Do a search for "TIP31 Cross Reference". First one I saw was this. If there is any doubt, look up the datasheets for the items in question and compare them. A little bit of searching with the right keywords goes a long way. Qa Note: for whatever reason, the link won't take. Here's the web address: http://english.electronica-pt.com/db/cross-reference.php?ref=TIP31(A...F) Copy and paste it into your browser's address line.