[Amps] Re: Which Vg2 for 4CX1500B SSB ?

[Will Matney <craxd1@ezwv.com>]

Peter,
Really, the screen voltage is set by the tube manufacturer for an 
allowable IMD, screen current, etc. by their voltage rating. The screen 
voltage can vary some from their ratings. The different screen voltages 
are done because of the design of each tube itself in order to have it 
work correctly and withing specs. I have seen 4CX250B's ran anywhere 
from +280 Vdc to +400 Vdc screen voltage. I think the factory spec is 
around +350 if I recall without looking. It will also change by what 
mode of operation it is ran at A, AB1, AB2, etc.). Those ratings are 
found on the manufacturers spec sheets for each tube. If the screen 
voltage is raised, it amplification (gain) is raised thus increasing the 
IMD. Decreasing the voltage would do the opposite by dropping the gain. 
Really, where you would personally set the G2 voltage at is up to the 
builder and how clean he is trying to build it.

Will

Hi all, I am new to this list and need some help.

In various ( linear SSB ) 4CX 1500B PA designs I have seen various Vg2
voltages from + 225 V until +300V.

As far as I could recall, the lower the Vg2 the lower the IMD3 (?)

What could be the reason for designing a ( SSB linear ) 4CX1500B circuit
with  Vg2 at 300 V ?
End of all, one of the reasons to choose for a 4CX1500B is the relative low
IMD3.
What are pro's and con's of such relatively high Vg2 ?

EIMAC's " Care and feeding.. " does not resolve this question for me .
Who could ?

Thanks for any explanation.

Peter, PE1E


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