That is exactly what the fuse is there for. I doubt it is ruined. At the least, you should try replacing the fuse first, and cross your fingers. I have known of two other JR transmitters that were connected to Futaba chargers, and they were both fine after replacing the fuse.
Radio Shack has fuses that will fit your transmitter.
http://tinyurl.com/2g6pfl
You can also buy them from Horizon Hobby.
http://www.horizonhobby.com/Products...ProdID=JRPA030