When I needed some very quiet 6sl7 tubes for a phono preamp Andy at Vintage Tube Services recommended Sylvania. He set me up with a NOS pair that were excellent. I sold the phono pre shortly after I received the tubes as I acquired a different pre with phono built in but still have those tubes. Also have the RCA 5691 red base tubes. Sylvania a little more air while the RCA had a little more meat on the bones…
