KPA100 operation - is this normal?

[Darwin, Keith]

I noticed some things with the KPA100 that I wasn't expecting.  Are
these normal?
 
1.  Power output fluctuated during a single CW TX session.  I'll see the
PO indicator on the K2 go up & down by 1 LED on a frequent basis (maybe
switching every few seconds).  Thinking that I was right on the edge of
an LED transition or something, I changed the power output level.  The
behavior continued at the new higher power level.  I also see the output
power on my outboard power meter change.  The changes appear to be
fairly small, maybe 10 watts at the 100 watt level.  Is this normal?
 
2.  Fan came on.  My shack is a chilly 62 degrees F.  I set the temp in
the K2 per the instructions.  During a CW QSO, the fan came on about 1/2
way through my TX session and stayed on for about 1/2 of the other guy's
TX session.  Power out was 100 watts, SWR is flat enough to not deflect
the REV meter on the Palstar.  The heat sink did feel warmer than the
room but no way I'd say it was hot.  Is this all normal or is there an
issue?
 
- Keith N1AS -
- K2 5411.ssb.100 -
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[Vic K2VCO]

Darwin, Keith wrote:

> I noticed some things with the KPA100 that I wasn't expecting.  Are
> these normal?
>  
> 1.  Power output fluctuated during a single CW TX session.  I'll see the
> PO indicator on the K2 go up & down by 1 LED on a frequent basis (maybe
> switching every few seconds).  Thinking that I was right on the edge of
> an LED transition or something, I changed the power output level.  The
> behavior continued at the new higher power level.  I also see the output
> power on my outboard power meter change.  The changes appear to be
> fairly small, maybe 10 watts at the 100 watt level.  Is this normal?

Yes, but there's a mod available to reduce the variation.  See
<http://www.ac6rm.net/mailarchive/html/elecraft-list/2003-06/msg00550.html>
and <http://www.elecraft.com/Apps/Power_Control_Mod.html>

> 2.  Fan came on.  My shack is a chilly 62 degrees F.  I set the temp in
> the K2 per the instructions.  During a CW QSO, the fan came on about 1/2
> way through my TX session and stayed on for about 1/2 of the other guy's
> TX session.  Power out was 100 watts, SWR is flat enough to not deflect
> the REV meter on the Palstar.  The heat sink did feel warmer than the
> room but no way I'd say it was hot.  Is this all normal or is there an
> issue?

Yes, I think so. See what others say.
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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[Don Wilhelm-3]

Kieth,

You can increase the value of R98 on the bottom of the RF Board to reduce
the power fluctuation, but don't go so high that the power output on the
higher bands is reduced substantially.  Some experimentation may be in
order.

The fan may come on at strange times if  the menu CAL tPA parameter is not
set correctly.   The manual tells you to set it to the room temperature in
degrees Celcius - but there is a big dependency in doing that - the heat
sink must be at the same temperature as the room.  While the heat sink will
eventually acclimate to the room temperature, it will take a bit of time.
If you want to circumvent waiting for the heat simk to acclimate, you can
measure the temperature of the heat sink itself and set CAL tPA accordingly.

73,
Don W3FPR

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

>
> I noticed some things with the KPA100 that I wasn't expecting.  Are
> these normal?
>
> 1.  Power output fluctuated during a single CW TX session.  I'll see the
> PO indicator on the K2 go up & down by 1 LED on a frequent basis (maybe
> switching every few seconds).  Thinking that I was right on the edge of
> an LED transition or something, I changed the power output level.  The
> behavior continued at the new higher power level.  I also see the output
> power on my outboard power meter change.  The changes appear to be
> fairly small, maybe 10 watts at the 100 watt level.  Is this normal?
>
> 2.  Fan came on.  My shack is a chilly 62 degrees F.  I set the temp in
> the K2 per the instructions.  During a CW QSO, the fan came on about 1/2
> way through my TX session and stayed on for about 1/2 of the other guy's
> TX session.  Power out was 100 watts, SWR is flat enough to not deflect
> the REV meter on the Palstar.  The heat sink did feel warmer than the
> room but no way I'd say it was hot.  Is this all normal or is there an
> issue?
>
> - Keith N1AS -
> - K2 5411.ssb.100 -
>

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[Ben Hofmann K1NT]

LA3ZA's K2 mod web site has the mod for the K2-KPA100
power control.

http://www.qslnet.de/member/la3za/K2/modAny.html#K2-tweak

I am currently building a KPA100, and recently picked
up a 5k pot to fool with this when I get the amp
finished.

-Ben  K1NT
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