[Elecraft] Re-work of K1 #175

[Mike]

I just finished a job on my K1 that I was not much looking forward to,
using parts recently received from Elecraft.

(1)  Pulled the front panel and replaced the AF gain pot, which had
become scratchy several months ago.  I haven't heard anyone else report
K1 scratchy pots, so maybe just mine had a problem.  The new pot seems
to have significantly less shaft woble than the original pot.  I may
have to order another one and replace the RIT pot.

(2)  BIG JOB!  Pulled off all 16 of the old problematic ceremic trimmers
on the KFL1-4 PCB and replaced them with the "new" blue trimmers.  I
found it was easy to get the old trimmers off, since there was plenty of
room under the old trimmers to get something to pry one end up while
desoldering.  I didn't even damage them.  Getting the residual solder
out of the vacated hole, and forming the thicker leads of the new caps
to get them on the PCB was another story altogether.  I was never able
to get the holes so clean that the new caps would slip right in, so I
wound up just blowing most of the solder out, then heating the holes
alternately while I pressed the new cap down.  I did have one problem
that I didn't find until I was in the alignment phase.  Trimmer C1
adjustment had no effect.  I found quickly that the ground connection
PCB trace to C1, which was on the top of the PCB and therefore buried
under C1, was broken.  A short jumper installed below the PCB to the
ground side of C5 corrected that.  Though I can't honestly say that I
enjoyed this task, all in all it wasn't as bad as I had feared.

(3)  Changed C10 and CK in the 30m/40m portion of the pass band circuits
of the KFL1-4 from 3 uuf to 4.7 uuf.  Though this was recommended in the
KFL1-4 temperature stability bulletin as an alternative to replacing the
trimmer caps, that's not why I made this change.  I have a 170 kHz VFO
span option, but with the KFL1-4 I've never been able to align 40m such
that I could get the same power output on both ends of the band.  In
fact, if I aligned the KFL1-4 for 7 watts out at 7070 kHz, I was lucky
to be able to get 2 watts out at 7150 kHz, and 5 watts at 7000 kHz. 
Changing these two caps now allow my K1 to produce very near maximum
power all through the 170 kHz tuning range on 40m.  

(4)  Installed the new RFC9 in the attenuator relay circuit to eliminte
pop on switching.

(5)  Installed the new RFC8 in the 12v supply to the low level
transmitter stages, as recommended by Elecraft if an 80m board is to be
used.  I haven't started on rebuilding an old two band KFL1 for 80m/17m
yet, but I have parts now for those bands.  I can't think of any reason
not to have RFC8 in the circuit, even though the new K1 kits have a
jumper installed in its place unless an 80m board is to be used.

Anyway, my old K1 is back and better than ever.  Great rig!

Mike / KK5F