[Elecraft] KPA1500 Thermal problems

[Jim Miller]

I participated in the WAE RTTY contest this past weekend and was having
problems with thermal tripping.

I have resonant antennas for 80, 40 and 20m and had SWR between 1:1 and
1.2:1, power nominally set between 1400-1500w.

I found that I couldn't repeatedly CQ without temperature creeping up so I
paused to around 50% duty cycle to stop that.

However when sending QTC which amount to about 200 characters the
temperature would rapidly increase and eventually thermal trip.

I took several actions to try to compensate:

I opened the shack windows and bundled up. Shack then stayed at 60f or
below.
I immediately manually cranked the fan speed to max (5) when started to
send QTCs.
I rode the drive power downward as the power increased to stay below the
trip point of 105c.

Upon taking all these actions I was able to eventually send the QTC packets
but it was unnerving and unexpected.

This is a low serial number KPA1500 but with latest production firmware.

What have others seen?

73

jim ab3cv