Quote Originally Posted by mw0uzo View Post
(Heh, i'm still surprised I got any power out of it at all, let alone 400W!!! :D)
Yes. I finally looked at the IRF spec sheet and 400W is a little over spec @ 48W a piece. Also the slew rate is pretty limited to a minus 3 dB at 20MHz. So the transistors appear to limit the frequency range as Dale said.

It is an amazing work though. Good on ya.