Does anyone ever retube Sonic Frontier preamp. SFL2?

How you contacted Sonic Frontiers. They do have a procedure to accomplish biasing the new tubes. Put in some new old stock tubes like Mullard or Seimens "A" Frames, very nice. There are a lot of other good options to select.

I replaced the tubes as matched pairs and it worked OK. Of course, I had to roll tubes to lower the noise floor and obtain the preferred sonic flavor. Thanks for all of your help.

There are two small bias trim pots next to each of the two banks of tubes; however, do not touch them unless you have a voltmeter and have the instructions from Sonic Frontiers that they will fax to you. If you order the matched sets from Sonic Frontiers, they will include a drawing of these trim pots and where you should set them for the tubes you are getting from them.

However, I understand that it is not critical, and you can just leave them alone. If you get tubes from another source, I would not touch them, unless you do the voltmeter procedures outlined by Sonic Frontiers.

When I asked Kevin of Upscale Audio, he said he has never touched them or adjusted them and the replacement tubes he has sold have worked fine.

If you mean biasing the tubes, the tubes in pre-amps do not need to be biased. Sonic Frontiers will sell you matched pairs for your pre-amp, but matching is different than biasing. I have re-tubed my SF Line 2 with matched pairs of tubes several times. Good Luck. Craig