[R-390] RF Deck Mod 6?

[Jim Miller]

I have a Collins 390a SN248 order number 375-P-54 with a Collins RF deck.  The
RF deck has "MOD 6" stamped on it (on top of the sub chassis in the rear).  I
can find no reference to Mod 6 in any of my manuals,...Does anyone know what Mod
6 was?

Thanks
Jim N4BE