Ampeg SVT-AV needs help!

jefftaint · #1 08-14-2011, 07:13 PM

been having what I'm hoping is a bad tube issue, every once in a while, when i turn on my amp, no matter how long it warms up, i barely get anything out of it, just a very quiet fuzzy sound. i found that if i turn the volume and low knobs up all the way and pluck the strings, it will kick back in, and then i can reset the knobs and it works normally, though sometimes that trick doesn't always work, especially when I'm really counting on it, needless to say, the amp has been sitting unused for quite a few months now because i cant afford to do anything about it at this time. so I'm hoping someone can at least explain what this issue may be, hopefully tube related, power tubes aren't that old, and weren't used much since. not sure if all preamp tubes were changed last time, i think maybe only 3 were. the owners manual says something about bad preamp tube can cause it to stop working, so I'm hoping that's all it is because it seems like the least expensive fix. any opinion on this would be greatly appreciated. is there a way to tell which preamp tube may be bad? also which is the driver tube and what effect does that have on things? could that be the issue? I've been using tube amps for a long time and never bothered to learn anything about them, except that they are fragile. a crash course in the area would be very helpful. I'm praying this isn't something more serious and expensive, I miss my baby so badly and really want it back on stage with me.

**B-string** · #2 08-14-2011, 07:22 PM

Not likely to be a tube failure. Sound like a cold solder joint or maybe a relay problem. Jerrold Tiers would be good to PM.

rickdog · #3 08-14-2011, 09:12 PM

The AV has "preamp out" and "power amp in" jacks on the back, right? The power amp in jack is switched so it disconnects the preamp and accepts a signal from an external source if something is plugged in.

Sometimes the switch contacts get a little bit of corrosion that breaks the connection from the preamp to the power amp. Try inserting a plug in the power amp in jack a few times, perhaps give it a little shot of contact cleaner through the jack. That might clear it up. Or try just patching from the preamp out to the power amp in.

Jerrold Tiers · #4 08-14-2011, 09:58 PM

Contact cleaner on EVERY "loop" jack, AND the preamp type tube sockets at least (all the 12AX7 and 12AU7).

See if you can clean switches also, although that may not be as easy

For the loop jacks, the idea is to clean the "through" contacts, which are not as easy to get to, so a spray type may be good.

Then see where you are. Good chance that fixes it

jefftaint · #5 08-14-2011, 10:29 PM

Wow ,sounds like maybe a glimmer of hope. makes sense though, i heard of something like that before, but they said to do that with the effects loop, but unfortunately, there is no effects loop on this amp, so i thought i was just screwed. Thanks for the advice so far everybody, I'm crossing my fingers on this one, I'll be trying this approach tomorrow and I'll let you know how it turned out. wish it wasn't so late right now, I'd set it up now otherwise! highly anticipating.

Baconator · #6 08-15-2011, 10:35 AM

It's definitely worth developing a good relationship with an amp tech in your area. You might be surprised at how little it costs to get the amp checked out and whatever problem fixed. The last few amp problems I've had were fixed for $40 (1 hour) labour plus $5-10 in parts.

RickenBoogie · #7 08-15-2011, 10:49 AM

+1 on finding a good local tech- they can be life savers. And, fyi, the preamp OUT poweramp IN is exactly the same thing as an fx loop.

jefftaint · #8 08-15-2011, 04:45 PM

Quote:

Originally Posted by RickenBoogie

+1 on finding a good local tech- they can be life savers. And, fyi, the preamp OUT poweramp IN is exactly the same thing as an fx loop.

Oh cool, i did not that they were the same, thanks for the tip. as far as a tech goes, i had a really good one, but he doesn't have much time anymore, tho he says he still can, it just may take a little longer to get around to getting things done.

jmpiwonka · #9 08-16-2011, 06:48 AM

i had an svtII do the same thing.
turned out it was just a corroded amp in jack...

jefftaint · #10 08-20-2011, 02:05 AM

Quote:

Originally Posted by rickdog

The AV has "preamp out" and "power amp in" jacks on the back, right? The power amp in jack is switched so it disconnects the preamp and accepts a signal from an external source if something is plugged in.

Sometimes the switch contacts get a little bit of corrosion that breaks the connection from the preamp to the power amp. Try inserting a plug in the power amp in jack a few times, perhaps give it a little shot of contact cleaner through the jack. That might clear it up. Or try just patching from the preamp out to the power amp in.

I cannot thank you enough!!!! I did what you said, and that was exactly the problem, I'm totally up and running again, took it to a gig tonite for the first time in a year (this has been going on that long) and it worked perfectly all nite. I can't believe that's all it was this whole time, I thought for sure that I'd be spending a few hundred to get this fixed, and was putting it off for so long. I almost forgot how truly awesome that amp is. this forum is the best thing ever, thank all of you for your help, life is so much better now.