I have looked up and down for answers on this and haven't found anything. I've been experiencing an issue where the output signal from my head starts to crackle and cut out. The interruption sounds like someone raising and lowering the volume. It seems to happen at random and is completely unprovoked. I have replaced the tubes, cracked it open and everything inside looks totally fine. I've troubleshooted my entire set up and it is definitely something with the head. Anyone have any idea what it might be?