I recently purchased a used Tektronix 2445 oscilloscope. It’s a 4 channel 150 MHz analog scope.
I also purchased a Tektronix 2430 digital scope which is en route. The digital scope has the key advantage that it can capture and display a single frame from a trigger. The digital scope will show readings from the Langmuir probe in the Sydney experiment.
It has taken me a few days of reading the manual and playing around with the scope to get a grasp. But I’m getting the hang of it, and wow… it’s a new way to explore the world!
My first discovery is that one of my bench DC power supplies is rather noisy:
The other bench power supply looks much cleaner:
But neither DC power supply is as clean as the perfectly flat signal you get from a battery.
I also used my iphone to display some sine waves:
Prometheus Fusion Perfection 
Nice. I really have to resist the urge to buy used osciloscopes when I see them at swap meets or garage sales.
In the spirit of never assume I offer the following (probably stating the terribly obvious, but here I go)….when one buys a used osillyscope, one should have it re-calibrated so you know you’re getting accurate measurements. I have mixed feelings about buying used test gear from a dealer who claims a unit was re-calibrated as part of the deal. As always – caveat emptor. This is just me – if I were in need of truly precision measurements, I’d buy the used gear from one guy, and get the gear calibrated by someone else. To each his own, of course.
Cheers.