Check out the Carver Cherry 180 or Black Beauty 350 monoblocks. There are reivews of these two very powerful tube amps, in Absolute Sound by Jonathan Valin, EnjoyTheMusic.com by Dick Olsher, and video reviews on avshowrooms.com and on YouTube. I use the earlier Black Beauty 305's to drive my MagnepN 20,7's. Excellent amplifiers!
http://www.enjoythemusic.com/superioraudio/equipment/0512/bob_carver_cherry_180_tube_monoblock_amplifier.htm
http://www.stereotimes.com/post/carver-cherry-180m-mono-block-amplifier
http://www.avshowrooms.com/
http://www.theabsolutesound.com/articles/carver-black-beauty-305-power-amplifier/