Paul, I do not witness what you are seeing. You may also have an antenna issue, slight but problematic?
72 & 73, Bill K9YEQ FT’er for K2, KX1, KX3, KXPA100, KAT500, W2, etc. -----Original Message----- From: elecraft-boun...@mailman.qth.net <elecraft-boun...@mailman.qth.net> On Behalf Of Paul Baldock Sent: Friday, March 15, 2019 4:47 PM To: donw...@embarqmail.com; Gary J Ferdinand <alapa...@w2cs.net>; elecraft <elecraft@mailman.qth.net> Subject: Re: [Elecraft] KPA1500 PA Current I believe its universal that as the KPA1500 warms up the gain drops. I have mine set up on each band for around 1500WPEP when cold. If I operate it enough by the time the amp gets up to 70C its down to around 1300W. I try to operate the amp conservatively so I don't increase the input to raise the output back to 1500W, I just leave at 1300W,. The issue is in the amp, not in your antenna or feeder, balun etc. I had a SPE1.5K for a short time and this exhibited a similar effect. -Paul KW7Y At 02:10 PM 3/15/2019, Don Wilhelm wrote: >Gary, Have you considered that there may be something in your antenna >system that is heating up or otherwise changing with the 1500 watts >power? The first thing I would suspect is a balun that is heating, or a >connector that is not quite tight enough. Those kind of problems will >not show up at lower power, but at 1500 watts may become troublesome. >73, Don W3FPR On >3/15/2019 3:25 PM, Gary J Ferdinand wrote: > I’m in the process of >checking out my amp. I have two dipoles (40 and 80). At resonance >both show a 1.2:1 SWR with ATU totally bypassed. With ATU on, it >remains bypassed on 80, but shows only the ATU ON LED on 40. In >both cases the resultant SWR is 1.2:1. SWR >measurements are from the KPA1500 display. > > When I use the amp with >my K3 and drive it up to 1500W, I am occasionally getting an excessive >PA current fault at 63A. From a cold start it’s 60A, but as it warms >up in contest usage I find the power drops off, so I have to adjust the >K3 to bring it back up to 1500W. At that point the PA current goes >over 60A. > > Interestingly, into a dummy load the 1500W point shows a >PA current of only 55A. So the 1.2:1 SWR, be it via a bypassed ATU or >using the ATU, is sufficient to raise the PA current eventually to >excessive levels. > >______________________________________________________________ >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 ______________________________________________________________ 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 ______________________________________________________________ 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
