I recently came across this in my room--thought it had gotten tossed accidently...but is had NOT. ANyway--it is a GE "techni tips" bulletin from the fall of 1963.

They discuss picture tubes on the first page. They talk about how their first 114deg. tube-from 1959, did not hold up well enough for them...after 2000 hour life test--roughly 75% of cathode emission remained. This did not do--so GE 'redesigned" the gun--and the cathode--and THEN, after that 2000Hr. test--98% of emission remained !! I am not sure how linear decay would be--but IF it is a linear scale from the beginning--that would be OVER 40K hours of life !!

Not sure I agree with that , at least on GE BW tubes of the era. Maybe on late-model Hitachi bonded tubes--as used in a LOT of RCA sets from the late '80's to the mid "00's--and the Zenith Chromacolor tubes WILL last 40K hours--or MORE. SO will the Hit. Projo tubes from the same time frame as their DV ones.

I scanned this bulletin, hopefully it will be readable.

I love the GE Techni-Talk bulletins. I have a folder of those myself, along with two Tele-Clues binders :)

We used to figure 2000 hours was equal to one year of use, if I remember correctly; so 75% at that point in normal use would not be good enough. However, they did say "accelerated" life test, so I wonder what the exact conditions were.