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Old 30th December 2006, 05:53 PM   #1
Tom7227 is online now Tom7227  United States
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Default Rockford FETS MT75N05

Hello fellow technicians,

I am so glad I found this forum to share car audio amplifier repairs.

I am looking for a replacement FET for the MTP 75N06 FET used in this Rockford Amp.


Finding the Holy Grail seems easier than finding the exact FET, I know there is a substitute and a replacement SMT gate resistor, but locating were the info is ...challenging to say the least.

And info would certainly be very helpful.

Tom
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Old 30th December 2006, 06:45 PM   #2
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You can use almost ANY 75 amp rated FET. May I suggest IRF-2807 or IRF-1010. The 60 volt rating can also be as high as 100 volts without issue.
I use 75339P By Intersil, or 75645P by Intersil Fairchild.
The IRF numbers are slightly higher current rated, which does not hurt withing reason. I also use IRF-3205 for heavy duty replacement, but you might have to lower the gate resistor value abit to get proper gate operation.
Just about everybody makes a general purpose 75 amp rated FET. I would only be worried about the the ON resistence of the two different FETs, as this does affect the total on power for the power supply.

Good Luck and pls use http://www.findchips.com/avail for your part search.
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Old 30th December 2006, 08:50 PM   #3
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I'd use the IRF3205s. If the gate resistors are 51 ohms or less, they are OK. 68 ohm resistors are borderline. 100 ohm resistors won't work.

The symptom for too much gate resistance is excessive current draw at full duty cycle. Generally, you'd run your bench power supply near 13 volts. This will cause the duty cycle to be cut back because the supply can easily hold its target power supply voltage with 13v input. When you turn the voltage down below 11 volts, the duty cycle will increase. You want to turn it down untill the duty cycle no longer increases. If the current draw is more at the low voltage, you need to decrease the value of the gate resistors.

Of course, this assumes that the driver transistors are intact. The transistors labeled 2A typically fail. On occasion, the 1A transistors will fail. The TLx94 IC in most Rockford amps will operate with no B+ voltage (only ground and remote connected). With the new FETs in place, you can look at the gate waveforms to see that they're turning off quickly (sharp vertical fall on the right side of the waveform).
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Old 31st December 2006, 08:02 PM   #4
Tom7227 is online now Tom7227  United States
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Thanks for the replys,

I will try the 3205's, cause I have alot of those.

Tom
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Old 1st January 2007, 07:53 AM   #5
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Quote:
Originally posted by Tom7227
Thanks for the replys,

I will try the 3205's, cause I have alot of those.

Tom
They will work fine. Hope your good at working with MESHA. I do about 10 or 12 a week currently.

Happy New Year !
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