Fwd: [Elecraft] KPA100 Failing to Produce High Power

[Don Wilhelm]

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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