[Elecraft] KPA100 R 19 R20 question

[Dr. Werner Furlan]

hi Don, 

I have been quite successful yesterday thanks to your suggestions. 
The major advance was grounding the microphone shell. I did it from the left 
side with a piece of desoldering braid and a lot of heat. This cured most of 
the distortion in my signal and all of the wiggle of the microphone shell I had 
noticed before.

Next step was modification of the SSB board. I had no 15k resistor at hand 
but one at 5k so I put it in series with the existing 10k resistor, the resistor 
between Q1 and pin 6 of P1 is mounted "elevated style" with one lead very 
short at P1 the body  60° up and a longer lead to Q1 going down again. (I 
had no 1/8 W resistor.)

The last part was the power supply. 
I had a clear signal on 80m but my buddies reported some clipping on 20m 
and 10m at high power. I had attached the low power cable to the main 12V 
supply of my station, and the high power supply to a different 20A PS. This 
turned out to cause the problem - probably a ground loop with the antenna 
system.
When I connected both 12V lines into the 20A power supply I had a good 
signal on all bands (at least it sounds good in my monitoring receiver)

Test on air will follow, but I think everything is working now.

Thanks a lot, 

73! de Werner
OE9FWV



On 27 Nov 2007 at 11:13, Don Wilhelm wrote:

> 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.


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Inside of a dog it is too dark to read." Groucho Marx



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