Weird Mk IV problem?

[MaxBoogie]

Okay, so I was practicing with my band today, and 4 or 5 times my amp started emitting this ugly "noise"... hard to describe really... It was a solid, static-y, steady noise that made the amp unplayable... It would last maybe a minute, then disappear. Nothing in particular would set it off, and nothing I could do to stop it, even turning off the power and back on would not do it. It definitely sucked.

Should I assume maybe it was either power, or preamp tubes? I have extra preamp tubes, but no power tubes to even try swapping them out. There's nothing burned out, and the power tubes all had the same orange glow. Anyone more experienced than I who can suggest some things to try??

 

[fdesalvo]

With the panel removed to gain access to the preamp tubes, fire the amp up . Try to recreate that noise and pull and replace the preamp tubes- one by one- until the noise disappears. Sounds like a failing preamp tube to me

 

[mightypudge]

I had the same problem when I first bought my new Mark IV. The culprit must have been a bad preamp tube because I swapped them all for JJ's and the bad noise stopped.

 

[MaxBoogie]

Okay, thanks for the responses. I can't keep having my band mates giving me the evil eye, so I'll just swap out all the preamp tubes and see how it goes.

 

[Boogiebabies]

I would tell my bandmates to piss off and then take control of the band.
Fire the drummer and replace the singer.

Yep, sounds like a bad pre.

 

[MaxBoogie]

I would tell my bandmates to piss off and then take control of the band.
Fire the drummer and replace the singer.

Yep, sounds like a bad pre.

Ha ha... The drummer and the singer are the only two nice ones!!
Be glad to sell you a used bass player real cheap though...

 

[MaxBoogie]

UPDATE: I downloaded the Mark IV manual from Mesa's site and it gives some good tips for self-diagnosis. Based on their description, it sounds like I might have had a microphonics problem. I've exchanged tube "A" and will give it a try tomorrow's practice. Luckily I have 5 extra new tubes but since the manual says to only replace one at a time until I find the culprit, I'll give that a go.