[Elecraft] KPA runaway issue

[Guy Olinger K2AV]

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) <w1go at icloud.com> 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:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to k2av.guy at gmail.com

-- 
Sent via Gmail Mobile on my iPhone