Mark IV problem

Mark I's, II's, III's and the almight IV

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SgtPatton
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Mark IV problem

Post by SgtPatton » Thu Jul 16, 2009 10:22 am

Hi

I have strange problem with my MK IVa-medium head. When I turn power switch to full power, the amp starts to buzz and sizzle, like a huge power generator. I can play with the full power, but that buzz stays as a background noise. When I turn to tweed power, everything is okay. The sound of amp is overally also a little muddier than before.

The buzzing sound seems to come from the huge power tranny next to power cable. I opened the amp and everything seemed okay. I have quite new tubes, so I don't believe that's the problem.

Any ideas? Amp is from 1992, so it could be, that tranny or the filter caps are goin' bad.
Mesa Boogie Mark IV (A) Medium Head
Mesa Boogie Mark V - head *SOLD*
Mesa Boogie Rectifier 4x12

+Bunch of expensive guitars

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Boogiebabies
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Re: Mark IV problem

Post by Boogiebabies » Thu Jul 16, 2009 11:50 am

Sounds like it's time for a cap job.

SgtPatton
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Re: Mark IV problem

Post by SgtPatton » Sun Jul 19, 2009 6:37 am

[quote="Boogiebabies"]Sounds like it's time for a cap job.[/quote]

If it was the caps, shouldn't that resonating and buzzing electric noise occur also at tweed power? I get that noise only in full power-mode. Otherwise the sound is ok.

When i opened the amp, there was no visual problems. Caps (those big blue ones?) looked just fine. If that was the problem, how would they sound? And how would bad caps look like?
Mesa Boogie Mark IV (A) Medium Head
Mesa Boogie Mark V - head *SOLD*
Mesa Boogie Rectifier 4x12

+Bunch of expensive guitars

Monsta-Tone
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Re: Mark IV problem

Post by Monsta-Tone » Sun Jul 19, 2009 8:50 am

It might not be affecting the amp in Tweed mode just yet because the voltages are lower.
It might not be the caps, but that's the most likely culprit.
They won't usually even look bad, but they will cause mushi-ness and loss of volume or tone and background noise.

All of my 100 watt Mesa amps hum. This is due to the power transformer vibrating against the chassis. Mesa uses cardboard shims that wear out over time.


I would say that if your amp was made in '92, it is time for a check up and cap change anyway.
Elvis said.......
Amp techs do get shocked. :shock:

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