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Old 18th April 2008, 11:04 AM   #1
spooney is offline spooney  United States
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Default MTX Thunder 421D

I have one of these here with blown power supply fets.The FETs are HUF75339P's . I am wondering what the board designation and value of the gate resistors are for these parts.I am also curious if HUF75337P's will work in this amp as replacements.They seem to be very similiar parts with the exception of the power dissipation unless I am missing something.
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Old 18th April 2008, 01:18 PM   #2
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They have slightly different specs, but not different enough to make a difference. I don't think the power dissipation matters much; if they ever need to dissipate that much power there is something seriously wrong.

I've been using HUF75337P in a couple different amps that originally have IRFZ44N. I use 47R gate resistors and they seem to run perfectly fine.

EDIT: OK, I see that with a (Tc) case temp of 50C the HUF75339P can do a continuous current draw of ~75A and the HUF75337P can only do ~70A. Only a 5A difference and they will never be required to do a continuous >70A (I hope).
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Old 18th April 2008, 09:41 PM   #3
spooney is offline spooney  United States
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gate resistors appear to be board designations R628 and R629.They look to be 47 ohm smd parts.One is way out of tolerance and the other appears to be fine.as long as I have to order new resistors I think I am just going to get the original FET's as well.
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Old 18th April 2008, 10:05 PM   #4
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Can you send me a photo of the guts?
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Old 19th April 2008, 03:22 AM   #5
spooney is offline spooney  United States
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I sure can Perry.The resistors I believe to be the gate resistors read 47R5 on them.Are these 47.5 ohm resistors? Anyways I'll send you a pic of the guts asap.
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Old 19th April 2008, 03:40 AM   #6
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47R5 would be 47.5 ohms. As was stated before, 47 ohm resistors will work just as well.

Check the PZTA56s and the 10 ohm resistors below them.
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