[Milsurplus] Pre-WW2 USAAF nomenclature

[Hue Miller]

Okay, so far we know, for AIRCRAFT at least:

SCR-AB-XYZ

X relates to input voltage, of course. 
1= 12-14  volt
2= 24-28 volt

For two different equipment set-numbers YZ, the
two sets can use some of same exact BC components,
but have a different set purpose. For example,
communications for one, and radiocompass for the other.

Since the unique Y,Z letters place the equipment in the
series and the purpose is contained in the definition 
next to the X, Y, Z in the list, letter A probably won't
be the purpose or type designator.

I also note that SCR letter B does not need to use the 
same B letter in the BC nomenclature. To explain,
SCR-AB-186 uses receiver SCR-AE-179. Neat system,
yes?

So - was this already speculated here? can letter A 
represent the manufacturer? I have pawed thru 
schematics and system drawings in the back of my
manuals but nowhere is there seen, the name of the
manuafacturer of the overall set.
-Hue