[Elecraft] k2 vco alignment

[Rob Gault]

Don,

Thank you, with this it only took me 3 minutes to fix it with this info.
 The coverage on T5 was the critical factor here.

The good news is that I've spent the last 4 hours confirming that
EVERYTHING else around the VCO is correct!

73, Thanks again!
kc2vmp


On Sat, Sep 28, 2013 at 5:11 PM, Don Wilhelm <w3fpr at embarqmail.com> wrote:

> 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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