A little knowledge is a dangerous thing. Couple that with, sometimes staggering levels of, naivety…………
Not all can remember the telly man calling every once in a while to empty the 6d's from the wind-up box at the back, or to fiddle with and change a couple of valves, or the googlebox that took minutes to, literally, warm-up.
I am sure that that all applies to most sellers, as well as punters.
LLLLOL - I just Googled Tektronix 555
If nothing else, at least you can get to all the controls/adjustments dead easily.....