Johnk, the post was worded right. The upper power limits of SETs in a way are more of a function of the output transformer that it is the tube! The bigger you make the transformer, IOW to handle more power, the less bandwidth it will have. If you try to optimize it for bass, the highs will be rolled off and vice versa.
Since many high efficiency speakers (99db+) have limited bass response, SET builders usually sacrifice the bass performance in favor of the highs, since speakers that go below 40 Hz in the high efficiency world are few and far between.
IME experience the bigger SETs also have less detail. This is based on my personal listening experiences, but you will notice that one of the revered 'king' tubes in the SET world is the type 45, which usually makes less than one watt at full power. IOW, the smaller you make them, the better they sound, which is a common theme with amps in general (although OTLs seem to be one of the few exceptions), both SET and P-P.
I've also noticed that it is exceedingly rare to compare like technologies in the SET world. People often compare say a 300b SET against a P-P EL-34 amp (with the results in favor of the SET), but how often is a 300b or other SET compared to a P-P DHT class A amp of the same power rating? IOW to be scientific, this is where one would start if looking for real answers.
