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Re: [CQ-Contest] Elecraft KPA 1500 vs.OM 2000A

To: cq-contest@contesting.com
Subject: Re: [CQ-Contest] Elecraft KPA 1500 vs.OM 2000A
From: N4ZR <n4zr@comcast.net>
Date: Wed, 11 Mar 2020 12:33:26 -0400
List-post: <mailto:cq-contest@contesting.com>
I just heard V55A's end of our 10-meter QSO, running about 1400 watts to my KPA-1500, and I'm blown away.  It sounded just the same as when I play my recorded messages here.  Granted, I was careful not to drive it into ALC, but still...

73, Pete N4ZR
Check out the Reverse Beacon Network
at <http://reversebeacon.net>, now
spotting RTTY activity worldwide.
For spots, please use your favorite
"retail" DX cluster.

On 3/11/2020 7:49 AM, alannottage--- via CQ-Contest wrote:
One other thing, Bill - have a listen to your intended LDMOS PA on phone.  I have NOT knowingly 
heard the above one, but there were one or two sigs this past ARRL DX SSB that sounded short of standing 
current.  Probably cheaper units with insufficient cooling but just saying.  This almost 
never happens with a valve PA.  You don't want to spoil your reputation for fine contest audio!
Al G0XBV

-----Original Message-----
From: rjairam@gmail.com <rjairam@gmail.com>
To: john@kk9a.com <john@kk9a.com>
CC: CQ-Contest <cq-contest@contesting.com>
Sent: Wed, 11 Mar 2020 1:33
Subject: Re: [CQ-Contest] Elecraft KPA 1500 vs.OM 2000A

Correct. I did mention that.

But 3:1 is not an issue for many. The filter is the weak point.

Tubes have failures under high SWR, particularly heat and arcing
(sputtering). They aren't infallible.

Ria
N2RJ

On Tue, 10 Mar 2020 at 20:16, john@kk9a.com <john@kk9a.com> wrote:
I have little RF amplifier knowledge however I believe that your 66:1 SWR comment is 
for pulsed service which has a much lower duty cycle than a typical amateur radio 
transmission, especially the popular FT8 mode.  A higher duty cycle with high 
SWR creates more heat that needs to be dissipated. A LDMOS can definitely fail, even 
on commercial amps with protection circuits.

John KK9A


Sent via the Samsung Galaxy 7 edge, an AT&T 4G LTE smartphone.


On Tue, Mar 10, 2020 at 10:32 PM rjairam@gmail.com <rjairam@gmail.com> wrote:
LDMOS itself does not require perfect SWR. The older MOSFETS did. LDMOS do not. 
They can be operated at 66:1 SWR. This is a dead short at full output. There 
are videos of them arcing with them and welding. Probably not for extended duty 
cycle, but guess what- neither can your ceramic tube amp with tubes made of 
unobtainium.

The fragile parts in a solid state amp that are affected by high SWR are the 
filter network, the capacitors and inductors.

The software in modern amplifiers, if properly implemented will absolutely 
protect your amplifier and antenna system. If you throw high SWR it will shut 
down or fold back (de-rate).

The KPA1500 has an internal antenna tuner that can handle up to 6:1 SWR.

Other amplifiers such as the PGXL (which I have) can operate at high SWR with no tuner. I can 
run mine at 2.5:1 with software derating. I get about 1.3kw out of it at that high SWR. With 
about 3:1 SWR I can do about 500w depending on the band. Beyond that I get a fault. With 2:1 
SWR I can do 1.5kW. There is a tuner being developed for that one as well. I don’t 
abuse it and I try to run my antennas resonant. I’ve had this amp since it was being 
alpha tested and run it through a variety of antennas and duty cycle.

I also ran an Alpha 91B so I have an idea of what a tube amp can do. The solid 
state amps work well and in terms of SWR tolerance are pretty good. Elecraft 
and SPE did a very good thing by including built in antenna tuners. The SPE 
implementation is excellent as it follows CAT. From my limited use of the 
KPA1500 it seems To do the same thing.

This is based on my actual experience and not assumptions.

73
Ria, N2RJ



On Tue, Mar 10, 2020 at 6:11 PM <john@kk9a.com> wrote:
Those are two completely different animals, one is lightweight and has
LDMOS finals that need an antenna tuner or a perfect antena and the
other uses a ceramic tetrode that can tolerate 3:1 SWR. A tetrode
tunes differently than a triode but perhaps the auto tune takes care
of this.  I am not sure if there is an OM power list but there is an
Elecraft list where you can follow any issues or complaints that
people may have.  Is quietness a concern? Is quickly setting it up
without a lot of adjustments a concern?

FWIW, I have used an Acom 2000A several times and basically I just
plugged it in and it worked plus it's super quiet. The only issue I
have saw with this amp is that it is sensitive to arcs in the antenna
system.

John KK9A



K4XS wrote:

Looking for a backup amp for the new station.  Probably going to run
SO2R so auto-tune is important.  I'm running a K3S and the second
radio will also be a K3S.  I really don't care if the amp "matches"
the K3S in looks.  Like most of you guys I'm concerned about
performance.  Both rigs are equal in price.
Here's the question:  If you were buying a new amp and were buying it
to satisfy the above criteria, which would you choose and why?
K4XS


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