Bad Mesa MkIV

[welshboogie]

Hi Guys,

I'm after a little advice..

My IVA has started to sound a little sick, has had a recent revalve and gets used for about 4-5 gigs a month.

In the last few weeks, I have noticed a strange "buzz" on note decays on R2 and the now the same on R1..

However, last night, I was unable to get the loop to work at all, lights were on etc but no effects coming through the loop (the amp was also down on power), tried the usual "plugging into the effects loop" to try and pinpoint a possible faulty preamp tube but got no volume or just a really farty/buzzy sound.

Changed the 12ax7 tube between main preamps and powers (as per manual instructions) and it didn't make a difference.

However, when I switched the amp between Class A and Simul, everything came back ok but it still doesn't sound as clean/clear as it should.

Any ideas?, should i try swapping out the preamp tubes in the first instance or does it sound more sinister????

 

[Shep]

I would switch all the pre amps one by one. You may also want to change power amp tubes too.

I would say for now it sounds like a Pre amp. Write back when you have tried that and let us know.

 

[welshboogie]

Thanks Shep, it does indeed look like a bad preamp tube.

The thing that really annoys me is that these are less than 12 months old and were bought as these cryo treated valves that are supposed to be longer life/better tone.

To Be Honest, the old valves which were put back in last night instantly sound better!!!! - the low end fart/buzz is gone and the Boog is back!!!