In high school, I scored a Tektronix 514D oscilloscope that Hughes Aircraft had scrapped. I don't have a personal photo, but it looked like this
Here's a link where you can zoom in to view the controls.
https://mitmuseum.mit.edu/collections/object/1988.058.012.01
Introduced in 1950, it was one of the first models with a triggered sweep--something we don't even think about today. This was made possible by a broadband all-pass filter delay line that delayed the signal, giving time for a rising or falling edge to be detected and for the horizontal sweep to be triggered. The delay line is shown in this photo
It shows the board with all the trimmer capacitors that needed to be tuned to produce a flat frequency response. The instrument bandwidth was 800 kcps (kHz) full scale and an impressive (for its time) 10 Mcps at reduced amplitude. It also had an X axis port for displaying Lissajous figures and a Z axis (cathode) port for intensity modulation.
To use it, one adjusted the trigger threshold level with one knob and the horizontal sweep oscillator regeneration level with another such that oscillation was not quite self-sustaining. These settings interacted with each other and with the horizontal time base selector and with the vertical sensitivity, of course, so setting up to measure a recurring signal required a bit of fiddling. Turning the regeneration up put the scope into free-running, un-triggered, mode.
In around 1970, I wrote to Tektronix and they sent me a brand-new copy of the user and repair manual. (I was impressed that those were still in stock.) When I went off to grad school, my parents rather reasonably requested that the beast (it weighed over 60 lbs.) be removed from my former bedroom, so I gave it to a friend. I wish I still had it now. It was a trip to use!