I have a query into Parts Connexion to see if they can clarify. I can vouch for the tube's robustness. I just realized that I've been playing it for half a day at 12 volts.

That's what happens when you're too quick on the trigger.

My dyslexia is in fine form today. I rechecked the tube and the print is actually 8606 (not 8086), which I suspect means June 1986.
Ever have one of those days...