[Elecraft] KPA500 High Reflected Power Fault

[Nels Anderson]

Been enjoying KPA500 #32 for a couple of days now. Haven't yet made a 
lot of QSOs with it, but the extra power on RTTY and to bust a couple 
SSB pile-ups has been welcome.

However, the amp does not like my 40m setup. As soon as I transmit it 
instantly goes into high reflected power fault and shuts down. My 
antenna is a 120 foot center fed wire using 1 inch ladder line and an 
LDG 1 kw auto tuner. SWR on 40m is under 2:1 and the K3 and other rigs 
I've used it with have always been happy with the antenna arrangement.

In experimenting I used the K3 tune function and reduced the power in 
steps to see if I could reach a low enough power level that it would 
operate, but even at 1 watt of drive the amp still instantly went into 
fault.

On 80m it did the same thing the first time I tried it, but then I 
manually tweaked the antenna tuner, got a lower SWR reading and then the 
amp worked. On the higher bands that I've tried there has been no problem.

So, any idea what is causing this?

73 Nels K1UR