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Hi,
So I have here a Mesa Express 5:50 which has that annoying crackling noise. Not loud but even with all controls at zero you can still hear it at the background.
I narrowed down the problem to V3B at the FX loop. When C31 is shorted to ground the noise is gone. With pin 2 shorted the noise is still there. What I did so far:
1/ tried different tubes - NO change
2/ suspected leaky cap C31 - tried a new one - NO change
3/ lifted one end of C30 - NO change
4/ resoldered all components around V3B - NO change
By this time I ran out of ideas. Any suggestions would be appreciated.
Another thing is switching Standby OFF produces a loud pop. I fixed that by installing a 100nf/630V cap across the Standby toggle switch but I have the feeling the actual problem was masked and not solved but this can wait for now.
Express 525-550 schem.pdf
So I have here a Mesa Express 5:50 which has that annoying crackling noise. Not loud but even with all controls at zero you can still hear it at the background.
I narrowed down the problem to V3B at the FX loop. When C31 is shorted to ground the noise is gone. With pin 2 shorted the noise is still there. What I did so far:
1/ tried different tubes - NO change
2/ suspected leaky cap C31 - tried a new one - NO change
3/ lifted one end of C30 - NO change
4/ resoldered all components around V3B - NO change
By this time I ran out of ideas. Any suggestions would be appreciated.
Another thing is switching Standby OFF produces a loud pop. I fixed that by installing a 100nf/630V cap across the Standby toggle switch but I have the feeling the actual problem was masked and not solved but this can wait for now.
Express 525-550 schem.pdf
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