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KPA100 D16/D17 still blowing

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NZ0T

KPA100 D16/D17 still blowing

Hi all,

Since adding a KAT100 to my K2/100 about a month ago D16 and D17 in the
KPA100 have blown 3 times. The first time I thought it was caused by
antenna static buildup during a blizzard but the last 2 times it happened as
the tuner was attempting to tune an antenna. Could there be problem with
the tuner that is causing this? Everything is well grounded and the
antennas are not bedsprings but a G5RV and twin sloper.

I'm getting real tired of replacing those diodes!

73,

Bill NZ0T

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Don Wilhelm-4

Re: KPA100 D16/D17 still blowing

Bill,

That is not normal - BUT -
Before I can offer a single suggestion, can you say whether your KPA100
is the older T/R switch design or is it a KPA100 that shipped after Nov
2006? If it is the older design, has it been updated with the
KPA100UPKT - and if it has been updated, was C31 also changed to 0.22 uf?

*If* you have the older T/R switch design, there is a possibility of a
parasitic that can show up during tuning, particularly on 40 meters.
With the new design, *if* C31 was not changed to 0.22 uf, there is a
possibility of a low frequency oscillation that shows up when operating
on 160 or 80 and sometimes on 40 meters. It might be possible for an
oscillation to create a sufficiently high RF voltage to zap the diodes
during a tuning cycle of the KAT100. (Note that there are many 'ifs'
here, thus the reason for the questions to be answered - it depends on
the level of your KPA100).

If your KPA100 is the older design, I suggest the KPA100UPKT may cure
the diode zapping, but if you already have the update (including the new
C31), then there is some other problem.

73,
Don W3FPR

Bill Carpenter wrote:

> Hi all,
>
> Since adding a KAT100 to my K2/100 about a month ago D16 and D17 in
> the KPA100 have blown 3 times. The first time I thought it was caused
> by antenna static buildup during a blizzard but the last 2 times it
> happened as the tuner was attempting to tune an antenna. Could there
> be problem with the tuner that is causing this? Everything is well
> grounded and the antennas are not bedsprings but a G5RV and twin sloper.
>
> I'm getting real tired of replacing those diodes!
>
> 73,
>
> Bill NZ0T
>

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Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
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Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

NZ0T

Re: KPA100 D16/D17 still blowing

My amp is the older design shipped in August, 2006 but the KPA100UPKT was
installed. If the new C31 was part of that kit it's in there but if not I
don't think it is. Question - would it make sense to tune at low power
until I figure out the problem? I'm thinking that would avoid blowing the
diodes and still allow me to use my new KAT100.
----- Original Message -----
From: "Don Wilhelm" <[hidden email]>
To: "Bill Carpenter" <[hidden email]>
Cc: "elecraft list" <[hidden email]>
Sent: Monday, January 07, 2008 8:19 PM
Subject: Re: [Elecraft] KPA100 D16/D17 still blowing

> Bill,
>
> That is not normal - BUT -
> Before I can offer a single suggestion, can you say whether your KPA100 is
> the older T/R switch design or is it a KPA100 that shipped after Nov 2006?
> If it is the older design, has it been updated with the KPA100UPKT - and
> if it has been updated, was C31 also changed to 0.22 uf?
>
> *If* you have the older T/R switch design, there is a possibility of a
> parasitic that can show up during tuning, particularly on 40 meters. With
> the new design, *if* C31 was not changed to 0.22 uf, there is a
> possibility of a low frequency oscillation that shows up when operating on
> 160 or 80 and sometimes on 40 meters. It might be possible for an
> oscillation to create a sufficiently high RF voltage to zap the diodes
> during a tuning cycle of the KAT100. (Note that there are many 'ifs'
> here, thus the reason for the questions to be answered - it depends on the
> level of your KPA100).
>
> If your KPA100 is the older design, I suggest the KPA100UPKT may cure the
> diode zapping, but if you already have the update (including the new C31),
> then there is some other problem.
>
> 73,
> Don W3FPR
>
> Bill Carpenter wrote:
>> Hi all,
>>
>> Since adding a KAT100 to my K2/100 about a month ago D16 and D17 in the
>> KPA100 have blown 3 times. The first time I thought it was caused by
>> antenna static buildup during a blizzard but the last 2 times it happened
>> as the tuner was attempting to tune an antenna. Could there be problem
>> with the tuner that is causing this? Everything is well grounded and the
>> antennas are not bedsprings but a G5RV and twin sloper.
>>
>> I'm getting real tired of replacing those diodes!
>>
>> 73,
>>
>> Bill NZ0T
>>
>

Don Wilhelm-4

Re: KPA100 D16/D17 still blowing

Bill,

Unfortunately, the new C31 value has not yet been included in the
KPA100UPKT BOM.
Send a request to [hidden email] and ask for one. It is important
to install it - in some updated KPA100s, the old C31 value is not great
enough to act as an effective bypass and the KPA100 will self-oscillate
(often at full power) at a frequency somewhere between 600 and 800 kHz.
The oscillation will usually start when there is a high SWR present (and
that situation does occur when the KAT100 is searching for a match).

73,
Don W3FPR

Bill Carpenter wrote:

> My amp is the older design shipped in August, 2006 but the KPA100UPKT
> was installed. If the new C31 was part of that kit it's in there but
> if not I don't think it is. Question - would it make sense to tune at
> low power until I figure out the problem? I'm thinking that would
> avoid blowing the diodes and still allow me to use my new KAT100.
> ----- Original Message ----- From: "Don Wilhelm" <[hidden email]>
> To: "Bill Carpenter" <[hidden email]>
> Cc: "elecraft list" <[hidden email]>
> Sent: Monday, January 07, 2008 8:19 PM
> Subject: Re: [Elecraft] KPA100 D16/D17 still blowing
>
>
>> Bill,
>>
>> That is not normal - BUT -
>> Before I can offer a single suggestion, can you say whether your
>> KPA100 is the older T/R switch design or is it a KPA100 that shipped
>> after Nov 2006? If it is the older design, has it been updated with
>> the KPA100UPKT - and if it has been updated, was C31 also changed to
>> 0.22 uf?
>>
>> *If* you have the older T/R switch design, there is a possibility of
>> a parasitic that can show up during tuning, particularly on 40
>> meters. With the new design, *if* C31 was not changed to 0.22 uf,
>> there is a possibility of a low frequency oscillation that shows up
>> when operating on 160 or 80 and sometimes on 40 meters. It might be
>> possible for an oscillation to create a sufficiently high RF voltage
>> to zap the diodes during a tuning cycle of the KAT100. (Note that
>> there are many 'ifs' here, thus the reason for the questions to be
>> answered - it depends on the level of your KPA100).
>>
>> If your KPA100 is the older design, I suggest the KPA100UPKT may cure
>> the diode zapping, but if you already have the update (including the
>> new C31), then there is some other problem.
>>
>> 73,
>> Don W3FPR
>>
>> Bill Carpenter wrote:
>>> Hi all,
>>>
>>> Since adding a KAT100 to my K2/100 about a month ago D16 and D17 in
>>> the KPA100 have blown 3 times. The first time I thought it was
>>> caused by antenna static buildup during a blizzard but the last 2
>>> times it happened as the tuner was attempting to tune an antenna.
>>> Could there be problem with the tuner that is causing this?
>>> Everything is well grounded and the antennas are not bedsprings but
>>> a G5RV and twin sloper.
>>>
>>> I'm getting real tired of replacing those diodes!
>>>
>>> 73,
>>>
>>> Bill NZ0T
>>>
>>
>
>
>
>