http://elecraft.85.s1.nabble.com/KPA-1500-Efficiency-As-A-Function-of-Input-Power-tp7644454p7644455.html
> What is the Oh Jeeze about? I found K5UA's efficiency data surprising that
> the amp dissipates nearly the same amount of heat regardless of power
> level. Your comment was "I really do NOT understand why this data is so
> surprising." You obviously know much more about RF amplifiers than I do. I
> subscribe to this list to learn. So, my next question was if the heat
> generated is approximately the same with all power levels, why do RTTY ops
> use lower power. I am assuming that heat is what destroys finals or other
> amp components. Perhaps there is a power supply limitation or that tube
> amps have a more linear efficiency so lower power really means less heat.
> Of course RTTY has a higher duty cycle than CW and SSB, that was not my
> question. The RTTY duty cycle is the same whether you run 500 watts or
> 1500. If the amplifier heating is about the same at both power levels due
> to higher efficiency at higher power than why not use the maximum power
> for RTTY (assuming that you have an antenna and coax that can handle it)?
>
> John KK9A
>
> Sent via the Samsung Galaxy 7 edge, an AT&T 4G LTE smartphone.
>
>
>
>
> Charlie K3ICH wrote:
>
>
> Oh Jeeeze.......
>
> Almost ALL amps in current use are NOT rated for continuous power output.
>
> Only the most recent SS amp builders which use devices themselves rated for
> 3x or 4X their rated output would dare to specify 100% duty cycle.
>
> Only a few tube type amps are rated at 100% duty cycle too and they also use
> severe over-kill in their PA devices, such as a pair of 8877's or maybe
> three, 3-500ZG's etc.
>
> I would venture to say that 85% of the current amplifiers in use today are
> NOT rated for 100% duty cycle, so THAT's why they back off on the RTTY
> output.
>
>
> 73, Charlie k3ICH
>
>
>
>
> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net <elecraft-bounces at
> mailman.qth.net> On
> Behalf Of john at kk9a.com
> Sent: Friday, August 17, 2018 9:43 AM
> To: elecraft at mailman.qth.net
> Subject: [Elecraft] KPA-1500 Efficiency As A Function of Input Power
>
> So why do most RTTY users run their amps at reduced power?
>
> John KK9A
>
>
> From: Charlie K3ICH
> Date: Fri Aug 17 09:24:18 EDT 2018
>
>
> I really do NOT understand why this data is so surprising.
> It all seems to me to be perfectly normal with the amplifier's highest
> efficiency occurring at near max output.
> Which curiously, I would assume, is the way the amp was designed.
>
> Think zero output with zero drive = zero efficiency.
> Apply some drive, read some output and the efficiency goes up from there.
>
> 73, Charlie k3ICH
>
>
>
>
> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net <elecraft-bounces at
> mailman.qth.net> On Behalf Of john at kk9a.com
> Sent: Friday, August 17, 2018 8:57 AM
> To: elecraft at mailman.qth.net
> Cc: charles at k5ua.com
> Subject: [Elecraft] KPA-1500 Efficiency As A Function of Input Power
>
> Interesting data, Charles. I assumed that running the KPA1500 (or KPA500)
> at lower power would keep the fan from running as much. I knew that
> efficiency changed with output power but I did not expect that it was this
> significant. If your data is correct there is 1000++ watts of heat to
> dissipate no matter what power level you use.
>
> John KK9A
>
> ______________________________________________________________
> 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]