[Amps] 160m mosfet linear amplifier problem with ferrite cores

[sasas asasas]

HI. i have constructed this linear amplifier 500w rms (2kw pep) (50ohm) with 12 mosfet irfp360, http://tzitzikas.webs.com/linear500w.jpg for 160m band.
When i gave 3watts of driving r.f power, it gave to output only 190w at 106VDC (6A current). Two radio amateurs who have construct this linear claim tha it gives 500w
r.f power at 110vdc.
But when i tried to give 4watts of driving r.f power the ferrite Cores (43 material) 
of transformer T3 broken! Which do you think is the problem?? 

some pictures 
http://tzitzikas.webs.com/linear20a.JPG
http://tzitzikas.webs.com/ferrite_broken1.JPG
http://tzitzikas.webs.com/ferrite_broken2.JPG

the feerite cores that i use are:
http://uk.farnell.com/fair-rite/2643626402/ferritecore-196ohm/dp/1463423
from manufacter:
http://www.fair-rite.com/cgibin/catalog.pgm?THEAPPL=Suppression+Components&THEWHERE=Cable+Component&THEPART=Round+Cable+EMI+Suppression+Cores#select:freq1
Round Cable EMI Suppression Cores
Broadband Frequencies 25-300
MHz (43 material)
some radio amateur told me that maybe this cores are improper for these frequences. But the designer of this linear
claims that we must use 43 material cores for the transformers.
Thank you.