I've been reading through threads on Mesa 400/400+ tube issues and just wanted to make sure I have things straight in my head and to get any additional advice specific to the 400+. Sorry if I'm being a bit redundant. I've just purchased a new 400+ which should arrive in a week. I assume the tubes won't need to be replaced right away, but I'd like to upgrade to high quality tubes either sooner or later. So correct me if I'm wrong but: The tubes I'll want to replace are the 12 6L6's. However to do so the amp will need to be modified to include an "adjustable bias control". Once this is done I can put better tubes in without fear of hurting the amp, and in the future tubes can be easily switched out, and and the amp adjusted accordingly, or fixed, with less hassle and cost. Is this pretty much correct? And with the above in mind, what tubes should I use to replace the stock 6L6's and where can I get them for the lowest price? Also, should I replace the 4 12AX7 tubes as well? And for the bias mod I'm looking at about $200 bucks for that on top of tube cost? Anything else I should know about Mesa 400+ amps and tube issues? Thanks!