Thank you for all your input. You have all been verry helpful. What do you think of these 2 options.
1 Tektronix TDS420 Four Channel Digitizing Oscilloscope 150MHz for 200$ shipped
2 rigol ds1052d for 200$ shipped.
What do you think would be the best option and why.
Obviously I completely understand that i’m taking a risk buying a used unit.
I think you will be disappointed with the TDS 420 as a general purpose Oscilloscope, for the following reason.
Early DSOs have very limited memory, so that when you use them at longish time/div settings, they have to reduce the sample rate to fit into this low memory.
This is OK if you only look at sine waves, but things like looking at analog video signals at field rate are pretty much impossible.
In many specialist applications this is not a big handicap, but as I said above, they are not good general purpose instruments.
Modern DSOs , by & large, do not suffer from this problem.
i do not have one, or, indeed, any DSO, but the DS 1052d is well regarded by many on this forum, so I would recommend it as the best choice.