K2 VCO Shielding mod

[Ron ZL1TW]

Hi
    Recently I got a few small parts off Elecraft, and for the want of
nothing better to do, I also got them to send me the "K2 VCO Shielding
kit", which I installed yesterday.
It is a very easy kit to install and it took less than an hour to do. I was
quite impressed when I did the upper and lower voltages for each band and
found the whole lot were well within range, and no adjustment to the
winding was necessary. Comparing the voltages with the original ones I took
during my build of the K2, shows the actual range of voltage between upper
and lower band edges on most bands are quite a bit smaller. The only band
that has voltages identical to the original setup is 80m.
Why did I put the mod in?.......because it was available and I am suffering
solder fume withdrawal (SFW) I guess  :-)
Actually, while I had the set apart, I changed R19 and R20 in the KPA100
and totally cured my "High Current" problems on 20 and 17m as well. (my
KPA100 is a very early one and I believe this problem is not "pandemic"...)
I proved the set still worked fine by having a few 40m European CW contacts
on the Grey Line, and later taking part in a small SSB contest on
80m....even worked another K2 (VK2LCD #3666)
   Cheers.......Ron ZL1TW
K2/100  #2204
K1          #575


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[Ron D'Eau Claire-2]

I was one of the guys who, six years ago, found himself suddenly afflicted
by a bad-sounding signal from my newly-built K2. It was maddening because
every time I buttoned up the rig it would hum. When I pulled the cover off
to investigate, the hum went away. After going through that several times,
it occurred to me that when I "buttoned it up" I also put it back on its
perch atop my small linear power supply! It didn't help that in commercial
service we commonly mounted transceivers atop their power supplies for fixed
station use to avoid taking up unnecessary desk space. I had never seen a
problem with the magnetic field getting into the commercial transceiver.
Then again, those were 800 and 900 MHz FM transceivers with receivers that
suppressed any amplitude modulation.

My power supply has long since been banished from the operating desk, but
since that hum is something that one cannot hear unless one checks the
signal with an oscilloscope or monitors it on a suitably well shielded
monitor receiver it seemed a good idea to take the precaution of installing
the mod. (The signal on a normal receiver often sounds bad simply because
very low level modulation inaudible a short distance away may come roaring
through, even with the receiver's antenna terminals shorted!)

The mod doesn't make the K2 "bullet-proof" in terms of avoiding hum on the
signal if the rig is immersed in a magnetic field, but it sure helps!

Ron AC7AC

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