Ampeg PF-500 Main MOSFET question

[Stuggi]

I got my hands on a bass amplifier, a PF-500 which seems to be a Class D 500W amp. However, it has an issue that the PSU part of it starts, and then resets probably due to overcurrent, dropping the main caps down, restarting the switchmode power supply again, which produces a 1 Hz ticking sound on the output. I traced the issue to a blown MOSFET on the speaker output, which according to the scematic should be an IRFB4227, however the amp is fitted with a pair of FDP33N25, which according to my eyes seems to be a much punier FET. The board also had a ceramic cap/resistor in series fitted between drain and source on both MOSFETs, a bodge that isn't on the 2009 schematic at least.

So, should I go with the IRFBs or the FDPs? Any idea what the bodge is for? Schematic attached for your viewing pleasure, it's Q10 and Q11.

[Stuggi]

I tore into the bodges, and it's a 1000pF ceramic capacitor in series with a 10 ohm / 1 Watt resistor. Some sort of snubber? 

[Vicus]

For shure a snubber. It looks like the 33n25 is easier to drive. To me replace with what they use in OM.

[Stuggi]

Well, it turned out to be a bit of a theoretical question, as the 33N25 was essentially the only MOSFET in that ballpark that I could get my hands on. The new FETS did however fix it, which was nice!

[Vicus]

It happen that the blown mosfet is not the only faulty component.