Ultralinear vs. Triode vs. SET

Paul, I suspect that the lower output impedance/higher damping factor of the 4 ohm tap (probably a factor of 2 different compared to the 8 ohm tap) was also a significant contributor to the differences you heard. That would be particularly so because your speakers, like a lot of others, have very wide impedance swings in the bass region, iirc.

Best regards,
-- Al

IS there any consensus (not kidding:)) that for a given circuit, fewer output tubes always sound better than more IF there is sufficient power to drive the speakers? Maybe it was Sam Tellig who once said that some of the best sounding tube amps tended to be 40-60 watt tube amps, most if not all with just a pair of tubes per side, I wonder how important that is and whether running 2 pairs per side makes it that much harder to get the "purity" of sound you get with a single pair (or just one output tube). Again, assuming the lower power rating does not present an issue for driving the speakers.

No- no consensus. Sometimes its true and sometimes it isn't. If the designer paid attention to the idea of current sharing amongst the power tubes, more tubes will not be a big deal.

If you have a transformer-coupled amp and its designed for 4 power tubes, pulling 2 out may not work right any more- it really depends on how the circuit is designed.