ampeg b2re - volume fluctuations

You need to supply us with the ohm ratings of your cabs to answer your question.
I believe your amp has a 4-ohm minimum rating.

I've never heard of a 4x15 Hartke cab, but I'd assume it would be rated at 4-ohm by itself. Adding your 1x10 may very well be producing a combined ohm load that your amp wasn't designed to tolerate and its causing the amp to heat up, malfunction and possibly be damaged.

Read this:
http://www.talkbass.com/forum/showthread.php?t=144244

 

Ok, it sounds like your fine on the ohm thing.
(you sure that Hartke isn't actually an 8-ohm 4x10 ?)

Your problem does seem heat-related. Your amp could just be defective but...
Is your rack case (or anything else) blocking any of the amps cooling vents?
Is your amps internal fan working? (if equipped)

Do you play your amp extremely loud?
(If so, you might just be asking more than this particular model can deliver for long periods of time)

For something easy and cheap, you could just try placing some sort of additional fan directly behind your amp to see if it helps. (I bet it will)

 

Ok, well just speaking from experience on my own SS ampeg and several others I have worked on over the years here is what I suspect is wrong.

I believe that the amp was run at a lower than 4 Ohm load at some time in it's life causing the output FETS to overheat and some of them are now going faulty when they get heat soaked.
These amps cannot handle too low of a load at all. They overheat pretty quickly at a 2 Ohm load and once that happens there isn't much you can do to save the FETS.
I loaned my SVT350H (Same circuit design as the B2RE) to a buddy who ran it for several hours with 2 4Ohm cabs connected to it. Needless to say when I got it back it was not working very well. It would do the exact same thing your is doing, volume would jump up or down once it warmed up. I pulled all of the FETS and replaced them with matched sets and it has been a monster ever since.
I have had to do this to other SS ampeg bass amps as well.

Now this might not be the problem, it could just be a dirty switch contact in the effects loop jacks, or a bad solder joint on the input connection, or any one of a hundred other things. It's something to think about though.

 

I've never seen that happen due to mosfet problems, and I have beaten the daylights out of all sorts of amps, Ampeg, and the other SLM brands, testing them..... For sure I have had them on lower than intended ohms for days at a time, so that they overheated and shut off regularly, cycling regularly. I'm not sure I can come up with a decent theoretical explanation either, unless it is a simple solder joint problem or the like.

And, btw, the OEM Mosfets in the amps are already matched, graded parts (or at least that is what used to be spec'd).

As far as the original poster and the problem, if the amp shuts off cleanly and later comes back on cleanly, that is one thing, probably a true overheat situation.

But if it is variable, wavering up and down, it may have a solder joint problem. Usually that will appear sooner than a couple hours, but.........

 

Do You Use the limiter?

 

Well, I guess it could have been solder joint problems on the MOSFETs as that would have been fixed when replacing them. They were the only parts I replaced on the amp. You of course have had much more experience with Ampeg amps than I have and have probably seen way more failures then me.

 

FETs is short for MOSFET which is short for metal–oxide–semiconductor field-effect transistor
This is the type of power transistor used by Ampeg in your amp.

 

I don't.
Make sure nothing is blocking free-flow of air from the fan. If it's in a rack-case, check that there is plenty of ventilation from the sides of the amp-case.

 

Are the 4 rubber feet missing and is the amp sitting flat on a carpeted surface like a speaker cabinet?

I'm wondering if the previous owner removed the rubber feet and didn't put them back when sold to you (or possibly he bought it used w/o the feet, too).

I've got an blue-face model which is usually stored in a rack case. One day I had it out of the rack and sitting flush on my cabinet and it got almost too hot to the touch in back by the air vents.

If you're experiencing heat-related issues this might be a cause.

 

It could be sag in the power supply capacitors: you do something that requires a lot of power to reproduce, like slapping, and the capacitors are lacking power for a bit while they recover, which puts a damper on volume and tone. I've only seen this happen in a very poorly designed power section, though, which the B2RE has not.

Just to test, try using the limiter.

 

You've already tried your amp without the wireless... right?

and just a thought:
If you play an active bass, have you tried replacing its battery?