Peavey Triple X got noisy all of a sudden

[jgcable]

I have an original 1st year model. It has been retubed and bias'd. I use this amp ALOT. Its beat to crap but has always sounded great.
I have been getting a fair amount of 60hz hum on the crunch and ultra channels lately. If I unplug the instrument cord its dead silent. Its only when I plug in a guitar. I have tried several different guitars and several different cords. The results are the same. I have tried not using the loop or jumping it. Same result. I have tried my other amps plugged into the same wall outlet and they are dead silent so its not a ground problem or interference at my house.
Any idea's? What should I be looking at? Filter caps?

[Hellbat]

Cheap easy troubleshooting would be to swap out the preamp tubes one at a time to see if that fixes it or not.

[jgcable]

It ended up being 3 bad instrument cords! Go figure.