[Amps] KPA1500 Efficiency vs. RF-Kit B26

[Adrian]

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 at telus.net <
> jim.thom at telus.net> wrote:
>
>> Date: Thu, 8 Jul 2021 14:50:40 -0400
>> From: <john at kk9a.com>
>> To: <amps at 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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