[Elecraft] KPA-1500 Efficiency As A Function of Input Power

[David Gilbert]

Not sure why that's a surprise.  It's a linear amp ... the bias point is 
what draws the current, and therefore essentially determines the 
dissipation.  There's nothing remarkable about it.

Amplifier 101.

Dave  AB7E


On 8/16/2018 10:17 PM, charles at k5ua.com wrote:
> Thanks for the replies.
>
> Upon further testing, I have found that the efficiency of the KPA-1500 
> is varies greatly with driving power.  The following table illustrates 
> the relationships between exciter power, voltage, current, 
> power-in(voltage x amps), power-out, efficiency, and dissipated power. 
> The following test was made with the KPA-1500 into a dummy load and 
> readings from the KPA-1500 utility software.
>
> (Exciter)(Amps) (Voltage) (Power-In) (Power-Out) (Efficiency Pout/Pin) 
> (Dissipated Pwr)
>   10w     29a     52.7v     1528w       375W        375/1528 = 
> 24.5%     1205w
>   15w     37a     52.7v     1950w       620w        620/1950 = 
> 31.7%     1335w
>   20w     43a     52.6v     2262w       861w        861/2262 = 
> 38.0%     1413w
>   25w     47a     52.6v     2472w      1060w       1060/2472 = 
> 42.8%     1451w
>   30w     51a     52.6v     2682w      1227w       1227/2682 = 
> 45.7%     1420w
>   35w     53a     52.5v     2782w      1380w       1380/2782 = 
> 49.5%     1412w
>   40w     55a     52.5v     2887w      1497w       1497/2887 = 
> 51.9%     1382w
>   45w     56a     52.5v     2940w      1600w       1600/2940 = 
> 54.4%     1313w
>   50w     57a     52.5v     2992w      1703w       1703/2992 = 
> 56.9%     1315w
>   53w     59a     52.5v     3097w      1825w       1825/3097 = 
> 58.9%     1306w
>
> The remarkable thing is that DISSIPATED POWER appears to be relatively 
> constant from 375w output through 1825w output.  This implies the 
> KPA-1500 will need to dissipate nearly the same amount of heat at low 
> power output as at high power output, if I am interpreting the data 
> correctly. I would like to know from Elecraft if this is normal behavior.
>
> Charles  K5UA
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