1980 iib - Volume Swells

[Dude2Dude]

Hi all,

I have a Mesa Boogie IIB from around 1980. Recently, I started getting the occasional "volume swell" — I'll be playing, and then the amp volume climbs precipitously high all of a sudden, to the point where I have to hit the standby switch.

I called Mesa and the guy I talked with thought it was a failing power tube. (Believe it or not, the original 6L6s -- STR387s -- were still in the amp.) So I replaced the entire set with four new Mesa tubes, the STR-440s. But the problem recurred. This doesn't happen all the time; it's sporadic. Not sure, but I think it has happened in both channels.

Could it be a preamp tube? (I swapped out the Sovtek 5751 that was in the V1 socket for an old 12ax7 - 7025 that I had kicking around; improved the tone a bunch, but the problem remains.)

Would really like to hear your thoughts. Thanks in advance.

 

[mxr2000]

you should take your amp to a good amp tech for a check up test and see if there a problem... And a good clean up of the knobs pots and Effects loop jacks ...

 

[Dude2Dude]

Thanks very much for responding, mxr2000. Think I'll take you up on that.

But if this is something that others have experienced, and I can remedy myself (i.e., buy preamp tubes; insert preamp tubes...) I'd much rather go that route.

Input gratefully accepted.

 

[RustyChops]

I have an early '80 IIB that was doing the same thing. Mine started to do it all the time. I talked with Mesa and they said it could be the tubes, so I replaced the whole set but the problem persisted. My amp had sat around virtually unused for a long time. Anyways, I contacted BoogieBabies, you can find him here on the boards. He did a complete cap job done, as it way past due...and he found some other little things that needed fixing. Now it sings like new once again.

I suggest you try to talk with Boogie Babies and see what he suggests.

-

 

[kdorsey]

I have an early '80 IIB that was doing the same thing. Mine started to do it all the time. I talked with Mesa and they said it could be the tubes, so I replaced the whole set but the problem persisted. My amp had sat around virtually unused for a long time. Anyways, I contacted BoogieBabies, you can find him here on the boards. He did a complete cap job done, as it way past due...and he found some other little things that needed fixing. Now it sings like new once again.

I suggest you try to talk with Boogie Babies and see what he suggests.

-

+1

After these electrolytic caps get to be 20+ years old, they start to dry out and do freaky things. And from the rave reviews and great advise on these boards, BoogieBabies is one to ask.

 

[okgb]

something charging and discharging slowly like that sounds
like a cap possibility .
If ordering caps , makes sense to get the higher heat tolerance
105 degree caps instead of the more common 85 degree ones
I looked at the caps that just arrived for mine , D'oh !

 

[Dude2Dude]

Thanks to all for the responses.

Here's a weird thing. I blew out the sliders with compressed air, then twirled the pots a few times -- I tend to set my amp and leave it -- and.... The problem seems to have rectified itself. I'm knocking on wood here, since I don't want to tempt fate too much.

Gotta give props to mxr, who said I should clean the pots and faders.

Amps are strange animals.