There's an even easier way on older Trinitrons - the bulge of the glass is different. Notice how the left and right sides of the glass are straight vertical li

There's an even easier way on older Trinitrons - the bulge of the glass is different. Notice how the left and right sides of the glass are straight vertical lines, and only the top and bottom edges are curved: https://spectrum.ieee.org/the-consumer-electronics-hall-of-fame-sony-trinitron https://spectrum.ieee.org/the-consumer-electronics-hall-of-f... Versus a standard CRT, where all four sides are curved: https://fineartamerica.com/featured/vintage-tv-scott-chimber.html https://fineartamerica.com/featured/vintage-tv-scott-chimber... Of course, the final-gen Trinitons (circa 2000 onward) had truly flat glass, so there was no tell-tale curvature to look for. And once Sony's patents started expiring, there were competitors like Mitsubishi's Diamondtron displays with glass shaped like Trinitrons. I'm not sure if they had the two horizontal lines like Trinitrons.