One point to consider is the output network that is used to match the output device impedance to 50 ohms. It is a fixed value or ratio. Thus if designed for rated power then at 1/2 or 1/4 power the value would not seem to provide a proper match for effective transfer of energy. This can attribute to overall efficiency.
Bob, K4TAX Sent from my iPhone > On Feb 10, 2020, at 9:38 AM, Doug Turnbull <turnb...@net1.ie> wrote: > > Hello Andy, > > I do not have the numbers and also would like them. I understand > that efficiency decreases as one derates from the maximum of 1500W output. > It surprises me that the power dissipated would peak at half power output or > 750 Watts. This may be so. If so then almost certainly the Mean Time > Between Failures or MTBF is worsened. I am not in a position to > determine any of this but maybe some guidance from Elecraft itself would be > helpful for both KPA 500 and 1500. > > 73 Doug EI2CN > > > > From: Andy Durbin <a.dur...@msn.com> > Sent: Monday 10 February 2020 14:04 > To: Doug Turnbull <turnb...@net1.ie>; elecraft@mailman.qth.net > Subject: Re: [Elecraft] QRO - KPA500 Failure > > > > Doug, > > > > "I would like to know if running 2/3, 1/2 or even 1/4 maximum power output > increases reliability and MTBF." > > > > I have no experience of amplifier design but I would expect reliability of > the finals to depend on temperature. Finals temperature will depend on the > power dissipated in the finals (PA dissipation) and the effectiveness of the > cooling design. > > > > To understands finals dissipation one would need to produce one's own test > data or rely on the work of others. My test data for the KPA500 shows PA > dissipation peaks at about half power output. So far no one has disputed > the validity of my test data. > > > > It is my understanding that running an amplifier at reduced power only > reduces PA dissipation if the finals voltage is adjusted give a good load > match for that reduced power condition. The KPA500 has no provision for > adjusting PA voltage for the reduced power case. For reduced power the PA > voltage is actually higher than for full power because the high voltage > supply is not regulated. > > > > As I said, I have no experience in amplifier design and would appreciate > comments from those who do. > > > > 73, > > Andy, k3wyc > > > > > > > > ______________________________________________________________ > 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 rmcg...@blomand.net > ______________________________________________________________ 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 arch...@mail-archive.com
