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

[O. Johns]

Dear Don,

Nice tip.  Thank you.  Do you or does anyone have a pointer to the  
place where Gary Surrency describes this mod and what in detail it  
does?  If one does the KI6WX "Increased RF Gain" mod, and also puts a  
2.2K resistor across R1 as described in KI6WX's "KSB2 Reduced  
Intermodulation Distortion Modification", is the mod you describe  
below still a good idea?  Or at least not a bad one?  I have a 10 watt  
K2 that may or may not ever have the 100 watt amplifier.

And welcome back.

73,
Oliver Johns W6ODJ

On 25 Feb 2008, at 5:31 AM, Don Wilhelm wrote:

> 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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