Power output of tube amps compared to solid states

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.

Kirkus, Thanks! Your explanation of longer duration of headroom makes a lot more sense to my ignorant understanding of things than any of the other explanations offered so far.
I hate to use "my" current amplifier as a point of contention, but, my scope is somewhat limited. The manufacturer of my older cap coupled ss amplifier claims that it can double it's rated output for up to a couple of minutes at a time. Is that realistic? Is it due to it not being DC coupled design? Is it something all together different? What about ss amps like the Ayre that use chokes? I guess what I'm asking is whether tube amplifiers will always have this advantage over ss, or is it a matter of application?
It would appear to me that, while what you posted might very well be true, ss can usually offer more steady out-put power for the same dollar as most tube amplifiers. If so, wouldn't that negate some of the advantages you suggest for tube amplifier headroom duration?

Kirkus, "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." Thank you for your insight! Finally, we now have something that tangibly advances the conversation.

My position throughout this thread has been that we are clearly measuring the wrong things (the most obvious being WPC), and that we need SOMETHING to bring us into the world of calculus, as opposed to arithmetic/algebra. Again, the complex relationship of loudspeaker/amplifier/music is not a static or steady state, but a dynamic phenomenon. Distortion, another steady state parameter, is most definitely not the answer.

What Kirkus has laid out on the duration of dynamic headroom pushes the discussion into the promised land of calculus. For that, praise, admiration, and congratulations are in order. Again, I thank you!