Old Tubes and Tube Tester in 2-Channel Home Audio Posted December 24, 2010 If you can buy a restored/calibrated mutual conductance tester within your budget from a reliable seller, that's great. Usually, the better units, like Hickoks, go for $500 give or take. But, if you just want to know if a tube is good or bad, look around for something like a Sencore Mighty Mite tester. They can often be found in the $75 price range and are very reliable testers within the context of what they can do. What makes you think that the tester that you have doesn't work? Do you have the manual and tube chart for it? If not, those can usually be found online for free from various sites.