Amp blowing fuses

I have a pair of quicksilver kt-88 monos and one is blowing 3A slo-blo fuses instantly on powerup. I have swapped all the tubes from its mate and looked at the chassis wiring which is discrete, point to point. It looks clean with no hints of overheating or trouble. I've thought about trying a 4A fuse but wanted to get opinions as maybe one of you have had a similar problem... thanks for any help, opinions etc...
In addition to all of your helpful posts, I would like to especially thank Frank (Metro04) who spent a lot of time with me in detail checks and troubleshooting. Without that help, I think I would still be down as there are no service outlets available here for the product.
was it in the filament supply????
Thank you Ray (Rawinsonde). It was a pleasure and glad you're back to enjoying them again.

For those interested, these amps have hybrid rectification for the high voltage supply which consists of a single 5AR4 tube and two diodes configured as a "bridge" rectifier. The two diodes were shorted, thus shorting the transformer's HV winding to cause the fuse to blow. The filament supply is exclusively A.C.

Ray had a multimeter, took various measurements, bought replacements from Radioshack, soldered them in, done, except....... now the other channel no longer worked.

Ray performed systematic troubleshooting and found that his other amp was the culprit with a non-functioning rectifier tube - possibly caused when swapping tubes into the shorted amp early on. He had several used 5AR4's on-hand, measured them initially for shorts (one was), then tried the remainder in the amp until one yielded a working amp (two did not).

Well done, Ray!