What I found interesting is these refractors may be well over 35-40 years old because GE started using the shallow glass in the M-1000s in the early 1980s.
Hmm. That's pretty odd considering NGrid has only been in the USA since the 90s. I guess whatever the former utility companies had in stock NGrid took over. I'm surprised they didn't simply chuck them after all these years. Unfortunatly that's not uncommon.
when did GE start using the shallow M-400 glassware?
National Grid took over Niagara Mohawk around the early 2000s but didn't change over to National Grid until around 2008. GE started using the shallow M400 glass around the mid 60s on both the M400 and M400A1. It was in 1984 that GE reverted back to the deep glass.
Also, did the 60s M-250R always use a shallower glass than the M-250A and 70s M-250R or did they juggle between the two like they did with the M-400 glasses?
When the M250 originally came out, it was basically an M400 housing with a poly refractor, the smaller M250R was always shallow refractor during the silver era, and early grey. About the same time the M400 went shallow, the M250R went deep. Now, here's where it gets really tricky. During the mid-60s, the M1000 used the shallow glass for a short time and during the 70s and 80s, the entire M250 line went back and forth before settling on the shallow glass.
Ahh yeah I've noticed some 70s bail latch M-250Rs have the deep glass while others have the shallow. My M-250A from October 1967 has a deep glass. Are the prisms on the shallow M-400, M-250R, and M-1000 refractors the same as their deep counterparts? I have a shallow and a deep GE small sized glass and the prisms are almost the same, but the shallow glass doesn't have the wavey like pattern on the rear of the glass. I'm trying to figure out if i have a 60s shallow glass or an 80s shallow glass used on the M-250R2 before they totally redesigned the M-250R2 glass. Did the M-250R2 ever use the deep glass? I maybe recall seeing one or two but maybe they were replacement refractors.
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when did GE start using the shallow M-400 glassware?