What’s the best tube for a Sonic Frontiers SFL-1 preamp

Just ordered.a NOS Mullard 6201 hopefully that will sound better than the JJ, which isn't terrible but not my first choice

Those 6201 sound great .   I’m thinking about sending it to Chris at Parts Connexion but not sure which level to do

oddiofyl

The SF SFL-1 is a nice preamp, well made but I would strongly suggest to leave it as is and just enjoy it. No doubt Chris can improve upon his earlier work but at what cost? Before I would spend the money, I’d buy a used ModWright SWL 9.0 SE and compare the two and sell the one you feel is the lesser of the two. I did this and kept the MW. The ModWright is in another level and will cost you less than modding your SFL-1. I also ran the Mullard 6201 in my SFL-1. Been awhile since I looked up what a SWL 9.0 SE go for but I’d guess around $1200. The ModWright is built equally as well and Dan can mod it I’m guessing for less if you later get the itch.

Look, get a couple different tubes, give them each a twirl and sit back and enjoy; It's really terrific piece. I've since moved to a different pre but I find it no great upgrade over the SFL-1. New piece has more tubes and a different presentation. Not necessarily better, just different... keep the Sonic Frontiers pre & play it til the wheels fall off. I still have mine albeit on the shelf for now. 

Congrats on the buy. I am an original (1994) owner of an SFL-1 still in use today with 0 issues. The original tube, which I still have, was a Shunguang Golden Dragon 12AT7A ECD-81. The only tube I have replaced it with every 6 years or so comes from Upscale Audio, Cryo treated NOS Mullard 6201 Gold Grade 12AT7. I only think to replace it when the system starts to sound grainy. Never the amp, always that one tube long into its lifespan then falls off quick. Next one will be Cryo treated from Kevin's stash of NOS because I just gotta know. Start with the 6201 at the least.