Background of the 2N709 used in the CDC6600 supercomputer in the 1960s: https://cpldcpu.wordpress.com/2020/02/14/what-made-the-cdc66...

https://www.computerhistory.org/revolution/digital-logic/12/...

The functionally similar NPN switching transistor to the ancient 2N709 is still available. Search for PMBT2369.

Acronyms, BJT: Bipolar junction transistor