Can 6AJ8's be safely substituted for 6KA8's?

Thanks to everyone for clearing this up for me. I really appreciate it.

@oddiofyl +1

 Lord! I just got a flashback of spending hours with my dad on a Hickock tv10 testing tubes. Ahhh, those were the days.😁

A lot of good equipment has been hurt by the wrong tube.  I always use exact spec when possible.    

Brent Jessee' website is a valuable resource also.   Lots of info there.  When i think about it that's where I'd start .  I go there occasionally,  I have gear with obsolete tubes