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Old 17th January 2012, 08:31 PM   #11
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TO-3 with grease is about 0.9°C/W in my book.

BeO2 is about 0.17°C/W.
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Old 17th January 2012, 09:51 PM   #12
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The mica adds 0.3C/W, does not imply that Rth c-s is the same number.

(polished heatsink, polished TO-3 surface, best mica grade. mica rates from thin to thick, from best to worst origin)
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Old 17th January 2012, 11:00 PM   #13
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0.09°C/W, moved the decimal one place.
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Old 18th January 2012, 04:11 PM   #14
alibear is offline alibear  United Kingdom
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many thanks for all the assistance, much appreciated.
Andrew T, yes the 120mm fan will be fitted at the bottom of the heatsink.
Slightly off subject, using K Amps Class A Calculator I get the following results:
23V rails
3Pairs output devices
0.5 Ohm emmiter resistors
1.6Amp bias per rail
= 41W RMS and 74watts per channel heat dissapation.
Does this sound correct?
thanks
Alan
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Old 18th January 2012, 04:18 PM   #15
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You'll be very surprised as to how little air stirring you actually need in order to improve the heatsink transfer function of the heatsinks.

In my Pass Aleph 4 I'm ditching over 400W of heat into 8 heatsinks. Using two 50mm fans running at half voltage (ie the 2 x 12V fans in series across 12V). I've reduced the heatsink temperature by nearly 10 degrees and the fan noise is almost inaudible.
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