They are interchangeable but not the same entirely. As oddio points out, the 6922 and 7308 are special 10,000 hour versions of a 6DJ8. My experience is that you will get a shorter life with a 6DJ8, but perhaps not enough to warrant the difference in price. Many say they think the 6922 sounds better than the 6DJ8. I have less experience with the sound of the 7308.
6922 Tube Question
I need to replace a pair of tubes in my VAC Signature. They are 6DJ8 6922's. Though I've had tubed pre-amps for years, this is my first tube replacement. So I have a real newbie question. Are all 6922's interchangeable? Can I use any 6922 or must they be 6DJ8 6922's?
ps - ya, I know, bad time to need tubes given the world situation.