[Elecraft] Power oscillation problem (KPA500+KAT500)

[Clay Autery]

NOT directly related, and MAY not be related AT ALL.... but consider 
clearing the tuning solutions stored on a section of the band where it 
oscillates and let it RE-tune at a power level JUST below what it was 
oscillating at....

Then turn her up and see if it still does it.  Likely will, but just 
wanted to eliminate the tuner/tuners fighting.

Ideally, I would clear the memory on the KAT500 and internal ATU 
altogether, but that's a lot of "work" stored across there, so it's a 
decision you have to make.
Just a wild ass suggestion....

Do you have an ATU in the transceiver?  Do you have it turned off when 
using the KAT500?

Have you tried using the internal ATU with the KAT500 taken OUT of line 
and run the KPA500 through a well-tuned freq. at 100W or so?

If you don't have an internal ATU, is there a resonance frequency where 
you can run 100W without a tuner inline?  If so, do that too.

Basically, you need to construct circumstances that isolates or 
eliminates ONE device at a time.  ONCE you pin down what device is 
having the issue, then you can start figuring out what is causing the issue.


Apologize, but I got here late and missed some of the original details.  
Just trying to help.

Be well.

Clay E. Autery, Jr.
KY5G

On 11/21/2023 6:50 AM, 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
>
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