Opinions on Oscilloscopes

[RR]

Hi,

I'm in the process of teaching myself analog electronics. I figure that my
understanding of components and circuits will be enhanced by being able to
measure and view behaviour on a CRO.

Initially I'll be building low voltage circuits (9V, 12V) in both AC and DC.
But I would like to be able to measure mains (I think I just a differential
probe with any scope for this) later on.

My local ebay has two CROs that seem interesting and good value to me:
- a McVan BWD826
- a Tektronix 475

I've read elsewhere on sci.electronics good opinions about BWD824 and Tek
465b.

Opinions on the above?

Also, my other option is to buy a real cheap new 10MHz unit from a local
electronics store. A problem I see with it is that its minimum sensitiviy
is 5mV (I notice that usually it's 1mV or less). But, I guess 5mV is
probably small enough for my needs.

It's also single channel. For what I want to do, am I going to need 2
channels?

Opinions please?

Last question: if a scope says "Trigger Max. Input Voltage: 400V peak",
does that mean it will handle 240VAC input (I think 240VAC RMS is 400VDC)?
Would it still need a differential probe for this purpose?

tia,
RR

 

[mike]

Hi,

I'm in the process of teaching myself analog electronics. I figure that my
understanding of components and circuits will be enhanced by being able to
measure and view behaviour on a CRO.

Initially I'll be building low voltage circuits (9V, 12V) in both AC and DC.
But I would like to be able to measure mains (I think I just a differential
probe with any scope for this) later on.

My local ebay has two CROs that seem interesting and good value to me:
- a McVan BWD826
- a Tektronix 475

I've read elsewhere on sci.electronics good opinions about BWD824 and Tek
465b.

Opinions on the above?

Also, my other option is to buy a real cheap new 10MHz unit from a local
electronics store. A problem I see with it is that its minimum sensitiviy
is 5mV (I notice that usually it's 1mV or less). But, I guess 5mV is
probably small enough for my needs.

It's also single channel. For what I want to do, am I going to need 2
channels?

Opinions please?

Last question: if a scope says "Trigger Max. Input Voltage: 400V peak",
does that mean it will handle 240VAC input (I think 240VAC RMS is 400VDC)?
Would it still need a differential probe for this purpose?

tia,
RR

It's my opinion that if you need two channels, you're not gonna be happy
with a single channel scope.

The key to buying a scope is patience.
You can't hardly go wrong with a TEK 400 or 7000 series scope.
Prices run from "way too much" to "dirt cheap" depending on where/when
you buy one. Patience...
You can find good deals on EBAY, but you have to know the right
questions to ask and hope the answers are honest. Anything that says,
"can't test it" is suspect.

Search out a ham radio operator. Go visit a ham club meeting.
Those guys have spare scopes for their spare scopes in the attic.
Ham radio swap meets are a great place to buy scopes.

Take someone with you who knows how to test a scope. It's not unusual
to find a scope can put up a green worm, but has significant problems
when it comes to actual use. Scopes are relatively easy to fix, until
you get to a bad part that you can't get any more. Problem is that
you usually need a scope to fix a scope.

There's no reason to EVER put 240VAC into a scope. You'll always be
using at least a 10X probe. Worry about the probe specs, especially
on cheap probes.

I'm gonna repeat myself. Scope probes are designed to be insulating
and safe to use. Hanging random wires on 240VAC and stuffing that into
a scope is a recipe for DEATH. Maybe not today, but eventually. Just
don't do it.

mike

--
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MAKE THE OBVIOUS CHANGES TO THE LINK
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[Jim Yanik]

Scope input is rated *DC plus peak AC*.
At least that is how Tektronix specs their scopes.
Why are you going to put 250VAC into the TRIGGER input? The scope usually
has an internal trigger pickoff AFTER the attenuator,to keep trigger
signals small but useable. External trigger is used when you have a clean
reference signal to use,like H or V drive from a video generator when
looking at composite video,eliminates the need for a sync spearator..

It's my opinion that if you need two channels, you're not gonna be
happy with a single channel scope.

The key to buying a scope is patience.
You can't hardly go wrong with a TEK 400 or 7000 series scope.

7313,7500 series scopes SUCK big time.and TEK-made ICs are only available
thru cannabalizing other scopes,they are out-of-production and/or stock.

Prices run from "way too much" to "dirt cheap" depending on where/when
you buy one. Patience...
You can find good deals on EBAY, but you have to know the right
questions to ask and hope the answers are honest. Anything that says,
"can't test it" is suspect.

Search out a ham radio operator. Go visit a ham club meeting.
Those guys have spare scopes for their spare scopes in the attic.
Ham radio swap meets are a great place to buy scopes.

Take someone with you who knows how to test a scope. It's not unusual
to find a scope can put up a green worm, but has significant problems
when it comes to actual use. Scopes are relatively easy to fix, until
you get to a bad part that you can't get any more. Problem is that
you usually need a scope to fix a scope.

There's no reason to EVER put 240VAC into a scope. You'll always be
using at least a 10X probe. Worry about the probe specs, especially
on cheap probes.

I'm gonna repeat myself. Scope probes are designed to be insulating
and safe to use. Hanging random wires on 240VAC and stuffing that
into a scope is a recipe for DEATH. Maybe not today, but eventually.
Just don't do it.

mike

The worst part about inputting line voltages is the grounding;in
switchers,what you think is ground may only be "common",and potentially hot
referenced to earth ground.

 

[RR]

Scope input is rated *DC plus peak AC*.
At least that is how Tektronix specs their scopes.
Why are you going to put 250VAC into the TRIGGER input? The scope usually
has an internal trigger pickoff AFTER the attenuator,to keep trigger
signals small but useable. External trigger is used when you have a clean
reference signal to use,like H or V drive from a video generator when
looking at composite video,eliminates the need for a sync spearator..

Down the track (lots of learning to do), I'm interested in creating and/or
working with alternative power sources (solar to battery then inverted to
mains power).

I know I'll probably buy a lot of the equipment for doing this, but it
always helps if you understand the circuit, especially when it stops
working.

So, if the input is 12VDC and the output is 240VAC, I suspect I'm going to
need to put a scope on both sides at some stage.

I'm just thinking ahead, and maybe I'll never need to look at mains through
the scope.

And even if I do, I may have bought a much better scope by then. Besides,
my research indicates that differential probes are specifically designed for
looking at high voltages (hence putting that question in my OP).

thx,
RR

 

[tekamn]

Down the track (lots of learning to do), I'm interested in creating and/or
working with alternative power sources (solar to battery then inverted to
mains power).

I know I'll probably buy a lot of the equipment for doing this, but it
always helps if you understand the circuit, especially when it stops
working.

So, if the input is 12VDC and the output is 240VAC, I suspect I'm going to
need to put a scope on both sides at some stage.

I'm just thinking ahead, and maybe I'll never need to look at mains through
the scope.

And even if I do, I may have bought a much better scope by then. Besides,
my research indicates that differential probes are specifically designed for
looking at high voltages (hence putting that question in my OP).

thx,
RR

If you think about the 12V DC/240V AC setup, then go thais way for a
solution: 2 ch scope with HV isolator (e.g. Tektronix A69xx or
something like this, Jim please help my memory and give the right
description).

You will not go wrong with a Tektronix, but besides all "patience" that
was recommended in buying: A good working well kept Tektronix is all
time more expensive than a worn out one that (might) need maintenance.

Keep this in mind when you compare a price offer, and don't simply go
for a low price -- your mileage may vary.


hth,
Andreas

 

[Walter Harley]

[...]
Also, my other option is to buy a real cheap new 10MHz unit from a local
electronics store. A problem I see with it is that its minimum sensitiviy
is 5mV (I notice that usually it's 1mV or less). But, I guess 5mV is
probably small enough for my needs.

It's also single channel. For what I want to do, am I going to need 2
channels?

Don't bother with a single channel scope (why would they even make them any
more!?). You'll find that it's very useful to compare waveforms, and for
that you want a two-channel scope at least. But 10MHz, or more commonly
20MHz, is enough bandwidth for what you'll initially be doing.

I used a Hitachi V212 for many years, before I got my Tek 2465A. I love the
Tek and use it as my primary scope; it is much more capable. But I still
use the Hitachi for audio work, and it works great. I've seen those on eBay
for under $100.

There are plenty of inexpensive Chinese-made 20MHz dual-channel scopes out
there, at least in the states - Leader, for instance. Probably fine, for a
first scope. The difference between that and something like a Tek will be
in things like the accuracy of the input stages and the sensitivity of
triggering on short spikes, and maybe features depending on what models
you're looking at.

If it were me, I'd recommend getting a new Chinese scope as a first scope,
unless you can land a used Tek or HP that is in guaranteed known good
working order. There's no sense struggling to learn how to use a scope that
doesn't work; even working ones can be tricky to fully understand. Later on
when you understand how to work with it and what it *should* do, you can get
a scope of high quality but unknown condition.

Last question: if a scope says "Trigger Max. Input Voltage: 400V peak",
does that mean it will handle 240VAC input (I think 240VAC RMS is 400VDC)?
Would it still need a differential probe for this purpose?

A differential probe lets you look at small signals riding on large signals,
e.g., the voltage drop across a resistor on the high side of a transformer.
Useful for working on power circuitry, certainly.

But for most mains-power work, you would just use a x10 probe, which
(confusingly) divides the voltage by 10. This is the commonest of probes -
practically any off-the-shelf inexpensive scope probe is either fixed x10,
or switchable x1/x10. You can also get x100 probes, for high-voltage work.

240V * 1.4 = 336V, by the way.

In any event, as someone else pointed out, at the trigger input you would
rarely want to apply high voltage.

 

[mike]

If you think about the 12V DC/240V AC setup, then go thais way for a
solution: 2 ch scope with HV isolator (e.g. Tektronix A69xx or
something like this, Jim please help my memory and give the right
description).

There's an A6902A for sale here:
http://nm7u.tripod.com/homepage/te.html

You will not go wrong with a Tektronix, but besides all "patience" that
was recommended in buying: A good working well kept Tektronix is all
time more expensive than a worn out one that (might) need maintenance.

Keep this in mind when you compare a price offer, and don't simply go
for a low price -- your mileage may vary.

A lot depends on where you live. I'm surely not typical, but I've had
to repair almost every scope I've purchased. And the ones advertised as
"works perfectly" often took more time and $$ to repair as the ones
advertised as "dead".

The most important information about a used product is, "Have they tried
to fix it?" I've had good luck with busted stuff from people who don't
know anything about it. I've had BAD luck with "needs minor repair"
stuff from experts, or from hamfisted repairers. This goes for test
equipment, cars, washing machines...
I've also had some very interesting email discussions with a well-known
equipment refurbisher who advertises stuff on EBAY as "no way to test it"
under an email address that looks like an individual. They routinely
calibrate this stuff. Why would they advertise it as untested???
And why would they vanish when you called them on it?

So, bottom line (for me) is, "Price is THE ONLY object." Assume
everything is busted and offer accordingly. YMMV.
mike

hth,
Andreas

--
Wanted, Serial cable for Dell Axim X5 PDA.
Return address is VALID but some sites block emails
with links. Delete this sig when replying.
FS 500MHz Tek DSOscilloscope TDS540 Make Offer
Bunch of stuff For Sale and Wanted at the link below.
MAKE THE OBVIOUS CHANGES TO THE LINK
ht<removethis>tp://www.geocities.com/SiliconValley/Monitor/4710/

 

[mike]

Scope input is rated *DC plus peak AC*.
At least that is how Tektronix specs their scopes.
Why are you going to put 250VAC into the TRIGGER input? The scope usually
has an internal trigger pickoff AFTER the attenuator,to keep trigger
signals small but useable. External trigger is used when you have a clean
reference signal to use,like H or V drive from a video generator when
looking at composite video,eliminates the need for a sync spearator..




7313,7500 series scopes SUCK big time.and TEK-made ICs are only available
thru cannabalizing other scopes,they are out-of-production and/or stock.

Good point. I don't think I've EVER seen a 7300 or 7500 mainframe for
sale. I'll ammend my recommendation to 7700 mainframes. I've had
excellent luck with $10 7704s.

One more point. If you buy used equipment, try to get manuals and
probes with it. A single manual or a single probe can easily cost you
more than the equipment itself.

mike

The worst part about inputting line voltages is the grounding;in
switchers,what you think is ground may only be "common",and potentially hot
referenced to earth ground.

--
Wanted, Serial cable for Dell Axim X5 PDA.
Return address is VALID but some sites block emails
with links. Delete this sig when replying.
FS 500MHz Tek DSOscilloscope TDS540 Make Offer
Bunch of stuff For Sale and Wanted at the link below.
MAKE THE OBVIOUS CHANGES TO THE LINK
ht<removethis>tp://www.geocities.com/SiliconValley/Monitor/4710/

 

[RR]

Don't bother with a single channel scope (why would they even make them any
more!?). You'll find that it's very useful to compare waveforms, and for
that you want a two-channel scope at least. But 10MHz, or more commonly
20MHz, is enough bandwidth for what you'll initially be doing.

There are plenty of inexpensive Chinese-made 20MHz dual-channel scopes out
there, at least in the states - Leader, for instance. Probably fine, for a
first scope. The difference between that and something like a Tek will be
in things like the accuracy of the input stages and the sensitivity of
triggering on short spikes, and maybe features depending on what models
you're looking at.

If it were me, I'd recommend getting a new Chinese scope as a first scope,
unless you can land a used Tek or HP that is in guaranteed known good
working order. There's no sense struggling to learn how to use a scope that
doesn't work; even working ones can be tricky to fully understand. Later on
when you understand how to work with it and what it *should* do, you can get
a scope of high quality but unknown condition.

Yes, a new Chineses scope is the way I'm leaning. My local (Australia)
electronics chain has a 10MHz (1 Channel) for about US$120. The 20MHz (2
Channel) is about US$300.

The low cost of the 10MHz seems great to get started for me. Then when I
get to the point I need a "real" scope, I might look at a PC-based digital
like the Stingray DS1M12 USB- I've got a couple of old PCs (133 and 120MHz)
sitting around doing nothing.

Though I keep reading mixed messages about PC-based scopes. OTOH, it seems
to me that to look at signal all you need is a fast A-to-D converter and the
right software; it's simple and obvious - unless I'm missing something.

But, I hear what you're saying about the 2 channel. So maybe I should go
for the 2 Channel Chinese and then I'll have a usable analog scope that will
last me for many years.

It's not like I'm a "professional repairer" and it's not going to be used 10
hours a day. In fact, it will probably spend 11 months of the year just
switched off (after my initial burst of study).

240V * 1.4 = 336V, by the way.

Thanks, yes I reviewed the RMS definition.

Thanks again for your advice, and also to others for their comments.

I must say the second hand market is a bit too hard for me to figure out as
a beginner.

Though I missed out (forgot to bid) on a Tek 2336 last week that went for
about US$300. The individual seller claimed it worked perfectly except the
screen was a little darkened and it was missing a case clip. It certainly
seemed like a real bargain at that price.

There's now a Tek 2215 in perfect order (with probe) currently bid at about
US$340. Very tempting....but like posters have alluded, who knows about its
calibration, and whether it will die in short time. And what about parts,
etc. etc. etc.

regards,
RR

 

[Rich Webb]

On Fri, 30 Sep 2005 21:30:29 GMT, "RR"

[snip...snip...]

The low cost of the 10MHz seems great to get started for me. Then when I
get to the point I need a "real" scope, I might look at a PC-based digital
like the Stingray DS1M12 USB- I've got a couple of old PCs (133 and 120MHz)
sitting around doing nothing.

Though I keep reading mixed messages about PC-based scopes. OTOH, it seems
to me that to look at signal all you need is a fast A-to-D converter and the
right software; it's simple and obvious - unless I'm missing something.

There are fast A/D converters and there are FAST A/D converters. Pretty
much every PC-based USB scope that I've seen tops out at 100 Msps (often
shared by two channels). For comparison, the lower-end Tek digital
TDS-1000 series sample at 1Gsps per channel. Their high end digitals
sample at 20 Gsps; those are the DAMN FAST A/Ds.

Ignore the "equivalent sampling rate" numbers.

 

[Walter Harley]

[...]
Yes, a new Chineses scope is the way I'm leaning. My local (Australia)
electronics chain has a 10MHz (1 Channel) for about US$120. The 20MHz (2
Channel) is about US$300.

The low cost of the 10MHz seems great to get started for me. Then when I
get to the point I need a "real" scope, I might look at a PC-based digital
like the Stingray DS1M12 USB- I've got a couple of old PCs (133 and
120MHz)
sitting around doing nothing.

Though I keep reading mixed messages about PC-based scopes. OTOH, it
seems
to me that to look at signal all you need is a fast A-to-D converter and
the
right software; it's simple and obvious - unless I'm missing something.

But, I hear what you're saying about the 2 channel. So maybe I should go
for the 2 Channel Chinese and then I'll have a usable analog scope that
will
last me for many years.

It's not like I'm a "professional repairer" and it's not going to be used
10
hours a day. In fact, it will probably spend 11 months of the year just
switched off (after my initial burst of study).
[...]

I would really push you to go with two channels. Being able to do things
like looking at both the good channel and the bad channel of a stereo, at
the same time, is very useful. And you need two channels to do Lissajous
curves, and to do curve tracing of semiconductors - all useful stuff.

As I said earlier, one of the big differences between okay and excellent
scopes is the quality of the triggering. That statement is probably
meaningless to you now, but you'll come to appreciate it over time... and
good triggering is all about ANALOG, even for a digital scope. Being able
to reliably trigger on a short erratic pulse, being able to *ignore* a short
erratic pulse - this is stuff that can't be done in software; you have to
just plain have good analog circuitry. Maybe there are PC scopes that have
good analog sections, but I'm sure there are more that don't

But don't sweat it too much; you'll get there eventually. Get a cheap
dual-trace one way or another and start playing with it.

 

[RR]

I would really push you to go with two channels. Being able to do things
like looking at both the good channel and the bad channel of a stereo, at
the same time, is very useful. And you need two channels to do Lissajous
curves, and to do curve tracing of semiconductors - all useful stuff.

I'm convinced.

As I said earlier, one of the big differences between okay and excellent
scopes is the quality of the triggering. That statement is probably
meaningless to you now, but you'll come to appreciate it over time... and
good triggering is all about ANALOG, even for a digital scope. Being able
to reliably trigger on a short erratic pulse, being able to *ignore* a short
erratic pulse - this is stuff that can't be done in software; you have to
just plain have good analog circuitry. Maybe there are PC scopes that have
good analog sections, but I'm sure there are more that don't

Yes, that makes a lot of sense.

But don't sweat it too much; you'll get there eventually. Get a cheap
dual-trace one way or another and start playing with it.

Thanks again. I'm going to take your advice.

cheers,
RR

 

[quietguy]

Have you had a look at the DSE 20mhz 2 channel scope for $399? Looks like a
good buy to me, and I plan to buy one next week

David - who bought one of those 1 channel 10 mhz scopes but finds it too
limiting (so will flog it on ebay)

 

[RR]

message

Have you had a look at the DSE 20mhz 2 channel scope for $399? Looks like a
good buy to me, and I plan to buy one next week

Yes, that's what I'm looking at getting. I think Jaycar have the same or
similar unit.

David - who bought one of those 1 channel 10 mhz scopes but finds it too
limiting (so will flog it on ebay)

Thanks for that....I won't buy one of those then.

cheers,
RR

 

[Jim Yanik]

Yes, a new Chineses scope is the way I'm leaning. My local
(Australia) electronics chain has a 10MHz (1 Channel) for about
US$120. The 20MHz (2 Channel) is about US$300.

The low cost of the 10MHz seems great to get started for me. Then
when I get to the point I need a "real" scope, I might look at a
PC-based digital like the Stingray DS1M12 USB- I've got a couple of
old PCs (133 and 120MHz) sitting around doing nothing.

Though I keep reading mixed messages about PC-based scopes. OTOH, it
seems to me that to look at signal all you need is a fast A-to-D
converter and the right software; it's simple and obvious - unless I'm
missing something.

But, I hear what you're saying about the 2 channel. So maybe I should
go for the 2 Channel Chinese and then I'll have a usable analog scope
that will last me for many years.

It's not like I'm a "professional repairer" and it's not going to be
used 10 hours a day. In fact, it will probably spend 11 months of the
year just switched off (after my initial burst of study).


Thanks, yes I reviewed the RMS definition.

Thanks again for your advice, and also to others for their comments.

I must say the second hand market is a bit too hard for me to figure
out as a beginner.

Though I missed out (forgot to bid) on a Tek 2336 last week that went
for about US$300. The individual seller claimed it worked perfectly
except the screen was a little darkened and it was missing a case
clip. It certainly seemed like a real bargain at that price.

There's now a Tek 2215 in perfect order (with probe) currently bid at
about US$340. Very tempting....but like posters have alluded, who
knows about its calibration, and whether it will die in short time.
And what about parts, etc. etc. etc.

regards,
RR

I find 2200 scopes to be very useful,good scopes.I have a 2213 myself.
Far better than some other TEK scopes such as 434,any 5000 series scope.
IMO,2213/15 are one of the most repairable of the newer TEK analog scopes.
Calibration is not meant to be "long-lasting",TEK recommended at least
yearly calibration.

 

[BFoelsch]

I find 2200 scopes to be very useful,good scopes.I have a 2213 myself.
Far better than some other TEK scopes such as 434,any 5000 series scope.
IMO,2213/15 are one of the most repairable of the newer TEK analog scopes.

For a scope to "fool around" with, I would suggest the OP look at a Tek
2225. They typically go for $50 - $100. They are also almost completely
discrete, so repairs are feasible in most cases. Definitely not a "high-end"
unit, but certainly enough to teach you the basics.

 

[Jim Yanik]

For a scope to "fool around" with, I would suggest the OP look at a
Tek 2225. They typically go for $50 - $100. They are also almost
completely discrete, so repairs are feasible in most cases. Definitely
not a "high-end" unit, but certainly enough to teach you the basics.

A great beginner scope would be a T922 or T932/35;they have no TEK-made ICs
or special transistors in them.Very simple switches,too.