Hello, Tom here. Recently my Orange AD200 has been making a faint fizz/pop sound when playing certain notes on the A string on my bass. At first I thought it maybe my guitar as it was sounding through the amp, however I tried it through a different amp and the guitar was fine. On further inspection when playing these certain notes one of the power tubes in my amp glows bright blue!! I was wondering if anyone has had this problem and if it indicates re-tubing the amp? If this is the case could anyone recommend the best current valve manufacturer for the job? I figure if I have to replace the valves I may aswell do the whole lot and do it properly. Also has anyone got experience of re-valving an Orange AD200 and if so could you give me any pointers? Thank you and look forward to your responses, Tom.