Watts! How many do we need?

"is an unltralinear watt identical to a triode watt? That’s a serious question, I am not intending to be sarcastic."

Basically, yes. But ultralinear operation has plusses and minuses. and a lot of those depend on the quality of the output transformer, the percentage of the screen taps relative to the plate taps, etc. You can get essentialy twice the power of triode operation (or more) but you also introduce stability and distortion factors that must be addressed. In a typical feedback amplifier, switching from triode to ultralinear operation requires adjustments in the feedback components to optimize the amp’s performance and stability. So a big question when buying a switchable amp is, does switching from one mode to another involve correctly adjusting the feedback components to allow for optimal performance? An amp oprimized for triode operation can encounter some serious issues when switched to UL mode, and vice versa. If no such arrangements are made, then one mode or the other is going to suffer. Often times, people with switchable amps will report that they tried the triode switch but didn’t like it because the sound quality was reduced. Or, they’ll report that triode mode was more "open" but the bass control was worse, etc. Usually these negative impressions are the result of the amp not being properly designed to optimize each mode of operation.

The Sanders paper is very interesting.  But one should remember a couple of things:

1) He's talking about ESL speakers in the main;

2) I think he exaggerates the frequency and extent of clipping in an appropriately matched system.

I would venture to suggest, at the risk of possible ridicule, that an audiophile in 1950 with a pair of Klipsch Cornwalls and a 15 wpc Wliiamson amp would rarely have encountered clipping and was probably enjoying a better musical experience than a lot of the power-eating systems available today.  In modern terms, I'll also stick my neck out and suggest that an audiophile with a pair of Vandersteen 1Cs and a well-restored Eico HF-87 will find a good deal of musical contentment with that arrangement, with far fewer headaches and travails than an amateur attempting to joust with walls of drivers and 600 wpc. ;-)

As a counter-argument to Sanders, I enjoyed this interview with amp designer Justin Weber, who essentially maintains that most audiophiles need *less* power than they think.  He also offers a very amusing and (IMO) very pertinent discussion about single-ended amplifiers:

"You don't need walls of drivers and the only jousting with 600wpc is financial/spouse approval."

My point was that I have seen systems so expensive, so complicated and striving for so much power and scale that they become unmanageable for the owner.  They're often difficult to listen to as well.

"I was using a 10 watt class A amp to drive a pair of Super Tablettes (86 db I think) in a 13x14 listening room with zero issues. So then I thought, "What the hell!" and put in my 2A3 integrated amp. Still no issues and the speakers sound great."

ProAcs are rather famously amenable to lower-powered tube amps. My first audio heartthrob was a pair of Studios with the little Cary stereo 300B amp I heard in a shop. I was thrilled a few years later when a friend sold me his Response 2’s. Thirty years on, with one set of replaced drivers and two sets in storage, I’m still enjoying them. ;-) I used 300B amps with them for years but the quest for better bandwidth and slightly more power led me to my current 20 wpc Williamson amps.