Hi everyone, I'm having a little bit of trouble with my Mesa Boogie F50 combo, it's loaded with 2 Svetlana Winged C 6l6GCs and 4 12ax7s (I can't remember what make/model they are) the amp is making weird crackling noises a little bit like frying bacon lol (even when nothing but the power cable and the speaker cable are plugged in and it's on the clean channel) I've tapped the tubes with a pencil one 6l6 makes a dead thunk sound when tapped, the other has more of a ping, preamp tubes 1 and 2 are very loud when tapped (they are heard through the speaker) 3 and 4 ping when tapped but not very loud (I don't think they're coming through the speakers, if they are it's quiet) should I replace all the valves? or do you think I could get away with just changing a couple, should preamp valves v1 and v2 make a lot of noise when tapped with a pencil? any help anyone can give me at trouble shooting this would be great cheers
valve key -
https://imgur.com/HOs9T3gvid of the amp crackling -
Comments
It's unlikely you need to replace all the valves, the chances are it's just one.
It looks in the video as if the noise is affected by the master volume control, is that correct? If so the problem is in the preamp.
If you don't have a spare 12AX7, you could temporarily swap V4 (furthest from the input jack, which is the phase inverter and not in the preamp) with the other three positions one by one and see if the noise stops.
It could also be a non-valve fault - that type of crackling is often caused by a failing resistor or sometimes cap.
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