McCormack , Aragon or Forte

Yes Unsound you are correct, the one I had I in for bias control repair I think I remember now were BJT (bi-polar), 2N3055 & MJ2955 or MJE15003 & MJE15004. Don't know were I got the IGBT from. They can still push current as just as well also into those Apogee's

Cheers George

Nelson Pass did design most of the Forte4; and I remember company brought in this engineer from Sweden who instituted the IGBTs, to whom Nelson Pass gave full credit. As a tube guy I just loved the Forte 4. My favorite solid state amp of all time. I admit I only have experience with a dozen or so SS amps.

I use a McCormack on my Apogee Duetta Sig's, but it is the DNA500, with tons of SS current. I doubt that the DNA .5 would be sufficient to run your Centaur's. You should look at a DNA 1 rev A, or a DNA 125 at least. But probably a 225 would even be better.

Years ago I had a Forte model 3 (200 watts)with Dahlquest DQ 10's and it was outstanding!It was a Fet amp with tubelike sound!

Yogboy:
I believe the Forte 3 is the same as the Forte 1 which is lower rail voltage and pure Class A to 50w. And is only Fet input but BJT (bi-polar) output, Nelson kindly posted the circuit diagram here.
http://www.diyaudio.com/forums/attachments/pass-labs/125282d1233198501-forte-audio-model-3-caps-schematics-forte1.jpg

Cheers George