[old_tv_nut]

Jeff, CRTs, like all tubes, are in wear-out mode from the first use. The speed of wearout depends on the cleanliness of the manufacture plus the current density of the cathode, that is one of its design aspects. The size of the cathode affects the spot size and resolution of a CRT, so there is a balancing act between gun design, resolution, brightness, and life. I don't think Sylvania had a particularly bad process, but running these particular type numbers surely had more stress on the guns to make up for the dark glass, and may have had comparatively more stress if the guns were designed with a bias toward finer spot size. There's no free lunch.

You can find plenty of notes on this site about certain Zenith CRT types that had poor life compared to others that were long-term performers - all produced by the same company.

Another anecdote about electron guns - when Sony came out with high definition Saticons for HDTV cameras, the cathodes were so small (in order to get the fine scanning spot) that they were guaranteed for only 800 hours. At Zenith, we replaced the tubes in our $800,000 experimental HDTV camera as a precaution, somewhere around twice that number of hours, at a cost of $85,000. I recall our CEO asking if we could leave the camera running for impromptu demos, and quickly changing his mind when we explained the facts of CRT life.