[Elecraft] K-2 /100 Power Output Drop

[Dennis Utley - AF7Y]

Thank you for your response to my post, Don.  I did some more checking with a
watt meter that works better at QRP levels and found I don't have the power
drop below 10 watts.  Following  your suggestion I also tested the radio in
CW, and Tune modes.  The results are as follows:

CW
====
Power Set at       Actual Power 

110                    69
80                      49
50                      26

Tune
=======
106                    62
87                      49
50                      26

SSB
=====
100                   100 for a couple of seconds when cold
80                     40
47                     28
40                     18

The failing stage would seem to be the 100 watt amp board. 

It's surprising the "set power" and output readings are so different from CW
to TUNE modes.

Are there any adjustments on the PA board that might account for the power
out deficit?

Thanks for your input on my problem, and judging by your many posts, you
also help many others..

73
Dennis, AF7Y
===========

quote author="Don Wilhelm-4">
Dennis,

Such a problem is usually caused be a poor solder connection somewhere.  
The challenge is to find where.
You indicated this problem occurs on SSB.  What about CW?  Does it do 
the same thing?  How about when you do a TUNE?
If the problem occurs during a TUNE, then it will be easy to find the 
offending stage by the procedure below, but if it happens only on SSB, 
then we should look at the KSB2 board.

Since the problem occurs when the power is set to less than 11 watts, it 
is likely in the base K2, so remove the KPA100 and test only the base K2 
without the KPA100 attached.  If it does the same thing, then you should 
construct the RF Probe from the parts provided with your K2 kit (or tell 
us that you have an oscilloscope available), so you can trace through 
the transmit chain "backwards" and find the stage where the power is steady.

Let us know if my "guesses" are correct (please answer the questions 
above), and we can lead you to the failing stage, and after that you can 
find the failing component.

73,
Don W3FPR

Dennis Utley - AF7Y wrote:
> First the good news.  The receiver seems to be working well, even transmit
> power is
> at a full 100 watts (for a few seconds).  Then output drops quickly 
> to 50 watts.  Thats the bad news.
>
> I can set the power knob for output from 110 down to QRP power, and the
> first
> few seconds of transmission are at the selected power.  After the
> first few seconds power goes instantly to almost exactly 50% of what
> was manually selected.   100 watts becomes 50, 60 watts becomes 30,
> and 40 watts becomes 20 watts prox, (Peak indicated power on a
> calibrated digital peak reading  meter.)  (Model P-3000 by RF
> Applications, digital readout into dummy load on 40 meters.
> Indicating 1/1.  Same behavior if input to 1.1/1 SWR 40 meter beam.
>
> After this 50% drop, transmission continues normally, quality reports
> are good, and all is well, except my power is 50% of what it should be. 
>
> Maximum power after a few seconds of transmission is only about 55 watts
> Peak
> SSB.
>
> If I turn the radio off and wait a few moments.  It will again output
> full 100 watts peak SSB output for a few seconds then drop to 50%.
>
>   
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