[Elecraft] KPA500 Temps?

[Jim Brown]

On Mon,1/16/2017 8:02 AM, Wes Stewart wrote:
> Furthermore, IMD performance of the driver (K3) is likely better at 
> higher power. It's for sure better at 20W than 10W.

Actually, the reason IMD performance is worse at 10W than at 20W is that 
at 10W you're still in the 10W section of the radio, while at 20W you're 
using the 100W amp. Once you're into the 100W amp, IMD performance 
degrades with increasing power. The K3 is capable of 120W, but since IMD 
increases rapidly above 100W, output is limited to 110W in firmware.

As I see it, IMD is most important when a radio is driving a power amp, 
and most modern amps will get to rated power with about 50W. The KPA500 
needs 25-30W drive. As indicated by measured CW keying bandwidth, the K3 
is a VERY clean radio below 60W.

IMD performance also degrades with reduced DC supply voltage. As I 
understand it, 13.8V is the nominal design voltage, and 15V is max rated.

As to the original query about temperature -- Wes is exactly right about 
low power and efficiency.  I do little or no ragchewing and mostly 
operate CW and SSB, but I do run RTTY for contesting and some digital 
modes that run keydown for about 50 sec and repeat every minute. When I 
do that on 6M, where the amp has the lowest efficiency, the fan will get 
pretty loud before the end of each TX cycle. That can be reduced a bit 
by setting the idle fan speed higher. It's a menu setting.

73, Jim K9YC