Looking for guidance on small transistor replacement

[RobCalm]

Hello everyone,

I am trying to deal with noisy transistors in an old Sansui 300 receiver, but I am really new to transistor substitution.

I successfully replaced some really noisy 2SC458 transistors in the power amp section with 2PC945, after finding someone else had done that in a general search from google. the 945 specs seemed to indicate higher ratings all round.

So here is my question. What are the important things to look out for when making substitutions of these small transistors? Could I replace 2SC870 in the preamp with 2PC945 as well??

I apologise if my question is naive, but I'd love any help. If I need to provide more info, just ask

Rob