Amp sounds like someone is blowing into a microphone...why?

[GlennW]

I have a Peavey Prowler and when I play notes from about the 9th fret E on the G string to about the 12th fret on the B string there's often a sound like someone blowing into a mic.

It isn't the speaker, and I'm pretty sure it isn't a tube (I've replaced them one at a time and the noise persists, sometimes quieter). I don't think it's the pickup either.

It has two 6L6GC output tubes, two 12AX7 pre-amp tubes, and a 12AX7 PI/Driver. It has reverb, but it isn't tube driven, and the noise is still there when the reverb is on 0.

The worst notes are three E's; 14th fret D string, 9th fret G string, 5th fret B string.

Any ideas? Thanks.

[stokes]

Hard to tell from your description,but it sounds like it could be ghosting caused by old filter caps.How old is this amp?Have the supply caps ever been changed?

[GlennW]

I don't know the age, I could email Peavey and find out. Peavey's online Owner's Manual is dated 1999, so I'd guess it's no older than 15.

I'll try changing all three 12AX7s at once with tubes from an issue free amp and see what happens.

Edit: After swapping all three pre tubes the noise is still there.

[CharlieP]

I don't know the age, I could email Peavey and find out. Peavey's online Owner's Manual is dated 1999, so I'd guess it's no older than 15.

I'll try changing all three 12AX7s at once with tubes from an issue free amp and see what happens.

Edit: After swapping all three pre tubes the noise is still there.

I would suspect a preamp tube. I had my VK112 do the same thing. It was a preamp tube. Prowler is identical to the VK112. Prowler USA VK112 China!

[pdf64]

Is this a combo?
Can you plug it into a seperate speaker cab / disconnect the internal speaker (maybe the speaker of another combo)? The important thing is physical isolation between amp and speaker.

[GlennW]

After more messing around I think it was one of the output tubes.

I'd tried different speakers in and ext cab with the internal speaker disconnected and the noise was always there. Changing the 12AX7s didn't cure it, so I tried a new set of output tubes. It behaved. Then to be sure the old output tubes were reinstalled and the noise returned.

I'l' try it again tomorrow when the volume can be turned up. Thanks for the help.

[CharlieP]

After more messing around I think it was one of the output tubes.

I'd tried different speakers in and ext cab with the internal speaker disconnected and the noise was always there. Changing the 12AX7s didn't cure it, so I tried a new set of output tubes. It behaved. Then to be sure the old output tubes were reinstalled and the noise returned.

I'l' try it again tomorrow when the volume can be turned up. Thanks for the help.

That symptom is usually a tube. It can do it with preamp or output tubes. I suggested the preamps first thinking it would be lucky that the cheaper ones would cure it. I was lucky with mine, it was a preamp.

[GlennW]

The volume was very low when I checked it last night. Today the noise is there, mainly on the 11th fret B flat.

It might be the filter caps or something in the power supply. I'm not a tech so I don't know.

I don't have any new pre-amp tubes, but I'm about 99% sure it isn't the tubes or the speaker. I'm 100% sure it's annoying.

[GlennW]

I think I got lucky...it looks like the culprit was an old Tung-Sol 12AX7 I recently stuck in V1. I'll put the Bogen/Mullard back and hope that does it.

Thanks again for all the input.

[CharlieP]

I think I got lucky...it looks like the culprit was an old Tung-Sol 12AX7 I recently stuck in V1. I'll put the Bogen/Mullard back and hope that does it.

Thanks again for all the input.

It wasn't the tubes Huh!

[GlennW]

TubeS is right. After my last post the old output tubes were reinstalled and the noise was back, but shifted back to mainly E. One of them (at least one) was bad as well as the 12AX7 in V1. That might explain why the offending notes moved around while I was swapping tubes. I put the new 6L6GC's in and all is well; I think the old ones were made in 1965.