dubnew,
The Heil AMT is over 30 years old. Back then, there was quite an excitement over how efficient that unit was. There was at least one article on how to build one yourself. I'm not sure of the source, but I seem to think it's the old Audio Amateur publication. I have a copy of that, but at the present, can't remember where it has been stored. If I ever find out, I'll let you know. But, don't expect it to be real soon.

Isn't there a way to measure the impedance by sending in a frequency sweep and checking the volt-current phases?