Ampeg SVT 3 Pro Issue

[dave74200]

Hi all,

I've just bought a used 3 Pro and it seems to have an issue. It sounds, even at low volume, slightly distorted, almost like a driven valve head. Ironically it sounds quite nice but I've heard a few and know it's not right. I've read a lot about the mosfets needing biasing on these amps, but then it could be a bad tube?

What do you advise? Do I change the tubes and see if that makes it ok? The guy I bought it from says it was fine before he sent it.

Any help would be greatly appreciated!

 

Thanks, Dave.

[Twincam]

Unfortunately no way of knowing till its properly looked at. Certainly these do have an bias issue, it could certainly be a bad valve from shipping. Or it could be the seller knew it was funny. Could have cracked a board in transit or any number of other solder joints.

I would be inclined to want a full refund. If you got it at a really good price then maybe yeah take it to a tech or if and only if your competent have a look yourself. Bare in mind that you can get seriously electrocuted when an amp has been off for a long time nevermind biasing it while on! The biasing I doubt will of changed during transit so more likely a valve(s) issue. Thats if the seller is honest and it was ok prior to sending. However if it's not the valve(s) then the seller can say you've messed with it and refuse to refund you. And your left out of pocket.

It could be a valve came unseated slightly. I suppose that can be checked easy enough. Once again I can't stress enough that you can be electrocuted badly!!! Even while the amp is off. I know because I've been zapped by capacitor discharge and was lucky not to of been seriously hurt, and it also totally broke the amp. And I would say that I've got a fair bit of experience, rebuilt a valve amp and so on. 

Edited March 25, 2020 by Twincam