{Collins} Need help -- 30K-1 downward modulation problem


I need some suggestions or advice for a 30K-1 I am working on.  When 
with 125 to 150 milliamp peaks on the modulator plate meter, I get serious 
modulation in the PA plate current and output.  The PA is loaded to 150 
at 2 kv and shows 200 watts output into a Bird wattmeter.  The PA plate 
varies downward by as much as 25 milliamps with the wattmeter showing a 
downward peak also.

I have checked the various voltages to make sure they are steady under 
HV only varies by 20 volts or so at 2 kv.  The modulator grid bias, PA grid 
bias, and PA screen voltages are steady under modulation.  I have swapped 
modulator tubes.

Can anyone offer an suggestions as to what to check next?  I'm just flat out 
of ideas
as to what might be causing this.

thanks, 73, Phil

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