[Elecraft] KPA500 output on 6 meters

[Pete Lascell]

Operating my K3 on 6 meters with the KPA500 ( S/N 1009 ) is new ground for me.

The amp has been performing on lower HF frequencies with expected results, but on 50 MHz the power output into a dummy load is questionable.  If I try to tune with CW carrier (XMIT putton) , I can only get about 200-250 watts before the amp "faults" and shows PA DISS.  The HV is about 60 volts and current 14 amps with 24 watts drive for 250 watt ouput level before "fault".  

If I key CW dots or dashes, then I can increase the drive to 40 watts for 450 watts output into dummy load with 1:1 SWR.

HV unkeyed is 75VDC, operating on 120 VAC.  (Don't remember where the transformer tap is)

Specs seem to indicate the RF output should not degrade on 50 MHz and is rated for 500 watts PEP CW / SSB / DATA.  Can I assume I should be able to get 500 watts RTTY carrier for 15 seconds ?  I get a "fault" within half a second if driving it for power out levels higher than 250 watts.  My TEMP has never gone above 60 C.

Am I doing something wrong?

Do I have a hardware failure?

What should I expect to be normal operation on 6 meters?


Pete W4WWQ