An Advent was a three tube projection system. It had a triangular arrangement of the CRT's, one red, one green, one blue. You had to focus and align them yourself, but with a good screen you could get a pretty good looking 60" television. It required a dark room.

Since it sat in the middle of the floor, it was subject to kids bumping into it (in my grandparents home anyhow) and also then subject to grandfathers shouting.

He later replaced it with a front projection set that bounced the CRT projectors off a mirror onto a screen. It was a beast.

It says at the bottom: "“Advent” was not a religious sanctuary, it was the demo room with the $3,000 projection TV[1] that we used for demos to Important People."

[1]: http://i.ebayimg.com/t/Vintage-Advertisement-1978-ADVENT-VID...