Magnetorestrictive delay lines and a charactron. http://bitsavers.org/pdf/rca/terminal/70_750/70-01-752-U_Model_70_752_Video_Data_Terminal_Maintenance_Manual_Oct73.pdf
We got one (no keyboard) a couple days ago with the manual. I'm still cleaning it up. It had something nesting in it and the inside has sunflower seed husks in it. It was made with plastic DIP ICs, no idea of the logic family. The keyboard was made by IBM, don't know what character code it produces. Pretty funky if it encodes ASCII.
