Amp Problem - Suggestions?

[shreddermon]

So I've got an early Carvin Bel Air 2x12 combo. Pretty cool vintage-style amp, but I don't use it much anymore, so I had been thinking of putting it up for sale. Before hanging the "for sale" sign, though, I plugged her back in to make sure all was good. Unfortunately, I was surprised to find out no.

Once the amp has warmed up, after 5 or 10 mins of playing, I get an occassional nasty sound out of her. It's only on the left side speaker, and sounds like a very deep flatulant "brrrt" as a note or chord rings out longer. For example, if I hit a low open E, the note will ring out fine, then wait a sec or two, then it's followed by the "brrrt" as the note trails off. It's like something eventually resonates - in a bad way - a bit after the original note. Only seems to occur with notes/chords down low, not up high.

Any ideas what this might be? I'm thinking something has gone wrong with the left speaker, or something is loose internally and might be making the speaker resonate. I pulled the back cover off, and everything seems tightly secured. Speakers, tubes, etc. Then again, the fact that it takes a few minutes for this to kick in (i.e., warm up), makes me wonder if this might be a sign of a tube going bad?

Anyone have experience with this? Suggestions?

[Twitch]

Sounds like it could be the speaker is blown. As the chord resonates, it will begin to feed back low frequencies which the speaker may not be able to handle any longer.

Swap it with a spare speaker if you have one or plug the amp into an external cab if it has that capability. If the problem persists, then its something beyond the speaker. If thats the case, Im not sure I have an other suggestions.

[Cygnus X1]

A shout out to Carvin might be in order if you can't find something simple.
Word on the street is they are great for customer service whether in warranty or not.

[VitaminG]

are you able to switch the speaker connections around? If the problem stays on the left, you know it's the speaker.

[Twitch]

^^^ Doh, why didnt I think of that. Ill just get back in the cage with the rest of the monkeys now. Someone throw me a typewriter. Maybe Ill fling some poo later.

[shreddermon]

That's a great idea, VG. If there's enough lead, I'll see if I can try switching them around this weekend.

The extension cab idea might be good, too, but I'm not sure if that would shut down the internal speakers with this model. I suspect think that's not the case with this amp.

[shreddermon]

Thread resurrection!

So I finally got around to testing this out today. The way this amp is wired, I couldn't switch around the speaker leads. However, I did pull the connection to the internal speakers and hooked up a separate 2x12 cab, instead. Sounds perfect through the extension cab, so it's definitely a blown speaker.

Oh well, guess I'll replace the speakers before deciding to sell her.

[Twitch]

Funny you bring this one back up. Weve got an amp doing this and its not the speakers. You got lucky.

[rstites]

Funny you bring this one back up. Weve got an amp doing this and its not the speakers. You got lucky.

Filter caps?

[Twitch]

Filter caps?

I havent got into looking at it yet. Its a SS and just started acting that way all of the sudden. Open chords produce a low volume but if you palm mute, then all the power is there but it sounds like the speakers are blown. Just a horrible flubbing sound.