Ampeg SVT2 Pro problem

[Blade3dge]

Nothing posted so far covers the obvious, so here it is:

1) Have you tried using a different bass?

2) Have you tried using a different instrument cable?

3) Are the basses you're trying active, and do they have known good batteries?

4) If it's none of those, then I would check the input jack on the amp and make sure it's clean. I've heard of equally weird problems that were just from dirt in the input jack.

Yeah we've tried all of that already, aside from checking for dirt (which I'll do now) but at this stage I'm 99% convinced the problem has to be the amp unless all of my gear has failed simultaneously.

 

[JimmyM]

You don't have the -15db pad on, do you? Have you tried running a cable plugged into the pre and power amp jacks on the back? Sometimes they get corroded after time and will cause problems similar as well.

Failing that, maybe Hodgy or Jerrold Tiers will have something for you when they log on.

 

[StuartV]

Yeah we've tried all of that already, aside from checking for dirt (which I'll do now) but at this stage I'm 99% convinced the problem has to be the amp unless all of my gear has failed simultaneously.

Yep. Sounds like it's the amp. And, like I said earlier, you should definitely check the input jack. After that, it's pretty easy to do some tests to figure out if it's in the input section or the power section.

Once you know that, you can decide if you want to open it up and mess with stuff inside.

As an aside, if your first tech installed brand new tubes and they all fried right away, I don't see how he could say there's nothing wrong with the amp. And I hope he paid for the second set you put in!

 

[StuartV]

ps. With what you posted about not being able to get the input Peak light to come on, it sure sounds like the input jack or something in the early part of the preamp.

 

[Alex1984]

Yes, definitely sounds like it's early in the chain. Hope you kept the "blown" tubes that were swapped out on your visit to the second tech.

 

[cellkirk74]

I know this was long dead, but how did it turn out? I got am similar situation where I need to push the master gain to more than 2'o clock to get rehearsal volume against two loud Guitars. The input led just starts to light up occasionally.

Are there known issues with the input gain? May new AU7 tubes help to get more gain? I also have the feeling that the amp starts off louder and looses volume over time while running.

 

[bobyoung53]

No matter what is wrong with the amp (and yes if the tubes fried after 3-5 gigs your first condescending tech should pay for them) any tech worth his salt should be able to fix it and if they talk down to you that is either because they are too lazy to find the fault or they are too incompetent and can't find it (probably both). You need to find a tech who knows what he's doing. If you get an amp back from a tech and it is significantly different, worse than when you brought it in, don't take a bunch of gobbledygook for an answer, insist he fix it or give you your money back and don't back down. I would not poke around in an SVT, they are sections with 700 volts, that can kill you dead, unless you know what you're doing bring it to a tech who knows tube equipment especially SVT's, they're out there.

Woops another long dead thread, I'm going to have to start checking the dates before I post

 

[cellkirk74]

I was not the original OP back then, but thanks for your answer...

 

[cellkirk74]

Did someone try swapping the 12AU7s in the svt2 pro with the
JJ12BH7A:
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Can 12bh7s be used or would that require more bias adjustment than the amp provides with the bias controls on the back?