My JVC 100 watt amp blew a fuse 125v - 6.3a. is there and alternate replacement fuse?

You can buy replacement 6.3 amp fuses at Radio Shack, but in a pinch you can substitute a 6.5 amp fuse. It's only slightly higher in value, so it will still blow soon enough if there's a problem.

However, this doesn't answer the question of why the original fuse blew. Fuses very seldom "just go bad", so before you start replacing a blown one you should find out what went wrong. Check the power supply rectifier diodes and filter capacitors for shorts. They sometimes break down with age or because of power line surges. Also look for shorted output IC's or transistors. If you can't do this yourself, see if any of your friends have experience servicing or let a professional fix it.

Please, don't just stick in larger fuses (or worse, wrap foil around them) when they blow. Many times I've seen what would have been a simple repair turned into scrap that way. Hope this has helped, and thanks for using Fixya!