>
>>> Amen to that, Carl. 3mA to 10mA of grid current is bad news for a
>>> 4CX10000A. For a pair of 4CX800As, its downtown nutsville. OTOH, there
>>> is no FCC spec. for spurious feculence/splatter INSIDE the ham bands.
>>> Rich---
>
>Hi guys,
>
>... ... As a user of an ETO91b which uses a pair of 4CX800A/GU-74b's can
anyone
>tell me what the grid current is when the red 'grid max' light
>illuminates. Is it in the 3-10mA range that is 'nutsville'. I'd hate
>to damage the tubes as I believe they are quite delicate in the grid
>current area, even if they are cheaper than 3CX800's.
The "bad news" is not damage to the tubes' 2w-rated grids, Andrew. The
"bad news" is rotten splatter. In a grid-driven amplifier, a small
amount of grid current means a large amount of intermodulation
distortion.
According to Svetlana's spec. sheet, 3rd order IMD from a grid-driven
4CX800A is a respectable minus 30db with ZERO grid current. However,
with 3 to 10 mA of grid current, substantively higher distortion is a
certainty.
Rich---
R. L. Measures, 805-386-3734, AG6K
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