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



Hello,

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

I have checked the various voltages to make sure they are steady under 
modulation....
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
W5BVB 

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