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

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

$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!

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.