Bob, what are the TX IMD3 specs on the KPA1500 if you know please?
The SPE uses a switchmode PSU, so voltage switching is simpler to provide
A current draw higher in lower power ( current value 25 -30 amps seems
to be the most efficient range),
using lower voltage. So controlling the voltage keeps the current draw
higher in the efficient range,
is my take on it. I have the SPE 1.5KFA here as you know. The biggest
threat to the LDMOS if temperature is managed,
is sudden changes in load impedance , short or open antenna line.
However at low voltage the survival rate is vastly improved.
Running a new antenna is low power profile is a good start to test the
antenna integrity, before higher power is applied.
I have replaced one LDMOS myself, a good experience using a stove
hotplate to sweat the old LDMOS off and on with the new.
http://vk4tux.duckdns.org/1.5KFA/LDMOS/20210412_113924.jpg
I am also setting up a water cooled LDMOS replacement using a GPU heat
exchanger ;
http://vk4tux.duckdns.org/1.5KFA/LDMOS/20210617_112316wc.jpg
The KPA1500 has a transformer supply ?
regards
Adrian Fewster
On 12/7/21 11:55 am, Bob Wilson, N6TV wrote:
On Sat, Jul 10, 2021 at 10:36 AM jim.thom jim.thom@telus.net <
jim.thom@telus.net> wrote:
Date: Thu, 8 Jul 2021 14:50:40 -0400
From: <john@kk9a.com>
To: <amps@contesting.com>
Subject: Re: [Amps] FT8 power with the KPA1500
<From an amplifier heating standpoint it probably makes very little
<difference what power level you use with an Elecraft KPA1500. See the
<Elecraft post on efficiency in the link below. I am not an amp guru but I
<believe SPE Expert amps have different PA voltages which increases their
<lower power efficiency.
<http://mailman.qth.net/pipermail/elecraft/2018-August/259502.html
<73,
<John KK9A
### Per the link above, the KPA-1500 only makes 51.9% eff at 1.5 kw
output. The german B26 amp is 70% eff at 1.5 kw.
The 51.9% efficiency appears to be worst case at 1500W output.
The efficiency of the KPA1500 (Pout / Pin) varies from amplifier to
amplifier and from band to band.
The same may be true of the RF-Kit B26, but I have no way to measure one.
If someone on this list does have one, please post numbers.
I just measured the efficiency of two KPA1500s at 1500W out on the six main
contest bands, and here is the result.
*Band* *KPA1500 A* *KPA1500 B*
160m 52% 59%
80m 60 60
40m 50 54
20m 60 62
15m 61 51
10m 66 67
73,
Bob, N6TV
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