[Tubeglow20]

Ok, here's an update. I had a GT style 12SQ7 tube in the radio and just to see what would happen, I tried a metal 12SQ7.  The loud hum/buzz went away on most of the 50L6 tubes that I have. Actually the schematic calls for a metal tube instead of a GT tube and on this radio, pin 1 has nothing attached to it under the chassis. I have swapped metal and glass tubes on other radios, but there was never a change in how the radio played. The radio has been playing now for several hours with one of the 50L6 tubes that was causing the loud hum/buzz and all is fine for now. Thanks for all the suggestions.