I'd be pissed that some tech decided I need new pre amp tubes, and also decided what kind. You were not asked to approve this? You may have had power tubes that were on the outs but pre amp tubes just get changed? That aside, how does it sound. I would never go to that tech again unless it sounds great, better than when you brought it in. Even so I would still want to discuss the work before it's done. Unless you told them, "just do whatever you think is best".... Which I have learned the hard way not to do. It's too bad but a lot of techs suck and return amps in worse shape than they went in.
I remember on the Marshall forum some dude sent his head into the factory for a "tune-up" and he got it back with all his NOS glass pulled and some new CP JJ's or whatever in the amp.
IMO you should only get your amp serviced if it doesn't sound right, or if you have vintage gear that needs a cab job, or some such thing.