[Elecraft] KPA runaway issue

[Don Wilhelm]

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.