Tube testers

Probably the best is the Aplitrex tube tester.  It is extremely easy to use (no looking up tube types to set operating parameters), it gives both real numbers (emissions, transconductance, noise) and the standard values for each of these numbers for the particular tube type) and it tests at full power (which means its values are conservative).  The big downside is that it is quite expensive.  

Here is the one Larry mentioned.

http://amplitrex.com/

I had a quality tube tester, really didn’t use it much. I bought new tubes from well known suppliers that have already done that work. Used tube testing is a crap shoot. An old tube can measure perfect and be at the end of it’s life the next day. Unless you are in the business of selling tubes, skip it and just buy good tubes from good suppliers.

Transcendent Sound made an excellent tube tester kit; discontinued many years ago but if you can find a working unit used, I highly recommend it.

With that said, I hope to replace it with an Amplitrex unit, hopefully one day soon.

For a whole lot less money, this little fella looks pretty cool:
https://www.dos4ever.com/uTracer3/uTracer3_pag0.html