Once upon a time. When I was in childhood i have travelled in this train once. On that day i think the link is EMD.
While I deboarded 12639 at SBC. I have waited for 12786 upto 3hrs. When the train has shunted to a platform all UR Pass are rushed to GS coach then finally i have sat on upper seat i.e., on grills. On that day almost gone on time to KCG. At that time PENUKONDA route is not electrified. At KCG i have spotted 12798 and other trains.