Here’s the deal with tube testing:
A tube tester can tell you if a tube is bad, and if so, it can tell you how the tube is bad. But generally speaking, a tube tester can’t tell you with certainty whether a tube is actually good for a particular application. I find tube testers to be helpful in weeding out shorted power tubes so I don’t install them and cause damage to an amp. It’s still possible, though, to have a tube tester declare a tube as “good” and then have the tube exhibit problems of one sort or another (microphonics, noise, weakness, nonlinearity, instability, etc.) when it is installed in an amp and operating at full voltages under duress.
Tube testing takes time. I clean the pins on used tubes before putting them in my tester; most old tubes have dirty and/or corroded pins and I don’t want to introduce any of that crud into the sockets on the tester and cause potential tester problems or incorrect readings. It takes time for each tube to warm up and stabilize before any readings can be taken. And I’ve found it helpful to check certain tubes in two different testers because they can check for different characteristics under different conditions. Even after all of that, I’m able to say that some tubes are definitely bad, and the rest, I can only say, “Maybe good.” Even the best testers still can’t duplicate all critical operating conditions. We still won’t know for sure until the tube is actually in the amp – and even then its performance can vary depending upon where it is in the circuit.
It’s a time-consuming process, and as a result, it can become expensive. The bottom line is that even with rigorous testing, a tube may be good ‘by the numbers’ and still not perform as desired in actual application. The amp itself is always the final exam.
So – with all of that as a caveat… Yes, I can test tubes. Is it worth it? You’ll have to decide.