The SKA6516 (P/N 151-0367-00) is a Selected NPN Transistor

NB Incomplete and/or incorrect info

Testing discrete component lookup

I'd guess they're used in the 464, 466, 475A and maybe 475M - not yet check the service manuals.

Zenwizard Studios found thirteen of these in a 475 and thirteen of those tested as having a parasitic reverse diode junction.

I've listed eighteen from the 475 Service Manual in the 475 Repairs page.