[AMRadio] 4-400 (epilogue)

VJB wa3vjb at yahoo.com
Sun Mar 25 08:55:32 EST 2007

~~~~~~~~~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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