i would stay away from mesa tubes only because they are re-marked tubes from other manufacturers that are marked up in price. you can talk to any reputable online tube-dealer guy and tell him you have a mark iv, and he will sell you tubes cheaper than mesa that will work perfectly for you and you'll save a few bucks. just my opinion. I've been running JJs for the past few years and they have worked just fine. The GT mullard reissue was also nice, but didn't last very long. pre-amp tubes are cheap enough (unless you get rare NOS) where you can buy several brands and choose to taste.
