[mikethedruid]

First thing I would do is take a battery powered transistor radio, and listen to the AM band using it alone, the Philco OFF. See what interference you hear across the band with that, and where the stations come in well. See if that "hum" is there in the transistor set too. If it is, that would mean the problem comes from outside the radio. If there is no hum in the transistor set, then look to the radio. Where I live, for most of the evening half the AM band is swamped by a bad sodium vapor lamp on my neighbor's house. I know it is the cause because it always happens when that particular light is on, every time, and not when it is off. From 550KC to about 1000KC there is a horrible 60 cycle buzz. The light usually goes out about midnight, and after that I get great reception across the AM band. Good luck hunting down your culprit.