Power output of tube amps compared to solid states

Atmasphere, I'm not sure that many speakers actually necessitate that the partnering amplifier use feedback.
You say that the use of negative feedback contributes to the amp sounding "shouty". I find that ironic, in that "shouty" attribute is one of the most prominent ones that I find so objectionable in the speakers that are usually paired with tubes.
It would appear to me that in some case lower impedance would offer benefits that the speaker designer feels outweigh whatever negatives that tag along.
Again, I suppose this where we disagree. I would suggest that if a speaker manufacturer builds a superior speaker that requires an amplifier with a particular set of parameters to be effective, then so be it, make and use that amplifier. You on the other hand seem to suggest; that I can make a superior amplifier so long as the speaker works within it's parameters. As I feel the speaker/room interface presents the most challenges for the prospective system builder, I would propose; that the speaker be the determining factor in determining an amplifier/speaker interface. You, on the other hand would propose; that the amplifier(s) should be the determining factor in an amplifier/speaker interface. I suppose we have a conundrum, as to just who is seeing the forest from the trees?:-)

Two different recipes that both can produce some very good soup.

Atmasphere's is a more unique recipe I'd say that might deliver some very special results if followed properly.

In the last 20 years the use of SETs has really increased a lot. It has resulted in a lot of speakers that were simply not available 20 years ago. So these days its ten times easier to find a speaker that works with 'current source' amplifiers than it used to be.

Unsound, I can think of three speakers that if you put a tube amp on them, the result will be shrill, and all for the same reason: the amp will not double power as impedance is halved (or conversely, cut the power to 1/2 as the impedance doubles): the B&W 802, the Avalon Isis and the mbl101e. So if you are working with speakers that have similar impedance curves, I can totally see where you are coming from.

BTW the speakers on that short list are all examples of Voltage Paradigm technology, and its been my experience that when you mix Voltage and Power technologies, you will get a tonal aberration; 'shrill' is a common resulting aberration. Several others have been mentioned above, such as the 'wooly bass' that Duke was commenting too.

Atmasphere, I wasn't talking about those kind of speakers. I was talking about horns and others that are supposed to be tube friendly.

If I may steer this thread a bit back to the original question . . . there's are two characteristics typical of tube amps that I think make the perception common that "tube watts" are more powerful than "solid-state watts":

First, as others have alluded to . . . tube amps (as a group) have less offensive overload behavior, so it's possible for a slight bit of clipping to be much less noticeable than for a typical solid-state amp.

But there's also the fact that the overwhelming majority of both solid-state and tube amplifiers use unregulated power supplies, meaning that the voltage available to run the circuitry goes down the harder the amplifier is driven. And exactly how much it goes down is a function of the power supply's total capacity and its ability to store energy . . . in relation to the energy peaks required by the music being played.

And the particular set of energy-storage dynamics between a typical tube-amp power-supply and that of a typical solid-state amp are VERY different. ("Typical" here means push-pull outputs operating in Class AB or B, SS direct-coupled, and tubes transformer-coupled with C-L-C filtering.) The tube amp generally has significantly longer time-constants in its filtering in relation to the currents required by the output stage . . . meaning that whatever "dynamic-headroom" power is available (short-term peak power above the maximum available steady-state power) can be delivered over a longer period of time.

There are several mechanisms at work here. First, a push-pull tube amp reflects its impedance back to the power-supply as two full-cycles for every output cycle. Second, the output transformer primary inductance acts as effective energy storage for signal waveform asymetry. And third, the impedance transformation of the output transformer works backwards as well, drastically reducing the peak current demand on the power supply.

So a hypothetical 40-watt push-pull vintage tube amp may have 40uF of capacitance on the main plate supply and 5K transformer primary, and let's say we're using a 4-ohm output tap. 40uF seems chincy by today's standards, but this is equivalent to more like 100,000uF for a direct-coupled solid-state amp . . . and for comparison, a good quality 150w/4-ohm solid-state amp usually has something like 25,000uF. And while the SS amp does have two caps, since the output current is half-wave rectified (rather than frequency-doubled as in the P-P tube amp), their effective capacitances don't add together. And then the tube amp usually has another 40uF of capacitance and a choke in front of it, which probably gives about 2-1/2 times again the total energy storage for the power-supply.

So it's entirely possible that this hypothetical 40-watt tube amp may have similar (amount in dB) of dynamic headroom to the hypothetical 150-watt SS amp, but is able to maintin its dynamic power rating for ten times as long . . . let's say 50 milliseconds instead of 5 milliseconds. With a typical music waveform, this is a dramatic difference.