[Elecraft] Questions about new crystals

[Ron D'Eau Claire]

I have K2 #2636.  Now that I've ordered new crystals as part
of the upgrade package, please tell me once again why I'm
doing this?!  Are these better matched than what came with
the kit? 
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Newer K2's do NOT need new crystals from what I've seen. It all started
because, over the years, Elecraft has discovered that the spex on the
crystals were not tight enough to ensure that they would all produce the
desired filter performance. The filters in MOST K2's were fine, but a
few had problems. So they have progressively tightened up the spex.
Those who had older K2's SOMETIMES saw an improvement by changing the
crystals. I had a mis-matched set for the SSB OPT1 filter in my 2+ year
old K2. A new set of crystals fixed that, but even then Wayne/Eric were
very surprised that I had a mis-matched set. By then (2 years ago) they
thought they had replaced all of the older crystal sets. 

I, too, have seen a few comments about the crystals "fixing" low gain
situations. My K2 has always had plenty of gain, so I can't comment on
that. My problem was a too-narrow SSB filter (OPT1) on the SSB module.
Fixing that with new crystals also required me to replace all of the CW
filter crystals on the r-f board too, in order to have a matched set of
filters when I was done. Changing the crystals for the CW filters
changed their characteristics, but did not offer any improvement. Nor
was any needed. 

The reference that you've seen to removing a crystal has to do the a
recent mod to improve the stability of the K2. The K2 uses parallel
crystals in VXO circuits and it has been found that with better spex on
one crystal, one crystal can be removed. That yields better overall
stability. If you order the BFO/PLL stability mod from Elecraft you will
get the proper crystal and other parts to change that will improve the
stability. I THINK (check their info on the reflector) that this only
applies to K2 BEFORE S/N 3000. I believe that these changes were
incorporated in newer K2 kits. So your would probably benefit from
adding the BFO/PLL stability mod kit. If I recall correctly, it'll set
you back about $10. It's a bargain.

Ron AC7AC
K2 # 1289