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 <[email protected]> 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:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [email protected] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
