My 2 cents on tube testers is that they are marginally useful for everyday
work unless you are heavily into restoration. I have restored many tube
radios, and a dozen or so tube TVs. I own several tube testers, basically
because I like old test equipment. But in the everyday world, they are only
used to quickly test for dud/very weak tubes when I get in a new item.

You can test for duds by measuring continuity between the tube's filament
pins with an ohmmeter. If you don't have a tube manual, you can look up the
tube's basing diagram (i.e., pinout) at http://www.nostalgiaair.org/Tubes/ .

For many consumer radios, a tube that tests "maybe" on even a cheap
emission-type tester will still work just fine. Why? Because those radios
were made with wide design tolerances, and many of them weren't that
demanding in the first place. If you replace that "maybe" tube with a
brand-new one that tests "A-1" on a $1000 tester, the radio may work exactly
the same as before. The only difference is that you have wasted money buying
a tube you didn't need.

Some circuits in TVs and complex boatanchors will be more fussy about a
tube's performance, but it sounds like you're not at the level of worrying
about such things.

The best test for any tube is to try it in an actual working circuit doing
the job for which it was designed. If you have some working restored radios
in the house, and one of them happens to use tube type whatever,
substitute your suspect tube type whatever in the right socket and turn on
the radio. If the radio works, the tube is good.

Conversely, if you have a stock of known-good tubes, you can pop a type
whatever tube into the right socket in your suspect device and see whether
anything changes. If it magically improves, then your old whatever tube
was a major problem. (This won't reveal other/multiple problems, of course.)

If you want to spend several hundred $$ for a top-end tube tester, it's your
money. Keep in mind that old test equipment will always need restoration
(recapping, cleaning controls, etc.), like everything else of that vintage.
Plus, it may require calibration and expertise beyond simple parts
replacement. If you don't already have a lot of equipment and experience,
that could put you in a chicken-and-egg situation. Uh-oh, I need to buy
another (reliable) tester to test things on the (probably unreliable) tester
.. . . .

Have fun.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html