I know this may be a strange question, but has anyone tried an SET amp with 805 tubes putting out around 50 watts into a Duetta? Would that drive it?
Not a strange question. I labored to use SET with my Stages.
In the day, I ran Apogee Stages with active tubed Luxman crossover in a three way using Two Wavac MD 572 stereo amps and a subwoofer, bypassing the passive crossover. Subwoof was crossed over at 80 Hz. Several picky audiophiles heard that one and were very positive in their response to that setup. Some of these guys unkindly would pan other systems that I actually liked.
MD 572 claimed 50 w/channel, but I think that is optimistic, and they probably put out maybe 35 to 40 watts, vs. the more likely 50 watts or so of 805 based units.
Active crossover saves you about 2-3 db of insertion loss taken out by the Apogee passive crossover. 3db represents double the power efficiency. Other issues with active crossover, too, is the native impedance of the separate ribbon elements. SET's have 4 ohm outputs, but generally operate best into 6-8 ohms. I have used impedance matching transformers with good results on ribbons, but another thing to mess with.
It would probably work with Duettas as well with active crossover (no insertion loss from crossover) and two 805 stereo amps. I doubt it would work as well as you would like with just one 805 stereo amp into a passive crossover based Duetta. You might get something, but not likely at the volume and dynamic reserve that you would like.
You could alternatively use a high quality, higher power SS amp on the bass ribbon with active crossover and use 805 on the midrange ribbon, but that would be subject to experimentation. However, that much effort might just be a long run for a short slide just to shoehorn SET onto an Apogee.