[Elecraft] k2 vco alignment

[Don Wilhelm]

Rob,

There is either too much inductance or too much capacity in the VFO 
circuit - the high voltage means that the K2 is trying to reduce the 
capacity to bring things into line.

Count the turns on T5 very carefully.  Each wire through the center 
counts as one turn - a full wrap around the core equals 2 turns.

If the T5 turns are correct, spread the red turns of T5 out as much as 
possible to see if that resolves the problem.

Worst case, you may have to remove a turn from T5.

BTW, if you discover an extra turn on T5, you might want to count the 
turns on the other toroids you have wound to be certain they contain the 
right number of turns.  Winding an extra turn on toroids is not uncommon 
for builders with limited experience in winding toroids.

73,
Don W3FPR

On 9/28/2013 4:16 PM, Rob Gault wrote:
> K2 #7449 VCO alignment difficulty.
>
> Cannot get 4.0 MHz R30 voltage to change at all - it measures 7.97V.  Have
> confirmed all the cap values, varicap diodes are correct parts, T5 wound
> and wired correctly.
>
> Have scoped the area comparing to a second operational K2 & the wave forms
> look and behave the same as the rigs are tuned. The voltage on R30 is
> simply too high at 4.0 MHz.
>
> I set the K2 to 3.5MHz and adjusted L30 for the lowest voltage, this gave
> the following results:
>
>   3.50   4.14    4.00    7.97
>   7.00   4.39    7.30    6.30
> 10.00   5.08   10.15    5.86
> 14.00   3.84   15.00    5.98
> 18.00   4.42   18.20    4.67
> 21.00   3.83   21.45    5.38
> 24.80   5.92   25.00    6.40
> 28.00   4.64   28.80    5.66    (29.70   6.87)
>
> Should I continue the build or what else should I check?
>
> THANKS & 73,  Rob  KC2VMP
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