[Jamie]

Thanks Ron. I worked on the 620 for several hours today. I traced the schematic as best as I can and I can't find anymore errors. I used sandpaper on the tube shields, and double checked all the grounds. At this point, I think the slight hum is coming from a bad tube. The volume control has some issues too, and it could be coming from that. I'm calling it good for now. I'll get some tubes to swap, and find time to take the volume control apart at a later date. The radio plays well and the remaining hum is barely audible.

I tell you, I learned a lot from this radio. I feel a lot more confident reading schematics now. And I know I am capable of spotting and repairing old wiring errors.

Thanks to everyone who tried to help me. I really appreciate your time and effort. You guys are a life line to a newbie. If we should ever meet, dinner is on me.