Tube Amps Watts vs SS amp


Can someone explain is there is a difference between the watts of a tube amp vs vSS amp, Looking to get a tube amp ,but i see that the watts are much less than the SS amps, So how do these Tubes amps with 25 -70 - wpc drive these high end speakers, I have a vintage pair of AR 9s and 2 mcintosh MC2200 amps in mono (400 WPC) to drive these ,what tube amp will power these under 3-4k new or used, Thanks 
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As others have said, tube amps provide a more usable power band than most solid state amps.  I've been in audio for over 40 years, and have listened to countless amps, and of this I have no doubt.  Another point on most tube amps is that the output transformers allow these amps to deal with complex loads quite well.  Sonically, I have always found tube amps to be less fatiguing in the mids and highs.  

That said, the tradeoff is the low end.  AR9s, even with a massive tube amp, will be soft in the bottom end.  This is the biggest tradeoff in my view.  That, and the dynamic compression that occurs at higher volume on tube amps, will lead to a choice.  If recreating the energy of a concert, with gut punching bass is what you're looking for, best in class solid state is hard to beat.  
Roberjerman, I went back and looked at the Heresy's timeline. It does date back to 1957 but it was called the H 700. It was given the Heresy name with an update in 1972 which was probably the year I got them as they were marketed at the time as new speakers. The K horn is the longest running production speaker of all time! I remember listen to them at the store I eventually got the Heresys at. They were being powered by Marantz Model 9 mono amplifiers and a Model 7C preamp. The turntable was a Thorens TD 124 with an SME arm. I don't remember the cartridge. That was the absolute State of the Art at the time. It had no problem doing realistic volume levels.
My understanding is that the concept of “bandwidth” is very important. Perhaps more important for tube amps than solid state. But I have a First Watt SIT-3 which is a low watt solid state amp. It apparently has some bandwidth to it because it drives my Magico A3s well. They have a sensitivity of 88dB, an impedance of 4 ohms and recommended minimum power of 50 watts. The SIT-3 drives them just as well as my Bryston 4B3, which has a lot more power. But what I would like to know from the group is: how is bandwidth measured? How do you calculate bandwidth?

Bandwidth is important to keep phase shift at a minimum. To this end, phase shift is minimized if bandwidth is 10x the maximum frequency to be amplified (20Hz, so 200KHz required) and also 1/10th the lowest frequency to be amplified (20Hz, so 2Hz response required). Bandwidth is measured by either a sine wave or square wave; with a sine wave the signal is applied to the circuit and the output observed to be within usually + or - 1/2dB to be considered ’flat’; with a squarewave rounding of the edges can be seen to show a rolloff at high freqencies and tilt on the top of the squarewave shows a rolloff at low frequencies. This is fairly easy for transistor amps, and there are tube amps that meet the ’2Hz-200KHz’ requirement too, but to my knowledge they are all OTLs (Output TransformerLess).


Keeping phase shift linear has to benefits: more accurate presentation of the soundstage and more accurate presentation of tonality. As an example of the latter, if there is a rolloff at 10Hz, phase shift will cause a lack of impact up to about 100Hz despite the amp measuring flat to 20Hz on the bench. This is why if there is a problem at 50KHz it can often be heard as well, since phase shift artifacts will exist down to 5KHz. Again, this will be interpreted by the ear as a tonality.


So one takeaway: three things affect tonality: actual frequency response (which is different from bandwidth), distortion and phase shift. 
The tubes vs SS discussion should focus more on the type of music one prefers rather than the technical merits of each amp. I have multiple tube and SS amps that I interchange frequently. If you primarily listen to Jazz, voice, acoustic music of any kind there is nothing better than a quality tube amp.

The only time I would caution someone about moving toward tubes is if they primarily / exclusively listen to rock & roll at higher volumes. i don’t feel the benefits of tubes are realized in that case. I prefer listening to that type of R&R music on my SS amps. But that being said, most guitar amps use the EL34 tubes so when I listen to earlier R&R with guitar emphasis they sound more live on my EL34 amp.

The reason tube watts seem louder than SS is not because tube watts are more "powerful" but because you can listen to tube amps louder than SS without as much fatigue. The listenable / enjoyable wattage range of tube amps is greater than an equal SS amp.

I would also recommend an EL34 tube amp as a starter / first tube amp because the EL34 really hits the sweet spot of tubes. If budget is any consideration, you can buy a quality used one very reasonably and latter upgrade to a new tube amp if you find that tubes are for you. That is what I did and got a very good price on a Cary V12R EL34 amp and then latter bought a new tube amp. I still own the V12R and enjoy it daily.

I have two listening systems one with difficult to drive speakers. I bi-amp them both with a tube amp on top and a SS amp on the bottom pushing the woofers. This works very well with difficult speakers that demand more power.
This is what you want.  Monobloc pair at $125 watts each.

http://www.tubes4hifi.com/bob.htm#M125

You can buy it as a kit and build yourself, saving a fair amount, or buy it fully assembled and tested.

kit - no tubes:  $1778
kit - with tubes:  $2213
Wired - no tubes:  $2595
Wired with tubes:  $2935