CRT longevity in different chassis.
Many years ago I remember reading an LLJ tv mag article stating the reason Mullard A56-120X (plus the other sizes too) lasted so well, in the ITT hybrids compared to sets such as G8, A823 and BRC3500 etc was due to much lower cathode drive voltage.
I also asked in the 90's some of my old tv shop chums (sadly all now passed away) why tubes never lost emission, in the ITT hybrid range and the same answer was given. " Owners and renters using ITT hybrid sets didn't use their sets all day everyday compared to owners renters of sets such as Pye 205 Brc3000/3500 who tended to be at home all day, with the tv only being switched off at the end of transmissions"
One tv shop owner in Doncaster told me " I had a 22" CVC8 out on rental for 10 years, 1975 to 1985 with only a few repairs, mains filter capacitor and valves, set scrapped after lopt failure, but the tube got to live on in a GEC set, all transistor model sold by a trade disposal outlet as "new old stock neck cracked found in the back boxed since 1974" The GEC sadly died after 4 or so years after the new owner had a party and a pint of beer was poured in the back while switched on for a drunken joke. The owner of the GEC turned up at my friends shop and told him of the sad fate of the set, and he wanted to buy a second hand cheap portable set so he could hide it, in case it met the same fate at his next Birthday party.
I own a ITT CVC9/1 dated Sept 76 their "swan song" last colour hybrid with simple remote and the picture when last used was superb!
As long as the CRT is operated within its normal parameters, the lifetime must be attributable to the quality in its design and manufacture.....
Reviving an old thread.
I think you hit the nail on the head.
Quick heat tubes were very sensitive to heater voltage fluctuations. How well they were regulated depended on the chassis design.
@sundog As mentioned by others, high resistance heater feed can look like poor emission. I wonder if this could explain the differences in apparent CRT life. I've certainly experienced intermittent brightness due to poor contact at the heater base pins. Perhaps different makes of sockets performed differently?