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KPA runaway issue

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W1GO (Joe)

KPA runaway issue

Elecraft faithful,

Any guidance with trouble shooting a KPA500 / K3 issue would be helpful.

Problem: KPA500, primarily in SSB, “redlines” (600W+ LED) after a few seconds of transmission / speech. This seems to be independent of band. With the KPA in standby, the K3 output power holds rock steady as indicated in the KPA.

Conditions:
- Only about 20W of drive in SSB can result in the “redlining” … To eliminate the redlining, I have to turn drive down to about 18W. … about 20W in CW provides about 500W fairly solid.
- The K3 is powered by a 70A supply that does not sag much upon K3 keydown (14V to ~13.7V indicated on K3)
- KPA is powered off 240 … I tried two different KPA transformer taps as I noticed with yellow tap the supply voltage right about 60V and occasionally a little below on key down. Supply voltage stays well above 60V with red tap but same “redlining” of the KPA.
- Have tried various mic gain compression settings using dynamic mikes. Without amp in-line I do fine with gain 30, compression 20 (10db). I’ve gone as low as gain 15 / compression 15 (~5db) with no impact.
- I’ve tried various TXG VCE rating from -1.5 to 1.5 … no impact.
- ALC on … ext ALC off …. varied these to see if there would be an impact. None.
- SWR (to different antennas) is <1.7 w/o KAT500 and <1.3 w/ KAT500

What I’ve tried / done:
- Gain / compression changes as above
- Checked K3 supply voltage and no significant voltage drop on key down
- Changed power supply to a 35A powering K3 with no change
- Varied KPA transformer taps to ensure supply above 60V
- Changed coax between K3 and KPA and KPA and KAT500
- Tried with two different antennas / coax runs and had same result
- Varied TXG VCE from -1.5 to 1.5
- Performed gain calibration on K3

I’ve had the KPA for about 9 months but primarily operated CW so not sure if this is a recent occurrence. Any other suggestions would be appreciated.

Many thanks, all, and have a wonderful weekend.

Kindest regards,

Joe
W1GO

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Guy Olinger K2AV

Re: KPA runaway issue

Run the 5 and 50 watt TX power calibration on the K3. It's in the K3
utility program.

73, Guy K2AV

On Sat, May 6, 2017 at 12:51 PM W1GO (Joe) <[hidden email]> wrote:

>
> Elecraft faithful,
>
> Any guidance with trouble shooting a KPA500 / K3 issue would be helpful.
>
> Problem: KPA500, primarily in SSB, “redlines” (600W+ LED) after a few
> seconds of transmission / speech. This seems to be independent of band.
> With the KPA in standby, the K3 output power holds rock steady as indicated
> in the KPA.
>
> Conditions:
> - Only about 20W of drive in SSB can result in the “redlining” … To
> eliminate the redlining, I have to turn drive down to about 18W. … about
> 20W in CW provides about 500W fairly solid.
> - The K3 is powered by a 70A supply that does not sag much upon K3
> keydown (14V to ~13.7V indicated on K3)
> - KPA is powered off 240 … I tried two different KPA transformer taps as
> I noticed with yellow tap the supply voltage right about 60V and
> occasionally a little below on key down. Supply voltage stays well above
> 60V with red tap but same “redlining” of the KPA.
> - Have tried various mic gain compression settings using dynamic mikes.
> Without amp in-line I do fine with gain 30, compression 20 (10db). I’ve
> gone as low as gain 15 / compression 15 (~5db) with no impact.
> - I’ve tried various TXG VCE rating from -1.5 to 1.5 … no impact.
> - ALC on … ext ALC off …. varied these to see if there would be an
> impact. None.
> - SWR (to different antennas) is <1.7 w/o KAT500 and <1.3 w/ KAT500
>
>
> What I’ve tried / done:
> - Gain / compression changes as above
> - Checked K3 supply voltage and no significant voltage drop on key down
> - Changed power supply to a 35A powering K3 with no change
> - Varied KPA transformer taps to ensure supply above 60V
> - Changed coax between K3 and KPA and KPA and KAT500
> - Tried with two different antennas / coax runs and had same result
> - Varied TXG VCE from -1.5 to 1.5
> - Performed gain calibration on K3
>
>
>
> I’ve had the KPA for about 9 months but primarily operated CW so not sure
> if this is a recent occurrence. Any other suggestions would be appreciated.
>
> Many thanks, all, and have a wonderful weekend.
>
>
>
> Kindest regards,
>
> Joe
> W1GO
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
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> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

--
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W1GO (Joe)

Re: KPA runaway issue

Guy,

Yes. I did that. I meant to say TX calibration below … I said gain calibration.

Thanks.

Joe

> On May 6, 2017, at 1:07 PM, Guy Olinger K2AV <[hidden email]> wrote:
>
> Run the 5 and 50 watt TX power calibration on the K3. It's in the K3 utility program.
>
> 73, Guy K2AV
>
> On Sat, May 6, 2017 at 12:51 PM W1GO (Joe) <[hidden email] <mailto:[hidden email]>> wrote:
>
> Elecraft faithful,
>
> Any guidance with trouble shooting a KPA500 / K3 issue would be helpful.
>
> Problem: KPA500, primarily in SSB, “redlines” (600W+ LED) after a few seconds of transmission / speech. This seems to be independent of band. With the KPA in standby, the K3 output power holds rock steady as indicated in the KPA.
>
> Conditions:
> - Only about 20W of drive in SSB can result in the “redlining” … To eliminate the redlining, I have to turn drive down to about 18W. … about 20W in CW provides about 500W fairly solid.
> - The K3 is powered by a 70A supply that does not sag much upon K3 keydown (14V to ~13.7V indicated on K3)
> - KPA is powered off 240 … I tried two different KPA transformer taps as I noticed with yellow tap the supply voltage right about 60V and occasionally a little below on key down. Supply voltage stays well above 60V with red tap but same “redlining” of the KPA.
> - Have tried various mic gain compression settings using dynamic mikes. Without amp in-line I do fine with gain 30, compression 20 (10db). I’ve gone as low as gain 15 / compression 15 (~5db) with no impact.
> - I’ve tried various TXG VCE rating from -1.5 to 1.5 … no impact.
> - ALC on … ext ALC off …. varied these to see if there would be an impact. None.
> - SWR (to different antennas) is <1.7 w/o KAT500 and <1.3 w/ KAT500
>
>
> What I’ve tried / done:
> - Gain / compression changes as above
> - Checked K3 supply voltage and no significant voltage drop on key down
> - Changed power supply to a 35A powering K3 with no change
> - Varied KPA transformer taps to ensure supply above 60V
> - Changed coax between K3 and KPA and KPA and KAT500
> - Tried with two different antennas / coax runs and had same result
> - Varied TXG VCE from -1.5 to 1.5
> - Performed gain calibration on K3 (TX calibration)
>
>
>
> I’ve had the KPA for about 9 months but primarily operated CW so not sure if this is a recent occurrence. Any other suggestions would be appreciated.
>
> Many thanks, all, and have a wonderful weekend.
>
>
>
> Kindest regards,
>
> Joe
> W1GO
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft <http://mailman.qth.net/mailman/listinfo/elecraft>
> Help: http://mailman.qth.net/mmfaq.htm <http://mailman.qth.net/mmfaq.htm>
> Post: mailto:[hidden email] <mailto:[hidden email]>
>
> This list hosted by: http://www.qsl.net <http://www.qsl.net/>
> Please help support this email list: http://www.qsl.net/donate.html <http://www.qsl.net/donate.html>
> Message delivered to [hidden email] <mailto:[hidden email]>
> --
> Sent via Gmail Mobile on my iPhone

______________________________________________________________
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Vic Rosenthal

Re: KPA runaway issue

In reply to this post by W1GO (Joe)

Just a guess, but if it happens in SSB but not CW, look for RF feedback into audio circuitry.

Vic 4X6GP

> On 6 May 2017, at 19:49, W1GO (Joe) <[hidden email]> wrote:
>
>
> Elecraft faithful,
>
> Any guidance with trouble shooting a KPA500 / K3 issue would be helpful.
>
> Problem: KPA500, primarily in SSB, “redlines” (600W+ LED) after a few seconds of transmission / speech. This seems to be independent of band. With the KPA in standby, the K3 output power holds rock steady as indicated in the KPA.
>
> Conditions:
> - Only about 20W of drive in SSB can result in the “redlining” … To eliminate the redlining, I have to turn drive down to about 18W. … about 20W in CW provides about 500W fairly solid.
> - The K3 is powered by a 70A supply that does not sag much upon K3 keydown (14V to ~13.7V indicated on K3)
> - KPA is powered off 240 … I tried two different KPA transformer taps as I noticed with yellow tap the supply voltage right about 60V and occasionally a little below on key down. Supply voltage stays well above 60V with red tap but same “redlining” of the KPA.
> - Have tried various mic gain compression settings using dynamic mikes. Without amp in-line I do fine with gain 30, compression 20 (10db). I’ve gone as low as gain 15 / compression 15 (~5db) with no impact.
> - I’ve tried various TXG VCE rating from -1.5 to 1.5 … no impact.
> - ALC on … ext ALC off …. varied these to see if there would be an impact. None.
> - SWR (to different antennas) is <1.7 w/o KAT500 and <1.3 w/ KAT500
>
>
> What I’ve tried / done:
> - Gain / compression changes as above
> - Checked K3 supply voltage and no significant voltage drop on key down
> - Changed power supply to a 35A powering K3 with no change
> - Varied KPA transformer taps to ensure supply above 60V
> - Changed coax between K3 and KPA and KPA and KAT500
> - Tried with two different antennas / coax runs and had same result
> - Varied TXG VCE from -1.5 to 1.5
> - Performed gain calibration on K3
>
>
>
> I’ve had the KPA for about 9 months but primarily operated CW so not sure if this is a recent occurrence. Any other suggestions would be appreciated.
>
> Many thanks, all, and have a wonderful weekend.
>
>
>
> Kindest regards,
>
> Joe
> W1GO
>

W1GO (Joe)

Re: KPA runaway issue

In reply to this post by W1GO (Joe)

All,

One additional factoid of interest … when in ESSB mode, the runaway issue doesn’t occur; only in standard bandwidth mode. I’ve used standard bandwidth recently with out the KPA500 on and I’ve had no power out issues of poor audio reports. Hence, it seems that somewhere after the K3 there are oscillations resulting (or at least only noticeable) from the narrower bandwidth signal. Interesting.

Take care, all. If and when i figure it out I’ll share. BTW, I did switch miss from a boom with foot pedal to a short cable desk mic just to rule that out.

Joe

> On May 6, 2017, at 12:49 PM, W1GO (Joe) <[hidden email]> wrote:
>
>
> Elecraft faithful,
>
> Any guidance with trouble shooting a KPA500 / K3 issue would be helpful.
>
> Problem: KPA500, primarily in SSB, “redlines” (600W+ LED) after a few seconds of transmission / speech. This seems to be independent of band. With the KPA in standby, the K3 output power holds rock steady as indicated in the KPA.
>
> Conditions:
> - Only about 20W of drive in SSB can result in the “redlining” … To eliminate the redlining, I have to turn drive down to about 18W. … about 20W in CW provides about 500W fairly solid.
> - The K3 is powered by a 70A supply that does not sag much upon K3 keydown (14V to ~13.7V indicated on K3)
> - KPA is powered off 240 … I tried two different KPA transformer taps as I noticed with yellow tap the supply voltage right about 60V and occasionally a little below on key down. Supply voltage stays well above 60V with red tap but same “redlining” of the KPA.
> - Have tried various mic gain compression settings using dynamic mikes. Without amp in-line I do fine with gain 30, compression 20 (10db). I’ve gone as low as gain 15 / compression 15 (~5db) with no impact.
> - I’ve tried various TXG VCE rating from -1.5 to 1.5 … no impact.
> - ALC on … ext ALC off …. varied these to see if there would be an impact. None.
> - SWR (to different antennas) is <1.7 w/o KAT500 and <1.3 w/ KAT500
>
>
> What I’ve tried / done:
> - Gain / compression changes as above
> - Checked K3 supply voltage and no significant voltage drop on key down
> - Changed power supply to a 35A powering K3 with no change
> - Varied KPA transformer taps to ensure supply above 60V
> - Changed coax between K3 and KPA and KPA and KAT500
> - Tried with two different antennas / coax runs and had same result
> - Varied TXG VCE from -1.5 to 1.5
> - Performed gain calibration on K3
>
>
>
> I’ve had the KPA for about 9 months but primarily operated CW so not sure if this is a recent occurrence. Any other suggestions would be appreciated.
>
> Many thanks, all, and have a wonderful weekend.
>
>
>
> Kindest regards,
>
> Joe
> W1GO
>
> ______________________________________________________________
> 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]

Nr4c

Re: KPA runaway issue

My KPA500 needs less than 20 watts on all bands. Are you just driving it too hard?

Sent from my iPhone
...nr4c. bill

> On May 6, 2017, at 3:01 PM, W1GO (Joe) <[hidden email]> wrote:
>
> All,
>
> One additional factoid of interest … when in ESSB mode, the runaway issue doesn’t occur; only in standard bandwidth mode. I’ve used standard bandwidth recently with out the KPA500 on and I’ve had no power out issues of poor audio reports. Hence, it seems that somewhere after the K3 there are oscillations resulting (or at least only noticeable) from the narrower bandwidth signal. Interesting.
>
> Take care, all. If and when i figure it out I’ll share. BTW, I did switch miss from a boom with foot pedal to a short cable desk mic just to rule that out.
>
> Joe
>
>> On May 6, 2017, at 12:49 PM, W1GO (Joe) <[hidden email]> wrote:
>>
>>
>> Elecraft faithful,
>>
>> Any guidance with trouble shooting a KPA500 / K3 issue would be helpful.
>>
>> Problem: KPA500, primarily in SSB, “redlines” (600W+ LED) after a few seconds of transmission / speech. This seems to be independent of band. With the KPA in standby, the K3 output power holds rock steady as indicated in the KPA.
>>
>> Conditions:
>> - Only about 20W of drive in SSB can result in the “redlining” … To eliminate the redlining, I have to turn drive down to about 18W. … about 20W in CW provides about 500W fairly solid.
>> - The K3 is powered by a 70A supply that does not sag much upon K3 keydown (14V to ~13.7V indicated on K3)
>> - KPA is powered off 240 … I tried two different KPA transformer taps as I noticed with yellow tap the supply voltage right about 60V and occasionally a little below on key down. Supply voltage stays well above 60V with red tap but same “redlining” of the KPA.
>> - Have tried various mic gain compression settings using dynamic mikes. Without amp in-line I do fine with gain 30, compression 20 (10db). I’ve gone as low as gain 15 / compression 15 (~5db) with no impact.
>> - I’ve tried various TXG VCE rating from -1.5 to 1.5 … no impact.
>> - ALC on … ext ALC off …. varied these to see if there would be an impact. None.
>> - SWR (to different antennas) is <1.7 w/o KAT500 and <1.3 w/ KAT500
>>
>>
>> What I’ve tried / done:
>> - Gain / compression changes as above
>> - Checked K3 supply voltage and no significant voltage drop on key down
>> - Changed power supply to a 35A powering K3 with no change
>> - Varied KPA transformer taps t

Don Wilhelm

Re: KPA runaway issue

In reply to this post by W1GO (Joe)

Joe,

That may be "no problem at all". Unfortunately, you will not know that
answer unless you can borrow a 'scope that can observe the RF input to
the KPA500.

Some microphones and combinations of mic gain and compression may cause
power output of the K3 to exceed the level obtained by a K3 keydown in CW.

Those peaks will cause the KPA500 output to go above the level obtained
with CW.

Reduce the K3 power setting if you find that effect disconcerting.

73,
Don W3FPR

On 5/6/2017 12:49 PM, W1GO (Joe) wrote:

>
> Elecraft faithful,
>
> Any guidance with trouble shooting a KPA500 / K3 issue would be helpful.
>
> Problem: KPA500, primarily in SSB, “redlines” (600W+ LED) after a few seconds of transmission / speech. This seems to be independent of band. With the KPA in standby, the K3 output power holds rock steady as indicated in the KPA.
>
> Conditions:
> - Only about 20W of drive in SSB can result in the “redlining” … To eliminate the redlining, I have to turn drive down to about 18W. … about 20W in CW provides about 500W fairly solid.
> - The K3 is powered by a 70A supply that does not sag much upon K3 keydown (14V to ~13.7V indicated on K3)
> - KPA is powered off 240 … I tried two different KPA transformer taps as I noticed with yellow tap the supply voltage right about 60V and occasionally a little below on key down. Supply voltage stays well above 60V with red tap but same “redlining” of the KPA.
> - Have tried various mic gain compression settings using dynamic mikes. Without amp in-line I do fine with gain 30, compression 20 (10db). I’ve gone as low as gain 15 / compression 15 (~5db) with no impact.

briancom

Re: KPA runaway issue

In reply to this post by Nr4c

Hopefully AGC is not being used at all.
73 de Brian/K3KO

On 5/6/2017 23:46 PM, Nr4c wrote:

> My KPA500 needs less than 20 watts on all bands. Are you just driving it too hard?
>
> Sent from my iPhone
> ...nr4c. bill
>
>
>> On May 6, 2017, at 3:01 PM, W1GO (Joe) <[hidden email]> wrote:
>>
>> All,
>>
>> One additional factoid of interest … when in ESSB mode, the runaway issue doesn’t occur; only in standard bandwidth mode. I’ve used standard bandwidth recently with out the KPA500 on and I’ve had no power out issues of poor audio reports. Hence, it seems that somewhere after the K3 there are oscillations resulting (or at least only noticeable) from the narrower bandwidth signal. Interesting.
>>
>> Take care, all. If and when i figure it out I’ll share. BTW, I did switch miss from a boom with foot pedal to a short cable desk mic just to rule that out.
>>
>> Joe
>>
>>> On May 6, 2017, at 12:49 PM, W1GO (Joe) <[hidden email]> wrote:
>>>
>>>
>>> Elecraft faithful,
>>>
>>> Any guidance with trouble shooting a KPA500 / K3 issue would be helpful.
>>>
>>> Problem: KPA500, primarily in SSB, “redlines” (600W+ LED) after a few seconds of transmission / speech. This seems to be independent of band. With the KPA in standby, the K3 output power holds rock steady as indicated in the KPA.
>>>
>>> Conditions:
>>> - Only about 20W of drive in SSB can result in the “redlining” … To eliminate the redlining, I have to turn drive down to about 18W. … about 20W in CW provides about 500W fairly solid.
>>> - The K3 is powered by a 70A supply that does not sag much upon K3 keydown (14V to ~13.7V indicated on K3)
>>> - KPA is powered off 240 … I tried two different KPA transformer taps as I noticed with yellow tap the supply voltage right about 60V and occasionally a little below on key down. Supply voltage stays well above 60V with red tap but same “redlining” of the KPA.
>>> - Have tried various mic gain compression settings using dynamic mikes. Without amp in-line I do fine with gain 30, compression 20 (10db). I’ve gone as low as gain 15 / compression 15 (~5db) with no impact.
>>> - I’ve tried various TXG VCE rating from -1.5 to 1.5 … no impact.
>>> - ALC on … ext ALC off …. varied these to see if there would be an impact. None.
>>> - SWR (to different antennas) is <1.7 w/o KAT500 and <1.3 w/ KAT500
>>>
>>>
>>> What I’ve tried / done:
>>> - Gain / compression changes as above
>>> - Checked K3 supply voltage and no significant voltage drop on key down
>>> - Changed power supply to a 35A powering K3 with no change
>>> - Varied KPA transformer taps t
>
> ______________________________________________________________
> 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]
>

K8TE

Re: KPA runaway issue

In reply to this post by W1GO (Joe)

Joe,

Did you come to a solution to this problem? I have the same issue with my
K3 #2 (not S) and accomplished all the possible fixes you did.

73, Bill, K8TE

--
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