A bit late but I was curious yesterday and measured my Consonance Cyber 845. It managed 24.5W into an 8 ohm resistive load, using the 8 ohm output tap. 4.0% THD at that power level, which was just before the onset of visible clipping on the oscilloscope. That was with an 845B tube, using an 845C it made 21W but THD dropped to 2.2%, which is pretty good for an SET. It ran 20W @ 2% THD with a 4 ohm load/4 ohm tap. These were all at 1kHz since that is pretty standard, I'm sure it would fare worse with say a 30Hz signal.
The F3 should be really nice, hard to imagine being unhappy with that.
