Posted by
Steven Pituch on
Jun 10, 2005; 2:41am
URL: http://elecraft.85.s1.nabble.com/Installing-the-Q7-Q8-Mounting-Parts-tp379192.html
Hi all,
I ordered 2 shoulder washers, 2 spacer washers, and a bunch of the soft
plastic thermal insulators from Elecraft so I can finalize the job of
doing the upgrade mods on K2 #402.
I was just wondering about the theory of this layout. The tab of the
transistor is pressed against the thermal pad by the spacer which is
tightened by the mounting screw. I guess you need to only tighten it so
much as to not puncture the soft insulator.
I am confused because there is a 2-D fastener at this location situated
in such a way as to appear to be a spacer. If the 2-D fastener actually
governs the height of the circuit board above the case heat sink, then
tightening the screws for the transistor heat sinks would not work
because the 2-D fastener would prevent the movement. Tightening the
screw would only warp the board. If the 2-D fastener did not restrict
the tightening of the heat sink screws then why are they there? You
would think the 2-D fastener would be the exact height to prevent the
plastic insulator from being over-compressed, but it doesn't seem to be
that way.
My old spacers are so warped, probably from heat, that they look like
truncated cones, wider at the base. My guess is that in this state they
were not putting any pressure on the transistor tab to force it into the
plastic insulator. In that case its a wonder I didn't burn the
transistors out.
What about using a mica insulator? That would never puncture. Is mica
worse at being a thermal conductor than the soft plastic ones used in
the K2?
72,
Steve, W2MY
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