The "rumble" in the receiver was due to modulation by the NB of the +8V railįeeding the low-level receive audio amplifiers. I've posted info about it on my AM Mode page at: I can run a much higher PEP with a lot less heat! The amp is much happier, though, and runs much cooler. I guess this is partly determined by the detector used in the receiver of the receiving station. Listening to it on my Yaesu 901, it seems much cleaner, but I can't hear any difference on my Heathkit SB-301. When the 756 is modulated the amp produces about 600 watts pep, but runs very cool. I can now operate the rig at about 10 watts carrier, which drives the amp to about 150 watts. I built the little curcuit from W8JI's page this afternoon. 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). 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!). In order to get decent power out, I would have to run my amp harder than I care when operating AM. 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. 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.
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