Tweeter/Mid minimum amp power rating for magnepan 20.1 in active setup?

It really depends on how loud you want to play. A beefy 60 wpc would work for me but you don't want to cut yourself short with big Maggies. I'm a 100% tube guy but maybe a solid state amp is best for 20.1s. Big beefy tube amps cost a lot of money and make a lot of heat. 

What does the impedance curve look like for the mid/tweet section of your 20.1's?   Imo the impedance curve plays a significant role in amplifier matching.   

Are you using an active crossover, or the passive crossover in the speakers?   If the latter, I suggest checking with the tube amp manufacturer to make sure the amp is comfortable with the load it will be seeing. 

Duke

unfortunately, I can't seem to find any graphs for impedance but I know they don't drop below 4 ohms. I think I will need to home demo a few amps and see how it goes.

I'm using an external active crossover.

Thank you, psilonaught.

Eyeballing Stereophile’s impedance curve of the MG-20, it looks like 4 ohms nominal (for the mid/tweet section) with a ballpark 12-ohm peak a little south of 2 kHz. That’s a 3-to-1 peak; not horrendous, but not insignificant within the context of tube amps. And assuming the 20.1’s impedance curve is similar, and that it was designed with constant-voltage (solid state) amps in mind, imo that impedance peak is worth paying attention to.

You see, a solid state amp will deliver 1/3 as much wattage into that 12-ohm peak as what it delivers into 4-ohm portions of the impedance curve. The designer presumably took that into account when he "voiced" the speakers.

Tube amps tend to deliver much closer to the same wattage into that 12-ohm peak as into the 4-ohm-nominal rest of the spectrum. So a tube amp may result in a frequency response emphasis in that region, because there the speaker will be getting more wattage than the designer anticipated. Imo one solution is to make the impedance curve more tube-amp-friendly.

EVERY TIME I have been able to thoroughly investigate someone trying a specialty tube amp and not liking it, I have found a plausible explanation in the loudspeaker’s impedance curve. I’m NOT saying "don’t try it" - quite the contrary; Maggies + tubes can equal MAGIC - but I suggest that you work with someone who is at least aware of the issue.

(The 3.6 was a particularly tube-friendly Maggie. It had a relatively small and narrow impedance peak at about 1.5 kHz, which also happened to be where it had a frequency-response DIP with a solid state amp, so the synergy with tubes was really good.)

Best of luck to you.

Duke

Reference: http://www.atma-sphere.com/en/resources-paradigms-in-amplifier-design.html

Duke has it right. I'm 50% with tube amps on Maggies, some work some don't. Magnepan has never demoed with tube amps, that might tell you something.