"09-11-12: Atmasphere
Switch mode supply??! I figured this thing had a big toroid..."
They appear be two large toroids. If not, they would be the largest SM "inductors" I've ever seen for fairly moderate current demands of this nature, and I believe their distance and wire lengths would be of issue in a SMPS as well. If we could see what’s under the amp’s internal/central panel, I’d expect to see a bank of large electrolytics for a linear PS.
"So what is the outlet voltage while the amp and the cord are doing their thing? Bet it does not drop as much."
I can't recall if a measurement was taken at the outlet WITH the 50 Ft ext cord incorporated, but without it, the voltage dropped from 118 to 112 at the same outlet right when the mag breaker tripped.
"Based on that I would replace the AC receptacle, and make sure the screws on the receptacle are tight!
Note: The amp trips exactly the same way via 4 or 5 other outlet locations within his apartment per sailcappy.
"It would be a really good idea to see how this amp behaves in another apartment in the same building..."
I concur, as Jim and his EE friend has suggested, though not yet not tested by sailcappy. I recall Jim even suggesting he try to locate a service outlet outside or between apartments (if a cooperative neighbor wasn’t available).
Frank