The “heart” of the FRR-49 Receiver. You can find extensive descriptions on Google. Heavy.Thanks for watching:Letizia G.
NOTE:I took over (at stratospheric price!) the entire collection of military equipments belonging to an elderly engineer (once living in the same Residence of mine) who moved to Portugal in October 2018. He purchased all his items,many times ago,declared  functioning by European collectors friends or Military auctions.
I transcribe the description that the previous collector / owner left for each item.