I don't think it's an input issue assuming that you mean the hum is there when the amp is in standby mode- no B+ to the OT. Is that what you mean and is that your configuration? Is the hum there when the amp is running (out of standby mode) and with the volumes down?
If this is correct and I read you correctly, I'm wondering about your filament supply. Can you draw up how your filament supply is wired? Is there a center tap on the filament windings, virtual ground, etc. ?