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I have a Marshall JCM 800 and the amp seemed to run cold. I bought new power tubes for the amp took it to the tech to get the bias done and when i got the amp back it was still the same. I called him up and he said that the old tubes only biased at 10 and the the pots were full out. the new ones biased at 28 and still the pots are full out. Anyone have a clue on what goin on with this amp? He was telling me that he might add some kind of resistor to boost the bias. Anyway if anyone can give me some insite on this