That "tube sound" and power ratings

Wow. Quick first responses! But before this gets too far in, I better qualify that I didn't mean that I'm new to EE or Physics or high-end audio listening. However, I am new to tubes as they're used in audio equipment. So my question is only partially about the physics/engineering behind tube implementation in audio. I realize that theory and circuitry may very well be part of any good explanation, so I don't want to discourage it. But the main question is about what tube enthusiasts like to hear and how they achieve that sound at their preferred listening levels.

I think Atmasphere understands where I'm coming from. In fact he/she may have answered part of my question, but I'd like to hear other viewpoints.

Mapman, I'm sure you have some good insight now that (hopefully) I've explained a bit better. I'm sure you know more about the subject than me and I look forward to more input from you. However my question is more subjective than came across. How does a tube enthusiast choose the right power for their system given that they actually may prefer more distortion of the right harmonics? If they choose a higher power amp I'm assuming (and yes I might be wrong!) that there will be less of the DESIRED distortion that adds to the fun of tubes.

Czarivey, I appreciate the input but you misunderstood the point that not all watts are created equal. They most certainly are not, or we'd all have $200 Bose equipment and stop there.

OK. Let's please get off my "not all Watts are the same" comment. I didn't realize it would be so badly misunderstood - my mistake. Just so it's understood - I'm perfectly aware what a watt is and is not, so let's move on ...

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.