[Amps] Problem with 500w AM Linear with mosfet IRFP360

[sasas asasas]

Hi. I have construct this linear 500w rms (2kw pep) (50ohm) with 12 mosfet irfp360, http://tzitzikas.webs.com/linear500w.jpg 

schematic.
The manufacturer and other radio amateurs from a greek forum have construct it successfylly.
The manufacturer tells that the linear requires only 2 watts r.f driving power for full 500w output r.f
power. The supply is 70-110vdc and for maximum power with 110vdc tha current is 13A (without am modulation).
Without driving power, we must adjust the current at 200mA (when the linear is cold).
My problem is this: When i tried to adjust the current at 200mA without driving power, when the current close to 
160mA (by tuning the variable resistance 5Kohm) suddenly the current takes the value 3A and some smoke comes out
from the input transformer. 

some photos from my linear and pll here:
http://www.tzitzikas.webs.com/linear10.JPG
http://www.tzitzikas.webs.com/fet.JPG
http://www.tzitzikas.webs.com/linear11.JPG
http://www.tzitzikas.webs.com/linear12.JPG
http://www.tzitzikas.webs.com/pll10.JPG
http://www.tzitzikas.webs.com/pll11.JPG
http://www.tzitzikas.webs.com/pll12.JPG
http://www.tzitzikas.webs.com/pompos.JPG

With 2w input driving power from my pll and supply at 110vdc, and 150mA current without input r.f power, the output power was 

only 60w and the current was only 3,5A without modulation.
Witch do you think is the problem? Thank you very much and sorry for my English.