KPA-100 Heat Sink Compound

[Jim Wiley-2]

Gang -


When assembling the KPA-100, is it permissible to use standard
zinc-oxide filled heat sink grease and mica insulating washers in place
of the supplied silicon-rubber washers?  It seems to me that the grease
option wouldn't require re-torquing because any "flow" would happen
immediately when the transistors are snugged down to the heat sink.  


I've got lots of mica washers for TO220 size transistors that would seem
to be about the right size.  I might need to do a bit of trimming for a
better fit, but I've got lots of them.  Many times TO220's are used on a
PCB just standing up in air, thus the leftover mounting hardware.


Yes, the grease can be a bit messy, but I've been using it for years
(with other projects of course), and never had a failure.  You don't
need much per applications, either.  A 5-ounce tube of Dow-Corning 340
purchased 20 years ago is still more than half  full, even after lots of
home-brew projects.


What say all?



- Jim, KL7CC


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[Vic K2VCO]

Jim Wiley wrote:

> When assembling the KPA-100, is it permissible to use standard
> zinc-oxide filled heat sink grease and mica insulating washers in place
> of the supplied silicon-rubber washers?  It seems to me that the grease
> option wouldn't require re-torquing because any "flow" would happen
> immediately when the transistors are snugged down to the heat sink.

First of all, the transistors don't need to be insulated from the heat
sink, so you wouldn't need the mica washers. Second, Elecraft has said
that they do not recommend using heat sink compound because the plastic
sheets that they use do a better job of ensuring heat transfer.
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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