First things first disconnect the speaker and do not connect the speaker until the amp has been repaired. Do you own or have access to a multimeter to measure resistance and voltages? Something is drawing excess amount of current and is blowing the fuse. You said you heard a humming and that is probably DC voltage hitting your speaker before it blew the fuse, hopefully the speaker is not blown too. When you reinstall the fuse do not simply turn on the amp or you might just blow another fuse and, well, your right back where you started. Instead research and build a light bulb limiter (a.k.a. Dim bulb tester and Poor Man's Variac) which will allow you to power the amp on with out blowing fuses. The light bulb limiter will light the bulb up bright if the amp is pulling excessive current which will save your new fuse from blowing. When you first power it on via light bulb limiter do not have a speaker connected. Here is a schematic for that amp and hopefully it matches up to yours. Do your research and approach the amp repair using troubleshooting techniques offered through correspondence on this site. Do not just pull parts and replace without justification.
Light Bulb Limiter
The problem is probably due to shorted output transistors or a shorted bridge rectifier, but it could be other issues beyond that too.