Amp trouble

[marlond]

So when I play my SVT-2 pro very loud it begins to buzz really loud after about minute or two. Usually after playing a big note.

It sounds like when your guitar jack gets pulled out of the bass and is laying on the floor. No bass is heard, just really loud buzzing.

The kicker is that the pre and post volumes don't do anything while it is happening. When I flip it into standby it goes away and when I turn the amp on everything is fine, for another minute or two.

It seems to have nothing to do with time of playing, but with volume.

Also once the sounds sputtered and faded out and the protect light started to go green/red/green/red/etc. But that was only once. And it has not done so since.

I have changed the power tubes with known good ones and I have switched the head into a different power conditioner. Both have not fixed the problem. (FYI: on a side note, KT88s are MUCH louder in the SVT-2 pro than normal 6550s)

Are there any other things I could test before I take it to the repair shop? Maybe someone has come across this problem.

[ridgeback]

i would say its the tubes myself..Faulty bias ...

[BassmanPaul]

When you switched to KT88s did you rest the bias to suit them??? They are similar to 6550s but not the same tube.

Paul

[marlond]

I bias'ed them both.

It is simple right? turn the bias pots in the back until they are a solid green on both sides. Maybe I'm missing something there... I don't think so though.

I thought it was the tubes too, but I took the 6550's out of my new SVT-CL (that is working fine) and it did the same thing.

It took longer to get the amp to do it though. I think it was due to the fact that the 6550's were not as loud as the KT88's.

It is something to do with high volume spikes. It only happens when the amp is cranking and you start playing something that is fast or heavy and really saturating the room with sound.

Then it just starts buzzing really loud like the guitar cable just go pulled out. But the Pre and Post gain does nothing.

[BassmanPaul]

You are using a system designed to correctly bias your amp for the 6550. KT88s require a different bias level. You should take the amp to a tech.

Paul

[B-string]

Tech time, you may have some filter caps that are marginal or some cold solder joints. Have you also tryed new driver/PI tubes?,

[marlond]

Originally Posted by BassmanPaul

You are using a system designed to correctly bias your amp for the 6550. KT88s require a different bias level. You should take the amp to a tech.

Paul

Oh... ok. Then the bias might have been off the whole time. The guy that sold it to me said he just took it to "his" tech and had it looked over.

But both the green bias lights were on for the KT88s

So maybe "his" guy doesn't know ****. Very possible.

And yes it could be cold solder joints and stuff.

Basically, tech time. There is a great local tech that is working on my Mesa trem-o-verb, so I will just pop the SVT beast over there.

what a shame!!! I'm headlining a show on Sat. and that SVT-2 sounds soooooooooo good (when it is working).