[Elecraft] KPA100 Failing to Produce High Power

[Curt Milton]

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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