If you had a dozen pairs of classic vintage ubes in your closet

Are you talking about tubes as investments or tubes as electronic devices that are needed for music amplification?

As one who has been doing this for more than 45 years, I disagree that a tube tester is a requirement. Second, I especially disagree that a cheap tube tester is a requirement. If a tube has an internal short, you will know it immediately without testing it formally. You will throw that tube away. If the tube is wearing such that it affects sound quality, your ears will tell you that. If you have a voltmeter, you can test a tube in the chassis by measuring its associated voltages. A really good and therefore expensive tube tester is nice to own, because it gives you something to play with. However, even the common expensive tube testers cannot test a tube at the voltages and currents that usually exist in functioning equipment. Therefore, you would get a false impression of the performance of the tube in circuit. For most of us, it is best to just Use your ears. To acquire a tube tester that can actually test tubes under real world conditions will cost you well over $1000, more like $2000.

Martin! Travelshooter! It's been too long.

Nice to see your setup, I would love to hear your system, south of Miami Beach correct? I sold my boat in Dania Beach, no plans to go down now.

I've been 'off' of photography for a while, got back to my audio system, added a very cool TT with 3 arms, shown here

https://www.ebay.com/itm/133640511355

I've been meaning to take some decent photos and add them here, just lazy.

All the Tubes apart from one,  I have purchased over the past 2 Years have been purchased as NOS Tubes with close to the manufactures measurements being presented by the Vendor.

I have purchased under a agreement they are tested when received at my end, and can be returned if the Tubes do not measure to a acceptable standard on a friends AVO Test Machine.

I have had to return Valves due to low measurements and the offered exchange Valves also showed low measurements.
This was the Vendors proposal as a resolve before a refund was made.
I am fortunate to have used Vendors who are willing to honour such prior made agreements.

This purchase arrangement has been put in place for ECC83, E88CC and 6SN7, with the ECC83 being the Valve that has been the one needing replacements and a refund.
I bought a Early 60's E88CC from Japan (no return) and another from Germany (return arranged) about Six Months Later, at about 40% of the going rate for a matched pair, both measured close to the Manufacturers Guide, so this was a Punt that worked out as the Japan Valve was very cheap and was added to a package that was being produced for export by a Buying Service   

For the Buyer the Market does demand an attitude of Caveat Emptor.  

@lewm.....   you have a point.  My ears have told me when it is time to change for the last three decades.
@pindac     ..  there was a time when NOS meant New Old Stock, not that the tube still reads close to new.  I'm talking perfect old lettering and pins that look like New Old Stock + a tube test.

You will most likely not be able to consistently tell a used tube from new with a simple emissions tube tester. Shorts yes and that is about it. If you buy a tube tester buy a true transconductance tester. Many Dynamic Mutual Conductance testers only test for transconductance on some tubes (B7K 707 for example). 

It is also true that suitcase testers do not test most power tubes are real world levels and as such they do give these tubes a true test. I have found that gm testers like Hickok and Triplett do a fine job on everything but power tubes.