Roger,
I see that Bill posted some of our private interchange here! No problem
with me. But now I feel that I have to reply to your comments!
>> I just looked up values for solders: Common 60/40 solder conducts
>> heat about one fifth as well as copper,
> This is the reason we use heat transfer compounds like Artic Silver
But Arctic Silver conducts heat about ten times worse than 60/40 solder!
That's not to say anything against Arctic Silver. It still seems to be
the best thermal compound available. But it's a grease with metal and
oxide filling, which just cannot come anywhere close to the thermal
conductivity of 100% metal, like solder is!
>> In a catalog from an aluminium supplier I found some extrusion
>> stock that looks much like an Omega sign, but closed. Like a round
>> tube
>
> I'd stick with solid copper with a machined water way and a cover
> silver soldered on rather than one with a removable cover.
I will see what I can do. Certainly teh specially machined copper block
should be better. But if I can buy that aluminium stock at very low
price, and use it almost without modifications, that's a powerful advantage.
The core issue is that I need to calculate this stuff! If it turns out
that the cheap aluminium extrusion is all I need, why should I bother
with machining a copper block? On the other hand, if the aluminium
extrusion proves to be unable to cool these MOSFETs well enough, while a
machined copper block will do, then of course that's the deciding factor.
>> m here? That's no issue for me. It would go into a closed container
>> under the desk, holding maybe 20 liters of water.
>
> Find for casual operating, but what about contesting.
True, for contesting you need to place a coil of copper tube in that
container, and run some tap water through it. But I'm not into
contesting. I'm a technical ham, I like building equipment, and my
operation on air is not intense. I calculated that such a container with
20 liters of water would warm up only by 15 degrees, during the wildest
operating sessions I ever have!
> You are looking for ohms per CM^3 or were you just measuring the
> resistance between two probes?
I filled a 1 meter long hose with water, and measured end-to-end using
just the multimeter's probes.
> It's rare to find tap, well, or spring
> water with more than a few hundred ohms per cubic CM.
Even that might be good enough. If not, I can still buy some de-ionized
water. And then watch it eat ions out of my cold plate over time!
;-)Anyway, first I have to decide on the more electronic aspects of my
amp! I'm still waiting for the samples of a few candidate MOSFETs,
ordered a month ago. With international shipping and VERY slow customs
processing, one needs to have patience...
Manfred.
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http://ludens.cl
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