On 12/12/2013 6:56 AM, Carl wrote:
I use a Starrett Grade AA 12x18" granite surface plate I found at an
equipment auction decades ago. Close to 100# if I remember and it hasnt
moved from its perch since I got it home.
I had one of those at work (bout 18" X 18" or so), back in the old
technician days and they are heavy. Wish I had one now. You know
surfaces are flat when you put two together dry and they stick!
73
Roger (K8RI)
Carl
KM1H
----- Original Message ----- From: "Steve Thompson" <g8gsq72@gmail.com>
To: <amps@contesting.com>
Sent: Thursday, December 12, 2013 3:35 AM
Subject: Re: [Amps] Arctic Silver
I'll echo other's comments about Arctic Silver, which I've used on
numerous high power transistor amps.
Taking for granted that the copper heatspreader and main heatsink are
milled truly flat, the crucial thing is to get the transistor flange
flat as well. The majority I've handled are not anywhere near flat,
and always bowed upwards in the centre (something that hasn't improved
since the package style first appeared ~30 years ago). I use the
method mentioned by others - fine emery face up on glass. Mirror glass
is good, as it tends to be made better and any imperfections in the
surface show up.
If the copper spreader is thick enough, the heat is spread over a
large enough area whereby the heat sink compound is less significant
and the regular white stuff can be used - but even that varies in
quality. I stick to Dow Corning or Emerson.
Don't assume your copper spreader is flat just because it was machined
so in the workshop. Most of it is rolled and it's quite normal for it
to change a bit after the hard outer layer is skimmed off (just like
timber).
Steve
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