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Old 3rd September 2008, 06:59 AM   #1701
juma is offline juma  Serbia
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set 2
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Old 3rd September 2008, 02:46 PM   #1702
BFNY is offline BFNY  United States
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HEAT SINKS

If anyone is looking for F5 heatsinks, the Conrad heat sink group buy is closing soon. These black heat sinks will come milled and drilled for top and bottom covers, and with black bolts, cost about 62. USD each, delivered in the US. Further up in the thread, someone had indicated these would be a good choice for the F5.

See final info on the group buy here -

http://www.diyaudio.com/forums/showt...00#post1589700

Bob
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Old 4th September 2008, 09:50 AM   #1703
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Default Bias

In AudioXpress magazine, I've read Pass say at least twice that you need to overate power transistors by a factor of 6 if you want any kind of reliability. This just happens to be a bias of 1.3A as he designed it. Though, I'm sure there some flexibility here, with proper heat sinking. But not 3 amps IMO.

If I'm wrong I'm sure he'll chime in.
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Old 4th September 2008, 05:06 PM   #1704
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Depends on what you mean by any kind of reliability. At 25 watts, 150 watt
devices don't seem to ever break. At 50 watts they break rarely.
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Old 4th September 2008, 05:25 PM   #1705
Magura is offline Magura  Denmark
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Default Re: Bias

Quote:
Originally posted by Johnloudb
In AudioXpress magazine, I've read Pass say at least twice that you need to overate power transistors by a factor of 6 if you want any kind of reliability. This just happens to be a bias of 1.3A as he designed it. Though, I'm sure there some flexibility here, with proper heat sinking. But not 3 amps IMO.

If I'm wrong I'm sure he'll chime in.

The key words here are "adequate" and "heatsinking"

You can push a mosfet real hard, if the temperature is kept down.


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Old 4th September 2008, 07:09 PM   #1706
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Sorta like having nookie in the fridge or the sauna, right ?
(probably why those Eskimos last so long)
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Old 4th September 2008, 07:10 PM   #1707
zinsula is offline zinsula  Switzerland
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Default The die dies?

Quote:
Originally posted by Magura
The key words here are "adequate" and "heatsinking"

You can push a mosfet real hard, if the temperature is kept down.
40V, 3A 120W
Well, if you are going to cool down your mounting flange to 0°C, then OK. But if your sink is at 30°C (!!) and the thermal resistance between junction and sink is around 0.80- 1.0 K/W (on this value you don't have much influence), the poor MOSFET's die is above 120°C.


Tino
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Old 4th September 2008, 07:17 PM   #1708
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The thermal resistance from junction to sink always exceeds 1.
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Old 4th September 2008, 07:43 PM   #1709
zinsula is offline zinsula  Switzerland
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So I was even too optimistic....
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Old 4th September 2008, 08:37 PM   #1710
Magura is offline Magura  Denmark
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I have tested this sort of abuse for approx. 2.500 hrs. Heatsink running at 35C.

I for one don't care if I have to do some maintenance every 2.500 hrs., if it means that I can get better sound

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