Prototype set is here

[John Folsom]

Pete, Great photos and commentary. Almost as good as being there!

After seeing the photo of the number stamped on the rim of Nick's prototype CRT, I closely examined my two down-to-air metal bell prototype CRTs and discovered numbers on their rims I had never noticed before. One had D76, the other had D111. Both of my tubes have 14 pin stems and bases, which I believe places them somewhere earlier in the prototype tube progression. By March of 1953, RCA had provided 477 tricolor CRT samples to 177 companies.

I speculate that these rim numbers may represent a serialization of the metal bells used to assemble the tubes.