Fwd: [Elecraft] KPA100 Failing to Produce High Power

Fri Jun 1 10:47:31 EDT 2007

Don and others who responded - thanks!  

(1) its hard to fix what isn't broke
(2) i have been using this rig many years ....
(3) somehow i falsely believed i could tweak the power
knob BEFORE hitting TUNE
(4) maybe i hard time believing i assembled this board
without any issues! 
(5) the two button routine to transmit full power is
actually nifty !  

my rig does produce 100 watts!  

i do notice the finals are too hot to touch when
transmitting, but they cool in a few seconds when
transmit ceases.  maybe this is normal (i have never
touched an operational 50 watt device before).  i
guess i need to find where the K2 will tell me its
temperature to see if all is well.    

73, curt

--- Don Wilhelm <w3fpr at earthlink.net> wrote:

> Curt,
> 
> How are you attempting to initiate transmit?  If you
> ae pressing TUNE, 
> then 20 watts is what should be produced - the
> KPA100 firmware limits 
> TUNE to 20 watts.  If you need to try at a higher
> power than that, you 
> must press TUNE and DISPLAY together.
> 
> OTOH, if you are already doing TUNE/DISPLAY, then
> check the KPA100 LPF 
> toroids for the correct number of turns - count the
> nmber of times the 
> wire passes through the center of the core.
> 
> 73,
> Don W3FPR
> 
> Curt Milton wrote:
> > I did some additional troubleshooting, but maybe
> there
> > is nothing unusual in these bias measurements?
> > 
> > Bias       Rx        Tx
> > D11       13.7    0.7
> > D12       0.7    129
> > D13       13.7   0.2
> > D14       0.7   129
> > Q1/2 base  0    0.6 
> > 
> > Still puzzled as why rig is limited to around 20w
> > output.  Current draw is proportional to RF power
> > output, as above 20w setting rig will neither draw
> > additional current nor output additional power.  
> >     
> > --- Curt Milton <wb8yyy at yahoo.com> wrote:
> > 
> >> Has anyone experienced this problem, or know if I
> >> should troubleshoot the bias, input, or output
> >> circuitry.  All is well with the low power bypass
> >> path, and rig seems to work up to around 25 watts
> >> output.  
> >> --- Curt Milton <wb8yyy at yahoo.com> wrote:
> >>
> >>> Date: Sun, 27 May 2007 12:08:40 -0700 (PDT)
> >>> From: Curt Milton <wb8yyy at yahoo.com>
> >>> To: elecraft at mailman.qth.net
> >>> Subject: [Elecraft] KPA100 Failing to Produce
> High
> >>> Power
> >>>
> >>> All has been well up until now, including
> setting
> >>> the
> >>> bias per instructions.  Without PA's my bias
> >> current
> >>> was 330 mA, so I successfully set it for 730 mA
> >> with
> >>> the PA's.  
> >>>
> >>> I had adjusted R26 for 5w and got the VSWR
> sensor
> >>> zeroed.  During my high power test (into a
> matched
> >>> antenna on a clear channel into a good antenna)
> my
> >>> VSWR is reading 1.2 on the K2 and similar on my
> >>> external meter.  When I transmit the PA devices
> do
> >>> get
> >>> very hot (too hot to touch after about 10
> seconds)
> >>> but
> >>> they quickly cool (maybe around 5 seconds or
> less)
> >>> after transmit ceases.  
> >>>
> >>> Here is the behavior i am getting.  First column
> >> is
> >>> K2
> >>> power setting (on 20m), second is what the K2
> >> reads
> >>> on
> >>> transmit, and third is my meter.  My meter is
> not
> >>> state of the art but it is reasonable with my
> >> other
> >>> rig.  
> >>>
> >>> K2 Setting        K2 Indicated       Meter
> >>>
> >>> 15                15                 20
> >>> 20                20                 28
> >>> 25                25                 30
> >>> 30                23                 28
> >>> 35                22                 30
> >>> 40                22                 35
> >>> 50                23                 32
> >>>
> >>> Thinking that maybe R26 was way off, i set the
> K2
> >>> for
> >>> 40 watts and tried to adjust R26 to read 40
> watts
> >> -
> >>> no
> >>> this got me no where.  
> >>>
> >>> I tried to operate on different bands with two
> >>> different antennas.  Same impact on all bands,
> >>> except
> >>> it has even lower output on 10m.  
> >>>
> >>> Troubleshooting suggestions appreciated!  
> >>>
> >>> 73, Curt
> >>
> >>
> >>  
> >>
> >
>
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> > 
> > 
> >        
> >
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