low power tube amp

Doesn’t the tonality issue apply to any amp given the not so flat impedance curve?
if my amp is able to drive the speakers without clipping at my listening level, then the tonality problem is the same as with a 200w amp correct?

When a speaker’s impedance varies widely over the frequency range, generally speaking the tonality issue that can arise as a result of the interaction between that variation and amplifier output impedance will arise to the extent that the amp’s output impedance differs from the output impedance the speaker’s designer anticipated the speaker would usually be driven from.

Nearly all solid state amps have effective output impedances that are near zero ohms. While tube amp output impedances vary widely among different amps, from a fraction of an ohm to several ohms or more. So if the speaker was designed with the expectation that it would generally be used with solid state amps, as may very well be the case with the Sopra 2, a tonality issue is likely to arise with tube amps to a degree that is greatest with those tube amps that have particularly high output impedances. Such as many single-ended tube amps, and tube amps which use minimal or no feedback. The power rating of the amp is not directly related to that.

The 155 watt ARC amp referred to in the review I linked to undoubtedly has lower output impedance than the majority of other tube amps, single-ended or not. So I suspect it (and many other ARC amps) would be a better match for this speaker in terms of tonality than most other tube amps.

Regards,
-- Al

Klee123, This is why I asked earlier in this thread if your amplifier utilizes NFB as this will lower the amplifier output impedance and likely making it less susceptible to widely varying speaker impedance loads. Problem is that NFB can have adverse effects as well (depending on the amount and how it’s used). Ralph (Atmasphere) has covered this in excellent detail numerous times on this forum.

For example my SET amplifier has no NFB and has an output impedance of 1.2-1.4 range. This is pretty low for a no NFB amplifier but would be considered very high for the typical solid state amplifier. This works out fine for me as my speakers are 14 ohm nominal and have a relatively flat impedance curve.

So as Al has clearly explained the amplifier and speaker must have reasonably compatible impedance characteristics. You need more information about your amplifier.
Charles

found the website

I will be using this with the sopra 2.  The kt88 doesn't sound as nice as this with my last speaker (quad esl 63)

http://www.finaleaudio.com/829b-special/

talked to the amp designer, it does have negative feedback

Klee123,
I’m unfamiliar with this double tetrode tube. I’m aware of the company Finale Audio and they have an established and good reputation. This particular amplifier seems to be an all out effort toward high quality. I get the feeling that this is a very good amplifier design. I suspected it’d have "some" NFB as tetrode/pentodes aren’t quite as linear as pure triode tubes. I hope you can hear  the pairing, it could be really good! I like their attention placed on high quality transformers and chokes, always a good sign.😊
Charles

Klee123,
If the Focal  speakers don't work out you should really consider looking at more efficient and easy to drive speakers.  I think that this 829 SEP  amplifier you have is special.  The right speaker match would allow the amplifier to shine to its full capability. 
Charles