You bet! Don't hesitate to contact me if you need more info. 73, Hal W7YNC > On 02/17/2026 12:38 AM PST Doug Turnbull via Elecraft > <[email protected]> wrote: > > > Dear OMs, > Mny TU for this information. It will inform my ongoing use of the KPA > 1500. Wanted to express my thanks. > 73 Doug EI2CN > > On Mon 16 Feb 2026, 19:29 Bob McGraw via Elecraft, <[email protected]> > wrote: > > > One should understand and adhere to the duty cycle at 1500 watts. From > > the manual: "100% ICAS for 100% duty cycle modulation modes (FM, RTTY, > > FT8, JT65, etc.) 1.8-30 MHz: Maximum 5 minutes key down / Minimum 5 > > minutes receive (after 5 minute TX) 50 MHz: Maximum 50 seconds key down > > / Minimum 50 seconds receive." > > > > These values must be considered using a 50 ohm resistive load. Hence, a > > simple 1.1:1 SWR does not necessarily indicate a 50 ohm non-reactive > > load. Also I would comment, person opinion and experience, a transmit > > time of 5 minutes and a receive time of 5 minutes equals a duty cycle of > > 50% with one cycle being 10 minutes. Yes, if one considered only the > > transmit time for referenced modes, the duty cycle is 100%. (But that > > isn't the way I was taught for pulse modulation.) > > > > As a reference, FT-8 duty cycle is slightly less then 50% based on > > RX/TX timing. MS-144, a meteor scatter mode, runs about the same but > > with longer transmit time and longer receive time. > > > > Yes I view from my measurements on the KPA500, the efficiency varies > > from a high of 60% to a low of 25% based on power level and band. For > > this amp, the dissipation high was 444 watts on 15M at 400 watts output > > to a low of 150 watts on 80M at 500 watts output. The gain of the > > amplifier was 13.7 dB to 14.8 dB, again depending on band and power > > value. It was clear that signal compression started in the 400 to 500 > > watt power range. My measurements were based on using two Bird 43 > > meters and suitable elements, one for input power and one for output > > power. A 1kW Bird 50 ohm load was part of the test equipment lineup. > > These are not considered to be lab grade equipment, but equipment of > > reasonable accuracy along with measurement methods employed. (FYI - all > > purchased new by me, thus not hamfest or e-bay, etc. products) > > > > My conclusion is the same measurements should be performed on the > > KPA1500, thus allowing one to see the variations, band to band, and > > power value to power value. The use of and Excel spreadsheet and simple > > formulas are an aid in producing reliable results and accuracy. > > > > 73 > > > > Bob, K4TAX > > > > On 2/16/2026 11:00 AM, [email protected] wrote: > > > essage: 15 > > > Date: Mon, 16 Feb 2026 09:32:03 +0200 > > > From: Victor Rosenthal<[email protected]> > > > To: Elecraft Reflector<[email protected]> > > > Subject: Re: [Elecraft] KPA1500 issues/blown finals > > > Message-ID: > > > < > > cajzhgajwd4_zpj8cnxlhwdprm31kesvvou7j-xlyrdr2ekb...@mail.gmail.com> > > > Content-Type: text/plain; charset="UTF-8" > > > > > > I recall Elecraft saying that the KPA1500 runs hotter at lower power > > levels > > > because it is designed for maximum efficiency at full output. > > > So while it's possible there will be lower voltage peaks when output is > > > reduced, heat might become an issue. > > > > > > Victor 4X6GP > > ______________________________________________________________ > > 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] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected]
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