Fwd: [Elecraft] KPA100 Failing to Produce High Power

[Curt Milton]

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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