Tube amplifier to power Sonus Faber speakers?

Thanks for your clarifications Al. Let me add one too.

Most ARC amps use negative feedback and have "low'ish" output impedances, especially off the nominally denoted 4 ohm taps. Al .. as we have discussed many times before, this means that ARC amps with low'ish output impedances perform somewhat like SS amps -- i.e., like voltage Paradigm amps.

As I recall, the ARC Ref 75 has a robust power supply (520 joules) and low'ish output impedance off the 4 ohm taps (1 ohm off the 8 ohm taps; probably less than that off the 4 ohm taps). Ergo, it might not be a bad amp to consider.

That said, if the SF speakers in question (a) present very low impedance plots and highly negative capacitive phase angles in the bass spectrum, and (b) are not very sensitive, then a safer bet might be a high current SS amp with lots of watts. Or, a bigger ARC tube amp such as the Ref 150.

(P.S. J Atkinson measured the Ref 75's output impedance off the 4 ohm taps to be .75 ohms at 20 Hz and 1K Hz. See: http://www.stereophile.com/content/audio-research-reference-75-power-amplifier-measurements)

Here is the simulated load graph that the Ref75 was tested with (1st link) as you can see compared to the flatness of the FR graph (2nd link)black trace, That this amp is relatively flat but is already dipping at 200hz.
But the simulated load at the 200hz is not that heavy and would be far lighter than the SF EPDR of 1.7ohms in the bass.
So even the mighty Ref75 might not fair too well in the bass with the SF speakers..

http://www.stereophile.com/content/real-life-measurements-page-2

http://www.stereophile.com/content/audio-research-reference-75-power-amplifier-measurements

Cheers George

Here's my suggestion and for a LOT less money than the ARC Ref 75....
see if you can source an ARC D70 Mk1, or better still, a Mk2. With my SF's, the D70 Mk2 makes beautiful music. If you think you may need more power ( which I would doubt), then look at a D115 or better a pair of M100's. These older W Z Johnson designs are still IMHO very competitive with some of the best tube gear around. Plus, with the older designs, one isn't stuck with having to run a balanced only preamp up-line.

I used to have B&W 805D2 with Mcintosh MC275 tube power and worked beautifully. I change the speaker to Sonus Faber Olympica II and still produce an great sound. Although I think I lost a little of high frequency because of diamond tweeter. But still its a great combo.