Folks - Let's keep it polite and non-personal. Eric Moderator /elecraft.com/
On 8/17/2018 10:27 AM, j...@kk9a.com wrote:
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:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to eric.swa...@elecraft.com
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