Ampeg SVT CL Static

[mlove]

So i just bought a used SVT Classic and 810 and the tone is killer but i noticed a low/medium level static that comes and goes. The static happens at the same volume no mater what the gain and master are set to and still happen if there is no bass plugged it. I've read a couple CL problem threads which lead me to think it might be a pre amp tube but thought I'd see what others thought.

[RickenBoogie]

I ALWAYS consider a trip to the tech as part of the price of buying a used tube amp. Every time. Could be very minor, like a tube, or could be something much bigger, which, if left un-fixed, could turn out to be even bigger, and more expensive. Only a bench test will reveal the truth.

[JimmyM]

Bum tube or cap would be my first guesses, with a tube being most likely. Could be pre, could be power. Unless you have a spare tube or two laying around that you can swap around, your best best is take it to a reliable tech.

[JGR]

I had this issue with one of mine, as did another TBer awhile back, and it turned out to be the same problem. I am going from memory now, but the main ground on the preamp board is connected to the chassis with a metal standoff. Crappy design. The head of the screw that secures the board ground trace to the ground standoff can develop an intermittent connection which will cause the intermittent static. I fixed it by simply putting a small washer under the head of the screw which provided better contact with the board (and fixed the problem).

[rickdog]

Originally Posted by JGR

I had this issue with one of mine, as did another TBer awhile back, and it turned out to be the same problem. I am going from memory now, but the main ground on the preamp board is connected to the chassis with a metal standoff. Crappy design. The head of the screw that secures the board ground trace to the ground standoff can develop an intermittent connection which will cause the intermittent static. I fixed it by simply putting a small washer under the head of the screw which provided better contact with the board (and fixed the problem).

Well, there's a hot tip on an easy fix! Thanks, I'm gonna remember that one.

Originally Posted by mlove

... The static happens at the same volume no matter what the gain and master are set to and still happen if there is no bass plugged it. I've read a couple CL problem threads which lead me to think it might be a pre amp tube but thought I'd see what others thought.

If the master doesn't affect it, the ground issue above is a real good guess (it will affect everything coming out of the preamp). But the phase inverter and driver tubes in the power amp are super easy to swap out (you have spares, right?). I'd try those before taking other stuff apart.

Half of V2 in the preamp is after the master volume... but it's not a gain stage, so I'd expect it to be less likely to be source of the noise.

And the usual disclaimers about the hazards of high voltage in tube amps apply! Unless you have experience working on these things, even JGR's simple fix should be something for a tech to do.