Hum issue – solved!
Okay, it’s been so long since I’ve posted an update it’s taken me awhile to remember how I was doing it! The strong hum issue with the amp has been fixed. Someone much more observant than I pointed out an apparent problem with my tube socket wiring. According to the schematic, pins 8 of V4 and V5 should be tied together. If you look at pin 8 of V4 in the following photograph you will notice that something is missing:
Power tube wiring
Since correcting the problem the amp runs much quieter! I’m glad the problem was discovered but I also feel kind of stupid. I supposedly did thorough double-checks of my wiring and yet I still managed to miss something this obvious!
I’m happy with how the amp sounds now, but I still plan to correct some lead dress issues with my AC lines feeding from the power cord socket.