Part Number : D1557
Function : 1700V, Low frequency amplification bipolar transistor
Package : TO-3PIS Type
Maker : Jilin Sino-Microelectronics
Pinouts : 
Image
Description :
D1557 is a high back pressure NPN bipolar power transistor, manufacturing The main technology employed: high-pressure technology mesa, triplet Diffusion of technology, the use of plastic full encapsulation structure. V cbo = 1700V.
Reference Site :
http://monitor.espec.ws/section27/topic78212.html
Datasheet PDF Download : 
Others datasheet of same file : 3DD1557
2SD1557