Okay then Gary, I think you're no doubt correct.
I just tested the Heathkit (again) by running an AF #310; I tried this engine because it does not have a smoke unit, so I figured the current draw would be (somewhat) less. It did fine for about a minute, then it over loaded.
I re-hooked up the MRC; it ran the 310 fine. I'm always impressed with how quiet this engine is.
I tried (2) different locos with smoke; a 312 and then a 302AC. Both ran well, with plenty of smoke and room to spare on the throttle. I will say that this unit does have very nice low-end speed control.
Dunno it this proves anything, other than I guess the Heathkit needs to stick with my other (DC) stuff...
Mark in Oregon