Dear Jim,

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While I was describing the method for employing a

non-inductive resistor in place of the tube circuit

in a grid-driven tetrode scheme, the methodology

carries into basically the same steps in tuning

in the input circuit of a triode.

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Does your amplifier have a way to fine-tune

the RF Input?

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Then, yanking the tubes and soldering in

an N.I. is the least destructive method of

starting to pinpoint the sweet spot.

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For now, leave off the SpecAn completely.

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The VNA looking into the amplifier input

port will provide a “notch” in the VNA

linear display such as determining the

Return Loss. The reason I mentioned

adding something like a 10pF silver mica

is for you to see the result of this both

in the linear return loss graph and on

the Smith Chart display.

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Adding tiny amounts of capacitance or

inductance will cause these displays to

change shape sharply, and may give you

a clue as to what may be needed to

move on to the 50 ohm, J-zero location

on the VNA Smith Chart.

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A method I find useful is to actually wire

up a Pi filter on the input circuit and use

some sort of reflectometer, like a Fwd/Refl

SWR meter, and to tweak the amp input in real time,

like a “double tune-up,” but all this takes

so much time while the ionosphere is boiling

away at the speed of light.

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Hal

W4HBM