That "tube sound" and power ratings

The tube amps that have the most unique sound compared to the norm are probably those made well and with little or no Negative feedback applied, like Atmaspheres.

I just went through this exact same question myself when trying to decide on amplification for a new system. In my case the speakers are rated for 100 watts. The amp I picked is tube and rated at 140 wpc. It sounds fine. Almost effortless. Would it sound even better with double the power? That would give me 3 db of additional headroom, a barely perceptible difference. As already explained clipping is bad, in addition to adding significant amounts of IM distortion, clipping can damage your speakers. Here is what I would do. Determine the sensitivity of your speakers. This is stated as so many db at 1 watt input, measured at 1 meter away. Then calculate how much power you need for the sound pressure level that you want to achieve. Every doubling of power adds 3 db. So for example: Assume the speaker sensitivity is 90 db at 1 watt. 2 watts = 93 db, 4 watts = 96 db, 8 watts = 99 db etc. Then add 3 db to your assumed max listening level for safety. Make sure your speakers can handle the power you calculate.

Hi-fi amplification is not the same as with guitars. You want want your amps to be running in their lowest-distortion range, every time (or as close to that as possible given your SPL needs) -- whether tubes or SS. And you can still clearly hear the effects of tube rolling even when amps are perfectly well within their "clean" range.

Too much power doesn't cause problems unless you're careless and let a very high-power signal through to your speakers -- besides that scenario, it's generally safer to have more power, to avoid clipping (which can be problematic for tweeters). When it comes to protecting your gear, there's no silver bullet -- some care and education will be required by yourself, whether you choose tubes or SS, high power or low power.

I run 250 Watt tube amps on 96db/Watt. So I'm definitely on the "too much power" side, and it works extremely well; I love it. The system gain structure is a little suboptimal, but that's a (kinda) different issue.

Thanks Bill, but your response answers the opposite of what I'm asking. I'm not trying to find out if tube enthusiasts like the sound of less clipping from more powerful amps. Rather, I'm asking if they prefer the sound from less powerful amps, and if so how to decide which power rating provides the best tube sound given an amp's characteristics together with the speaker sensitivity and the preferred listening level.

Maybe I need to explain how "tube sound" is partially related to distortion? I didn't want to do that here, and I'm not really the person to do it. An earlier post from Atmasphere explains the sound charateristics of push-pull circuitry. While that may be the most important influence on "tubiness", it's only part of the story. One also needs to consider harmonics that occur when an amp is almost or even softly clipping. These harmonics can be pleasing to the ear at certain levels.

Tube people, please feel free to add or subtract to my knowledge here. As stated I'm a tube audio newbie hence this post.

Anyone else want to take a stab at asking my question in an easier-to-understand way? Atmasphere?

Mulveling - thank you!

"You want your amps to be running in their lowest-distortion range, every time (or as close to that as possible given your SPL needs) -- whether tubes or SS. And you can still clearly hear the effects of tube rolling even when amps are perfectly well within their "clean" range."

Great answer. Does every tube enthusiast agree with this? I know I shouldn't believe everything I read, but it sure seems there are a lot of "audiophiles" who believe a great amp is a great amp tube or SS, and unless you're nearing or at clipping you probably won't hear the tube characteristics that drove your tube enthusiasm to begin with.

So ... if you never operate in this range are you happy with your tubiness?