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

Tue May 6 00:07:31 EDT 2008

Oliver,

The KSB2 ALC mod was documented by Gary Surrency way back ??when??.  You 
will have to search the archives for it.  My normal link through Swerre 
Holms Unofficial Mod page is not working right now.

The ALC mod is independent of the KI6WX IMD mod.

Do not install either unless you have installed the KI6WX KSB2 Increased 
Gain mod.

73,
Don W3FPR

O. Johns wrote:
> 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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>>>
>>>
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