KAT3 L10 burned

[Giulio Pico - IW3HVB]

Yesterday I paid a visit to a firnd, Giancarlo I3GKK, who was very
worried about an accident happened 3 days ago.
Suddenly, during a brief tx period (10 seconds) at 100 W into a Windom
antenna, he saw smoke coming out from the top panel of his K3.
Since then no power out on all bands (measured with an external wattmeter).
The internal wattmeter of the K3 reads correctly and the supply current
is regular, on both high and low power, so it seems that the TX stages
are ok.
Looking into the area for smoky parts I found that L10 (96 nH), at the
output of the KAT3 unit is badly burned. The enamel on the wire is gone
and with the ohmmeter the inductance measures more than 7 ohms :-/
My guess is that SWR was a little too high, but within the tuning range
of the KAT3. It was raining heavily when the fault has occoured.
Measured the antenna with the MFJ-259B and it seems almost ok on all
bands (less than 2 in the worst band, all the others less than 1.4).
Anyone have had similar experiences?

73 de Giulio IW3HVB

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[Ken Wagner K3IU]

Good Morning Guilio:

This is not an uncommon failure. About six(6) months ago the fix was to
remove L10 and jumper the holes where L10 was installed with a suitable
piece of wire. I did that on mine and have had no problems with it since.

Be sure to email [hidden email]. There may be another fix now
that I don't know about.

73,
Ken K3IU
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

On 1/6/2010 6:55 AM, Giulio Pico - IW3HVB wrote:

> Yesterday I paid a visit to a firnd, Giancarlo I3GKK, who was very
> worried about an accident happened 3 days ago.
> Suddenly, during a brief tx period (10 seconds) at 100 W into a Windom
> antenna, he saw smoke coming out from the top panel of his K3.
> Since then no power out on all bands (measured with an external wattmeter).
> The internal wattmeter of the K3 reads correctly and the supply current
> is regular, on both high and low power, so it seems that the TX stages
> are ok.
> Looking into the area for smoky parts I found that L10 (96 nH), at the
> output of the KAT3 unit is badly burned. The enamel on the wire is gone
> and with the ohmmeter the inductance measures more than 7 ohms :-/
> My guess is that SWR was a little too high, but within the tuning range
> of the KAT3. It was raining heavily when the fault has occoured.
> Measured the antenna with the MFJ-259B and it seems almost ok on all
> bands (less than 2 in the worst band, all the others less than 1.4).
> Anyone have had similar experiences?
>
> 73 de Giulio IW3HVB
>
> ______________________________________________________________
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>
>    

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[Julius Fazekas n2wn]

I've not seen such an issue with two different KAT3s and significantly worse mismatches.

What is the cause of the problem?

73,
Julius

<quote author="Ken Wagner K3IU">

"This is not an uncommon failure."

[Ken Wagner K3IU]

I'm not sure. When I spoke to Gary, he said there had been quite a few
instances of failure of this and/or the capacitor in this IF frequency trap.
73,
Ken K3IU
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
On 1/6/2010 8:37 AM, Julius Fazekas n2wn wrote:

> I've not seen such an issue with two different KAT3s and significantly worse
> mismatches.
>
> What is the cause of the problem?
>
> 73,
> Julius
>
>
>
> "This is not an uncommon failure."
>
> -----
> Julius Fazekas
> N2WN
>
> Tennessee Contest Group
> http://www.k4ro.net/tcg/index.html
>
> Tennessee QSO Party
> http://www.tnqp.org/
>
> Elecraft K2/100 #4455
> Elecraft K3/100 #366
> Elecraft K3        #1875
>    

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[wayne burdick]

Giulio,

The load impedance was probably extremely low, and at full power on  
this particular band, the power-handling capacity of the 8.2-MHz IF  
trap was exceeded. It's possible that the trap was mistuned (too close  
to 40 or 30 m). Note that L10's winding is adjusted at the factory and  
should not be moved.

If you contact support, replacement components (L10 and the associated  
capacitor) will be sent out immediately. Support can also explain how  
to adjust the trap to 8.2 MHz (or the parts may be pre-calibrated as a  
pair -- they'll let you know).

As a precaution, I will also be modifying the ATU matching algorithm  
so that it catches this case, preventing excessive reflected power  
that could damage the trap. I'm guessing that the load SWR was in  
excess of 10:1 or 15:1 at the time -- the KAT3 has a *very* wide  
matching range, and probably presented something close to 1:1 to the  
transmitter.

73,
Wayne
N6KR

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[Paul Kirley]

I certainly hope that this modified algorithm will not prevent me
from using my inverted vee (fed with ladder line) on some bands.
My trap hasn't fried (a year and a half), and I'd rather replace
it repeatedly--or bypass it--than be forced off some bands.

I'm surprised that it's at the output rather than at the input of
the KAT3.

73, Paul W8TM
K3 #1322


Wayne N6KR sed:
As a precaution, I will also be modifying the ATU matching algorithm  
so that it catches this case, preventing excessive reflected power  
that could damage the trap.

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[David Woolley (E.L)]

Julius Fazekas n2wn wrote:
> I've not seen such an issue with two different KAT3s and significantly worse
> mismatches.

How do you measure the degree of mismatch?  A mismatch has two
dimensions, one of which (reactance) can be positive or negative, and
the other can be high or low.



--
David Woolley
"we do not overly restrict the subject matter on the list, and we
encourage postings on a wide range of amateur radio related topics"
List Guidelines <http://www.elecraft.com/elecraft_list_guidelines.htm>
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[Julius Fazekas n2wn]

>From the original tuning of the various antennas, in this case three different antennas for 160, 80 and 40. I know the reactance sign from my test equipment at several points in the band.

160 seems to present the most difficult challenge, particularly running during a contest. There are several spots in the band where I keep a very close eye on the PS current meter, and back off on the power to play it safe. Periodic retuning using the KAT3 helps, but the problem is at the antenna and I've not determined a satisfactory broadband fix yet...

Julius Fazekas
N2WN

Tennessee Contest Group
http://www.k4ro.net/tcg/index.html
http://groups.google.com/group/tcg1?hl=en

Tennessee QSO Party
http://www.tnqp.org/

Elecraft K2/100 #4455
Elecraft K3/100 #366
Elecraft K3/100 #1875


--- On Thu, 1/7/10, David Woolley (E.L) <[hidden email]> wrote:

> From: David Woolley (E.L) <[hidden email]>
> Subject: Re: [Elecraft] KAT3 L10 burned
> To: "Julius Fazekas n2wn" <[hidden email]>
> Cc: [hidden email]
> Date: Thursday, January 7, 2010, 3:47 AM
> Julius Fazekas n2wn wrote:
> > I've not seen such an issue with two different KAT3s
> and significantly worse
> > mismatches.
>
> How do you measure the degree of mismatch?  A mismatch
> has two dimensions, one of which (reactance) can be positive
> or negative, and the other can be high or low.
>
>
>
> -- David Woolley
> "we do not overly restrict the subject matter on the list,
> and we
> encourage postings on a wide range of amateur radio related
> topics"
> List Guidelines <http://www.elecraft.com/elecraft_list_guidelines.htm>
>

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