No.tubelix said:Do preamp tubes (12AX7) also have to be matched like power tubes?
Yes, changing preamp tubes one-by-one is the best way to assess which, if any, is causing the problem. Mismatched power tubes can cause hum too, and sometimes one of a matched pair will drift. If you get to the power tubes, after trying preamp tubes, change them as matched pairs only.tubelix said:Thanks Timbre Wolf for clearing that out. Then it's possible to change one bad preamp tube at a time.
I have a .50 Caliber Combo (EL84 version) and I have noticed an increasing hum from it. I think it’s from a bad preamp tube. I’ll try to locate the bad one switching tubes one by one.
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