mosfet 450w irf240 / irfp9240 amp help

If anyone can help me out there, it would be greatly appreciated. I attatched a schematic for an amp that I have here. It was working fine, but then if burnt up R33 and R27. I replaced them, checked my voltages and powered it up again...everything AOK, or so I thought. This time when I powered it up, it promptly burnt up R25.
Any thoughts? Could it be as simple as my bias seting for Q2? or do I have some bad mosfets on my hands?

THANX!!
 

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Dragon2

Member
2005-05-15 6:59 pm
Canada
Mosfet amp

Hi

Seems to oscillate: layout for that kind of amp is CRITICAL!
Low values 47 ohm resistors on gates.
Must use star ground.
To check oscillation, install a zobel network at the speaker output.
4.7 ohm 2w in serie with 0.1 uf cap.
If the resistor is heating...
You can remove it when to amp will be ok.
Good idea to install low value fast fuses on rails after filter caps.

Good luck

Have a good day. :eguitar: