Thank You Steve
Kevin

The first versions of the TM-21 used the 21AXP22 CRT. Later viersions used the 21CYP22, and still later the ,21F types. I imagine not many or any survived with the 21AXP22 or 21CYP22 tubes, they would have all been converted to the later "better/brighter" CRTs. TV stations tended to run the monitors a lot, and kept them on service for a long time.