I agree with Charles. Also as he implied, not all 300b SET amplifiers are the same; and not all 300b tubes are the same.
300B PSET
I love singled ended 300B for its musicality, tone, refinement, basically that mid range magic. However 6-8 watt 300B in single ended configuration usually lacks low and high frequency extension. Is a well executed parallel single ended 300B amp putting out 18-20 watts the best of both world with better bass and yet retaining that mid range magic?