Power output of tube amps compared to solid states

I have owned several pairs of Dynaco MKIII monos and I have never heard of a Dynaco MKIII producing 100 watts.

Also, these 20 watt single ended amps that keep up with higher powered amps only do so on efficient speakers when everything is just right, but all it takes is a power hungry crossover and the little amps fall apart.

To be realistic, a 100 watt tube amplifier will drive most any speaker.

While there are no universal absolute rules, a common difference between tube amps and solid state is the manner in which they clip.

Many solid state amps clip harshly. The peaks above max output are flat-topped with a square-wave like edge. This generates a lot of higher order harmonic distortion that sounds harsh, metallic or edgy.

Tube amps generally have softer clipping when over driven. Since this is more pleasant sounding, it gives the impression of more power since you don't hit a brick wall.

Of course, there are a ton of variables to consider. The main ones are how loud you listen and the efficiency of your speakers. While tube amps have a devoted following they are not for everyone. Make sure you can audition an amp in your system before you commit.

tubes have high output impedance so they need transformer to convert its output voltage into current to drive nowdays speakers. hence the power of tube amps become less 'visible' to the lower frequencies due to the transformer limitation. this yields that they sound louder per given power because they do not spend their power onto the subwoofer frequencies as solid states do.
other than that power can't be solid state or tube it's just a product of voltage and current.

Sorry, Marakanetz, that explanation is not correct. First off, not all tube amps have output transformers. Mlsstl put his finger on the issue- odd ordered harmonics.

Smooth clipping is less odd-orders. Music is a very transient sort of waveform- when the transients clip the amp (even though the rest of the waveform does not), this will be a major factor in what separates the tubes from the transistors, **not** low frequency bandwidth. Odd-ordered harmonics are used by the ear/brain system as loudness cues; the transistor amp overloading on transients will be sounding very loud, whereas a tube amp might still seem to be asking you for more, without the associated harshness.

This is why guitar players prefer tubes as well.

BTW the difference between 250 watts and 100 watts in only about 4 db- not that much to the human ear.

The why rather than the how:

1) instantaneous power as it relates to distortion. In a very short increment of time, tubes can put out a lot more power than transistors or FETs for a given distortion level. This has mainly to do with electron mobility being a zillion times higher in a vacuum than in doped silicon, not to mention asymmetrical drift velocity issues in silicon. But I'll digress here. This is why 'soft clipping' is possible.

2) overload recovery of tubes is much better than solid-state. This is a follow-on to #1. After a transient, there is no reactive impedance to charge recovery in a vacuum like there is in semiconductors. This prevents frequency domain disruptions in tubes (the messing up of harmonics). This is the main point Lavardin has tried to resolve with their own solid-state devices.

There are other more-minor factors mired in the nitty gritty of device physics but these two are the most important, as I see it.

When it comes to steady-state signals, the power levels ARE the same if the Watts are the same. But music is most definitely NOT a steady-state signal. Nearly all measurements and graphs you will see on the performance of an amplifier are based on steady-state. These cannot be used to accurately explain transient phenomena. They can give an overall indication of performance ability, but nothing more. This is why many people believe measurements do not describe how a component actually sounds.

Getting back to the post, efficiency is a separate issue from power output. For Forests, a 50 or 60W tube amp will be great. We had a 55W Cayin on a pair for a long time and it was wonderful. Their impedance is high so they do not demand lots of current, making tube amps the way to go with Forests IMO.

Arthur