Werner,
If you look at the new KPA100 schematic and parts list (download the new
manual), you will see that C31 has a value of 0.22 uF. The KPA100UPKT
instructions tell you to change the value on the schematic, but there is
no new C31 included with the kit.
In fact, I was directly involved with testing the newer T/R switch
design for the KPA100 as a Field Tester and afterward I discovered the
C31 problem. Some KPA100s will oscillate at 600 to 800 kHz with the old
value C31 installed. I had one of the first updated KPA100 that had
those symptoms on my workbench and found that C31 was not acting as an
effective bypass, so the updated value was included for all new
KPA100s. It has not made it into the KPA100UPKT yet, but it should be soon.
Not all KPA100s show this problem, but many do, so it is best to change
C31 while you are adding the KPA100UPKT.
If you do not want to wait for the part from Elecraft, you can use most
any 0.22 uF cap rated at 50 volts or more - even 2 0.1 uf caps in
parallel (one on top of the board, the other on the bottom) will work
just fine too.
73,
Don W3FPR
Dr. Werner Furlan wrote:
Where did you get this information? In my KPA 100 Kit C31 was 0.033 µV
and in the latest manual and in the upgrade kit diagram it is also a 0.033 µV
(33N).
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