[Elecraft] Temp Compensation cct adjustment

[Ron ZL1TW]

Hi ,
          In an earlier posting I admitted to being somewhat disappointed 
with the Temperature compensation circuit, and it wasn't until a thread 
about the PLL range having to be a lot smaller than I had mine for it to 
work properly, that I realized what my problem was.
In my K2 , changing L31 back to 10uH reduced my PLL range from 24.89Khz to 
10.64kHz ,(YMMV),and at that stage the drift of my rig was considerably better.
However, after a bit of correspondence with it's designer, ( John KI6WX) I 
was encouraged to have a go at "fine tuning" the circuit to minimize drift 
further.
This procedure is outlined at the end of the Installation Instructions for 
the kit, and involves changing the value of one resistor ( RA) and is a 
relatively simple operation. The hardest part, if you have the DSP or KAF2 
installed is the removal of the filter, and the Control board, to be able 
to get to resistor "RA" which is installed parallel on the top of the 
Temperature compensation board.
It was a simple matter from there to heat each end of the resistor with the 
iron and gently remove it, one end at a time.
Replacement is simple and doesn't require cleaning the holes out. I just 
shaped the legs of the resistor I was trying and cut them short, then 
heated each end and slid the legs into the holes. A wee touch of solder and 
it was all done.
My next step may raise a few eyebrows, but I then reassembled the radio 
except for the KPA100, and *GENTLY*  heated the inside of the set with the 
XYL's hair dryer while monitoring WWV  with the "spot" tone activated. That 
gave me a *ROUGH* idea of how the circuit was working with that value resistor.
After a few subsitutions I ended up using a 39k resistor for "RA".
I re-installed the KPA100 and did tests with the set being driven into a 
dummy load to apply the heat this time.
The results were most gratifying.
  After allowing for a small amount of drift after initial boot-up, the set 
will now drift down about 10hz when the PA is heated to the point where the 
fan comes on, which is heaps better than it ever has been. Subsequent 
cooling and heating produced the same results.
  To finish the job, I used Wayne N6KR's method to set C22, and am pretty 
confident that my K2 is now calibrated about as accurate as I will ever get it.
73......Ron ZL1TW      ( cu EQP ?)


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