Tube testers

’something very good’.

then you have to find one that has been restored by a pro.

Since inheriting tubes in 1973, I check my tubes annually, before thanksgiving, ready for the holidays

My experience over many years:

1. stand in front of a monster tester at an electronic store checking everything from Fisher President II: fm tuner; am tuner; tape deck; two multiplex added; master control panel, two amps. legs, back and feet hurt, grumbling line behind me. maybe need 2 tubes in the whole lot.

2. wife got me a small portable tester of my own, wonderful. accurate? compared a few good and bad with the monster store unit, same results.

3. bought big jackson, had tech check the small one and it. they always agree.

4. stopped using the big jackson, use the small portable for myself and friends.

5. test new tubes when received, test annually, test when a problem occurs. found a few shorts; found a few weak; found a few ’unmatched’.

I recommend you and anyone who has tube equipment get a simple small portable tester. make sure the manual, real or download is available.

then, if you truly get serious, go for ’very good’. do real research and get one overhauled by a pro.

"...I can't imagine having to replace one tube at a time when something is not sounding right to find the bad one..."

That is exactly what you will do when testing tubes. Listening is often better than measuring. 

"...was wondering if others had the same experiences as @russ69 with sudden tube failures even when they tested well..."

Well, I’ve had brand new rigorously tested tubes that were bad right off the start. Mostly noisy preamp tubes in hi gain circuits. Also tubes can fail an infant death after just a few hours of use. Or they can degrade slowly and at different rates. In my experience one tube will sonically fail without warning and will need to be replaced, testing a failed tube is fruitless. I buy new production tubes that have been burned in and tested, no need to do that twice, then I run them until they fail, sometimes spectacularly!
Culling tubes that have not had good screening or used tubes is not always successful judging by the number of unhappy customers with some tube retailers.