Scope help.. How much voltage is too much?

[Michael Kennedy]

I have a old heathkit tube oscilloscope. It is a model I0-17. I was wanting
to learn a little about it and how to use it. My biggest question is how
much voltage can a scope usually handle? This scope doesn't have any probes.
Are there special probes for scopes that are different than those for
multimeters?

My first project I want to use it for is trying to find where I'm getting a
buzz in my stereo. It will buzz if my computer is hooked up to and it is
grounded. If the computer is ungrounded it doesn't buzz. The stereo only has
a two wire connector so it isn't groudned. I thought this scope could be
usefull in tracking down where the buzzing is coming from.. Anyhow I need to
know if I can plug this thing into the wall (120vac) or if it will blow up
if I do that.

 

[Ray L. Volts]

I have a old heathkit tube oscilloscope. It is a model I0-17. I was wanting
to learn a little about it and how to use it. My biggest question is how
much voltage can a scope usually handle? This scope doesn't have any
probes. Are there special probes for scopes that are different than those
for multimeters?

Different strokes for different scopes. Some will only handle a few hundred
volts before their front end will blow. Others, like Sencore analyzers, can
handle 2000+ vdc/ac quite happily. Scope leads have important
characteristics other than merely how much voltage they can safely handle --
such as capacitance. Also, there are multiplier probes which allow the user
to measure higher-than-usual voltages with the same scope.

The manual for your scope ($22) can be found here:

http://www.w7fg.com/manuals.php?manufacturer=Heathkit&page=5

or here ($18):

http://www.d8apro.com/heath2.htm

The manual is 60 pages, btw.

My first project I want to use it for is trying to find where I'm getting
a buzz in my stereo. It will buzz if my computer is hooked up to and it is
grounded. If the computer is ungrounded it doesn't buzz. The stereo only
has a two wire connector so it isn't groudned. I thought this scope could
be usefull in tracking down where the buzzing is coming from.. Anyhow I
need to know if I can plug this thing into the wall (120vac) or if it will
blow up if I do that.

Try a device called a ground loop isolator. This may seem counterintuitive,
since your stereo is not grounded, but isolators have been known to fix all
sorts of seemingly weird grounding maladies. Don't be phased (pardon pun)
by some online prices, as isolators can be had ultra cheaply; it's worth a
shot.

Most any scope easily accomodates 120vac, but even if the spec'd max voltage
is well above that, it's no guarantee yours won't "blow up". Yours is
afterall an OLD scope, which no doubt hasn't been checked for 100%
functionality, safety and calibration in quite some time.

 

[tempus fugit]

As for the hum, have you tried connecting bot stereo and computer to the
same wall outlet or power bar? Sounds like ground loop to me, and if so,
this should make it go away.

 

[Michael Kennedy]

The issue is solved by a ground loop isolator but when I run input in to my
vcr I also get bars on the screen. I think I have a grounding issue in the
building. The voltage spikes when the AC on the other leg of 120v starts up.
It is not a 240v ac it is on a seperate circuit on a seperate leg. I would
call it a sperate phaze, but it is really just off a different tap on the
transformer on the power pole. Anyway I'm going in to too much detail. I'm
sure you know what I mean. I think I may need to drive another grounding
rod.