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is there a chart or general rule of thumb of how the different power levels for a valve amp compare to an equivalent volume solid state amp?

for example,

  • 5 watt valve amp similar volume to 20 watt solid state
  • 20 watt valve similar volume to 100 watt SS...
  • some other arbitrary example
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It's not really meaningful to do such a comparison, as it depends heavily on how you use the dynamic range. A 5 watt solid state amp is actually louder than a valve amp of the same power, you just usually don't play it that loud because, while solid-state power amps sound simply unpleasant when you drive them to the limit, this is exactly the point where valve amps produce the best of their sweet distortion. But a modern solid-state amp with sophisticated limiting can actually reach the full power without going into audible distortion at all. –  leftaroundabout Aug 15 '11 at 1:16
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4 Answers

The simple answer is "no". All measures of the relationship between wattage and perceived loudness depend on a myriad of factors, tangible and intangible, and the results are ultimately subjective. You just have to line up different amps and speakers and cabinets and plug in your favorite guitar and your favorite effects and listen to what they sound like.

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The simple answer is that a watt is watt whatever produces it - and that a watt is a measure of power, not volume (acoustic pressure level - decibels, that is). The volume is a factor of power AND speaker efficiency (ie: how many decibels a speaker produces for one watt).

As long as we're talking about pure clean tones and not pushing your amp to it's limits, a SS amp and a tube amp set up to produce the same output power (watts) AND going thru the same loudspeaker will produce the same volume (db).

The a-bit-less simple answer is that a SS amp cannot produce much more power than what it's rated for - it will almost immediatly hard-clip your signal - while a tube amp will smoothly go into a more gentle soft-clipping, slightly warming up and compressing your signal but with still quite a lot of "less clean" available power. Given the very dynamic nature of a guitar signal, this means that when pushed to it's nominal power, a tube amp will still have some "not quite clean but pleasantly sounding" headroom where the SS amp will hit a brick wall.

If you factor in the fact that most SS guitar amps are budget practice amps with cheap cabs, cheap and inefficient speakers and more often than not very optimistic nominal power rating you understand where the myth of the "tube watts vs SS watts" comes from.

EQ (from the guitar, the preamp AND the speaker) also plays a huge role when it comes to perceived loudness, specially in a mix where you have to compete with other instruments. Guitar tone is essentially about mids, mids and then mids, so if you end up with a very scooped "V shaped" EQ you'll have to compete with the bass and kick in the lows and with the cymbals in the highs, and chances are you'll need much more power to be heard.

So to make a long story short: no, there's no "chart or rule of thumb", since it's not that much about how many watts but about how these watts are used.

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No. A watt is a watt. The apparent difference has to do with how the speaker interacts with a valve or a SS power stage. Read this http://lenardaudio.com/education/14_valve_amps_7.html It's science, not where you set your knobs.

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Good answers on this age old topic...

A tube amp with a specified 50w output from 100Hz to 10000Hz with 1% distortion will be similar in clean undistorted volume as a 50w mosfet amp with the same frequency specs and distortion level.

But the tube amp will start to clip gracefully with harmonic distortion and at 10% distortion you will still perceive it as fairly clean with a little bit of hair around hte note whereas the solid state amp will sound fairly terrible with 10% of harsh unmusical distortion. But also build and such is important.. A vintage 100w marshall SLP has large transformers and capacitors and can put out considerable more power than the 100W speicified.. I think I have seen numbers in the 160-170w with a big degree of harmonic distortion in the output stage...

But 4x the output from tube to solid state is exagerated. If the solid state amp is overbuilt and can deliever a lot of current under a wide range of impedances it will be fairly strong.. My transitor VOX VT50 was specified at 50W RMS and is was a loud amp.. Compared to a Laney cub 12r with two EL84 for 15 watts of output and dinky transformers the VOX through the same speaker was louder and much more punchy..

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