Hi there,fuses are really current dependent,we've all seen the 32 volt 15 amp fuse in an SVT,and it powers up fine.Are you sure on the back of the amp it doesn't say 300 watts,not volts? Anyway,if the fuse is blowing instantly,you have a major fault.Most likely power supply or output stage,something that draws a lot of current.If you don't know anything about transistor amps,take it to a tech.Good luck,Mel.