I have a Marshall 9200 poweramp (Dual mono-bloc) that I am having problems with. Channel A works fine, but when I turn on Channel B, I get no output, but rather I get this low pitched buzzing sound that becomes louder and louder. (Both channels work independently of each other, as in Channel A runs 4 6L6GC tubes and Channel B runs another 4 tubes)
Also, Channel B's tubes glow blue when it is turned on. (I never turn Channel B longer than 30 seconds after that buzzing sound starts) I was wondering whether it was a blown tube or whether it is something more sinister at work, i.e. a blown transformer.
FYI, the amp doesn't trip the fuse, but rather the tubes just immediately glow blue, like the gas in the tubes is on fire or something.
Thanks for your help guys.
Regarding your 9200:
A blue glow within the tubes indicated one of two things:
In either case we would recommend the amplifier is looked at by a qualified and experienced engineer to establish what is wrong.