[Tubeglow20]

Thanks for the reply. I installed a new R13 (150 ohm) resistor and the problem persists. It's weird,  I can use two different 50L6 tubes that both test good and one works perfectly while the other makes the radio hum/buzz. I tried the tube that makes the radio hum/buzz in another set with a 50L6 and that radio plays ok. I'm still stumped. The coupling capacitor between pin 6 of the 12sq7 and pin 5 of the 50L6 is a .0022 and that's what I replaced it with. I believe that adding the length of wire increases the capacitance; any thoughts?