5150 is squealing/whistling :(

[The Honorable]

When I turn the post-lead anywhere past 6(what I usually gig at) I get a lot of squealing/whistling from my amp. This is the 3rd time this has happened so I know that its probably one of the preamp tubes. I changed both my pre and power tubes only a couple months ago... I have the head under warranty so I just take it in to Long & McQuade and my buddy changes all the tubes and its fine again. My question is, why does this keep happening so often??

Oh yeah I use Mesa Boogie 6L6 STR440 power tubes and Mesa 12AX7 preamp tubes.

[nsubulysses]

What kind of guitar do you play? I used to have a 5150 II and I played an SG through it. At first I just had the stock pickups in the SG and I got an insane, annoying squeal of feedback whenever I stopped playing. At the time I had a Charvel Model 6 with an EMG in it and it didn't get squeal like that.

I was told that Gibson pickups squeal like that easier because of the metal pickup covers. I switched to an EMG and didn't have feedback/squeal problems anymore. This is just my experience so hopefully it helps.

[nhspike]

Hmmmm
Depends on a bunch of things, like how hard you push the amp and how often.
Could be something else in the amp that is sending too much voltage to one of the preamp tubes... tough to diagnose here.
Have you had the amp thoroughly gone over by a qualified tech?
Something sounds out of whack... bias?
Not sure.

Are you using a premium-grade mesa in the V1 (first preamp) position?

Most important, that one, since it's signal is repeatedly added onto up the preamp chain.

I would say that you have a gremlin in there somewhere... but that's just a guess.

It could also be the way you have the tones set, as well as the pre/post gain settings.

Download one of the Mesa owners manuals, and just read what they say about "reasonable amp settings" and when to expect what.

I know your amp is not a Mesa, but... the information is golden for any tube amp that has lot's of gain built in.

Good luck.

[finstah]

get a pencil and follow this:

http://www.ehow.com/how_2043383_-locate-microphonic-tube-amplifier.html

should help if it's tube related or not.

[Nazgul]

And I got an insane, annoying squeal of feedback whenever I stopped playing.

My 5150 is doing the same exact at the band rehearsals when I have it at 3 (lead post-gain). But the tubes are still stock....13 years old?

[Rsmacker]

. My question is, why does this keep happening so often??

Do you use the standby switch when turning the amp on and off?

[Spivonious]

Definitely sounds like either a preamp tube gone microphonic or you're standing too close to the speakers

I'd have an amp tech check it out since this is the third time it's happened. Something is blowing out one of your preamp tubes.

[DonP]

I was told that Gibson pickups squeal like that easier because of the metal pickup covers.

This is mis-information.

Any pickup can squeal if the covers are installed incorrectly. They need to be clamped down onto the pickup and then soldered. Many people have pickup covers that were removed then re-installed incorrectly without being clamped down, and then complain about the squealing.

Is the pickup wax potted? Many old pickups were never potted. Back in the 70's, people weren't using high gain 5150's. Pickups didn't need to be potted back then. Today, most pickups are potted, but since potting wasn't done to PAF's, pickups like Seths and Antiquities are not potted to be truer to the original PAFs. Some of the earliest (2001/2002?) Burstbuckers were not wax potted either.

[jgcable]

Usually thats a microphonic pickup. Swap pickups or get yours potted.
If its not a microphonic pickup its a microphonic preamp tube or tubes.

[The Honorable]

Pretty sure its a microphonic preamp tube. I use new SD Blackouts so it's definately not an issue of having old pickups. Besides the whistling happens even happens when I don't have my axe connected to the head. I figured it was a preamp tube, I'm just tired of it happening now . I hate having to take it to a qualified tech, wish I could just fix it myself. This will the be the 4th time changing preamp tubes and I've owned the amp for a little over a year.

[finstah]

Do the test I sent in the link and that will tell you if it's tube related or not

[cmh2007]

are the tubes biased correctly?

[surfreak]

+1, that would be a typical sign of a tube biased too hot, or possibly a leaking cap. I suggest you take it to a good electrician rather than a music store.