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How to determine ("non-destructively") tetrode input impedance

Discussion in 'General Electronics Discussion' started by Solidus, Dec 31, 2013.

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  1. Solidus


    Jun 19, 2011
    Hey all,

    The title is reference to the fact that if possible, I'd prefer to have the correct ideas played out on paper before having to test the hard way on a build in progress.

    I'm still working on schematics for the 4-1000A RF linear I have planned, and I've hit a small kink in the situation - the input tuning network; that is, what converts input line characteristic impedance (50 ohm cable) to the input impedance of the tube at the grid.

    Obviously, approximating Zo can be found in the rough at the power supply and current correlations, but Zi I'm finding to be much more difficult and unlike standard triodes, there aren't easy-to-find standard equations that allow for calculation, as well as the RF tetrode manufacturers being much less reliant in their datasheets to supply you with every value.

    That being said, does the standard methodology of the 'grid-load' resistor apply here - is the input impedance (resistance, in this case) effectively determined by the value of the resistor loading the grid?

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