Never realized that, but I checked dc input power vs output RF power
on my LDMOS amps and that appears to be true.
I had intended to run my 2m 1500w amp at 600w for SSB (to be kinder
and more linear), while running JT65 at 1300w which is where
saturation begins.
1385w RF: 37A x 47.2V = 1746w (disp = 361w)
600w RF: 25A x 48.5V = 1212w (disp = 612w)
http://www.kl7uw.com/test2.pdf
MRF-1K50N disp = 2941w at 25c (derate above 25c)
https://www.nxp.com/docs/en/data-sheet/MRF1K50N.pdf
But average current draw in SSB is less than JT65 (which is keydown
carrier). So I guess it depends on how long-winded your SSB talking is.
Typically voice duty cycle is 20% at max whereas JT65 is 50/120 seconds = 42%
Fortunately, I have a thermistor on the RF deck to monitor
temperature with a digital voltmeter. Control board illuminates
"overtemp" lamp at 43c and 50v is shutdown at 55c. Extended running
of JT65 shows heatsink is a shade under 43c (lots of fans cooling things).
http://www.kl7uw.com/144_1500W_PA.htm
73, Ed - KL7UW
Date: Sat, 31 Aug 2019 17:04:38 -0500
From: K9MA <[email protected]>
To: [email protected]
Subject: Re: [Elecraft] KPA-1500 on digital modes
This is nothing unique to the KPA1500: ALL class AB amplifiers behave
this way. Even an "ideal" class AB amplifier has a maximum dissipation
at around half of full output.
One thing running at lower output probably will buy you is lower IMD.
73,
Scott K9MA
73, Ed - KL7UW
http://www.kl7uw.com
Dubus-NA Business mail:
[email protected]
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