Fwd: [Elecraft] KPA100 Failing to Produce High Power

[Curt Milton]

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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