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k2 vco alignment

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kc2vmp

k2 vco alignment

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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Don Wilhelm-4

Re: k2 vco alignment

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
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

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kc2vmp

Re: k2 vco alignment

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 <[hidden email]> 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
>> ______________________________**______________________________**__
>> Elecraft mailing list
>> Home: http://mailman.qth.net/**mailman/listinfo/elecraft<http://mailman.qth.net/mailman/listinfo/elecraft>
>> Help: http://mailman.qth.net/mmfaq.**htm<http://mailman.qth.net/mmfaq.htm>
>> Post: mailto:[hidden email].**net <[hidden email]>
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
>>
>

Christophe F8ACF-56

Re: k2 vco alignment

In reply to this post by kc2vmp

goodnight,

I made a mistake for "T5", I put the black toroid "T3" while they should be yellow are both the same size only the color differentiated

If this can help you.

73 F8ACF K2 # 7369

73 , Christophe F8ACF-56

________________________________
De : Rob Gault <[hidden email]>
À : elecraft <[hidden email]>
Envoyé le : Samedi 28 septembre 2013 22h16
Objet : [Elecraft] k2 vco alignment

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
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html