I also blew the fuses out of my 15b. When I went to RadioShack and they did not have the identical fuse, I think it was a 7 or 7.5 amp fuse. So I replaced them with an 8 amp FAST-ACTING fuse in 250 volt. The fuse is 1/4" dia x 1-1/4" long 3AG or AGC-Type. The RadioShack cat number is 270-1014. This was the closest match I could find. I have been running this amp for about 6 months this way without any problems.
You can also get lamp bulbs directly from Sun Fire if you need them, I had to replace one of them on my TMF35 and found they were the same for the 15b.