[geeks] Tektronix TDS 220

[Dave McGuire]

On July 16, Joshua D Boyd wrote:
> >   It is indeed a digital scope.  The easier to use part doesn't really
> > have much to do with it being digital or analog, though.
> 
> That is good to know then.  I can stop thinking about digital scopes
> and think of cheaper but still usable things.

  There's one more VERY important thing to realize about analog
vs. digital scopes.  There is a widespread perception amongst newbies
(and, fortunately, some resellers!) that analog scopes are "older" and
that "modern" scopes are digital, and that digital scopes are just
high-end, better scopes than analog ones.  With things like CDs
vs. vinyl and stuff like that, it's a natural thing to assume.
However, this is dead wrong.  Digital scopes are nothing new...they've
been around for 25 years.  Analog and digital scopes are DIFFERENT
pieces of test equipment, and each has particular strengths and
weaknesses that make one better suited to a particular task than
another.

> >   If you learn about field-effect transistors, you'll have a good head
> > start on tubes.  Just watch out for B+. 8)
> 
> I'll have to look that up when I find more spare time.

  I'll save you the trouble.  B+ is the plate (anode) voltage used with
tubes...typically 100V or more, up to many thousands of volts for big
transmitting tubes.  This is used to attract and accelerate the
electron cloud formed by the filament and (if present) cathode.  On a
small low-power circuit, B+ will give you a solid jolt.  On a larger
circuit, it'll knock you on your ass.  With a big ham HF amplifier
with, say, a big fat 3CX1500A7 tube in the middle, one brush against
that B+ bus bar when it's powered, and you're dead.

> >   A DMM is the single most useful piece of general electronic
> > troubleshooting equipment.  A good analog scope (be it ones with
> > analog or digital controls, though I strongly prefer the latter) would
> > have to be next.
> 
> How about an analog multi meter?  I guess they aren't as good as a DMM
> for testing caps...  I just realized I typed DMM, but what I really
> have is a nice, not particularly cheap analog meter.

  Either is fine.  Sometimes an analog multimeter is better for doing
relative measurements (i.e. "peaking" an adjustment) where it's easier
to watch the needle moving back & forth than to look at a string of
numbers to decide if you've gone past the peak or not...but for many
years many manufacturers have addressed that issue in their digital
multimeters by including high-resolution bar graphs in the display.

  Generally speaking, unlike digital vs. analog oscilloscopes, digital
multimeters *are* newer, better meters than analog ones.

         -Dave

-- 
Dave McGuire                  "Needing a calculator indicates that
St. Petersburg, FL              your .emacs file is incomplete." -Joshua Boyd