[Elecraft] Power oscillation problem (KPA500+KAT500)

[Andy Durbin]

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