Strange distortion or flubby noise PROBLEM SOLVED I THINK...

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Vogelsong

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First of sorry it's so long, but there's a lot of info.

I was messing with the Mark V the other day. I was working on channel one Fat, bold, 45w, no EQ. I didn't do anything extreme just moving knobs a little and playing. I was trying to get a nice clean Fender tone just on the verge of breakup.

The knobs were set approx. g-12 mv-10 p-2 t-11 m-2 b-10 op-10 loop active, diode rec. I was playing my comanche on the neck pup. So I hit this open E chord and I get this weird distortion. It was one of those sounds that sounded like the amp was trying to break up or give some distortion but it was if something was crapping out or went weak.

Now the strange thing was when I would turn on the EQ it would go away. The Eq is on a up hill slant going from left to right with the far left cutting a little and they progressively get higher as you go across. The sliders basically sit on top of each other as they go across.

So my first impression was a blown speaker but it wasn't buzzy enough, I've heard plenty of blown speakers and this wasn't it. Not to mention that the sound was coming out of both. Not that both couldn't blow but at the volume I'm at it's highly unlikely.

So after messing some more I shut it down and decided to get some preamp tubes and come back. So I do the tap test and about 5-10 seconds after tapping v2 the amp starts to hum and feedback. Now I had turned the master and gain up all the way to test. I don't know if this is right but thats what I did. So I replaced all preamp tubes that effect channel 1, plug in the amp and hit my open E chord. Well to my shock I forgot to turn down the Master and the gain. But the weird sound was gone, it was a nice full chord with good strong tone and drive. One problem, it was way to loud, as soon as I turned the gain and MV back down to where it was the noise was back.

So my next thought was maybe this is the flubby or farty sound people talk about. The only problem is I've been playing this amp at about the same settings for a while and never had this issue. I didn't tweek things that drastically. But while changing tubes I did notice something else...

Now while playing in 45w the amp is running on v8 and v9 for the pwr tubes. So while pulling the 6L6's to get to the pre tubes. I noticed that v8 had a dark smokey grey spot on the side and it was much cooler than v9 when I touched it. So I took the inside 2 tubes moved them to the outside and put the others in the middle. Tested the amp with my open E chord and the noise was still there but not as bad. The surprising thing is when I went back in to swap the tubes back this time v8 was just as hot as v9.

So after reading all of this do you guys agree with me that this is really looking like a power tube issue?
 
Sounds more likely to be a failing preamp tube from my experiences. Try swapping V-1. If that doesn't work, try V-2.
 
BostonRedSox said:
Sounds more likely to be a failing preamp tube from my experiences. Try swapping V-1. If that doesn't work, try V-2.

I swapped out all 3, no change.
 
Hmm. Whenever I've had problems like this, they've been preamp tube related. Sorry I couldn't be more helpful. I'll have to check back to see what your final result was in case I ever run into similar problems with my Mesa.
 
Okay, so I go and get a new set of power tubes. I got a set of GT 6l6's. Thats whats available here in Harrisburg, PA and they don't void the warranty so thats what I got.

I go and test the amp, noise still there. I put in the new tubes and the noise was 80% gone. The rest I was able to dial out with the tonestack. So I'm guessing it at least had a little to do with the tubes and maybe possibly I found a weird combination on the knobs that also helped play a role in this. I just find that a little hard to believe since I really didn't do anything that drastic and the amp wasn't being pushed that hard.

So I'll play it this way and see how it goes.
 
BostonRedSox said:
Sounds more likely to be a failing preamp tube from my experiences. Try swapping V-1. If that doesn't work, try V-2.

V2 is exclusive to channel two.
 
SteveO said:
BostonRedSox said:
Sounds more likely to be a failing preamp tube from my experiences. Try swapping V-1. If that doesn't work, try V-2.

V2 is exclusive to channel two.

From the OP

Vogelsong said:
So I replaced all preamp tubes that effect channel 1...

This would be v1, and 3.
 
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