Tube Amp Watts vs Solid State Watts... Is this a red flag?

Tube amplifiers were in that power range 40-100W..
Basic issue with tube amplifiers is their higher THD...
A quality solid state amplifer Class A-B has very low THD until it is pushed to its design limits..

Just my $0.02..

Tube amps distort more "pleasantly" than solid state amps, so they can often be over-driven with less obvious negative results. If you want maximum accuracy and minimum distortion, then the 80-250 range is what you should aim for... even with a tube amp.

Really the watts are not a true indication say 40watts =60db's 80 watts will give you 63db. not much of a difference.The clipping you get in tubes are even order harmonics which round off the sound. So even though it is clipping you get a more listenable sound which is perceived as louder. With solid state units the clipping will sound harsh. Of course it also depends on the type of speakers you hook the amps up to. I've heard Avantgard floor standers w/a 6wpc tube amp play very loud. Of course the efficiency rating on the speakers was a 106db. Does it mean that a 6wpc tube amp is as powerful as a 200wpc Bryston? No, But if you added a pair of 83db Platnium Audio speakers. Both amps would be perceived as just as powerful, There's more to it than just watts. There are some other people on this forum that have more expertise than me and can give a more in depth explanation.

while distortion may contribute to a sense of loudness, the more likely reason folks sometimes say tube watts are louder than ss watts it that tube amps also compressquite nicely, which will certainly make everything sound louder.

And of course if you have speakers (or a room big enough to let you sit so far away that) 40 watts is 60 dB you need a do-over. but of course the basic maxim that doubling power yields a three dB increase holds true even with more typical speakers that are above 80 dB with one watt.

I have seen this before and have three thoughts, mostly echong what has already been said:

1. Most SS amps clip quickly past their power limit while tube amps tend to compress much more gradually. If the speakers are sensitive to clipping (which tends to send more HF energy to the speaker) then it makes sense to provide more headroom in the SS design.

2. Tube amplifiers tend to have more single-ended distortion characteristics, emphasizing the second harmonic, then 3rd and higher. SS amps tend to emphasize odd harmonics and thus sound harsher when over driven. So, while a tube amp may in fact have much higher distortion, it might not sound as bad to us. Distortion is still adding signal that is not supposed to be there, of course.

3. High-power tube amps are harder to find and much more expensive than SS amps. That is not to say there are not high-priced SS amps, but for $1k you can get a lot of SS power compared to a tube amp at the same price point (be prepared for a litany of exceptions). Given the added headroom and distortion characteristics, it makes (marketing) sense to suggest higher-power SS amps.

All IMO - Don

Also how an amp comes Out of clipping determines how "distorted" an amp may sound. From what I have heard some solid state amps "stick" and stay at clipping, before they come back to the "undistorted" state. Simply put many tube amplifiers clip much more gracefully and with a more benign distortion signature than many SS units. So therefore a lower wattage tube amp may sound as "loud" without distortion than a doubly powered SS unit.

All this aside, the "distortions" all amplifiers make is NOTHING compared to the distortion that most loudspeakers produce that our ear takes for granted. Any distortions produced by amplifiers is swamped by any SPEAKER "distortions" . Have you ever seen "distortion ratings" of speakers? Depending on the frequency it can be on the order of 20 percent to a low percent..

Whoa did he just say 20 percent? Indeed it is true!

Anyway I would really not pay much attention to any amp distortion ratings unless it is really, really high.

Tim

Just to clarify, you mean may sound as loud without an unpleasant a type of distortion, rather than "without" distortion because the distortion is there, in spades, even if it's not like driving an ice pick into your ear.

I have a ~30W tube amp and I think it sounds pretty good, but by the same token I don't proclaim it as equivalent to 60W of ss power because the distortion at that output might be somewhat more tolerable.

All of the "good" tube amps that I have heard in no way sound remotely distorted. Even ones that are rated at "less than 1%" Here are the specs of a very famous tube amp that has been in production since about 1960 (well this is the modern reincarnation):

"Output power: 75Wpc (18.8dBW) into 4, 8, or 16 ohms (stereo), 150W into (21.8dBW) 2, 4, or 8 ohms (mono). Frequency response: 20Hz–20kHz, +0/–0.5dB; 10Hz–70kHz, +0/–3dB. Signal/noise ratio: 100dB, A-weighted (no reference level given). THD: 0.05% at any power level from 250mW to rated power output. "

Distortion "in spades" I think not. And remember that doubling your amplifier power is a mere 3db increase in sound volume, all things being equal. Also from what I heard if an amp designer wants a better distortion spec at the expense of the Sound of the amp all they need to do is crank up some more negative feedback ....

Yeah, I've heard pretty much all the arguments and they all pretty much boil down to the only reason tube amp watts can be considered "more powerful" than SS watts is because you can drive them to higher levels of distortion before it becomes unpleasant. So, in fact, you are putting out more watts and it's no longer apples to apples..

Not dissing tube amps, as I said I have one and think it sounds just fine, just the "tube watts are more powerful" is bunk, apples to apples.