All color CRTs had to have the large metal-metal and sometimes metal-glass seal around the face plate (until the 21CYP22 came out in the CTC-7 a few years later) which is a seal failure point...one possibly for minor reliability improvement is if some makers used a glass evacuation stem. Most early color CRTs and some later all glass types (ie 21FBP22) had a pinched copper evacuation stem...of the later all glass types I've had ~20 in my ownership and 2 were gassy...Those 2 both had copper stems. I think the copper stems are a failure point. Using a glass stem on a 15G wouldn't fix the glass-metal-metal-glass face ultor ring failure point, but it would remove the neck evacuation seal as a failure point, and might have increased the survival rate some percentage.
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Originally Posted by colorfixer
I think the 15" Philco set at the ETF has a Sylvania tube. Rauland apparently claims to have made them as well.
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I've read that too. I wonder if Zenith/rauland sold it as a replacement or in any of the field sequential medical closed circuit color sets they sold or if it was for prototypes only. Zenith also had a prototype rectangular color CRT in 1954...It is rather fascinating with how much development the did that they waited till late 1961 to market their first consumer NTSC set.