One doesn't generally bias tubes in a preamp.
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As Truman says, there is nothing to balance in the Joule
preamp. What you do is buy tubes that are tested forn noise
and matched. I would call Jud and have him discuss the
issue. It sounds like you just got the preamp? If I remember
correctly, the preamp needs a 5751 and 6350 tube, and a pair
of OA2 and 6EM7 - I would recommend sticking with Jud for
tubes as long as he is involved and selling to the market.
There is a bias setting in the preamp for the driver tubes (I believe batteries are involved) and the manual discusses how the bias is set at the factory. IIRC the manual also states that changing the bias can allow one to tailor the sound a bit. Jud sent me the instructions for biasing a while back when I owned the LA-100 MkIII. I may still have them. I will warn you in advance they are a bit complicated and requires two volt meters to be used simultaneously. Send me an email and I will see what I can do.
The batteries in the Joule preamplifier are under no load and don't really have an effect on the bias settings used for the line stage. They will last many years. You don't really need two meters to set the bias... I normally do it with one DMM. I have LA 100 bias instructions scanned as a jpeg which I can email. They are not easy to make sense of (a diagram of the line stage board with some numbers scrawled on it), but they get the job done. It does require poking leads on points of the circuit board (there are no easy access test points to stick your meter), so one does need to tame appropriate care when poking around inside a live tube preamplifier.