Mark V Head - Noise/Feedback Problem - HELP?

[#2121313]

Okay, I had posted earlier in another thread about this problem, I thought I had fixed it, but the problem is still present.

PROBLEM:

I get very bad feedback/noise, almost sounds like air blowing or wind, it builds up quiets a little but for the most part keeps very constant - NOISE.

In between notes/riffs and playing, when there is silent you will hear a squeal - feedback. When this occurs I can then turn the volume down on my guitar and you will hear the air/wind like noise howling thru the speaker.

Here's what I have tried:

- Swapped Power Tubes

- Swapped patch cords

- I only plug into a Parametric (Rane) EQ in my FX loop, but I tried unplugging that and going straight GUITAR > AMP

- Tried different channels, this happens on all channels, but is more apparent with higher gain settings, so C+ mode is VERY noisy as apose to any of the channel 1 modes...

- Tried 10 watts, 45 watts, 90 watts full power, variac power and always the same problem

- Tried plugging into a surge protective power bar, plugging straight into the wall, different wall outlets in my appartment

- I have a Mesa/Boogie .50 Caliber + which works fine in my home - no noise/feedback or power grounding related problems

- The problem will begin once you send a signal to it, once I power everything on and start playing the problem will come, then I tried unplugging my guitar all together by unplugging the cord from the amp - amp is on, stand by is one but no cord plugged in, the problem is still there

- It goes away only when I turn the stand by off

- I have also tried plugging my 8 ohm speaker into both 8 ohm jacks and the 4 ohms as well (one at at time of course

- The fuse looks good too, I checked it

The problem is intermittent, I tried it out at the guitar shop for 30 minutes before I bought it, sounded fine, very quite actually for a high gain amp - as always with my Mark heads....

I have played it everyday for the last 8 days and have had the problem occur about 3-4 times sporadically since owning it.

Any thoughts?

I can bring it back to the guitar shop I bought it from, but they're not an authorized Mesa service center so they'll only do so much, the closest service center is an 1 1/2 away - SUCKS! I also don't want anyone outside of Mesa/Boogie touching my amp if it's not necessary.

Any help would be appreciated guys!!!???

 

[kiff]

- Swapped Power Tubes

but not the preamp tubes? sounds like that could be the prob...

 

[#2121313]

Lol, I should have mentioned...I am in the process of doing that right now.

I was dreading doing so, the pre-amps are burried and are sometimes a ***** to get at - especially when your eager to just play!

Even though, I knew in the back of my head I'd end up hear - all the signs pointed to the pre-amp tubes I know...

 

[#2121313]

- Swapped Power Tubes

but not the preamp tubes? sounds like that could be the prob...

Interesting discovery here...I started with V1 as by the looks of the tube configuration this is where you'd wanna start - so I have been told, anyway...

When I pulled off the cover for the V1 tube a small piece of wire, white, maybe 20awg wire about 1" or so fell out...WEIRD!?

Don't know where or if it was connected to anything, my thoughts were that it was probably cut while building the amp and just fell and got lost in there...

Since changing the V1 tube, the problem has gone away, although the problem is intermittent so I do not know if it is gone for good.

I also don't know if that wire, which did still have it's plastic jacket on, but don't know if this was causing some interference or not.

Time will tell...I will have to leave the new tube in for a few days to know for sure, then try the old tube to see, maybe the tube is fine and it was the wire?

I will report my findings...

 

[Octavarius]

- Swapped Power Tubes

but not the preamp tubes? sounds like that could be the prob...

Interesting discovery here...I started with V1 as by the looks of the tube configuration this is where you'd wanna start - so I have been told, anyway...

When I pulled off the cover for the V1 tube a small piece of wire, white, maybe 20awg wire about 1" or so fell out...WEIRD!?

Don't know where or if it was connected to anything, my thoughts were that it was probably cut while building the amp and just fell and got lost in there...

Since changing the V1 tube, the problem has gone away, although the problem is intermittent so I do not know if it is gone for good.

I also don't know if that wire, which did still have it's plastic jacket on, but don't know if this was causing some interference or not.

Time will tell...I will have to leave the new tube in for a few days to know for sure, then try the old tube to see, maybe the tube is fine and it was the wire?

I will report my findings...

V1 would make sense, as that is used in all channels (unlike some others that are used as gain stages for the other channels). It would also make sense in terms of more noise in Channels 2 and 3, as there, the noises would be further amplified throughout the signal chain as more tubes/gain stages would have been added, thus making the noise louder on the latter channels than when in Channel 1. I'm drawing to the conclusion that you simply had a microphonic tube in V1. :wink:

Now go to your dealer and get that tube replaced for free (as Mesa warrants all their new tubes for six months).

 

[#2121313]

[/quote]

V1 would make sense, as that is used in all channels (unlike some others that are used as gain stages for the other channels). It would also make sense in terms of more noise in Channels 2 and 3, as there, the noises would be further amplified throughout the signal chain as more tubes/gain stages would have been added, thus making the noise louder on the latter channels than when in Channel 1. I'm drawing to the conclusion that you simply had a microphonic tube in V1. :wink:

Now go to your dealer and get that tube replaced for free (as Mesa warrants all their new tubes for six months). [/quote]

I agree. I hope that's all it is, I must mention tho, accessing the V1 tube was a *****! Very difficult to get at...oh well.

Yeah thanks!