Just to further confuse the nomenclature issue, I'm using 845s from Sophia Electric, but they're the 845C, not 845M. I thought the "M" was proprietary to SuperTNT. In any event I like the 845Cs well enough that I recently bought TWO new pairs when one of my old ones bit the dust. I'm not good at describing sound, but these are the most musical 845s I've ever had in my amps. Good luck, Dave
PS The only downside is that some of the 845Cs fit so tightly into my tube sockets that they're very difficult to remove.