Where do you guys buy tubes?

@atmasphere  Is preconditioning what tube-sellers are usually talking about when they offer 24 hour burn in of power tubes?

Generally not.

Ralph,What value of B+?since  those tubes you got from the seller, he already applied B+ on them when they were tested.And one more thing about cathode poisoning if you run it for 3 days?

If the tube is going to be properly preconditioned, B+ simply should not be applied until after the preconditioning is complete.

Tubesandmore.com

This is antique electronic supply.  Greg is great

I just bought some Mullard CV4003 from upscale audio, communication/recommendations was excellent.  Not an opinion on the quality of the tubes as I have not received them yet.

i tried selling my used tubes on e-bay (Prima Luna EL-34 and AU-7. They weren't crap. I honestly believe they're in good condition (given their age).

I buy mine at hamfests and antique radio shows, and occasionally on ebay. On occasion, the shows can offer incredible deals, like 10 #26 DHT tubes for $50, or 15 #80 coke bottle rectifiers for $40, and there's usually someone there with a tube tester so you can check them out.
Sometimes you get skunked, too, so not 100% guaranteed to find stuff, but I like the hunting as much as I like the buying...