[Elecraft] KXPA100 Intermittent VSWR Issues

[Jim Stahl via Elecraft]

I've run into several occasions where in mid-CW transmission my KXPA100  
(with internal tuner) SWR takes a momentary jump from matched to maybe  3:1. I 
see the SWR jump on both the KXPA front panel LEDs and on  the KX3 VSWR 
display.  It lasts for maybe half a second, I hear  several clicks of the 
relays in the tuner, and them it's back to normal. When  normal the SWR is pretty 
much 1:1 on the KX3, and the second green LED lit on  the KX3. I've not 
seen it happen at the start of a transmission, but  rather several characters 
into a CQ or exchange..
 
In the ARRL 160 contest Saturday night this was happening perhaps once  
every 2-3 minutes. I'm using a fairly well matched antenna - not random wires. 
I  also encountered this problem on 15 meters when operating from W1AW/8 in 
WV  in October. In both cases I was running a pretty high CW duty cycle 
while  running at a pretty good clip. The amp was warm, but the heat sink air  
flow is not blocked.
 
Any thoughts?
 
 
73  -  Jim  K8MR