It’s hard to separate the sound of the particular output tube from the sound of the amp in which it is being used. Also, the sound of a pentode or beam tetrode when used in a SE amp as opposed to push-pull. For my money I prefer PP over SE, and my favorite output tube in a PP circuit is the 6L6GC. I don’t know how anyone can describe the “sound” of a 6L6GC because different makes sound so different. I have 4 sets that I use—-RCA blackplates, GE grayplates, SED Winged C, and Tung Sol STR, and they sound wildly different from each other. Of these only the T-S is currently manufactured, but the good news is it sounds great. I would have no problem using the T-S exclusively.