@jasonbourne52--some of the older Russian tubes like the DR Reflector 6h30 are now quite scarce, and often late production which is not, as I understand it, comparable to the earlier tubes (circa the '70s) that I use. They are now quite pricey.
@invalid- aside from a reliable vendor, there's indicia, from how the tube itself looks, to how it is wrapped and packaged. Some (keep in mind my tube knowledge is not deep, just long used tubes) were sold in bulk and that packaging is sometimes shown.
I would also hazard that some truly unused tubes could suffer premature failure, but I've had pretty good experience with vintage tubes.
Good luck-- it's a jungle out there.
@invalid- aside from a reliable vendor, there's indicia, from how the tube itself looks, to how it is wrapped and packaged. Some (keep in mind my tube knowledge is not deep, just long used tubes) were sold in bulk and that packaging is sometimes shown.
I would also hazard that some truly unused tubes could suffer premature failure, but I've had pretty good experience with vintage tubes.
Good luck-- it's a jungle out there.