I would like to see the KPA-1500 have a "Medium Power" setting with optimized
bias for that power level so the amp could be operated at 750-watts output and
good efficiency. While the KPA-1500 can operate FT and RTTY contests at 1,500
watts, I believe the amp operated at 750-watts with an optimized bias setting
for that power level would generate less heat and less fan noise, both of which
would be very desirable when full power isn't required.
I'd sure appreciate Elecraft adding a half-power setting with optimized bias at
that power level. While the KPA-1500 can be run at half-power now, the
efficiency isn't very good.
73,Dick- K9OM
In a message dated 2/10/2020 9:14:07 AM Eastern Standard Time,
elecraft-requ...@mailman.qth.net writes:
Andy, Yes, you are right and this applies to both KPA 500 and KPA 1500.
Theconditions for maximum efficiency are not necessarily those for
minimumdissipation or reduced stress. I would like to know if running 2/3,
1/2or even 1/4 maximum power output increases reliability and MTBF. It
wouldbe a considerable surprise to me if this were not the case and it would
begood to know the numbers. Improvement in MTBF can be several fold forsome
devices for a reduction in voltage, current or power of as little as10%.
Good design practice normally means that this is part of theengineering design
process. The proof of derating is looked for in designreviews. Too many hams
run their amplifiers flat out for very littlebenefit. Signal cleanliness is
still another issue; higher voltage butlower power seems to help here.
Using FT8 or WSPR on dead band (160M in daytime or 12M), I sometimesrun 20
Watts plus. This can be stressful on the K3 especially for WSPR.I crank the K3
down to a watt or so and drive the KPA 1500. Yes, my totalenergy consumption
is no doubt up but stress on either K3 or KPA is minimal.This however is not my
concern, I would like to know if running the KPA atlower power increases
reliability. In EI we can run 1500 Watts forcontests but outside of contests
can only run 400W max.
73 Doug EI2CN
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