Posted by
Doug Turnbull on
Feb 10, 2020; 5:08pm
URL: http://elecraft.85.s1.nabble.com/QRO-KPA500-Failure-tp7658244p7658347.html
Dear OMs, Maybe this is an advantage of the SPE 2KFA amp which has three power levels 2000, 1200 and 600 W output. I have both amps and prefer the KPA 1500. Which I find quieter both acoustically and RFI wise on RX. The KPA 1500 is also happier handling Data modes. The SPE will drop down to 600W for RTTY. 73 Doug EI2CNSent from my Samsung Galaxy smartphone.
-------- Original message --------From: K9MA <
[hidden email]> Date: 10/02/2020 16:29 (GMT+00:00) To:
[hidden email] Subject: Re: [Elecraft] QRO - KPA500 Failure Several others have posted test data for the KPA500 here recently. As I recall, it shows that dissipated power is fairly constant from about 50 percent to full output, at about 500 W, dropping a bit at lower power.If it were an ideal class B amplifier, which no solid state RF amplifier even approaches, the efficiency at full output would be 78.5 percent. It would then dissipate only 141 W at full output, and maximum dissipation would be at some lower output power level. This is probably what folks are thinking of when they assume maximum dissipation occurs at less than full output. REAL RF amplifiers don't behave that way, as the test results show.
https://en.wikipedia.org/wiki/Power_amplifier_classes#Class_B73,Scott K9MAOn 2/10/2020 09:23, Doug Turnbull 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 <
[hidden email]>> Sent: Monday 10 February 2020 14:04> To: Doug Turnbull <
[hidden email]>;
[hidden email]> 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:
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