The are many tubes out there you can consider to replace the standard 6922 tubes that comes with your SF line preamp such as mullards, nos, and etc. It really depends on the sound that you're looking to achieve. I recently re-tubed my line two with valvos. The bass is tighter and the highs and mid range are quicker. Hope this helps.
Re-Tubing A Sonic Frontiers Pre Amp
Has anybody had any experience re-tubing a Line One, Two or Three? If so, what kind of tubes did you use and what results did you get?