[Elecraft] QRO - KPA500 Failure

[Hisashi T Fujinaka]

The advantage I have is that it doesn't set off my fire alarm.

On Thu, 6 Feb 2020, Bob McGraw K4TAX wrote:

> I've never seen much if any advantage in running a linear below its 
> rated output.  I know the regulation state never run more power than 
> needed for adequate communications or terms like that.    The difference 
> between 500 watts and 100 watts is 6.9 dB or about 1 S unit.
>
> In fact, most all of the time, running at less than rated output is less 
> efficient.   It saves nothing.   Same for tube amps where I hear hams 
> say they are running at reduced power to "save the tubes".   Nope, not 
> the case.
>
> (RF output / DC input) * 100 = % efficiency         DC input watts  = DC 
> volts x DC amps
>
> Do the math and you'll see what I mean.
>
> A quick run of the numbers with my KPA500 into a dummy load. Output 
> measured with a Bird 43.  DC values taken from the KPA500 display
>
> 450 W out, 819 W input, 64 volts @ 12.8 amps for 55% efficiency Drive 
> pwr = 16.5W  14.3 dB gain     819 - 450 = 369 watts = heating factor = 0.88
>
> 210 W out, 576 W input, 67 volts @ 8.6 amps for 37% efficiency Drive pwr 
> = 7.0 W  14.7 dB gain     576 - 210 = 366 watts = heating factor = 1.74
>
> 100 W out, 393 W input, 69 volts @ 5.7 amps for 25% efficiency     Drive 
> pwr = 3.2 W  14.9 dB gain   393 - 100 = 293 watts = heating factor = 2.93
>
> 73
>
> Bob, K4TAX
>
>
> On 2/6/2020 3:07 PM, Rick Bates, NK7I wrote:
>> Running low output power from it, is far less efficient than pushing 
>> it hard (compare wattages consumed to RF watts output delivered at 
>> different output levels); which may have stressed the finals. Ideally 
>> you run the previous stages at low-moderate power for lower IMD, then 
>> punch it up with the amp. 
>
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-- 
Hisashi T Fujinaka - htodd at twofifty.com
BSEE + BSChem + BAEnglish + MSCS + $2.50 = coffee