Power Out of KPA100

[Steven Pituch]

Hi all,
I am wringing out my KPA100 and have come up with the following numbers.  I
did do the 2 capacitor mod while building the KPA100.
I used the dummy load in my MFJ-949E, which I measure at 56 Ohms.  I
connected the K2 to a Mirage MP1 Wattmeter to the KPA100 in the EC2 case, to
the KAT100, to the MFJ-949E.  I figured the KAT100 would offset the 50 Ohm
deviation in the dummy load.  For the SSB measurements I used a Kenwood MC43
mic.  The number in "" is the requested power from the K2.   For SSB, for
this very scientific test ;o) I said "Ahhhhh" into the mic.

SSB
80M 3773 100W "80"
40M 7251 100W "99"
30M 10114 90W "110"
20M 14290 70W "110"
17M 18136 100W "90"
15M 21350 110W "100"
12M 24950 100W "110"
10M 28400 100W "110"

CW
80M 3600 105W "60"
40M 7050 110W "70"
30M 10115 98W "110"
20M 14050 100W "70"
17M 18080 100W "70"
15M 21100 100W "60"
12M 24900 100W "60"
10M 28050 110W "70"

Scott at Elecraft sent me 2 new low inductance resistors just in case, but I
already replaced the 2 caps with higher values (5600 pf), and didn't save
the old caps.  But then again that was for a fix for 20M and 17M.

I repeated the SSB 30M and 20M test without the KAT100 in line and got the
same results.  So it looks like 30M and 20 M output is a little low on SSB,
but is fine on CW.

Any comments?

Thanks,
Steve, W2MY






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[Don Wilhelm-3]

Steve,

Put in the new resistors Scott sent to you (yes, the 5600 pf capacitors can
stay) and then calibrate the wattmeters in the KPA100 and the KAT100 and you
should be all set.  If you can buy, beg, borrow or otherwise acquire a good
50 ohm non-reactive dummy load you will find the wattmeter calibration much
more accurate.  I recommend using an RF Probe to measure the RF Voltage at
the dummy load rather than relying on any wattmeter - even the best are
spec'ed for only 5% of full scale when properly calibrated, so on a 100 watt
scale, even the best can be off by as much as 5 watts - the run of the mill
wattmeters can only be trusted to 20% of full scale (20 watts possible error
on a 100 watt scale) until proven otherwise.

73,
Don W3FPR


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

> Hi all,
> I am wringing out my KPA100 and have come up with the following
> numbers.  I
> did do the 2 capacitor mod while building the KPA100.
> I used the dummy load in my MFJ-949E, which I measure at 56 Ohms.  I
> connected the K2 to a Mirage MP1 Wattmeter to the KPA100 in the
> EC2 case, to
> the KAT100, to the MFJ-949E.  I figured the KAT100 would offset the 50 Ohm
> deviation in the dummy load.  For the SSB measurements I used a
> Kenwood MC43
> mic.  The number in "" is the requested power from the K2.   For SSB, for
> this very scientific test ;o) I said "Ahhhhh" into the mic.
>
> SSB
> 80M 3773 100W "80"
> 40M 7251 100W "99"
> 30M 10114 90W "110"
> 20M 14290 70W "110"
> 17M 18136 100W "90"
> 15M 21350 110W "100"
> 12M 24950 100W "110"
> 10M 28400 100W "110"
>
> CW
> 80M 3600 105W "60"
> 40M 7050 110W "70"
> 30M 10115 98W "110"
> 20M 14050 100W "70"
> 17M 18080 100W "70"
> 15M 21100 100W "60"
> 12M 24900 100W "60"
> 10M 28050 110W "70"
>
> Scott at Elecraft sent me 2 new low inductance resistors just in
> case, but I
> already replaced the 2 caps with higher values (5600 pf), and didn't save
> the old caps.  But then again that was for a fix for 20M and 17M.
>
> I repeated the SSB 30M and 20M test without the KAT100 in line and got the
> same results.  So it looks like 30M and 20 M output is a little
> low on SSB,
> but is fine on CW.
>
> Any comments?
>
> Thanks,
> Steve, W2MY
>
>
>
>
>
>
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> No virus found in this outgoing message.
> Checked by AVG Anti-Virus.
> Version: 7.0.338 / Virus Database: 267.9.7/60 - Release Date: 7/28/2005
>
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
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>
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> Elecraft web page: http://www.elecraft.com
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> Checked by AVG Anti-Virus.
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>

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[Steven Pituch]

Hi Don, and All,

All done.  Ken, K3IU, sent me his plots of various fixes and it convinced me
to change out the resistors.  The results seem to me to be dramatic.  Here
are the results before and after changing the resistors.

|--c80+c81=5600 pf only-------| +new r19+r20
________________________ ____________
SSB
80M 3773 100W "80" 100W "80"
40M 7251 100W "99" 100W "75"
30M 10114 90W "110" 105W "85"
20M 14290 70W "110" 100W "100"
17M 18136 100W "90" 100W "70"
15M 21350 110W "100" 105W "80"
12M 24950 100W "110" 105W "70"
10M 28400 100W "110" 105W "70"

CW
80M 3600 105W "60" 100W "60"
40M 7050 110W "70" 100W "60"
30M 10115 98W "110" 100W "60"
20M 14050 100W "70" 100W "60"
17M 18080 100W "70" 100W "60"
15M 21100 100W "60" 100W "60"
12M 24900 100W "60" 100W "60"
10M 28050 110W "70" 100W "60"

The fix definitely smoothed out the power on cw and ssb.  Still a dip at 20
and 30 meters, but Ken's plots show this and I get 100 W plus on all bands.

I got some hot rig here, a keeper.   I just got VC9W IOTA NA-014 on 14015,
first try with 100 Watts.  With all the techniques we have learned using 5
Watts or less, 100 Watts is like shooting fish in a barrel.  I can see how
the amp is nice for cracking really big pileups, and for traffic net work.

Someone, asked a while ago what K2 builders would have done different if
they could do it over again.  For me, I wouldn't change a thing!  The
mistakes I made were all inexpensively repairable, and I learned something
about the radio, and it gave me the confidence to know that whatever
happens, I can fix it.

I will redo the wattmeter calibrations soon for the KAT100/KPA100.  All
three of my external wattmeters were pretty close, so close enough for
government work.  I may even parallel a resistor in my MFJ-949E dummy load
to bring down the resistance a little bit.  I need to calibate my wattmeters
too with an rf probe.

Thanks to all,
Steve, W2MY
K2 #402

-----Original Message-----
From: W3FPR - Don Wilhelm [mailto:[hidden email]]
Sent: Sunday, July 31, 2005 5:29 PM
To: Steven Pituch; [hidden email]
Subject: RE: [Elecraft] Power Out of KPA100

Steve,

Put in the new resistors Scott sent to you (yes, the 5600 pf capacitors can
stay) and then calibrate the wattmeters in the KPA100 and the KAT100 and you
should be all set.  If you can buy, beg, borrow or otherwise acquire a good
50 ohm non-reactive dummy load you will find the wattmeter calibration much
more accurate.  I recommend using an RF Probe to measure the RF Voltage at
the dummy load rather than relying on any wattmeter - even the best are
spec'ed for only 5% of full scale when properly calibrated, so on a 100 watt
scale, even the best can be off by as much as 5 watts - the run of the mill
wattmeters can only be trusted to 20% of full scale (20 watts possible error
on a 100 watt scale) until proven otherwise.

73,
Don W3FPR


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