(K2) PROBLEM WITH SSB

[Michael van Hauten]

>
> Dear all,
>
> currently i work on my third K2 #5619. I have  problems with the  
> KSB2 after the ssb mod:
>
> The modulation is bad and it sounds as if there is RF in the  
> microphone line (the voice sounds modulated in it self). I use a  
> dynamic peiker mike and i have tested some other dynamic mics (eg.  
> Heil with HC4).
> The mods i have installed are the higher compression mod by  
> changing the the resistor network  to 5 single 150k resistors and  
> the other mods described by DL2FI and KI6WX.  I do not remember  
> whether the problem exists before the mod. All filters are adjusted  
> fine with the help of spectrogram and the receive sound is very  
> clear and good. I also see on my output meter a jump by slowly  
> increasing the mic input. It seems that the amplifier works not in  
> a linear mode or the alc works not correct. it seems that the sound  
> is much better on 80m than on 10 and 20m.
>
> Where is the problem? Thank you for your  help.
>
> Michael, DC0ZO
>

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[Don Wilhelm-4]

Michael,

When the KI6WX KSB2 Increased Gain Mod is added and used with the
KPA100, there is a good chance that the ALC circuits on the KSB2 board
will be overdriven.  This situation was identified about 3 years ago and
can be found in the reflector archives for those who wish to view the
original source.  Gary Surrency, Elecraft Technical Support identified
the problem and provided the additional ALC mods.

This ALC mod addition does not appear to be conveniently available, so I
am posting it here.
1) Increase KSB2 R9 to 15k
2) Cut the trace on the top of the KSB2 board between P1 pin 6 and the
base of Q1
3) Add a 1k resistor between P1 pin 6 and the base of Q1.  It is a tight
fit for a 1/4 watt resistor, and might be a good application for an SMD
resistor if you have one available.

Try making those changes and see if it corrects your problem.

73,
Don W3FPR

Michael van Hauten wrote:

>>
>> Dear all,
>>
>> currently i work on my third K2 #5619. I have  problems with the KSB2
>> after the ssb mod:
>>
>> The modulation is bad and it sounds as if there is RF in the
>> microphone line (the voice sounds modulated in it self). I use a
>> dynamic peiker mike and i have tested some other dynamic mics (eg.
>> Heil with HC4).
>> The mods i have installed are the higher compression mod by changing
>> the the resistor network  to 5 single 150k resistors and the other
>> mods described by DL2FI and KI6WX.  I do not remember whether the
>> problem exists before the mod. All filters are adjusted fine with the
>> help of spectrogram and the receive sound is very clear and good. I
>> also see on my output meter a jump by slowly increasing the mic
>> input. It seems that the amplifier works not in a linear mode or the
>> alc works not correct. it seems that the sound is much better on 80m
>> than on 10 and 20m.
>

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Elecraft web page: http://www.elecraft.com