[Elecraft] K2/KPA100 40M SSB ALC Problem?

[Don Wilhelm]

The conditions you describe are almost identical to the behavior 
experienced when the KI6WX SSB Increased RF Gain mod is added to the 
KSB2 board, *and* the KPA100 is also in-line.  The result of that 
combination is that there is more overall RF gain than the KSB2 ALC 
circuits can handle.  Your K2/100 may have a bit more available RF gain 
on 40 meters than the average K2.

The fix for the above is to change the KSB2 board ALC.  1) Cut the trace 
on the top of the board between P1 pin 6 and the base of Q1.  2) Install 
a 1k resistor over the previous cut (between P1 pin 6 and the base of 
Q1).  3) Change the value of R9 to 1.5k.  These changes were first 
suggested by Gary Surrency of Elecraft support.

You gentlemen may wish to try this even if you do not have the KI6WX mod 
installed.  I do not believe it will cause any other difficulties.

It is a mystery to me why the situation is not present with the display 
in ALC mode, but then I am not familiar with all the internal workings 
of the KSB2 firmware.  My guess is that the slight additional load 
provided when monitoring the ALC level is sufficient to control the 
overdrive.

73,
Don W3FPR

douglas.maxwell at virgin.net wrote:
> Hi All,
> My K2 ser no. 4688 and KPA100 bought 11/07 work FB on cw.
> On 40m SSB I have noticed a fault condition with my KPA100. On power cycle or mode change, if the power control is not set to maximum, but set so the KPA100 is 'in-line' say 20w. The power output by the KPA100 will be the full power output i.e. 100w and not 20w. This is correctly indicated on the K2 power meter accompanied with voice peaks coming through the speaker.
> You can imagine the problems this causes if driving an amplifier.
> This fault condition can be cured by doing either of the following:
> 1) Select ALC function on the K2 meter.
> 2) Whilst talking into the microphone vary the power ctrl to full then back down to the required power level.
> In both cases the ALC suddenly wakes up and brings the power down to 20w.
> The worrying thing is that I described this fault condition to another similar ser no K2 owner and he tried and found the same thing happening on his. It's early days yet and we have yet to get together and really nail down the similarities, but I ask you what hardware problem could be sorted by a simple front panel key press? I hesitate before suggesting this is a firmware problem as so many owners have not noticed this before. Please could any K2 owners of a similar ser no try this simple test and post their findings?
> Doug GM0ELP
>  
>  
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