If you want to test them, get it to do the same again (tapping on the tubes will often start it) then quickly pull one of the glowing tubes (make sure you use gloves or a cloth, that tube will be HOT!). If the other one stops glowing, you've got the bad one in your hand. If not, it's the one in the amp. Be careful and quick, since if the tube fails outright it could also take out the screen resistor, although this is fairly rare - so it's also not a good idea to leave it until one blows.

 

[ibanezrocker720]

Great! Thanks for the help, really appreciate it! I'll just keep the 2 that were still ok as backups and I'll replace all 4 of the power tubes. The amp is due for new tubes anyways, I haven't changed them since I bought it!

 

[94Tremoverb]

That's the best plan, if they're old anyway. Even the one that isn't the cause of the short has probably been fairly heavily stressed by running that hot, especially if it was for any length of time... there's usually a fair delay on drummers noticing things .