Possible issue with my amp, looking for advice.

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creep66

Well-known member
I have an old mesa c+. It sounds killer but recently I've noticed an overtone (dont really know how to describe it) when I'm doing low palm mutes. Theres a vibration like sound after I palm mute and hit the strings like a BRRrr type noise. I also noticed when I recorded awhile back I kept hearing almost a square wave noise after distorted notes like frying sound.

I have tried it with 4 different cabs as I thought the speaker was farting out at 1st, it's more prominent in some than others but always there. So its definitely not the speakers.

This is driving me nuts. Anybody ever have this? Is it tubes, a cap job or what?

Any suggestions are appreciated.
 
BeZo said:
Take a pencil and tap on your tubes with the eraser and see if you hear it. It would test for a microphonic tube.
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I will do this after work. The preamp tubes seem pretty new, the power tubes look old though.
 
You should promptly package it up, immediately send it to me, and instantly forget you ever had it. As a gesture of kindness, and to honor a fellow brother of rigtalk, I will take this tremendous and time consuming disaster off of your hands. The second it’s gone, you will feel a profound sense of calm and relief. No more issue. Why, do you ask, would I do such a thing? The answer is quite simple, because that’s just the kind of guy I am. Always willing to go out of the way to help a fellow tone chaser.

You will feel a profound sense of relief and calm

You will feel a profound sense of calm and relief

A profound sense of calm….. calm…

Profound sense of relief……relief….

When amp is gone all will be better….better…..better….

Profound relief…….relief…..

Peacefully calm….calm…..calm

Amp gone…..gone….gone…..

All is back to normal….normal…

Issue gone….gone….gone..

Repeat until ready…. Ready….ready….
 
Does it have reverb? If so, disconnect it and try. My first C+ was a 2C SRG that had a similar thing going on; not exact but close. I disconnected the Reverb (unplugged the leads) and I didn’t hear it again. Eventually I upgraded it to a + with Mike B but the strange noises never returned.
Other than that I’d guess a pre tube as others stated
 
Racerxrated said:
Does it have reverb? If so, disconnect it and try. My first C+ was a 2C SRG that had a similar thing going on; not exact but close. I disconnected the Reverb (unplugged the leads) and I didn’t hear it again. Eventually I upgraded it to a + with Mike B but the strange noises never returned.
Other than that I’d guess a pre tube as others stated
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I took the reverb off long ago as I didnt like it.
 
Replace your preamp tubes. Turn your presence and treble down and see if it does it. It sounds like parasitic oscillation in a preamp tube.
 
glip22 said:
Replace your preamp tubes. Turn your presence and treble down and see if it does it. It sounds like parasitic oscillation in a preamp tube.
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I can do the tubes and will swap some around tonight. But shouldnt I be able to have the treble and presence wherever I want? I'm using the settings from flemming rasmussins notes. So if james used em they shouldnt mess with my stuff right?
 
creep66 said:
I can do the tubes and will swap some around tonight. But shouldnt I be able to have the treble and presence wherever I want? I'm using the settings from flemming rasmussins notes. So if james used em they shouldnt mess with my stuff right?
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Sometimes too many highs can accentuate the oscillation.
 
creep66 said:
That makes alot of sense actually, thanks I'll roll some tubes tonight and hope that's all it is.
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Any luck? Also clean your input and output jacks. I would go as far as cleaning your pots also. Spray no residue contact cleaner in them and turn them fully back and forth several times. Clean your preamp tube sockets by spraying the tube pins and installing them a few times in and out of the sockets. Reposition your first preamp stage grid wires around, (A little elevated or down a little if they already are elevated). There should be two hitting your first pretube.

Crackling type odd issues will usually be coming onto the grid of the early stages. Also reposition your first stage heater wires a little. You want to do all these little things because you might get lucky. I have many times lol
 
glip22 said:
Any luck? Also clean your input and output jacks. I would go as far as cleaning your pots also. Spray no residue contact cleaner in them and turn them fully back and forth several times. Clean your preamp tube sockets by spraying the tube pins and installing them a few times in and out of the sockets. Reposition your first preamp stage grid wires around, (A little elevated or down a little if they already are elevated). There should be two hitting your first pretube.

Crackling type odd issues will usually be coming onto the grid of the early stages. Also reposition your first stage heater wires a little. You want to do all these little things because you might get lucky. I have many times lol
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I dug into it last night and it's a leaking cap, bummer but at least it didnt fry my board yet. Even if that's not the cause I'm guessing they will find the issue when they recap so I guess that's it lol. Thanks for all your advice though (everyone else too).
 

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creep66 said:
I dug into it last night and it's a leaking cap, bummer but at least it didnt fry my board yet. Even if that's not the cause I'm guessing they will find the issue when they recap so I guess that's it lol. Thanks for all your advice though (everyone else too).
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Where's the leaky cap in this photo ?
 
creep66 said:
I believe those are the filter caps. No expert though.
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Not what I'm asking

What are you referring to in that photo as "a leaky cap" ?

I don't see it..

edit: Ok, you posted a different photo and I see the leaky cap now.
 
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