Maybe search Decware posts/forums as this (6H1N?) may have been a candidate for use in one of their amps.
I researched the tube some time ago for a particular amp, but forget the details (as well as the amp being researched:-).
DeKay
Douk Audio T8 Pro vacuum tube equalizer
I recently bought a Douk Audio T8 Pro 7 band equalizer on a whim. I have a mid range system which consists of an Arcam A25 integrated amp, Arcam SACD player, B&W 704 speakers, Panamax m5400 power conditioner, and Project turntable. I don’t like the fact the Arcam has no bass or treble control so I actually like the addition of the Douk so I can move some of the vocals a little more forward and I do prefer a little brighter sound. I know what the purist thoughts are regarding recreating the true sound as the artist intended it so I don’t need any comments regarding that. I just like what I like. My question is has anyone swapped the vacuum tubes on the Douk and if so what did you find was the best tube for a more holographic warm tube sound? My previous set up consisted of Rogue Audio monoblock amps and Totem speakers and I’d like to recreate that sound as closely as I can without spending that kind of money.