On 8/25/2011 2:53 AM, Ian White GM3SEK wrote:
<snip>
>
> Another observation: if you have ever disassembled a CPU from its
> heatsink, another thing to note is that the film of heat transfer
> compound is extremely thin. The problem for manual application is to
> replicate this, which usually means smearing on the compound and then
> wiping almost all of it away.
We don't follow that technique. We start with a blob of the transfer
compound in the *center* of the heat sink. With spring tension applied
the heat sink is rotated back and fourth "with in tolerances" until the
compound comes out the edges. the excess is wiped off and the rotation
is again applied. This gets down until the film of compound is probably
no more than a few molecules thick. AT this point it is *almost*
impossible to even pull the heat sink off the device with out rotating
it to break the seal. There is very little sealant left in the
interface between the device and cooler and it becomes very efficient at
transferring heat.
>
> As Carl mentioned earlier, there's at least 20 years of good experience
> with water cooling of tube amps among serious 1.3GHz operators.
> Typically these amps use 3CX100 tubes in singles, pairs, fours, sixes or
> even eight at a time. The key article, which covers all the relevant
> points about water conductivity and monitoring leakage current, was by
> N6CA; it was in the ARRL Handbook for many years and can surely be found
> on the web.
>
> Regarding the size of the water reservoir, another 'data point' is a
> moonbouncer who uses a large plastic garbage can with no other secondary
> heat exchanger. Starting from room temperature, he can operate
> intensively for a whole weekend before the water is becoming a little
> warm. There are rest periods of 8-10 hours between moonset and the next
> moonrise, but this experience does show that secondary heat exchangers
> aren't always necessary.
>
>
> What all this adds up to is: let's not discuss this topic as if we were
> the first people ever to think of it - of course we aren't! There's
> loads of information and experience around, and most of it is readily
> available on the web.
>
73
Roger (K8RI)
>
>
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