[AMRadio] 4-400 (epilogue)

Mike Sawyer w3slk at hughes.net
Sun Mar 25 09:15:22 EST 2007

Can I take this out a little further: Wasn't the original post requesting 
when RCA first started producing 4-400's?

~~~~~~~~~PREVIOUSLY POSTED HERE ~~~~~~~~~~~
I talked with their Engineering Department today and
they confirmed that the
4-400 series began production in
the very late 40's and was first listed in the 1950
Eimac Tube Product

Since it is in my 1950 Eimac Catalog and not listed
earlier, I think we can
assume that Eimac is correct as to the dates of first

Eimac user for 55 yrs.
I missed this definitive posting from our friend
Bob/WSZ, as to when the 4-400 can be considered
first-available and in application.

Separately, does anyone have the precise distinction
among the suffixes "A,"  "C," and "PR?"  I know the
"PR" indicates Pulse Rated, but in years past I saw
some documents from Amperex indicating the "C"
designation was placed on Eimac's premium tubes only
as a result of hand-selection from the assembly line.

There was apparently no deliberate improvement made to
the "C" tubes, but rather, these were cherry picked
from the overall batch and had all the component
tolerances lined up just right. Statistical odds, not
a construction or design function.


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