[Elecraft] Power oscillation problem (KPA500+KAT500)

[Victor Rosenthal 4X6GP]

Perhaps check and see if the drive from the TS-590s is varying, or if 
the gain of the KPA500 is changing. What does the output meter on the 
590 say when this happens?

73,
Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
CWops no. 5
http://www.qsl.net/k2vco/

On 21/11/2023 14:50, Andy Durbin wrote:
> Thanks to those that replied with suggestions.
> 
> This morning I ran some additional testing.  I found I could induce
> the oscillation at 70 W KPA500 output power.  With KPA500 switched to
> STBY I could run 100 W from my TS-590S with no anomalies.  The only
> change in the antenna system configuration is that KPA500 is in STBY
> not OPER.
> 
> The time for onset of oscillation , and the frequency of oscillation,
> both depend on the power level. The higher the power the quicker the
> onset and the higher the frequency.  To me that suggests a thermal
> problem rather than voltage induced breakdown.
> 
> The only ferrite in the 40 m antenna system is in the KPA500 LPF and
> the KAT500 tuning inductors.  The KAT500 inductor configuration was
> the same for 100 W STBY and 70 W OPER test.   Those two facts would,
> if taken in isolation,  suggest a problem in the KPA500 40 m LPF.
> However, the LPF seems happy at 500 W with the dummy load.
> 
> I'm finding it hard to find a failure mode that fits all the test
> data.
> 
> 73, Andy, k3wyc
> 
> ______________________________________________________________ 
> 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
> k2vco.vic at gmail.com