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Old 25th January 2005, 05:55 AM   #1
Jean is offline Jean  United States
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Default Yet another heatsink question for Aleph 2s

Hello all!

I am about to place an order for 4 Conrad MF35-151.5 heatsinks and would like to check with you guys one more time before I order those.

They have a Thermal Resistance C/Watt for 80 C rise of 0.21. Here is a link http://www.conradheatsinks.com/produ..._350.html#MF35

Would they be fine or just barely enough ? I could use some help figuring out the temp rise using standard aleph 2 circuit with 6 irf's per side , using default rail voltage.

Thanks in advance.

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Old 25th January 2005, 11:11 AM   #2
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Those have approx 700 sq inches of surface area per heatsink. Someone else verify this please. 3 of them per monoblock would make me feel more comfortable, or using fans i think.

http://www.diyaudio.com/forums/showt...948#post559948

check out my post there, i forget how many sq in for cooling those heatsinks have that i was using...i think it was 1900 per sink, they are a little nuts, but two sinks are adequate for monoblock aleph 2. notice the paint can later!

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Old 25th January 2005, 01:45 PM   #3
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Default conrad mf35-151.5

I would use at least 4 of them for each aleph 2 with as many vents as possible on the front-, rear- and top cover of the amp.
With 6 of them per amp it would be best and quite close to the original aleph 2.
That is, if you intend to bias the amp @ 4 Amps.

Good luck,
Nick
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Old 25th January 2005, 02:13 PM   #4
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Default Re: Yet another heatsink question for Aleph 2s

Quote:
Originally posted by Jean

I am about to place an order for 4 Conrad MF35-151.5 heatsinks and would like to check with you guys one more time before I order those.

They have a Thermal Resistance C/Watt for 80 C rise of 0.21.
Jean,

I recently completed an Aleph-X using two MF35-151.5 and one MF25-151.5 per monoblock (375W after the power supply). The thermal resistance given on their web site seems pretty accurate, based on my final heat sink temperature. Just remember to correct the value for a 30 or 40 degree temperature rise, or whatever you select, instead of 80C. This will decrease the effectiveness of the heat sink by about 30%. So, you'll end up with about 0.27 C/W per heat sink. I am running at a bit less than +40C.

If running at 40 degrees above ambient doesn't scare you, then you only need two per channel (assuming 300W). If you want to get down to 25 degrees above ambient, well, you'll need four.

Or, split the difference and build like this.

http://www.diyaudio.com/forums/showt...062#post555062

Good Luck,

Jeremy
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Old 26th January 2005, 01:17 PM   #5
Jean is offline Jean  United States
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Thank you guys, I guess 2 per amp like I hoped for won't work
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Old 27th January 2005, 06:53 PM   #6
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Hey Jean,

I'm in the same situation as you are. Conrads MF seem to have to short fins but are relatively cheap.
Here in Europe I would tend to buy deltours (www.deltourheatsinks.nl).
They offered me a profile of 300mm x 150mm with 84mm fins not in the e-shop for some 40 Euros plus VAT at large quantities. Best offer I have up to now.
What is your choice second to Conrad?

Thomas
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Old 28th January 2005, 01:16 AM   #7
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important! Don't over look the fact that.......

You might want to over bias your 2's. They sound much better when you push the bias higher then normal so it would be more like 6 of those sinks to suffice at a higher running bias level.

Mark
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Old 28th January 2005, 03:45 AM   #8
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Hi Thomas,

You mean the ones you got offered aren't either one of these: DEF 26 or DEF 103? (Quite a bit of K/W difference between there BTW.. Wonder if the 103 really works that well; without a fan etc..) Also could you please elaborate a little bit more on what you ment about large quantities? 10+? Thanks in advance!
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