First thing first unplug the speaker before turning on the amp at this point. Nothing on the preamp side of things should be blowing fuses. My concern is first for the speaker and then being able to run the amp without blowing fuses. So it would be nice to build/use a light bulb limiter which there is a sticky thread and many threads about building one located on this site. Once you have the amp through a limiter then see if there is any DC voltage on the speaker leads so use a DMM to check. Got to figure where the short is on the amp and at this point a light bulb limiter will hopefully keep the amp from blowing fuses. Sure there could be bad solder joints and things going on, and an inspection of power amp area of the board is very important.
Got to make sure we didn't fry the speaker and using 9 volt battery touched on speaker leads listen for a pop.
Got to make sure we didn't fry the speaker and using 9 volt battery touched on speaker leads listen for a pop.