[Elecraft] KPA100 R 19 R20 question

[Don Wilhelm]

Werner,

That link pointed me to a page that includes the KI6WX Increased Gain 
Mod as well as a few other changes to the KSB2 board (increased 
compression, etc.).

The Increased Gain Mod alone may be your problem.  If you are to use 
that with the KPA100, make the following additional changes to the KSB2 
board:
1) Increase the value of R9 to 15k
2) Cut the trace (on the top of the board) between P1 pin 6 and the base 
of Q1.
3) Add a 1k resistor between P1 pin 6 and the base of Q1 - note that 
this is a tight squeeze for a 1/4 watt resistor, but it does fit - you 
may also use a 1/8 watt resistor or an SMD resistor if you have one 
available.

Make the above changes and then test again - it may correct all your 
problem.

The Increased Gain Mod will not show this problem at QRP.  It only shows 
up when the gain of the KPA100 is added to the RF transmit chain.

Grounding the shell of the Microphone connector is on the K2 front 
panel.  It can be accomplished without disassembling the front panel.  
Remove the left side panel and you can access the side of the microphone 
jack.  Scrape a bit of the solder mask material from an area near the 
mic jack to expose some of the copper (and tin that area).  Solder a 
short wire onto the shell of the mic jack (this takes a lot of heat, so 
use a larger iron or a high heat setting) and also onto the copper 
ground plane of the front panel.  It is a little easier if you 
disassemble the front panel board from its metal housing, so you may 
take your choice of how to proceed.

73,
Don W3FPR


Dr. Werner Furlan wrote:
> hi Don, 
>
> some questions I can answer now, some I have to look at in the "lab".
>
> On 27 Nov 2007 at 6:20, Don Wilhelm wrote:
>
>   
>> The KPA100 does not distinguish between CW and SSB - input RF is input
>> RF and it operates in a linear curve with a gain of approximately 10
>> dB, so 10 watts in will produce 100 watts out and 2 watts in will
>> produce 20 watts out and everything proportionally in  between.
>>     
>
> ok. Looks like my problem is only in SSB mode. 
>
>   
>> How does your base K2 behave in SSB mode?  Does it produce 10 to 15
>> watts output under similar conditions?
>>     
>
> yes it does. The base K2 has a good SSB signal and works fine all over the 
> range of 1-15 Watts (10W on 10m Band)
>
>   
>> I believe your problem may be either an ALC  problem on the KSB2 board
>> or an RF feedback situation.
>>     
>
> both seems possible to me. 
>
>   
>> First, I need to ask if you have any mods to the KSB2 board?  
>>     
>
> yes - I have modifications. I have made all modifications recommended in 
> this pdf:
> http://www.qrpproject.de/Media/pdf/ZusammenfassungMods.pdf
>
> it is in german, but I think you can understand it without knowledge of 
> german when you see the circuit diagrams.
>
>   
>> Specifically the KI6WX Increased Gain mod.  If that mod is present and
>> the KPA100 is added, the KSB2 ALC circuits may be overdriven.  There
>> is a fix that can be added, or the mod can be removed to restore
>> normal operation.
>>     
>
> I would like to make a fix if necessary, without loosing the good modulation 
> in qrp SSB.
>
>   
>> Even without the KI6WX mod, there still may be a problem in the ALC
>> area of the KSB2 board, but it will likely be found to be a bad solder
>> connection or an incorrect component (check the resistor values).  How
>> does the LED Bargraph behave when the problem arises?  If it goes full
>> scale in RF mode and lights many bars in ALC mode, then check the KSB2
>> board ALC section carefully.
>>     
>
> would this also be in QRP mode?
>  
>   
>> There is also the chance that you have RF feedback into your
>> microphone circuits.  That will not usually happen if you operate into
>> a dummy load, but will show up when you are connected to an antenna. 
>> If this is the case, the proper cure is to correct the RF feedback
>> situation at the antenna, but in difficult situations, ferrites on the
>> microphone lines can help somewhat.  If you have a data mode/soundcard
>> interface connected, remove it and check without it.  The interface
>> and its cabling produce additional cables and may be more susceptible
>> to RF pickup than a microphone cable alone.  You may also want to
>> ground the shell of your microphone jack if you have not done that
>> already.
>>     
>
> I'll check it again with sending into a dummy load. 
> I'll also check it without the EA3BLQ digital board.
> What do you mean by grounding the shell of the microphone shell?
> Is it on the K2 or on the microphone cable?
>
> I have another question about S-meter calibration with the Elecraft s-meter 
> calibrator. Do you set the S0-S9 limits with preamp enabled or disabled?
>
> 73! de Werner
> OE9FWV
>
> --  
> Pas de panique, Ca sera pire.
>
>
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