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Question for the tube guru's
Posted: 9 Feb 2012 12:06 pm
by Frank James Pracher
OK,so I have a new Peavey Classic 30 for my lap steels. While attemping to track down a mechanical rattle in the cabinet I broke one of the power tubes (EL84). I know a matched Quad is the way to go, but how bad would it be to just replace the broken tube for the short term? My local guitar shop said he has lots of spares (used, but good) that he would be happy to give me.
Are we just talking degraded performance or possible damage?
Thanks for you time.
Posted: 9 Feb 2012 12:44 pm
by Riley Hart
It would be best to check the bias and the current that the replacement tube is drawing of course, and pick the replacement that is drawing closest to the other 3, but if you can't do that, I would be very cognizant about making sure the replacement isn't running a lot hotter. Turn down the lights and make sure the plates are not getting cherry red.
Do not take my word as gospel, but I wouldn't be bothered about just replacing the one tube if you can get a good match....
Maybe get two or three tubes and try them all...
Posted: 9 Feb 2012 2:10 pm
by Larry Robinson
I would buy one tube made by the same mfg. as the other
el84's. Check that it isn't glowing cherry red after you plug in the new tube. If it sounded good before you broke the tube, it will probably sound good after replacement. I wouldn't replace all tubes just because I broke one.
Posted: 9 Feb 2012 3:40 pm
by Tim Marcus
not that important. You won't get a perfect balanced sine wave at the output, but it will certainly save you some money!
Even tubes from the same manufacturer vary a great deal. Its always a crap shoot.
The one thing I will say is that if the tube was very old - like an original tube from when they were not only made in Russia and China, you may want to replace them all. If it is a new production tube, you are ok with a new production replacement.
The reason I say that is that the new production tubes draw substantially more current than their brethren from the past. So that would create the largest mismatch.
If it makes you feel better, some players prefer unmatched tubes at the output for guitar. It only adds to the moderately controlled chaos that guitar amps already have.