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,
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.
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.
I think perception of loudness is much more relevant than technical specs. We use our ears to hear the amp not meters. I have had several amps over the years. 5 all valve amps. 3 Laneys, a Fender Hotrod deluxe and a Vox AC15. I have also had countless solid state and tube emulation amps. And what it boils down to is this: My 15 watt Vox will easily match an un-mic'd drummer. If I need louder I can mix the amplifier through the PA use the front of house to provide the volume. What is crucial to me and the only thing that should matter to you is what the amp SOUNDS like. The quality of tone has to be the primary consideration and on that score for me, I have never found a Solid State amp that sounds a fraction of good (or perceptively as LOUD) as a valve amp.
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.
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..
I remember reading that the magic ratio was three times, so a five watt tube amp would compare to a fifteen watt solid state. But like everyone else is pointing out, this is a perceived comparison, not real. There are many other factors involved. From experience I can tell you that I perceive this difference and appreciate it, but when you are playing with a drummer and you need say thirty watts to hear yourself, the ten watt tube amp isn't going to cut it.
