Amp help Marshall DSL 2000 100W

[potato]

sounds like thats the prob. i was mid way through a set and it happend,"the dog whistle sound(more like a dog getting raped by an elephant) but none the less a horrific sound.sadly, i didnt have an extra but i was back for the next set after a trip to lowes.

[donf]

ok, i got the head. Checked out the back and it seems that all tubes are lit ok. This is my first time in the back of a head that contains tubes.

When i tried hooking everything up, what a horrible squeal. I know i'm a at this. I don't have a manual, though I'm searching on line.

Looking at the configuration, 4 large tubes on the right and 3 smaller ones on the left. What am I looking at? And what would your next step be?