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

I am not familiar with SFL1 but a Valvo 6201 or 12at7wa will suit it nicely. 
Going sweeter a Mullard CV4024.

G

I run a Genalex, Gold Lion in mine,... fabulous! GL with yours @skipper320; it's a terrific linestage that paired with the right amp will bring you pure sonic joy. I've run mine with TAD, Hibachi Monoblocks, a Cary 808R tuber, and soon a Sugden Bijou (Class A) "AmpMaster". It's a wonderful piece

Mullard 6201 I believe is what I used to run when I had a SFL 1, but that was sometime ago. Very nice preamp with the right tube and for the money. Sold the SFL 1 and moved to a ModWright SWL 9.0 SE which I liked much better. I recall the Mullards were what everyone was using and UpScale Audio recommended too which is where I think I purchased from. I remember the Mullard was much better than the stock tube if that helps.

SFL 1 lean side of neutral so my favorite was Amperex / Phillip Holland.  

I just picked up a mint SFL-1 last night , had a "new"  Brimar NOS AT7 but when I set it up I was pretty disappointed....dark, compressed sound it was bad.  Put a new JJ ECC81 in tonight and it sounds great.  

I was actually looking for a pre for my brother but he doesn't want to deal with tubes so I couldn't pass on it for $500....     its built like a tank.  

It will see duty in a second system but for now I am really digging it 

$500 is a steal for an SFL-1 - good for you. It’s a wonderful pre with the right tube to match your speakers and setup. Not really a JJ fan but I’m glad it’s working well for you. I never tried one in this pre. Not surprised by the Brimar but it’s a kinda naturally bright preamp so the previous owner more than likely tried to tame it with his speakers. Genalex and Mullard - can’t go wrong with either if you decide at some point to try something different. GL!

I think I'm going to order a Gold Lion 12AT7, but it looks like there are a lot of NOS of this variety around so I think I'll order a Mullard also

This unit is in place of my Conrad Johnson Classic 2SE right now and it sounds so good I think I'm going to leave it in the system for a little bit. 

Build quality on it is nice, I couldn't pass it up.    I wanted this preamp when it came out but I was newly married ,kid on the way so.........

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.

Shuguang 12AT7A (Ei), sorry, and right channel went out in 2013, repaired with no further issues. Ordered the tube upgrade kit from the Parts Connection when they were a division of Sonic Frontiers, use the Pearl small tube cooler but never installed the Mullard CV4024 KQDD/K tube...jumped right over it to the 6201. Try either one or I have a tube never used.