Tube amp power watts equivalent to Solid State?

Actually a pound of cotton weighs more than a pound of gold...
Troy ounce... Its much more in the way they clip.

Hi Bob,

Thanks for the clarification. Bruce's (Bifwynne's) explanation of my comment that you questioned was a good one, and I think that your understandings that you've described are also correct. In the case of nearly all solid state amplifiers (excluding special cases such as some of the First Watt amps that have tube-like or higher output impedances), the interaction of amplifier output impedance and variations of speaker impedance as a function of frequency will not result in significant frequency response differences as a function of what amplifier is being used.

And I was not implying anything to the contrary in my previous posts. Note the two sentences in my post which followed the ones you quoted just above, especially the second sentence:

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.

My posts were addressing reasons why a tube amp, especially a SET amp, may seem more powerful and "authoritative" than its power rating would suggest. As you'll realize, one of those reasons is that its power delivery into the very large low frequency impedance rise I referred to will not decline as sharply (relative to its delivery into lower impedances at other frequencies) as it would in the case of nearly all solid state amplifiers.

So although the interaction of amplifier output impedance and variation of speaker impedance as a function of frequency will not cause significant differences in frequency response among nearly all solid state amplifiers, with many and probably most speakers it will cause significant frequency response differences between solid state and tube amplifiers, and often between different tube amplifiers as well. As Bruce indicated, if one such combination (solid state or tube) results in flat frequency response, the other one probably won't, unless the speaker has an uncommonly flat impedance curve (although some speakers do have an impedance curve that is flat enough to make this a non-issue).

Best regards,
-- Al

With typical speakers, though the impedance might change, the sensitivity also changes accordingly. A typical quality ss amp will more likely maintain flat frequency response with varying power output to the fluctuating impedance of typical speakers. A typical quality tube amp will more likely deviate from flat frequency response with steady power output to the fluctuating impedance of typical speakers.

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?