So I realize today that there is a significant volume loss when I plug into the top boost channel of my Vox AC15 hardwired amp. It gets especially worse when switched to Master Volume mode. Could this be something as simple as a bad tube? Unfortunately I don’t have any extra tubes laying around so I can’t swap and test. All the tubes light up from behind when on. I guess really the question is what tubes are in play when plugged into the TB channel with the MV mode on? Any insight would be greatly appreciated. thanks!