The Tektronix 465B oscilloscope has a MAXIMUM rated input voltage of 5V/division at the input terminals. That's 40V peak-peak max.
You can legitimately observe a screenful of signal when the displayed region is "sitting on top of" quite a lot larger pedestal - see below. In fact, US 110 VAC mains IS inside the overall spec - but far to close to the when-brand-spanking-new limit to be safe.
110 VAC is about 300 V peak to peak - over 7 times what you can usefully display.
- I lie, of course: if you put zero at the bottom of the screen you can display the positive half of a 80V p-p signal, and you can display a smaller variation on a large "pedestal", but you get the idea.
ie 110 VAC on a 1:1 probe into a Tek 4656b is a REALLY REALLY bad idea. The display will be well over scale (+/- 20V max, you would be putting in about +/- 160 V.
Tek have designed it to survive this , but that was when it was new.
Capacitors get old,
dust build up,
ants crawl, and die
materials get tired with heat and time.
IF mains does get through the front end and you are holding the probe or adjusting the scope then you may never get to see the magic smoke, or anything else thereafer.
Yesterday's 500 V_peak-to-peak limit is Murphy's playground.
Don't make his day.
The Tektronix 465B oscilloscope has a MAXIMUM rated input voltage of 5V/division at the input terminals.
The 10/20/50 Volt per division settings are for use ONLY with a 10:1 probe and signify the sensitivity as seen at the probe tip with a 10:1 divider so that the oscilloscope sees voltages 10% of what is at the tip.
Whereas oscilloscopes made by and for mere mortals usually require the user to work out this 10% or 1000% scaling (depending on which way you are looking) for themselves, the superheros at Tektronix added a nice touch which allows the scope scale to adjust by a factor of 10 when a 10:1 probe is adjusted.
The scope still sees a maximum of 5 Volts per division.
HOWEVER (bugles and horses hooves, stage off, right ...)
The guys & gals at Tektronix are real engineers and saw Y'All coming - so they have rated the input divider at 500VAC peak peak as noted here at up to 1 kHz. This means that US Americans CAN connect a 1x the probe directly across US 110VAC mains and reasonably expect it to survive. Note that reasonableness and certainty are variably correlated in the real world. Whether it will do so 30 or so years on is TBD.
This also means that an Antipodean Kiwi or Australian, or most Europeans, people in Taiwan & mainland China and anywhere else with 230 VAC (or 220 or 240) can reasonably expect to get magic smoke if they connect via a 1X probe directly across mains AC.
Knowing Tektronix it's possibloe that even antipodeans may get away with doing this (230 VAC = 650 V peak-peak) but Murphy says that 30 years or so on I should not connect my 465B across the mains to see what happens.
Note that peak-peak includes any spikes and local trash that may have come along for the ride.
Doing it with 110VAC is also not very smart, spec notwithstanding.
50+ page oscilloscope tutorial from Tektronix - The ABCs of oscilloscopes - useful.
5 page 'scope tutorial - OK.
Some more 465B specs
5 pages: http://www.aoc.nrao.edu/~pharden/hobby/Scope1.pdf
500 Vpp: http://www.testequipmentdepot.com/usedequipment/tektronix/oscilloscopes/tek465bspecs.htm