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I have a Fender "The Twin' red knob. I purchased 4 new jj 6l6's from guitar center online. they only sell matched pairs, and silly me assumed they would send me two matched pairs, but they did not. one pair is a medium and the other pair is hard. Will this be ok with a little biasing? If so, does it matter where the matched pairs go? I may be mistaken but I believe the tubes work in pairs in the amp? Basically I'm wondering if I'm out $45, or if I can make this work. Thanks in advance!
I don't know the answer to your question @scstowaway, but welcome to the forum. I'm sure there's someone who will come along soon with your answer.
they do work in pairs, however I can't recall how they work. If and I do repeat IF i recall it correctly, the outside two work together and the inside two work together. I seem to recall people trying to reduce the volume of large amps and being told to remove the outside two power tubes (but also being warned of the change in ohms but that's not an issue here).
The order in which you put the pairs probably won't matter, hard pair inside two or hard pair outside two; or medium pair outside two, etc. As far as biasing is concerned, you're going to need some technical consultation which is beyond my ken, I'm afraid. However, one thing comes to mind and it is one of the primary reasons why I never went with any amps that has 4 power tubes was the need for a matched quad and the difficulty in obtaining such. This leads me to believe that there is but one bias control and it is for all 4 power tubes.
It will probably come down to how big a difference there is between the hard and medium designation. Could you possibly return one pair and get another of the kind you keep? That would make your tube change much simpler.
Hey Dan, thanks for the tips. So, they would not take them back, non refundable item. I am familiar with biasing, well Ive done it once, with this amp when I obtained it. It was right where the manual suggests. As far as the tubes, I stuck them in with the pairs set as you mentioned, outer pair and inner pair. Biasing seemed more difficult, jumping numbers or no numbers at all. now this could be my 2 dollar meter. I switched them, pair to the left and pair to the right, and had a little more consistent results, however i did run into something that threw me off. When Biasing, the Volts suggested was within the range of what I could get with these tubes, but there was a negative symbol in front of them. And I can't remember if that's how it was last time. In watching a youtube video, a guy with the same amp as me, oddly enough, showed his bias procedure and his meter had a negative symbol. I know nothing about multimeters so I don't know what this means.
Amps are biased to the negative, so you’re GTG.
My man, thanks!
You’re welcome. I’m not an amp tech, but I do know a little. When you bias tubes or transistors you’re reading the cathode leg, so that’s negative voltage. That’s the short answer for you, but I’m sure you can find a more detailed explanation.
When mismatching tube pairs, one will draw more current than the other. Best to find a matched quad, (or buy a matched pair to the strengths you already have), and then bias.
On the web you can find folks who modified their amps to bias each tube separately, also an option, but personally I would get the tubes all matched.