K3 Assembly issue with bottom Heat Sink cover!

[williamsonr]

Hey gang,

Just spent 4 hours assembling K3 s/n 1318 and all went well except for one slight but potentially serious hardware problem.  When installing the bottom heat sink cover over the LPA I noticed that the required 4-40 x 1/4" screws bottomed out in the standoffs under the TO-220 LPA transistors before they would compress the cover to the transistors (and yes I can measure screw lengths).  This will leave a gap between the transistor and the heatsink and not provide proper heat sinking!  It is strange to note that one of the Manual Errata changes was to point out that the heat sink cover was "slightly" thicker than the other bottom cover.  Wonder if this part has changed?  Any way, I added 3 #4 stainless steel flat washers under the screw heads and that allows the screws to fully compress the heat sink against the transistors.  For a belts and suspenders fix I also added a dab of heat sink compound to the transistors as well.  I did not check the screws coming from the top side of
 t!
!
he LPA assy to see if the factory may have used the wrong/longer screws taking up extra standoff threads.  A #4 split washer could have also been left off of this top side screw and create the same issue or tol. stack up of the parts?

Any way HEADS UP!

73,

Rodger
N4NRW
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[Bob Serwy]

According to the assembly manual page 55, The NOTE states "The three screws
marked "A" must be "1/4" black pan head with inside tooth lock washers under
the screw heads."

Also read the CAUTION.


Bob Serwy - N9RS


Bob Serwy - N9RS

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of
[hidden email]
Sent: Wednesday, July 30, 2008 6:51 AM
To: [hidden email]
Subject: [Elecraft] K3 Assembly issue with bottom Heat Sink cover!

Hey gang,

Just spent 4 hours assembling K3 s/n 1318 and all went well except for one
slight but potentially serious hardware problem.  When installing the bottom
heat sink cover over the LPA I noticed that the required 4-40 x 1/4" screws
bottomed out in the standoffs under the TO-220 LPA transistors before they
would compress the cover to the transistors (and yes I can measure screw
lengths).  This will leave a gap between the transistor and the heatsink and
not provide proper heat sinking!  It is strange to note that one of the
Manual Errata changes was to point out that the heat sink cover was
"slightly" thicker than the other bottom cover.  Wonder if this part has
changed?  Any way, I added 3 #4 stainless steel flat washers under the screw
heads and that allows the screws to fully compress the heat sink against the
transistors.  For a belts and suspenders fix I also added a dab of heat sink
compound to the transistors as well.  I did not check the screws coming from
the top side of  t!
!
he LPA assy to see if the factory may have used the wrong/longer screws
taking up extra standoff threads.  A #4 split washer could have also been
left off of this top side screw and create the same issue or tol. stack up
of the parts?

Any way HEADS UP!

73,

Rodger
N4NRW
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[Jim Garland]

Rodger,
I assembled my K3 a couple of weeks ago (s/n 1217), and did not experience
your problem. The three transistors clamped nicely against the (thicker)
bottom cover using only the hardware specified in the instructions. As I
recall, there are both 3/16" and 1/4" screws in the kit. You sure you've
used the correct screws everywhere?

Took me about 10-11 hours to assemble my K3 (100W). I'm amazed you could do
it only 4 hours!

73, Jim W8ZR

 

> Hey gang,
>
> Just spent 4 hours assembling K3 s/n 1318 and all went well except for one
> slight but potentially serious hardware problem.  When installing the
> bottom heat sink cover over the LPA I noticed that the required 4-40 x
> 1/4" screws bottomed out in the standoffs under the TO-220 LPA transistors
> before they would compress the cover to the transistors (and yes I can
> measure screw lengths).  This will leave a gap between the transistor and
> the heatsink and not provide proper heat sinking!  It is strange to note
> that one of the Manual Errata changes was to point out that the heat sink
> cover was "slightly" thicker than the other bottom cover.  Wonder if this
> part has changed?  Any way, I added 3 #4 stainless steel flat washers
> under the screw heads and that allows the screws to fully compress the
> heat sink against the transistors.  For a belts and suspenders fix I also
> added a dab of heat sink compound to the transistors as well.  I did not
> check the screws coming from the top side of the LPA assy to see if the
> factory may have used the wrong/longer screws
> taking up extra standoff threads.  A #4 split washer could have also been
> left off of this top side screw and create the same issue or tol. stack up
> of the parts?
>
> Any way HEADS UP!
>
> 73,
>
> Rodger
> N4NRW
> ft.com

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[williamsonr]

Thanks Bob!

I bet this is it.  At midnight I was beginning to go cross eyed.  I must have missed the internal tooth lock washers!  Better RF ground this way as well.

Thanks Gang!

73,
Rodger
N4NRW

---- Original message ----

>Date: Wed, 30 Jul 2008 07:06:04 -0500
>From: "Bob Serwy" <[hidden email]>  
>Subject: RE: [Elecraft] K3 Assembly issue with bottom Heat Sink cover!    
>To: <[hidden email]>
>
>According to the assembly manual page 55, The NOTE states "The three screws
>marked "A" must be "1/4" black pan head with inside tooth lock washers under
>the screw heads."
>
>Also read the CAUTION.
>
>
>Bob Serwy - N9RS
>
>-----Original Message-----
>From: [hidden email]
>[mailto:[hidden email]] On Behalf Of
>[hidden email]
>Sent: Wednesday, July 30, 2008 6:51 AM
>To: [hidden email]
>Subject: [Elecraft] K3 Assembly issue with bottom Heat Sink cover!
>
>Hey gang,
>
>Just spent 4 hours assembling K3 s/n 1318 and all went well except for one
>slight but potentially serious hardware problem.  When installing the bottom
>heat sink cover over the LPA I noticed that the required 4-40 x 1/4" screws
>bottomed out in the standoffs under the TO-220 LPA transistors before they
>would compress the cover to the transistors (and yes I can measure screw
>lengths).  This will leave a gap between the transistor and the heatsink and
>not provide proper heat sinking!  It is strange to note that one of the
>Manual Errata changes was to point out that the heat sink cover was
>"slightly" thicker than the other bottom cover.  Wonder if this part has
>changed?  Any way, I added 3 #4 stainless steel flat washers under the screw
>heads and that allows the screws to fully compress the heat sink against the
>transistors.  For a belts and suspenders fix I also added a dab of heat sink
>compound to the transistors as well.  I did not check the screws coming from
>the top side of  t!
>!
>he LPA assy to see if the factory may have used the wrong/longer screws
>taking up extra standoff threads.  A #4 split washer could have also been
>left off of this top side screw and create the same issue or tol. stack up
>of the parts?
>
>Any way HEADS UP!
>
>73,
>
>Rodger
>N4NRW
>_______________________________________________
>Elecraft mailing list
>Post to: [hidden email]
>You must be a subscriber to post to the list.
>Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft   
>
>Help: http://mailman.qth.net/subscribers.htm
>Elecraft web page: http://www.elecraft.com
>
>
>

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