[Milsurplus] WWII Navy RU- Receiver Coils.

[David Stinson]

Re: Coil sets for the WWII Aircraft RU-series receivers.

Have manuals for RU-2A, -5, -8, -13 and -16.
The coil sets for all of these, when examined with
the coil rightside-up, label to the right, counting
the coil contacts from front to back, are:
4, 4, 4, 4, 6Dn (contact gap down, BFO coil).
This is also the configuration in my RU-15 receiver.

I made the assumption that all the RU coil sets
from RU-2A and following were the same
configuration.  Finally piled-up my stash of
RU coils and surprise- there are three 
seemingly incompatable coil configurations.
In this photo, the "front" of the coils is to
the right and I count them right-to-left.
https://goo.gl/photos/Lh4PRy9WiHQn4DWt9

One configuration looks like that 
for SCR-183 and will plug into that rig,
though I don't know if it works there.
It would seem there is no BFO in these.
That configurtion is 4-4-4-4-4.
The third has two 6-contact: 4-4-4-6Up-6Dn.

I have coils for:

4-4-4-4-6Dn
RU-5, RU-7, RU-12, RU-13, RU-15, 
RU-16, RU-17, RU-18.

4-4-4-4-4
RU-7, RU-11, RU-12, RU-18, RU-19

4-4-4-6Up-6Dn
RU-6, RU-12, RU-16, RU-18

Note that RU-7, RU-12, RU-16 and RU-18 all have 
multiple configurations, -12 and -18 having all three.
-18 and -19 were supposedly for Liaison use,
so "No BFO winding" makes no sense.
The coil nomenclature tags give the "correct" 
coil numbers.  
i.e. RU-16 4-4-6 and RU-16 4-6-6 have 
the manual-listed coil numbers like CW-47112.

The 4-4-4-6Up-6Dn coils do show some
evidence of being "Ham-burglered."  Was there
some CQ article on modifying these with an 
extra BFO coil?
However, the 4-4-4-4-4 coils do not look
as though they have been molested.  A mod
to get them to work in SCR-183 receivers?
The RU-16 manual does not show 
the 4-4-4-6-6 configuration.

What do you think?  Is there an explaination
 or did someone "ham-bone" these coils? 

Does anyone have RU-6, RU-7, RU-11,
RU-12. RU-18 or RU-19 manuals
that can shed light on the original coil contacts 
or explain the multiple configurations?  There's usually
a photo of the contact side of the receiver coil
set somewhere in the first 14 to 18 pages.

TNKS OM ES 73 DE Dave AB5S