Re: QRO - KPA500 Failure

Posted by Macy monkeys on Feb 07, 2020; 4:51am
URL: http://elecraft.85.s1.nabble.com/QRO-KPA500-Failure-tp7658244p7658265.html

I run my KPA500 output just below the level I feel I can get away with...without lighting up the neighborhood. About 350 watts :)

John K7FD

> On Feb 6, 2020, at 2:06 PM, Bob McGraw K4TAX <[hidden email]> 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.
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]