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) <w...@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@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 arch...@mail-archive.com
