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Extreme hiss and microphonic V1 tube circuitry

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NeverAfter:
Yesterday I had our bands rehearsal space to myself so I took the opportunity to get to know my MP-2 a little more intimately (no, not what you think!).

I noticed something was just not sounding right on the high gain presets. When I turned of the noise gate I got this extreme hiss on voices 6 and up. tapping the front panel of my MP-2 gave a microphonic sound through the speakers. (I haven't been able to reproduce that at home so it could have been a ground loop. I had my fcb1010 connected to a different wall outlet instead of the furmann.). Today I went to investigate this issue further and noticed that the V1 tube and it's surrounding caps and circuitry were very microphonic when tapping them lightly. The golden cap next to the tube socket seems to be the most microphonic, about as bad or even worse then the tube itself. The V2 tube does not seem to have this issue. I tried replacing the V1 as well as the v2 (and ofcourse both) with several tubes but to no avail. Below is a youtube vid where you can here the hissing and The microphonic sound I get when tapping the V1 tube. The hiss is much worse in real then it sounds on the video, same goes for the microphonics. At band volume the hissing is like static noise from a loud tv. In the video it sounds like the V2 tube is somewhat microphonic as well but that is just the board resonating along and making the V1 sound out a little.

https://www.youtube.com/watch?v=93vTEYIvc-A

I also noticed that one of the larger caps near the psu has started to 'bulge up' slightly so I guess that needs to be replaced as well. Maybe this is the culprit? I'm not an electronics expert but I can handle a soldering iron a little (I previously did a succesfull R611 and R913 fix as well as deep mod for my Mesa 20/20). I know what a resistor and a capacitator do but that's about it. ;D



So, does anyone have any suggestions as to how to fix this issue?

Thanks in advance!

MarshallJMP:
Start with checking the high voltage.There is a testpoint just above R913.(H.V.),should be 190V.

NeverAfter:
Thank you for the reply MarshalJMP,

I have no idea where and how to measure (but willing to learn!). I do have a good digital multimeter. Could you please tell me where exactly I should measure?

NeverAfter:
I mean I see the H.V. testing point but how to measure there?
Do I put the red probe on the HV test point and the black one across the R913?

MarshallJMP:
Red on the testpoint and put the black one in one of the screwholes of the mp2 (ground)

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