Ampeg SVT-3 Pro just died on me!

spectorbass83 · #1 10-06-2010, 07:34 PM

Little bit of background info -

I have a used SVT-3 Pro which I got on a trade right here on Talkbass about 2 years ago. The amp worked fine at first but then I noticed it lacked volume and it would distort easily at low levels. I swapped the pre-amp tubes and when this didn't work I sent it away to a certified Ampeg repair facility. The amp ended up getting a MOSFET Bias, some new connections and a good cleaning. Got it back a few weeks ago and it sounded great.

Tonight during band practice I noticed the amp started to clip and distort. I didn't change any of the EQ settings since last time. Gain and Master Volume at about 1 o'clock, -15dB pad engaged, EQ on and boosted a few dB's. I backed off the gain about 20% and then went back to playing. During the third song it just died on me.

Its not my bass, its not any of my pedals and its not the cab.
When I turned the volume and gain knobs I would hear faint crackling.

I took the top cover off and it appears that only one of the Pre Amp tubes is lit. The rest are not lighting up at all.

Could it be the pre-amp?

HELP!

T-Bird · #2 10-06-2010, 10:44 PM

Hi.

It may be the pre-amp, but on some tubes, the heater glow is almost invisible so that alone don't tell much.

If You have known working pre tubes at hand, try them first.

Jerrold and/or Dino will most probably chime in in no time, and they will be able to help way more.

Regards
Sam

spectorbass83 · #3 10-07-2010, 10:42 AM

Thanks Sam.
I actually called the repair shop that worked on it last and they said the same thing about the tubes. They also told me that they just recently got another SVT 3 pro in for repairs. These things are pretty unreliable.

rockstarbassist · #4 10-07-2010, 11:11 AM

Quote:

Originally Posted by spectorbass83

Thanks Sam.
I actually called the repair shop that worked on it last and they said the same thing about the tubes. They also told me that they just recently got another SVT 3 pro in for repairs. These things are pretty unreliable.

S'why I moved all 3 of the "temps" of those that I had. Just meh all around and yeah couldn't count on them to perform.

cap'n crunk · #5 10-07-2010, 11:22 AM

On the flip side, I played an SVT 3 Pro for four years, over a hundred gigs, countless rehearsals, and mile upon mile of banging around in its rack case in a van, an RV, and a trailer, and it never even hiccuped. And I beat that thing like a junkyard dog. I suspect that the reliability of most electronics boils down more to individual units (in most cases) than across entire makes and models. Unless, of course, those makes and models say "Behringer" on them.

Jerrold Tiers · #6 10-07-2010, 10:22 PM

never heard of 3 PRO being less reliable.......

Anyway, if a tube is bad, it likely won't work at all. You may find that you have some tube problem.

The power amp tube heaters are powered through a circuit that includes the fan. is the fan working? there is a fuse in that circuit, if anything drastic occurs, like a shorted tube heater, that might blow.

If so, the tubes in power amp are getting power to the heaters anyway, even if they don't light up. if either lights they both do, they are in series.

Preamp tube heaters are powered by a different circuit, but again, if ANY are lit they all are lit, even if you don't see it. The preamp heaters are in series.