[Amps] MLA 2500A repair

[CRISINA LAUWEREYS(p43a@setarnet.aw)]

Hi

I am looking into a Dentron MLA2500A for a friend and need some advise.

The R2 1 ohm resistor fuse blew up disintegrated, the wire going to the HV capacitor C16 is still in good shape (did not melt) as is the one going to RFC-2. C5 looks OK also.
Only other thing I noticed were the two resistors of the parasitic chokes RFC-5 and RFC-6 did not look that great.... 
Not sure, but I guess the amp was modded sometime in the past as in-line with both chokes are a couple of 1 ohm resistors in parallel that are not shown in the diagram and i did not see in on-line pictures.

So, what would cause R2 to disintegrate like this? Could it be a shorted tube? How to confirm this before we replace R2?

73's de P43A, Jean-Pierre