ADA Power Amps > Microtube 200 MT-200

MT200 Died Last Night

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davec69:
Need some help please.   For the past few weeks, my MT200 has been experiencing a slow death (apparently), until last night it finally gave up the fight.  (In the middle of a gig no doubt).

The symptoms started a few weeks ago, with occasional crackling and lowering of volume on the B channel.  The A channel appeared fine.  By quickly raising and lowering the B channel volume, I could get the volume to return.  My first thought was the tubes, so I pulled out a backup set last week, and replaced both tubes.  To be completely honest, I'm not really sure that the replacement tubes were 100%.  The symptoms would come and go for the last few weeks, until finally last night at a gig, I started to get this loud crackling sound in the middle of a song, sort of similar to the sound you get when plugging and unplugging a guitar into a Marshall stack repeatedly, with the amp volume maxed.  Eventually, it just became a long loud noise, and the volume of my guitar just faded away.  I reached over to turn down the volume on both channels, but the noise didn't stop.  Eventually, I had to turn off the power switch.  Fortunately, I was also going direct out of my Kemper amp, into FOH,so I could keep playing.

I'm going to try a new set of tubes tomorrow.  Any other ideas, as to what I should check while inside the amp?

MarshallJMP:
The pots are just after the input jacks so it could be a lot of things.Did you power off the amp of did you put it on standby?

davec69:
It happened really fast.  I want to say that after turning down the volume did not work, I turned the amp to standby first, and the noise kept going, but I'm not sure.  I may have just hit the power switch.

MarshallJMP:
Well try the new tubes first and we'll take it from there.

davec69:
Ok, so I swapped out the two 12AX7 tubes today, and the noise still persists. 

I have attached an mp3 recording, that may help.  (WARNING:  Lower your volume, prior to listening to the attached file)  It's basically just buzzing, clicks and pops.   At the 24 second mark, I put the amp in standby, and the noise stops, I then took it off standby, and you can hear even more noise return. 

The meter lights on channel B are lighting in sync with the pops and clicks.   The meter lights on channel A are not lighting.  The volume knob has no effect on the level of the noise.

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