Sunn Concert Bass Doing Strange Things

[Walt-Dogg]

I was using my red knob Concert Bass last night at a gig, I'm not gonna lie it was really being pushed (7-10), and out of no where the smell of an electrical fire filled the stage and the amp just started humming really loud through my cab (Ampeg SVT 8x10e, 4 ohms). So we shut down and I opened the amp up this morning. I took some pictures of what looks like what smoked/caught fire. I'm too afraid to turn it back on because I don't want to make it any worse. I have a guy that can fix it relatively cheap I'm just hoping you guys can assess the damage.

It appears to me that something went wrong with the eight white cylinders that are paired up into four inverted "V"s.

Here's more pictures:
http://smg.photobucket.com/albums/v167/moonraker/Amps/

[mckinnon audio]

   Hi there,I'd say by the looks of things you're going to have some shorted output transistors,and those resistors are baked.Possibly some damage to the traces on the solder side of the board.The loud hum you heard in your cab was probably DC volts being passed to the output because of the shorted trans.It's still very repairable,get your tech to check all the outputs and the power supply,etc.Good luck,Mel.

[Walt-Dogg]

Alright, then I'll finish getting read for the day (Even though it's 3 PM right now) and give my tech a call and see if I can't drop it off to get repaired today.

EDIT: Will repairing all of this prevent the problem from occurring again? Because I do plan to continue to gig with this head at high volumes

[Walt-Dogg]

Looks like it broke AGAIN... This time no smoke, but the sound just stopped so I shut it off right away and the heat sink on the back was burning hot.

[Walt-Dogg]

A new day, a new post.

So it turns out it's not busted, it just stopped producing sound for whatever reason. However I got sound out of it today, seems to be working just fine but it gets REALLY REALLY hot, specifically the heat sink on the back. I just had four transistors that went bad and caused it to do whatever the heck it did last time, so I have no idea what's going on this time.

Also this might help in getting a diagnosis, when I play the amp through my cab at low-mid volume levels I can hear a layer of distortion, but its not part of the main signal coming out, it's under that you have to listen for it. Oh and I'm running the head through a 4 ohm Ampeg 8x10. I hope that helps.

[mckinnon audio]

   Hi there,if the heatsink is getting that hot you still have an output stage prob.,bias could be off,could still be a damaged transistor in there.The key to this might be the distortion,get your tech to scope the amp to see where the distortion is coming from,could be a leaky transistor at the end of the preamp stage.Good luck,Mel.