[Elecraft] KPA100 SSB power control

[Don Wilhelm]

Trevor,

That behavior may be indicitive of a BIG oscillation in the KPA100, and the
KPA100 throttles the power back to protect itself.  In other words, it may
not be a power control problem after all - check carefully to determine the
real cause.  OTOH, it COULD be a power control problem, but check the
following first.

One thing to look at first is the presence of a high SWR condition
reported - if that occurs, it is confirmation that the KPA100 is oscillating
out of band (it will not be seen when working into a dummy load).  If you do
find a Hi Refl situation, first check the orientation of Q6 and Q7 in the
KPA100.

Then check to be certain you have the latest upgrade to your KPA100,  If
there is no R12 resistor mounted and L15 is not installed, then you have the
latest upgrade.  Change C31 to a .22 uF capacitor (you can obtain one from
mailto:parts at elecraft.com).

CAUTION:  If you have a KPA100 without these latest upgrades, DO NOT change
C31 to this new capacitor - the older design requires a 200 volt or greater
capacitor and the new capacitor from Elecraft is only rated at 100 volts.
The change of C31 is only to go with the new upgrade, it is not for
unupgraded KPA100s.

73,
Don W3FPR

> -----Original Message-----

>
> I have just installed a recently constructed KPA100 (including
> the latest upgrades)
> and appear to have run into the erratic power control problem.
>
> Using Tune + Display and an external LP100 meter, if I request 5w
> I get 5w out.
> Increasing power to 11w so as to engage the pa I also get 11w out
> - so all seems
> fine.
>
> Switching to SSB, and speaking steadily into the mic, at a
> requested 5w I get
> approximately 5-7w out on each band.
> However increasing the power to 11w I get the following:
>
> 80m  Req 11  Get 45
> 40m  Req 11  Get 80
> 20m  Req 11  Get 25
> 15m  Req 11  Get 30
> 10m  Req 11  Get 20
>
> Reading back through the archive I see that others have
> encountered the same
> problem but cannot see a definitive answer to the problem. Anyone
> have any
> thoughts as to where to start looking.
>
> 73 to all
> Trevor  G0KTN
>
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