[Fisherdude]

Old tube testers are pieces of old electronic equipment, just like an amp. They need to have out of spec components replaced before they can be calibrated. I'm not familiar with that model, but the testers I have sure have a lot more components than a few resistors. If yours is that simple underneath, I would suggest not putting much money into it. Otherwise, check whether or not the resistors are still good, clean sockets, do a visual check of wiring, etc. If the meter is bad, nothing will fix that. There are guys who work on old meters, but again, the cost will be more than the tester is worth.