Ampeg ba115 blows fuses

[zippoman]

my ampeg ba 115 blew its fuse the other day, so i opened it up and put in a new fast acting fuse, but as soon as i turned on, it blew the new fuse. any idea what might make it blow out like this?

[Enzo]

First thought, shorted output transistor. Second though, the other output transistor is shorted. Less likely, shorted rectifier in power supply. Even less likely, shorted filter cap. And a few things that are too unlikely to mention.