[Elecraft] QRO - KPA500 Failure

[Don Wilhelm]

John,

You are correct.  I am seeing a lot of confusion and erroneous 
conclusions based on the terms 'efficiency', 'dissipation' coupled with 
'power output'.
As an example, consider that a PA running at 50% efficient at 500 watts 
will dissipate 500 watts of heat and 500 watts of power out.  Input DC 
power will be 1000 watts.
Now back the power down to 250 watts - yes, the efficiency will be less, 
say 33%.  That is 250 watts of power output, but 67% of the total power 
into the amp would be lost as heat - 417 watts of heat.  Input power is 
less too at 667 watts.

That drop in efficiency at lower than max design power is true for any 
amp designed for their maximum rated power output (as most are).

The only ones who should be concerned are those who are monitoring their 
draw from the AC line and their resulting utility bill.

73,
Don W3FPR



On 2/7/2020 10:16 AM, john at kk9a.com wrote:
> There may be reasons for running at less than the amplifier max such as 
> the US 200 watt 30m band limitation.  I have no RF engineering knowledge 
> but after looking at your data I see less heat with lower output wattage 
> which seems to me like it would be less stress on finals.
>