Although I can't find it there anymore, the site for Brent Jessee Recording, as I recall, did mention at one point who they consider to be the top guy to repair and recalibrate tube testers. Maybe you could email or call them.
Vacuum tube tester repair
Do any of you virtual peoples out there know of any one who repairs Hickok tube testers, specificly the ones made for Western Electric? I'm a techhead, but I would have to take up methamphetimines before even considering trying to fix this problem. Everything is working except it won't measure pentodes correctly. A wire was broken off a switch pole and I soldered it back to where it looked like it went. Maybe not. This thing has about a 1/4 mile of wiring, custom made switches, and schmatic that looks like one of those optical illusion drawings.