Hey Dieter,
My RCA tube manual number 15 from 1947 lists a type 41 as electrically the same as a 6K6. Want to bet that a 6K6 with an octal base is no more than a repackaged 41 which had a 6 pin base?
If octals were the standard, then why re-invent the wheel, so to speak. Re-package a 41 and give it a standardized number and base. Voila , a 6K6 !!!
Food for thought.
TTFN
John G. VO1 CAT