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Power output of tube amps compared to solid states

I'm having a hard time trying to figure out how tube amp power output relates to solid state power output. I've been looking at the classifieds for tube amps and I see lots of tube amps with 50w or 60w output, but nothing close to the 250w output typical of solid state amps.

So I have no idea what type of tube amp is required for my set up, right now I'm using totem forests with a required power rating of 150w-200w at 8ohms. The bass is so powerful on these that I have the sub crossover set to 40hz.

My question is, are tube amps so efficient that 50w from a tube sounds like 150w from a solid state? Or will 50w output from a tube severely limit how loud I can play my speakers? If so, are tubes usually meant to be driving super-high efficiency speakers?

I had previously tried a tube pre-amp with a solid state power amp (both musical fidelity) and didn't like the results because the imaging suffered greatly, even though the music sounded nicer from a distance. Now I want to try a solid state pre-amp (bryston) with a tube power amp (no idea which brand to look at), but I don't know how much power output I need or if it will even be possible with my speakers. Does anyone know what I would require?
acrossley
dividebytube
50 posts
 
A tube amp can typically 'sound louder' than it's specified wattage. There is no hard and fast rule on this as it can depend on how 'soft' the power supply is, the output stage topology (PP versus SE, Class A versus Class AB) and how much voltage the driver stage can swing.

An example is the venerable Dynaco Mark III monoblock. Though specified for 60W, it can actually do short bursts of 100W.

Another example - I once had a pair of SE EL156 amplifiers good for maybe 20Ws. Up to really loud volumes, it could keep up with my 250W solid state volume. Then it would start to clip... not in a nasty way, but the bass would get sloppy and the sound would start to gently compress.
rrog
1,958 posts
 
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.
mlsstl
694 posts
 
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.
marakanetz's avatar
marakanetz
5,473 posts
 
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.
atmasphere's avatar
atmasphere
7,068 posts
 
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.
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