I've tried using my IC-756 on AM from time to time, as I enjoy this mode on 75, 40, 20, and 10 meters. Unlike my Yaesu 901 and Heathkit equipment, the output power of my 756 Icom would drop considerably when I would modulate the transmitter with voice. In order to get decent power out, I would have to run my amp harder than I care when operating AM.
When operating at 25 watts carrier from my 756, I was producing about 25 watts pep when modulated at 100% (because the power output would drop to about 8 watts!). My amp (AL-82) would run about 350 watts carrier, and would fall back to about 85 watts or so when I would speak (still about 350 watts pep).
I built the little curcuit from W8JI's page this afternoon. I now operate the rig at about 10 watts carrier, which drives the amp to about 150 watts. When modulated the amp produces about 600 watts pep, but runs very cool.
Listening to it on my Yaesu 901, it seems much cleaner, but I can't hear any difference on my Heathkit SB-301. I guess this is partly determined by the detector used in the receiver of the receiving station. The amp is much happier, though, and runs much cooler. I can run a much higher PEP with a lot less heat!
I've posted info about it on my AM Mode page at: