Need help with F-30 hum

[UsrName]

I was playing my F-30 at higher volumes the other day. I powered it up last night and it had a noticeable hum. It didn't have this hum before, or in the entire time I've had it.

When I played it louder, I had the masters around 10-10:30, and the gain about noon-2:00 on channel 2. I played for about an hour this way and powered down when I was done.

What do you guys think is going on? Has anyone ever had this happen to them? Did I fry a tube? I looked at all of the tubes and they seemed to be ok- none was glowing brighter than the others. I tapped on the power tubes but didn't really hear anything.

When I looked under the chassis, I noticed a long screw, about 4 inches, going through the chassis from bottom to top and sticking out about an inch on the bottom of the chassis. Does anyone know what this screw is for?

I also took it to the other side of the room and plugged it in. I made sure no appliances were running(washer, dryer, etc.). I even unplugged the upright freezer in my basement, which is where the combo is right now.

I tried it again this morning and the hum was still there. This is all with nothing plugged into the input.

 

[UsrName]

Well, I replaced the power tubes with new Sovtek EL84 matched and swapped the preamp tubes around with three JJ 12AX7 that I had. The hum is still there.

Any ideas? Anyone?

 

[rockhound76s]

Is your amp being plugged directly into a wall outlet, or are you using a surge protector of some sort? Reason I ask is because I once had a Rectoverb combo that acted similarly, and hummed when it was plugged directly into a wall outlet.

 

[UsrName]

It's usually on a surge protector, but I tried it directly into the wall and in different outlets througout the house. I'm trying to avoid taking it in because I don't have a warranty.

Anyone else?

 

[Dreads]

My amp has the screw thingy that sticks out too but I don't know what it is. Have you tried the amp with a different guitar? Also try switching cables... maybe 1 went south on you.

Barfly. :?

 

[UsrName]

My amp has the screw thingy that sticks out too but I don't know what it is. Have you tried the amp with a different guitar? Also try switching cables... maybe 1 went south on you.

Barfly. :?

I have tried it with a different guitar and the hum is still there with nothing plugged into the input.