Zenith VOT's are known to go BUT ....
I worked from 1970 on at one of the biggest Boston area Zenith dealers.
I was also jig man so I would have repaired most VOT jobs on big sets.
In all those years I may have replaced 4 ? of them all the way up to hybrids.
I put more in 9" & 12" Panasonic B&W's, so many we stocked them.
This seems to be an age related problem not overall mileage.
As far as QC goes I dont remember who built them. If someone can look
at one & get the EIA number that will tell who. Dont forget also TV's
were NOT supposed to last 50 yrs. If VOTs are popping 5 yrs down the line
QC probably isnt to blame.
BTW I have the price / substitute guide form @1977 & can check for subs etc.
73 Zeno
LFOD !