Tube amplifier to power Sonus Faber speakers?

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

Hi Frontier1, your speakers though advertised at nominal 4ohms, is not showing the whole picture. As the lab test results show in the link, they have an amp hungry impedance with -phase angle load of 1.7ohms in the bass. They maybe efficient but they are a hard load.

This to me says if you want to get the very best out of them, especially in the bass, you need an amp that gives good current, the ability to almost double it's watts down to 2ohms.
EG:
50w into 8ohms
100w into 4ohms
200w into 2ohms
These amps are good solid state with BJT (bipolar) output stages (not mosfet)This is also why even good P/P tube amps will wimp out a little down low, even with 4ohm taps.

http://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=0CC8QFjAC&url=http%3A%2F%2Fwww.perfect-sense.se%2Fwp-content%2Fuploads%2F2014%2F11%2FSF_Olympica-II_Hifi_News_2014.pdf&ei=JN58VIbNE4bc8AXerICgCA&usg=AFQjCNH3FtXaUGr8-3B3--LdKjP2VA7QYA&bvm=bv.80642063,d.dGc

Cheers George