[R-390] What's with the 5.3V filament

[Grayson Evans]

Can anyone tell me why the R390A IF deck 5314 limiter tube is run with a 5.3V filament?
while all the other tubes on the module run at 6.3?
Was there some reason to drastically lower the gain of this tube?  This is an odd way to do it. 
I read through the manual on the limiter section, but it makes no mention of the odd filament voltage.

Grayson
TA2ZGE - Ankara, Turkey
KJ7UM