Recommended 'Scope Probe confusion - Page 1
Forum section: electronics / beginners

author: jaunty
author_rank: Regular Contributor
timestamp: February 16, 2015, 01:12:14 am
content: Howdy. I'm totally new here though I've browsed the posts on and off for a few years.I just got a (new to me) 100MHz Tek scope and now I'm trying to find some suitable probes. and YES I've read through some of the more relevant posts on the subject but I'm still kind of confused. i have very little to no practical experience using scopes except for when i was a young kid I had an ancient one i used to mess about with.Most of what i'll be doing is repair work on some synthesizers. So most of that is going to be +/- 5 volt analogue signal hunting, checking op amps, signal degradation etc etc...from what I've READ here it seems the way to go is to find a decent quality second hand 10x Tek or other mfr probe - and to avoid the chinese knock offs. HOWEVER - when looking through all the available options on 'the bay' I'm seeing a LOT of different options in terms of loading and capacitance and I'm insecure enough with my knowledge to feel a bit bewildered by it. Is picking a garden variety PASSIVE Tek probe with 10pF and 10Mohm going to be roughly appropriate for what i'm doing - or am I making a mistake here?I'd really appreciate the advice... thanks

author: Fsck
author_rank: Super Contributor
timestamp: February 16, 2015, 01:50:56 am
content: it's perfectly fine for what you're doing.

author: jaunty
author_rank: Regular Contributor
timestamp: February 16, 2015, 03:13:05 am
content: alright thanks - so 'passive' is the way to go I assume?

author: jaunty
author_rank: Regular Contributor
timestamp: February 16, 2015, 04:28:22 am
content: ended up getting a used Tek P6109. Hope that works out. supposed to be good to 150MHz - as the scope is 150Mhz (not 100 as i thought)...

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: February 16, 2015, 06:00:53 am
content: Quote from: jaunty on February 16, 2015, 04:28:22 amThat's an awful lot of bandwidth. What kind of synthesizers are you talking about here? Audio I'm guessing?

author: jaunty
author_rank: Regular Contributor
timestamp: February 16, 2015, 06:34:03 am
content: Yes. 'audio' - Think: Moog etc. Mostly stuff from the 70s/80s... I wanted at least 100Mhz 'just in case' - it would be terrible to want to run some experiment or measure something etc and not have the bandwidth to do it.PS - Does anyone have an idea where i might find (other than ebay - but that's not yielding anything) a replacement fuse holder cover for a Tek 2221A that I haven't used in years because I lost the cap (?)

author: tautech
author_rank: Super Contributor
timestamp: February 16, 2015, 06:50:57 am
content: Quote from: jaunty on February 16, 2015, 06:34:03 amCheck the first post in the "Repair" board for a link to Sphere and if not listed on their site, email them.

author: jaunty
author_rank: Regular Contributor
timestamp: February 16, 2015, 06:52:35 am
content: Ah! Sphere! They still exist? I think I may have ordered something from them around 2000 or so. I think they're in british columbia or something?

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: February 16, 2015, 07:03:32 am
content: Quote from: jaunty on February 16, 2015, 06:34:03 amI think it's equally more terrible to spend time chasing fuzz because you're picking up the entire local FM broadcast band. You will want to use a bandwidth limit if your scope has one, if only to make the trace sharper.Sphere are still in business. As for the fuse cap, try the Tekscopes group, lots of help in there.https://groups.yahoo.com/neo/groups/TekScopes/conversations/messages

author: tggzzz
author_rank: Super Contributor
timestamp: February 16, 2015, 09:34:47 am
content: For your application, audio, virtually any *1 or *10 probe will do. A *1 probe is useful for low amplitude signals, but its capacitance (~100pF) may alter a circuit's operation. A *10 probe has lower capacitance (~20pF) but you won't be anle to see such low voltages.You should, however, ensure that a *10 probe's compensation range (e.g. 15pF-30pF) encompasses your scope's input capacitance. And do twiddle the compensation, even if you aren't looking at "high" frequencies.If you start to look at typical CMOS/TTL digital signals and you see ringing on the transistions, be aware that it might be your probe and probing technique. At that point come back and look at probes again.

author: w2aew
author_rank: Super Contributor
timestamp: February 16, 2015, 02:53:57 pm
content: Quote from: jaunty on February 16, 2015, 06:34:03 amHaving the extra BW can be useful. Yes, you'll be using the BW limit most of the time, but the extra BW can reveal things like high frequency oscillation that can sometimes happen unexpectedly, as this video shows.

author: jaunty
author_rank: Regular Contributor
timestamp: February 17, 2015, 04:53:31 am
content: thanks for the info guys... all good advice - and thanks especially for the video clip. I always wondered to what degree metal/air/metal connections influenced capacitance/noise... fascinating! But now you're making me think I should have gone for an even faster scope than 150MHz. I'm also glad i'm getting an old Tek CRO and not a digi-scope.