I first encountered this generation of Tektronix oscilloscopes in my first job at the Electronics Lab of SINTEF, Trondheim, Norway in 1978. Already at that time the main use for them was as heaters in the offices. That is, only if you wanted to work in the break between Christmas and New Year when the central heating was turned down.
Since then I have come across the two oscilloscopes shown here, and the collector (or is it hoarder?) in me has not been able to say no to them. They are really advanced for their time: regulated power supplies with tubes, ceramic stand-offs and lots and lots of tubes.
The oscilloscopes are 541A and 543, from 1959 and 1964 respectively, it seems. The plug-in units are 1A1, L, M, and 53/54K plus the cart. The 1A1 actually seems even to have FET-transistors, not only tubes like the others. The units work, but how well they work I am not sure about as they have been in storage for the last 5-10 years.