[Elecraft] RE: KX1 assembly/repair vulnerability & recommendation

[Ron D'Eau Claire]

Hi, Tom:

It is possible to mount the final so it holds the shoulder washer =
properly.
Mine stays snug and tight unless I catch it or bend the transistor on
something. (If it can go "wrong" I've done it at one time or another!).=20

If the leads for the final are "floating" in the solder pad holes before =
you
solder them, the transistor will naturally want to stay in place and =
"trap"
the washer even without a screw in place - as long as you don't "bend" =
it
accidentally.

To improve the "fit" after installation, I'd suggest mounting the =
transistor
to the standoff/shoulder washer just like you did originally, with the
mounting screw snug holding the transistor tab parallel to the board. =
Then
I'd desolder each lead in turn and shape each lead so it lays in the =
solder
pad hole WITHOUT pressing against it. That's where the tendency to =
"spring"
comes from.=20

WB and I discussed some additional instructions for positioning the
transistor so the washer doesn't come loose after soldering but Wayne =
didn't
want to recommend adjusting the leads while they are soldered. Trying to
form the final leads with them soldered means that any movement must =
occur
in the transistor and standoff. He is VERY concerned that in doing so =
the
transistor get tilted so it no longer presses FLAT against the thermal =
pad.
That could lead to overheating and failure of the final.=20

I see a note from Tom, N0SS, here that suggests that he is still =
discussing
the addition of some "fish paper" to the kit for the 30 meter module. =
That
stuff has the advantage that if something sharp is pressing hard against =
it,
it'll take years, if ever, to poke through. I'm not so sure the plastic =
tape
could stand up to a sharp lead pushing on it indefinitely. After all,
"plastics" are "plastic" and move slowly under pressure. For that =
reason, I
made very sure there are NO sharp points on the 30 meter module where it
faces the case!=20

Ron AC7AC


------------------------------
I've noticed the same thing. My final transistor doesn't want to lay =
exactly
flush such that at disassembly, the heat sink raises just a tad and the
washer can very easily shift in re-assembly. It took me several trys in
reassembly before the washer reset properly and I could complete the
closeup. I've learned to ring it out with the ohm meter prior to final
tightning. I wonder if there is an adhesive one could tac the washer to =
the
transistor heat sink so it can't shift?

Tom W0MFQ
KX1 # 307