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Old 16th March 2010, 02:24 PM   #7391
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Quote:
Originally Posted by sangram View Post
Also rub down the heatsink with a bit of 100 grit paper on a wood block so the mounting surface is uniform. You should see about 10 degrees difference between the FET tab and the heatsink.


Imo, regular everyday heatsink compound works well enough. No need to mess about with exotics.

Kapton is ok, mica is ok, the Bergquist silicone pads are supposed to suck up differences in surface, but I have never had good results with them. Kapton tends to "punch through" so you have to be careful with them, they are thin and fragile in my experience. I have never had good results with kapton either. <waaa waa>

100 grit is rather coarse.
I'd start with 360 or 400 and move down to 1600 for a mirror finish.
You need a dead flat backing for the abrasive, and the abrasive paper should be wet or dry type. I'd work with a bit of water to keep the paper from clogging... clean carefully when done.

First just try it with a mica pad and standard heatsink compound and see what the temps are, before doing anything else.

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Old 16th March 2010, 02:44 PM   #7392
npapp is offline npapp  United States
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Proop, I had very similar results when I first built my f5 using silpad insulators. Heatsinks were never that warm and as I turned up the bais my heatsinks remainded cool @ 0.7v I had 41c heatsink and 81c mosfet. Solution I removed the silpads and used mica and standard compound aka goo. Actually I split my mica using a razor blade to get it as thin as possible, following a suggest I read from Mr. Pass. My bias for the last 6mos been set a 0.7v (1.7a @ 23.5v) I typically measure 65-67c on the mosfet tab and 50-55 on the heatsink based on room temp and using a contact therm. Good luck

[QUOTE=prooptiki;2119998]I want to share some more impressions for the f5.

As I said I use large skins, so after many hours the temperature stays to about 40oC, so after reading I started playing with the bias...

0.60v >>> 40oC >>> 65oC (mosfet)
0.71v >>> 43oC >>> 80oC (mosfet after 30min)
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Old 16th March 2010, 02:54 PM   #7393
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Quote:
Originally Posted by sekess View Post
got it now.
Good for you, i certainly did not.
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Old 16th March 2010, 03:02 PM   #7394
eLarson is offline eLarson  United States
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Quote:
Originally Posted by bear View Post
100 grit is rather coarse.
I'd start with 360 or 400 and move down to 1600 for a mirror finish.
You need a dead flat backing for the abrasive, and the abrasive paper should be wet or dry type. I'd work with a bit of water to keep the paper from clogging... clean carefully when done.

_-_-bear
Would simply lapping the back of the FET to the matching portion of heatsink work here? Neither needs to be perfect, but only to match each other.
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Old 16th March 2010, 03:04 PM   #7395
massimo is offline massimo  Italy
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Quote:
Originally Posted by bear View Post
100 grit is rather coarse.
I'd start with 360 or 400 and move down to 1600 for a mirror finish.
You need a dead flat backing for the abrasive, and the abrasive paper should be wet or dry type. I'd work with a bit of water to keep the paper from clogging... clean carefully when done.
add a bit (or even less) of soap.....
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Old 16th March 2010, 05:31 PM   #7396
a.wayne is offline a.wayne  United States
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Quote:
Originally Posted by AndrewT View Post
as one speaker terminal voltage goes up the other goes down.
The voltage between the two speaker terminals is double what would appear between one speaker terminal and ground.

If the load impedance is the same the current will try to double.

Double the power into double the impedance.

NOT
quadruple the power into the same impedance.
Hmm, i had always thought bridging would give you 4 times the power ...


Question ! How many here are running snubbers in the power supply ? recommended ?

Last edited by a.wayne; 16th March 2010 at 05:37 PM.
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Old 16th March 2010, 06:11 PM   #7397
Renron is offline Renron  United States
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Quote:
Originally Posted by sangram View Post
Just use regular white compound. Arctic Silver will get you a slightly lower FET temperature but is highly capacitive even if it is not conductive.
Also rub down the heatsink with a bit of 100 grit paper on a wood block so the mounting surface is uniform. You should see about 10 degrees difference between the FET tab and the heatsink.
As has been corrected, 100 grit is TOO rough, start with 400 or higher and progress to 1600.
Could you please explain what you meant by "capacitive" when referring to the Arctic Silver compound? (IT is NON conductive!) Surely your not suggesting that it is electronically capacitive??? Which would surely fry a CPU with Billions of transistors.

Andrew T,
I believe he was referring to Arctic Silver, a thermal conductive compound designed for the mating surfaces of CPUs and it's respective heatsink.

Npapp,
Thank you, I too am using Silpads and I am not impressed by their performance. Tinitus generously sent me some of the Kapton thermal pads but like BEAR, I found them to be easily punctured (and I was careful!) which was one of the causes of my rebuilding my F5 3 times. (my fault for not checking continuity first) (grounded out at full voltage and Bzzzzzzttt.)

I had purchased some Mica pads but they turned out to be 1mm too small on the sides. What is the proper size? TO-247 ?

Ron
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Old 16th March 2010, 06:14 PM   #7398
Renron is offline Renron  United States
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Quote:
Originally Posted by a.wayne View Post
Question ! How many here are running snubbers in the power supply ? recommended ?
Snubbers? Yes,
Recommend? Yes (helps stop ringing when the diode closes)

Ron
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Old 16th March 2010, 06:21 PM   #7399
a.wayne is offline a.wayne  United States
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Snubbers? Yes,
Recommend? Yes (helps stop ringing when the diode closes)

Ron
What values are you using for the snubbers .......
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Old 16th March 2010, 06:23 PM   #7400
hags is offline hags  United States
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Default Sil-pads and snubbers

I've always had good luck with sil-pads, good heat transfer, easy to use and inexpensive. No complaints here.

I replaced the rectifier bridge in my Acurus A200 with an RFB02 board with discrete components. I used MUR6030s with 2 ohm resistors and 100nf caps.
The difference in sound was noticable and immediate.
Was that due to the snubbers? I don't know.

I have used the same recifier boards with my F5 build. I couldn't be happier with the subjective performance.
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