[Elecraft] KPA100 R 19 R20 question

[Don Wilhelm]

Werner,

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.

How does your base K2 behave in SSB mode?  Does it produce 10 to 15 
watts output under similar conditions?

I believe your problem may be either an ALC  problem on the KSB2 board 
or an RF feedback situation.

First, I need to ask if you have any mods to the KSB2 board?  
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.

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.

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.

Let us know if any of this helps.

73,
Don W3FPR

Dr. Werner Furlan wrote:
> in the meantime I have nearly finished my KPA100, the only part missing is a 
> housing and crimp pins for the low power supply. (I am waiting for the spare 
> part) 
> But  I could already try the PA without this plug, and it works, but there must 
> be some problem with oscillation I think. It is only in SSB mode, not when I 
> tune or send CW.
> In low power mode all is ok, when I turn power over 11 Watt, the PA draws 
> more than 18A when I whistle. The modulation reports I get describe it as 
> missing high frequencies. When I observe the amperemeter needle, it looks 
> very nervous, sometimes I have seen and heard it "vibrate".
> Sometimes I have had a normal behaviour though, with 80W on my 
> calibrated LP100 Wattmeter and a good signal report. But this was only a 
> very short time. Most of the time I get this peaks of output up to 150 W on 
> the LP100 peak meter.
>
> I have now put the PA in the EC2 with the KAT100. For allignment and 
> testing I have had it mounted besides the K2 and connected it directly.
>
>