Is it JJ's or biasing?

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paulschnettler
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Is it JJ's or biasing?

Post by paulschnettler »

On two of the TMB's I've built I seem to have a recurring problem. If I stuff the amp with GrooveTube branded 12ax7's and el84's I notice that if I drive the amp over say 8-9 on the vol pot all hell starts to break loose and I get hiss, whine and flutter. (non TMB channels aren't as bad) If I put in a set of NOS tubes from Terry Kilgore in either amp, things are fine and diming the amp isn't a problem.
Could the JJ's need a little bias change to tone things down a bit?
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zaphod_phil
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Post by zaphod_phil »

Can't think of problems I've encountered with JJ EL84s, 6V6s or 12AX7s. I wonder if GT is buying up some of JJ's rejects, burn-testing them, then relabelling and reselling the ones that survive....
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chabby
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Post by chabby »

I seriously doubt GT is doing that with JJ's. The tube industry is bad (new ones anyway), but not that bad-lol! GT guarantees their tubes so it's my guess they want them to work.
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chabby
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Post by chabby »

I will tell you this: I was repairing a VHT Pittbull last week adn when I called the factory to get a new PT for it he asked me what kind of tubes were in it. I said JJ's and he said that's what I figured, he went on to say they recommend not using them as they run hotter than nos EL84's and I've found that to be true on my own. It was nice to hear someone else tell me as well though.

There's a difference in JJ's versus nos don't let anyone fool you otherwise.
Its not only they run hotter, its also the way they are made. They are decent cheap tube, I own some too. But they are what they are.

I try and limit my use of them to Rectifer tubes these days. They make a good 6V6 too. Used to make a great 6L6 too, but over the last year 1/ 2 the ones I've bought were bad before I ever plugged them in.
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Plexi
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Post by Plexi »

Fender bought or owns GT now. You can find some info on other forums that tell a bleak tale of things most seemed to already know about the quality of the tubes. According to the posts from people who worked there,sub par stuff was being passed out the door. I know long ago i quit using the GT,because most were junk. Some right out of the box were bad.Not just a few but many i got at that time were either bad, or unuseable do to other problems with the tubes.
Now that fender has taken over ,i don't know how they are, but i haven't tried or used any for a long time.
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Post by rjgtr »

I have found JJs to be very reliable, but I get them from reputable dealers who test their tubes.

As for Groove tubes, it all depends on what model number tube you get. The tubes with an S suffix are usually JJs. Ones with an R suffix are Sovtek and a C suffix is for Chinese tubes.

I have found Chinese 12ax7s to be brighter, but good sounding in darker amps. However, in a brighter amp they can be too much of a good thing.

Sovtek tubes aren't bad, but not my favorite sounding. The NS Tungsol 12ax7s are the exception. Generally good sounding and pretty reliable.

NOS are generally the best to get, but there's no guarranty you're not getting a dud, unless you get them from a reputable dealer. And not all NOS tubes sound great or even better than new production. If you stay with proven NOS brands you'll be ok.
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