Posted by
Doug Turnbull on
Feb 10, 2020; 3:23pm
URL: http://elecraft.85.s1.nabble.com/QRO-KPA500-Failure-tp7658244p7658343.html
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
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