Tread carefully here.
Unlees you already know, you need to discover if this person has the necessary skills and temperment to make both a good manager and good trainer. Much of this can be discovered by observation on your part.
This person may be the best help desk tech you have ever worked with, but that doesn't mean he will make either a good supervisor or a good trainer. Technical knowledge does not directly translate to management or teaching skill as many IT departments have discovered the hard way. After you give him the raise is not the time to learn that he manages by terror or his teaching style is akin to "Here, read this. Come back with any questions."
Depending on his experience and background, some training may be in order for him.
I would suggest a trial period - say 60 days (or call it an internship). Lay out your expectations. Let this tech know that while you are letting run with the ball, you will be watching. But also let him know that you are there to help him. You can't just dump these kinds of resonsibilites on someone who hasn't done it before. Someone (you?) will need to act as a mentor for him. Let him know that if he meets your expectations (both as supervisor and trainer), there is a raise (and official promotion) waiting for him at the end of the trial. The length of the trial period can be adjusted as you see fit , but don't make it too short.
Hope this helps.