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Old 28th August 2003, 01:00 AM   #1
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Default Calling all Heatsink Experts!

Hi

I was looking at the following FS post on the forum -

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Gutting B & K amp for parts Post #1


The amp is a model 4330. Here is what I am selling:

Both heat sinks, each is about 10" long, 4.75" high, and the fins are about 1.5" long.

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If I input the dimensions into Rod Elliot's heatsink calculator (with 27 fins) I come up with a rating of approx. 0.35 C/W for heatsink temperature of about 55 C.
Jocko who posted the FS above, mentioned that the heatsink profile is close to something in a thermalloy catalog that has a much lower(less heat dissipation capabiliities).
My question is how much can I trust the heatsink calculator? Is 0.35C/W roughly what I can expect or is it likely to be off by a huge factor?

thanks much
vsr
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Old 28th August 2003, 02:12 AM   #2
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Hello -

Heatsink catalogs always list the thermal resistance for a given length of extrusion. For US companies, this is normally 3". The heat dissipating capacity increases as the square root of the extrusion length. So if you have 6" of extrusion, you will have 40% lower thermal resistance. That could explain part of the discrepancy.

However that heat sink sounds like a good one. I doubt you will get much more cooling than that without going to fan cooling. I would just use it and if the outputs are hotter than you'd like, you will just have to turn the bias down.

Hope this helps,
Charles Hansen
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Old 28th August 2003, 02:54 AM   #3
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FYI you can double-check the aavid thermalloy profile yourself - just go to their site and find the 'extrusion selector' tool, and enter the appropriate parameters. it will also let you enter the length, so you don't have to use guesswork to derive the value from a 3" piece.

/andrew
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Old 28th August 2003, 10:21 AM   #4
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Then after you have the sink, you can attach aluminum heat sink mount power resistors and see exactly what temp they will run with how many watts you plan to put in 'em.
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