How to get started with an oscilloscope?

[bluesbreaker18]

I am a hobbyist tube amp builder with a few amps under my belt now. I've been using my DMM for everything, and I recently decided that I'd like to learn the ins-and-outs of using an o-scope on my amps. I just purchased a scope and cheap signal generator (for what I felt was a good price).

Instek GOS-620:
https://amptechtools.powweb.com/scope.htm

Rolls MO2020:
http://www.amazon.com/Rolls-MO2020/dp/B001032HSY

After reading some online tutorials, I feel much more comfortable about getting started with the scope. I'm currently starting a new 18watt build and making some mods to my Marshall JCM602 combo. I have some concerns about damaging the scope with high voltages. The scope's manual gives the following information:

The withstanding voltages of the instrument input terminals and probe input 
terminals are shown in the following table. Do not apply voltage higher than 
the specification. When set probe switch at 1: 1, the maximum effective 
readout is 40Vp-p (14Vrms at Sine wave), set probe switch at 10: 1, the 
maximum effective readout is 400Vp-p (140Vrms at Sine wave).

Input terminal    |  Maximum input voltage
----------------- | -----------------------
CH1, CH2, inputs  |  300Vpeak
EXT TRIG IN input |  300Vpeak
Probe inputs      |  600Vpeak
Z AXIS input      |  30Vpeak

If an AC voltage which is superimposed on a DC voltage is applied, the 
maximum peak value of CH1 and CH2 input voltages must not exceed  ±300V, 
so if the AC voltages with a mean value of zero voltage, the maximum peak 
to peak value is 600Vp-p.

Does this mean that I should take great care to ensure that the scope's probe never comes into contact with B+?

If you know of other sources that would help someone with DMM experience become more competent with a scope, please let me know.

[Don Moose]

1 - use real 10:1 probes. If there's a switch, it will wind up in the wrong position.
2 - the 300V do-not-exceed rating applies to the scope input - a 10:1 probe will make a 300V connection 30V at the scope input, as you note.
3 - the probe's insulation rating starts to matter. If it's good for 600V, a B+ well under that (say 450 or so) should be OK. If you want to go higher than that, I'd be looking for some real HV probes.

The rules about hand-in-pocket are at least as true for scope probes as meter probes - there's (on most of them) a ring of GND connection surrounding the tip. Move carefully.

Hope this helps!

[tim]

I usually put heat shrink around that ground ring on the probe. I've zorched too many things in the past with that damned ring...all my probes now get the heatshrink treatment...

[Enzo]

I'm with Don and tim.

I almost never need the x1 probe setting, so a plain old x10 probe works 99% of the time. You only really need x1 when looking for teeny weeny signals. I usually have switchable ones, and I have the discipline to keep them set p[roperly, but for the novice a dedicated x10 is the way to go.

And dangling scope ground clips can be a hazard, so I rarely use them. I have a separate clip wire from the scope ground that I clamp to the chassis or other ground. it is separate from the scope probe itself. Very seldom does it matter that I don't have the scope probe ground in use. Again, using th very short ground clip on the probe really only matters when looking at teeny signals or high freq ones. ANd high freq means RF, not audio treble.

The ground ring on the probe tip is covered when using the spring hook tip. But if you pull that off to use just the pointed tip, then it is exposed, and covering it makes sense. Most probe kits come with little plastic covers that slip over that leaving only the very point exposed.