I bought some Tung-Sol 5998s (8 of them) from a dealer. They were sold as NOS, but I guess I've been ripped off.
Some are top getters, others bottom getters. Several of them have a hum, and one makes a cracking sound. My question is this: if a tube really is NOS, will it hum? Make cracking sounds? I don't have a tube tester, but am trying to find someone who does in the Copenhagen area, so I can get the tubes tested.