Here's an easy one for anyone who wants to make a start at playing by ear. It's in 4/4 time, Key of F concert which means G for Bb instruments (soprano and tenor and D for Eb instruments. The start note is E for Bb instruments and B for Eb instruments. By "start note" I mean the note that corresponds to the first word of the lyrics, "I" as in "
I went down to St. James' Infirmary...." (ignore the dranatically macabre intro) If you know the tune already, that makes it easier but if you don't, I suggest you break it up into phrases and copy first one, then the next until you can string them all together and play along with Satchmo. If you're new to playing by ear, don't worry about intervals and all the theoretical stuff. Simply start with the start note then hunt around for the next one, then when you've got that, hunt for the next and so on. That's how I started playing sax in the days when I didn't even know which way up the mouthpiece went!
I hope this works. I'm not a teacher but this method worked for me. Have fun and please let me know how you get on or tell me (and everyone else) if I'm plain wrong.
One other thing: take Colin the Bear's advice and learn the words, at least the first verse. That will help you to remember the tune.