http://elecraft.85.s1.nabble.com/K2-frequency-adjustment-tp445744p445745.html
> Today I decided to recalibrate my K2 using a very accurate
> 10MHz source, as well as replacing C31 in the KPA100 (Rev. D)
> to bring it up to the latest Rev. E.
>
>
>
> After leaving both the 10MHz source and the K2 turned on all
> day to stabilise, I made a start but the first problem
> encountered was that the filters were just too darned good
> and wouldn't let me find zero-beat. Plenty 10MHz signal was
> available and the S-meter lit up with a full line of li'l
> green apples, but as zero beat was approached, both the
> S-meter reading and audio dropped out of sight.
>
>
>
> To get round this problem, I altered the LSB widest filter
> (2.4kHz - OP 1) down in frequency and found a healthy S-meter
> reading could be maintained. The low beat note could both be
> seen (highest LED flickering in time with the beat) and heard
> as a slow rise and fall in background noise.
>
>
>
> Unfortunately, I was distracted by an artefact that appeared
> only when an SSB filter was selected with no antenna
> connected. There was a crackling/crunching sort of noise
> that was not present on any CW setting or filter. During the
> hunt for the culprit, I found that if a finger was dabbed on
> the cathode of D4 (DSB output from BM to xtal filter) the
> problem cleared up. Also, if a finger was dabbed on T2, the
> problem went away. Further finger-dabbing along the xtal
> filter was unhelpful as I was acting as an antenna.
> Soldering was checked and re-done but the problem remained,
> so D4 bit the dust and was replaced with a new 1N4148. No
> improvement.
>
>
>
> Ah well, time was passing, so I thought I'd return to the
> calibration task. No problems were encountered and the task
> was completed successfully. CAL PLL was followed by a CAL
> FIL where the adjusted LSB filter was returned to its
> previous setting and all other filter settings were moved
> around before restoring them to their original settings. I
> noted the last digit of the BFO frequency had decremented by
> 1 in every case.
>
>
>
> After this, I was pleased to note that the nasty background
> noise previously heard when SSB was selected had disappeared,
> so I'm thinking it was an artefact caused by everything
> warming up and drifting. Now I shall check tomorrow to see
> if the artefact has moved and is present when the rig is cold.
>
>
>
> Changing C31 in the KPA doesn't appear to have made any
> difference to its operation, so what was it for? The PA's
> power output reading still tends to jitter around by +/-10%
> or so when running into a high quality 50 ohm dummy load.
>
>
>
> 73 DaveL G3TJP
>
>
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