Valves on their way out?

Glaw343

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/HOs9T3g
vid of the amp crackling -

Wazmeister

@ICBM ;

ICBM

You won't hear much if you mic it there .

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.

Glaw343

cheers mate, yeah haha, the amps been moved about a lot and I haven't done any recording in a while so I haven't positioned it properly, havent even bothered plugging it in haha. Maybe it's time for a service then? probably been about 2 years since it last went in, I'll pick up some new preamp tubes anyway, I'm not crazy on these ones, they're low gain something or other and I'm not too keen, see what difference that makes and if it's the same problem I'll take it in for a service