[Elecraft] KPA500 Faulting on high SWR on power rise

[Victor Rosenthal 4X6GP]

Just to add to all the possibilities, there could be an arc at the 
balun. Most authorities suggest a 1:1 balun with a setup like this. As 
you know, the impedance seen at the balun will vary all over the map, 
depending on the band and the length of the 600-ohm line.

I've calculated that the voltage that appears at that point in my 
somewhat similar setup is as high as 7 kV when I'm running 1200 watts on 
one particular band. A 1:1 balun designed for tuner use (e.g., one like 
this:
<https://www.dxengineering.com/parts/dxe-bal050h10at> or this:
<https://www.dxengineering.com/parts/dxe-bal050h11ct>
would be suitable.

73,
Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
http://www.qsl.net/k2vco/
On 24 Feb 2018 07:42, Chris Hallinan wrote:
> Greetings from southwest Florida.
> 
> My KPA500 is kicking out with REFL HI warning (high SWR).  But here is the
> strangeness. My setup is K3->KPA500->40' coax->MFJ 600W remote tuner -> 4:1
> balun -> open wire feedline to 80-meter doublet.  In words, I have a remote
> autotuner feeding an 80-meter doublet fed with 600-ohm open wire line.  A
> Balun Designs 4:1 balun provides the interface from the open wire line to
> the tuner.
> 
> With the autotuner tuned at low power, the SWR shows 1.5:1 on my KPA500 and
> external SWR meter.  As I run the power up to 300, 400, 500 watts,
> somewhere in there all of a sudden the SWR instantly jumps off the scale,
> into the red LEDs on KPA500, and it faults.  It's as if the SWR were
> dependent on power.
> 
> Even stranger, when I back the power off to say 250 Watts, holding key down
> the SWR is stable in the green (<1.5:1), but when I key it at CW rates, the
> SWR bounces into the red on every dit and eventually faults, when at steady
> state key down it never leaves the green zone!
> 
> I fear it is the tuner falling over, but it should be able to handle the
> power.  I see this on all bands from 80-20.
> 
> Operating into my 20-meter resonant vertical, with no tuner, everything
> works fine.
> 
> Any ideas or hints on how to correct this?
> 
> Thanks,
> 
> Chris
> 73 de K1AY
> 
>