Tube amp power watts equivalent to Solid State?

03-16-14: Dopogue
My 12wpc SET monoblocks (845 output tubes, EL-34 drivers) designed and built by a friend sounded much more authoritative and powerful than the CJ Premier 12 monoblocks (140 wpc) I used to have.

So, for me, this contention -- tube watts delivering something more than SS watts -- must have SOME validity. It may not make sense, but I heard it, at length, playing all kinds of music, in my own system. Ten years later I'm still astonished at the twelve-watters. And my speakers are not of the ultra-sensitive variety.

Fortunately I'm not an engineer or I'd know this couldn't happen :-)

Not necessarily :-)

In addition to ZD's point, what stands a very good chance of having been a major factor, as alluded to by Lewinski and Unsound, is the amplifier's interaction with the impedance vs. frequency characteristics of the speaker.

Many speakers have impedances which rise to extremely high values (e.g., 40 or 50 ohms) at some frequencies in the deep bass region, and also to values of perhaps 20 or 30 ohms in the vicinity of mid-range crossover points. For a given input voltage, the power delivery of a solid-state amp relative to its power delivery into 8 ohms will decrease in direct proportion to that impedance rise, when the amplifier is operated within its maximum power capabilities. Its maximum power capabilities into those high impedances will also decrease dramatically, relative to its 8 ohm rating. Both of those effects will occur to a much smaller degree in the case of a SET amp, and many other tube amps.

It should be clarified, btw, that the CJ Premier 12 is a tube amp. However, it has an output impedance (measured by John Atkinson as 0.87 ohms at mid and low frequencies) that is much closer to being in the solid state camp than in the camp of nearly all SET's and the majority of other tube amps. Everything else being equal, that will cause the Premier 12's interaction with speaker impedance vs. frequency variations to be more solid state-like than that of most other tube amps.

Also, nobody has yet mentioned that the characteristics of the distortion rise that occurs with tube amps as their power output approaches and somewhat exceeds their rated maximum capabilities tend to be less offensive than in the case of solid state amps, i.e., they clip more softly. That can contribute to a tube amp being seemingly more powerful than its rating would suggest.

Also, see this thread, which includes extensive discussion of related issues by some very knowledgeable folks.

Regards,
-- Al