Tube amp power watts equivalent to Solid State?

Hi Unsound,

I essentially agree, except that I would substitute the words "the majority of speakers" for "typical speakers." I would put it that the majority of speakers are designed to provide flattest frequency response when driven by solid state amplification.

Best regards,
-- Al

There is an issue here that has not yet been discussed. It has to do with something called 'space charge effect' that often occurs in tubes and does not occur in transistors.

First- space charge: this is where a tube is conducting and some of the electrons bounce off of the plate and gather in its vicinity. This usually happens more near the point that the tube is about to saturate, depending on the tube. Pentodes BTW are designed to minimize space charge effect.

The space charge is thus an excess of electrons near the plate. This has the effect of reducing the tube's ability to conduct and makes it harder to completely saturate.

In practice, the result is that the tube will not hard-clip like a transistor will. This means that a tube amplifier will have a clipping characteristic that can be quite 'soft' if just barely clipping; the amp will enter saturation in a gradual or perhaps even graceful manner, with less of the odd ordered harmonics that are caused when clipping onset is immediate as in transistors.

Because some odd orders and in general higher ordered harmonics are present, which the ear uses as loudness cues, the amp will just tend to sound louder at this point, but without breakup that accompanies hard clipping.

But even with hard clipping, tube amps do not make as much odd ordered harmonic distortion due to the space charge in the power tubes. The result is they sound smoother to the human ear.

This is why guitar players tend to prefer tube guitar amps BTW.

So the bottom line is the reason tube amps often seem to operate with more power than they should has everything to do with how they overload; specifically the reduced amount of odd orders present at clipping. If you get rid of this 'soft clipping' characteristic you often need a lot more power to seem to do the same job. Makes sense now?

^ I would agree that the softer clipping of tubes might make the sound of tube amps seem louder than comparably powerful ss amps, but as tube Watts often cost more than ss Watts, one might be able to buy extra ss Watts for the same money to compensate for the clipping issue, and perhaps more readily dismiss it altogether. Perhaps it might be wiser to compare amps on the basis of cost rather than Watts? Of course, that is not to say one shouldn't consider power output ability when purchasing appropriate amplification.
Is this "...excess of electrons near the plate." consistent and/or linear?
Sorry but, I'm not sure that "This is why guitar players tend to prefer tube guitar amps BTW." is necessarily true. Creating sounds is quite a bit different than replicating them.

Interesting thread, and think this comment by Atmasphere is very significant,

Because some odd orders and in general higher ordered harmonics are present, which the ear uses as loudness cues, the amp will just tend to sound louder at this point, but without breakup that accompanies hard clipping.

as I have read many times that the distortion created by the soft, gradual clipping of a tube amp is perceived by the human ear as an increase in loudness, therefore thinking tube amp watts are more powerful.

As far as guitar amps, I have read that there can be a difference in the design of the volume control circuit between tube and solid state. A solid state amp will reach maximum output with it's VC at very close to fully clockwise to avoid hard clipping, while a tube amp will reach maximum with the VC at only 3/4 of the rotation. This allows adjustment for varying amounts of that desired distortion in a tube amp.

Best to avoid clipping totally, however # watts it takes.

As long as its done well.....