My Fireball makes a lot of unwanted white noise, even when there's absolutely no cables plugged in (keeping the speaker cable connected at all times of course). I noticed this when I plugged something in the effects loop, which only makes it worse. What is wrong with my amp and are my tubes broken? / Can I fix this in any other way?

I do not want to have a signature anymore.

try using a different speaker cable?

Are you maybe using a instrument cable instead of a properly shielded speaker cable?

Either that or a preamp tube could have gone out (gone microphonic).

Quote by think11270
Either that or a preamp tube could have gone out (gone microphonic).

All preamp tubes are microphonic, its just to what degree.

TS: Have you tried running a noise suppressor through the effects loop. This type of noise is common with high gain amps.
What does it do when the master volume is all the way down?
If turning the MV all the way down does nothing to the noise, you need to take it to a tech and have them check the power supply.
If it makes no noise with the MV all the way down, then you probably just need a new effects loop driver tube. Your manual should list which one that is, and then it's a $15 12AX7 to fix.

There's an outside chance it could be V1, but the effects loop issue makes me think it's farther downstream than that. My guess is that you've already tried turning the volume down and it does nothing, so it probably needs to go into the shop. It might just be the power tubes, but it needs to be checked out because this sounds a bit more involved than that.