Bill,
Unfortunately, the new C31 value has not yet been included in the
KPA100UPKT BOM.
Send a request to [EMAIL PROTECTED] 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" <[EMAIL PROTECTED]>
To: "Bill Carpenter" <[EMAIL PROTECTED]>
Cc: "elecraft list" <elecraft@mailman.qth.net>
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
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