You are not in tube hell.
If it was recently serviced, and not by you, is the service warranteed? Also, did you really get the feeling that the servicer was comfortable with the unit?
This isn't like modern stuff where, for the most part, you toss it when it breaks. Have faith.
Oh, and by the way, if you can do process of elimination work yourself, you may get at least part, if not all, of the way to resolving your own problem.
With the tube forum open, on the top, look through the tube amp stickies, and then use the forum search tools near the upper right and search on troubleshooting.