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KPA1500 Drive Power

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K9MA

KPA1500 Drive Power

I'm using the K3 with the Elecraft interface cable. I've noticed the
the CW drive power required by mine varies considerably, both with
temperature and SWR. If I set the K3 output for a KPA1500 output of
1500 W output initially, the output will drop to perhaps 1100 W when the
temperature stabilizes at around 65 C. (I've ruled out any change in
antenna impedance, etc.) A similar change occurs if the SWR goes from
1:1 to 1.2:1 when changing frequency or switching antennas. I haven't
changed the ALC from the default setting. Has anyone else noticed this?

73,

Scott K9MA

--
Scott K9MA

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Elecraft mailing list

Re: KPA1500 Drive Power

Yup, as the temp climbs the output drops some. Even though I'm glad I got the solid state amp I still prefer tubes, hi. The drop is anywhere between 100 to maybe 300 watts.I never really noted the exact numbers.
BillK3WJV
p.s. I'm thinking its a normal solid state thing.

On Wednesday, May 30, 2018, 4:23:47 PM EDT, K9MA <[hidden email]> wrote:

I'm using the K3 with the Elecraft interface cable. I've noticed the
the CW drive power required by mine varies considerably, both with
temperature and SWR. If I set the K3 output for a KPA1500 output of
1500 W output initially, the output will drop to perhaps 1100 W when the
temperature stabilizes at around 65 C. (I've ruled out any change in
antenna impedance, etc.) A similar change occurs if the SWR goes from
1:1 to 1.2:1 when changing frequency or switching antennas. I haven't
changed the ALC from the default setting. Has anyone else noticed this?

73,

Scott K9MA

--
Scott K9MA

[hidden email]

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Paul Baldock

Re: KPA1500 Drive Power

Can you safely increase the drive to get it back to 1500W?

Another question: Is the drive requirement (amp
gain) pretty flat from band to band?

- Paul KW7Y

At 08:10 AM 5/31/2018, Bill Stravinsky via Elecraft wrote:

> Yup, as the temp climbs the output drops
> some.Â Even though I'm glad I got the solid
> state amp I still prefer tubes, hi.Â The drop
> is anywhere between 100 to maybe 300 watts.I
> never really noted the exact numbers. BillK3WJV
> p.s. I'm thinking its a normal solid state
> thing. On Wednesday, May 30, 2018, 4:23:47
> PM EDT, K9MA <[hidden email]> wrote: I'm
> using the K3 with the Elecraft interface
> cable.Â I've noticed the the CW drive power
> required by mine varies considerably, both with
> temperature and SWR.Â If I set the K3 output
> for a KPA1500 output of 1500 W output
> initially, the output will drop to perhaps 1100
> W when the temperature stabilizes at around 65
> C.Â (I've ruled out any change in antenna
> impedance, etc.)Â A similar change occurs if
> the SWR goes from 1:1 to 1.2:1 when changing
> frequency or switching antennas.Â I haven't
> changed the ALC from the default setting.Â Has
> anyone else noticed this? 73, Scott K9MA --
> ScottÂ K9MA [hidden email]
> ______________________________________________________________
> Elecraft mailing list Home:
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> [hidden email]
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K9MA

Re: KPA1500 Drive Power

In reply to this post by Elecraft mailing list

Yes, it does sound like a solid-state thing. Not enough negative feedback? It may be a reason NOT to run the fans continuously: Once it reaches 60 C, the fan control keeps the temperature fairly stable.

73,
Scott K9MA

----------

Scott Ellington

--- via iPad

> On May 31, 2018, at 10:10 AM, Bill Stravinsky <[hidden email]> wrote:
>
> Yup, as the temp climbs the output drops some. Even though I'm glad I got the solid state amp I still prefer tubes, hi. The drop is anywhere between 100 to maybe 300 watts.
> I never really noted the exact numbers.
>
> Bill
> K3WJV
>
> p.s. I'm thinking its a normal solid state thing.
>
> On Wednesday, May 30, 2018, 4:23:47 PM EDT, K9MA <[hidden email]> wrote:
>
>
> I'm using the K3 with the Elecraft interface cable. I've noticed the
> the CW drive power required by mine varies considerably, both with
> temperature and SWR. If I set the K3 output for a KPA1500 output of
> 1500 W output initially, the output will drop to perhaps 1100 W when the
> temperature stabilizes at around 65 C. (I've ruled out any change in
> antenna impedance, etc.) A similar change occurs if the SWR goes from
> 1:1 to 1.2:1 when changing frequency or switching antennas. I haven't
> changed the ALC from the default setting. Has anyone else noticed this?
>
> 73,
>
> Scott K9MA
>
> --
> Scott K9MA
>
> [hidden email]
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

K9MA

Re: KPA1500 Drive Power

In reply to this post by Paul Baldock

Yes, turning the drive up a bit restores the output to 1500 W.

I haven't recorded it, but drive seems fairly flat band to band. (The K3, of course, saves the drive levels for each band.)

73,
Scott K9MA

----------

Scott Ellington

--- via iPad

> On May 31, 2018, at 10:16 AM, Paul Baldock <[hidden email]> wrote:
>
> Can you safely increase the drive to get it back to 1500W?
>
> Another question: Is the drive requirement (amp gain) pretty flat from band to band?
>
> - Paul KW7Y
>
> At 08:10 AM 5/31/2018, Bill Stravinsky via Elecraft wrote:
>> Yup, as the temp climbs the output drops some.Â Even though I'm glad I got the solid state amp I still prefer tubes, hi.Â The drop is anywhere between 100 to maybe 300 watts.I never really noted the exact numbers. BillK3WJV p.s. I'm thinking its a normal solid state thing. On Wednesday, May 30, 2018, 4:23:47 PM EDT, K9MA <[hidden email]> wrote: I'm using the K3 with the Elecraft interface cable.Â I've noticed the the CW drive power required by mine varies considerably, both with temperature and SWR.Â If I set the K3 output for a KPA1500 output of 1500 W output initially, the output will drop to perhaps 1100 W when the temperature stabilizes at around 65 C.Â (I've ruled out any change in antenna impedance, etc.)Â A similar change occurs if the SWR goes from 1:1 to 1.2:1 when changing frequency or switching antennas.Â I haven't changed the ALC from the default setting.Â Has anyone else noticed this? 73, Scott K9MA -- ScottÂ K9MA [hidden email] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email]
>

Don Butler

Re: KPA1500 Drive Power

I have experienced power level changes with s/n 45 since day one. I had envisioned setting the K3s config to ‘power per band’, adjusting the power level to just below 1500 watts on each band, and then being able to switch bands and magically find that the power level is still sitting exactly where I left it ….. but no deal … typically, after I return to a band where the level had previously been right at 1500 watts, the first couple transmissions (CW) will often jump up to 1600-1700 watts …. It drops a little after the first couple dits, but I almost always have to readjust and crank down the drive power .... so I now crank down the drive and readjust every time I change bands ….. not what I had hoped for … and yes, I also see small decreases in power level as the temperature increases as others have noted.

Don, N5LZ

Sent from Mail for Windows 10

From: K9MA
Sent: Thursday, May 31, 2018 9:42 AM
To: Paul Baldock
Cc: Elecraft Reflector
Subject: Re: [Elecraft] KPA1500 Drive Power

Yes, turning the drive up a bit restores the output to 1500 W.

I haven't recorded it, but drive seems fairly flat band to band. (The K3, of course, saves the drive levels for each band.)

73,
Scott K9MA

----------

Scott Ellington

--- via iPad

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K9MA

Re: KPA1500 Drive Power

In reply to this post by K9MA

Now I'm really confused. I observed the power drop when operating
several times, as described below. However, I just ran a test, both with
an antenna and a dummy load, and saw only a very small change in output,
perhaps 50 W, which is inconsequential. I even tried simulating CW
operating in QSK mode. I can't think of anything else which has
changed. In each case, I'm reading the power output on the KPA1500
display, but it appears consistent with the P3 TX monitor. Any ideas?

BTW, the specs I've seen for LDMOS FET's like the ones I presume are
used in the KPA1500 show quite a small variation in gain with
temperature. Feedback should reduce that further. That would be
consistent with my test results, but not the operating ones.

I'll do some more "real" operating in a couple days and report the results.

73,
Scott K9MA

On 5/30/2018 15:19, K9MA wrote:

> I'm using the K3 with the Elecraft interface cable. I've noticed the
> the CW drive power required by mine varies considerably, both with
> temperature and SWR. If I set the K3 output for a KPA1500 output of
> 1500 W output initially, the output will drop to perhaps 1100 W when
> the temperature stabilizes at around 65 C. (I've ruled out any change
> in antenna impedance, etc.) A similar change occurs if the SWR goes
> from 1:1 to 1.2:1 when changing frequency or switching antennas. I
> haven't changed the ALC from the default setting. Has anyone else
> noticed this?
>
> 73,
>
> Scott K9MA
>

--
Scott K9MA

[hidden email]

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