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

[rjairam at gmail.com]

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 at kk9a.com <john at 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 at gmail.com <rjairam at 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 at 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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