[Elecraft] KPA100 Standoffs between heat sink and board

[Don Wilhelm]

Ben,

Every KPA100 heatsink is milled in that area to remove part of the raised
platform that the PA transistors mount on and still allow for the standoff.
Just how much below the lower adjacent surface (large lower area) has your
heatsink been milled?  In most cases, it is only a tiny bit (1/64 inch or
less), and adding a washer would make the top of the standoff too high.  The
KPA00 board will tolerate some flex with no harm, particularly in the area
you are speaking of.

If your heatsink has been milled much deeper than that, you should contact
Scott or Brian at Elecraft and discuss the situation.  Perhaps a digital
photo would help.

73,
Don W3FPR

> -----Original Message-----
>
> I am slowly progressing on my KPA100.  I am at the
> part where the board and heat sink are temporarily
> mounted together to provide the proper spacing for
> soldering the final transistors.
>
> The five standoffs that go between the board and the
> heat sink are all 3/16", however, the heat sink has a
> machined depression around the hole for the standoff
> that is directly behind the center of the rear panel
> when assembled.  Unless I missed it, the manual states
> I should not use a washer or lock washer on any of the
> standoffs between the heat sink and the board either
> on this initial assembly, or on the final assembly.
> This being the case, there is a gap between the board
> and this particular standoff.  When I add the
> additional standoffs for mounting the shield later on,
> this will either prevent me from snugging the standoff
> down on this particular stud, or force me to warp the
> board at this point in order to get it snug.  Surely
> this cannot be the case.  While I haven't measured it,
> the depth of the machined depression in the heat sink
> would lead me to believe that a washer or lock washer
> is intended to be used either between the heat sink
> and the standoff, or between the standoff and the
> board during final assembly.  Anyone have any insight
> on this?
>
> -Ben  K1NT
>
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