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.  

Vinylvalet,

The tube tracer looks quite interesting, but it appears to be a pretty complex and tedious process (I suppose it is fun to some people).  The Amplitrex, if attached to a computer, will also trace the tube.  I lasso like the fact that it does not require calibration.

I admit that there is some fun in using something like the TV-7, but also some terror concerning mis-reading the table or incorrectly setting the dials which could mean damaging the tube and getting a bad reading.

Yes.  While I have personally been fortunate in that I've never had a tube failure, including tubes I've been running for 15 years or so.  But, I know of plenty of instances where a tube suddenly failed after testing strong on a TV-7.  It is just something that happens occasionally and I don't know if any tester would be able to predict that result (the Amplitrex, because it tests at high plate voltage and dissipation might cause a failure in a tube ready to blow).  But, at least a tester will give some indication as to how much life still remaining in the cathode.

a tube will test fairly strong over the vast majority of its life and will only start to test weaker at the relatively shorter end of its life.  On a tube that tests strong, most testers are showing you that it is still in its middle life, but, they will not show you how close they are to the declining part of their life curve.  Hence, most tube testers are sort of rough screening devices--better than nothing and something that affords one some peace of mind. 

The very first tube tested on my Amplitrex was a rectifier that a friend wanted to have tested because it came from a dubious source.  It tested zero voltage drop in both directions  (dead short).  It was far better to know this from a test rather than in the amplifier circuit.