You might want to audition an Audio Note SORO SE (about 17 or so watts a side single ended). It's an integrated. I have one but am not selling.
how much tube power is needed?
Let's say, for a 86 and a 92 dB efficiency speaker. SE triode fans say 10 W is enough, 20 W is more than you need. They use horns and high-efficiency speakers (> 92 dB sensibility). They say high-powered designs do not sound good at low volumes while driving high-efficiency speakers. Others (mainly push-pull fans) say that even though you have high-sensitivity speakers, the more watts, the better dynamic resolution. I don't want to launch a SE/PP war now. This is not meant to be a pure technical question, it also concerns musical taste. What is your experience with these?