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 On Mon, Feb 16, 2026, 07:59 dyno lab via Elecraft <[email protected]> wrote: > Sounds like you have a really good one and running it at 1250 Watts goes a > long way in keeping it alive. > I have a feeling you keep an eye on the match. > I have friend that runs her's at a full 1500 Watts all the time and gets > away with it. > > Hot Carrier Injection is a funny thing. It seems that some LDMOS RF Power > FETs can handle high voltage spikes forever while others of the same type > rollover and die at the slightest hint of over-voltage. > > The old vacuum tube Tektronix oscilloscopes had the same feature where > components would overheat and unsolder themselves from the porcellian > terminal strips and drop to the bottom of the scope. > > 73, Hal W7YNC > > > > On 02/15/2026 6:34 PM PST Jim Brown via Elecraft < > [email protected]> wrote: > > > > > > On 2/15/2026 12:05 PM, Jon Zaimes, AA1K via Elecraft wrote: > > > Was this your study Hal? Has it been shared with Elecraft? > > > Kind of defeats the purpose of buying a 1500 watt amp if it needs to > be run at lower levels to survive. There are less expensive amps for that. > > > > The study is in conflict with my experience. My KPA1500, purhased about > > a year after they started shipping, has been in service for more than > > six years, with no issues of the sort it describes. I'm an active > > contester, and regularly run it near legal limit on CW and RTTY. The > > only time it's been in for service was due to a failure in the antenna > > system that caused a failure in the tuner (an EXCELLENT tuner, BTW). > > > > I generally run it around 1.25 kW for VERY long duty cycle WSJT modes on > > 6M (meteor scatter, and weak signal work that utilizes TX cycles of as > > much as 2 minutes, and can extend for hours; there's a non-destructive > > failure mode caused by device heating that melts the solder and allows > > them to fall out of the board; repair consists of reinstalling them. > > > > I've found the amp to be EXTREMELY well protected -- at 84, I often make > > mistakes changing bands during a contest that activate the protection > > system. > > > > I recently bought a very early serial number unit in which devices had > > failed and been replaced. I sent it to Elecraft for repair. They said > > the amp was not working properly because the new devices had not been > > biased, which is a critical part of replacement. Unlike the JA mfrs, > > Elecraft makes running production changes over the years based on > > service experience, which may have happened with this product. > > > > I like to have spares for important parts of my station. My early > > vintage K3s, mostly upgraded to K3S, are spares for my K4. This used amp > > is a spare for the one on my operating desk. > > > > 73, Jim K9YC > > > > > > ______________________________________________________________ > > 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] 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]
