I’ve seen op amp oscillation well into the tens of MHz region, but you don’t necessarily need a scope to go that high...
If you bought a 20MHz scope and probed an oscillating op amp, you could zoom in enough to see a large blur across the whole screen and that’s enough to tell you it's oscillating ie you don’t need to see each individual cycle to know what's going on.
Having typed that, having ample bandwidth is always nice, but I'm spoilt by having 6GHz, 20GS/s scopes at work!
Nice one,
David.
m8o said:Somewhat OT, but related...
Question for those in the know, for the non-electronics-diy-newbz like me ...
If I want to check that my opamp-based amp does not ocillate, what MHz should I "check up to" ?
I ask, as this will define the ocilliscope bandwidth I should be looking for (and partially, how much $$$ I will need to spend). I have a -OLD- Heathkit scope my dad made when he took their self-study at-home courses. I'd like something better tho...
If that is too broad of a question to answer given all the variables that may go into it, is there a "frame of reference" that can be made based on the open loop gain frequency response of a opamp/device then? something like "check up to 1/2 the bandwidth" or "check up to twice the bandwidth", etc.?
thanx all
There may well be a rule-of-thumb, for that. I don't know. An opamp that is capable of a very fast slew rate, or that has a very high frequency capability, might be more prone to oscillation problems. But it seems like they can all oscillate very well, given the right conditions.
The first test I use is to try touching each opamp. If it's excessively warm (or blisters your finger!), and "shouldn't be", it might be oscillating pretty good. Higher frequency signals have proportionately-more energy, all other things being equal. So they will often generate a lot of heat.
With a scope, even if the bandwidth and trigger "bandwidth" are pretty far below the oscillation frequency, you can often still see the oscillation. If it's a low-amplitude oscillation, your signal's trace will look "thick". Then you can often crank the timebase up to its fastest speed and use a more-sensitive vertical attenuator setting to try to get a better idea of what you're dealing with. If it's oscillating with a higher amplitude, it will be more obvious.
- Tom Gootee
http://www.fullnet.com/~tomg/index.html
-----------------
This question has been explored on this forum many times in the past. I reccomend that you go back and do a search and you'll learn alot more.
There is only one answer to this question for a general purpose scope. 
Good used Tektronix 465B 100 mhz scope. Don'rt buy anything less than 100 mhz!!! I got mine for 75 bucks on E-Bay.
ALSO!
Don't buy a Digital Scope unless you can get a top of the line model(new or used). The inexpensive Digital Scope Meters cannot properly display all types of waveforms due to slow refresh rates of the display.
Bandwidth more than 20 mhz may be needed to check an oscillation in an amp/preamp!
Mark
Photo:
My Scope collection missing the TEK 465B and 7603 that are at work.
There is only one answer to this question for a general purpose scope. Good used Tektronix 465B 100 mhz scope. Don'rt buy anything less than 100 mhz!!! I got mine for 75 bucks on E-Bay.ALSO!
Don't buy a Digital Scope unless you can get a top of the line model(new or used). The inexpensive Digital Scope Meters cannot properly display all types of waveforms due to slow refresh rates of the display.
Bandwidth more than 20 mhz may be needed to check an oscillation in an amp/preamp!
Mark
Photo:
My Scope collection missing the TEK 465B and 7603 that are at work.
Attachments
To all those in the know...
Continuing this extraodinarily useful thread to us newbz (as I've been away from school, DIY, and associated tools used in both for a few decades now) ... What about probes?
Thanx everyone for the input so far. I settled on a decent looking (I have to see once it's delivered) Tek 465B with DM44 multimeter that I won for a good price on eBay. But no probes. As the seller wants something like 60$ for the 465B manual that he's selling in another auction (but not convering the DM44 ; forget about it either way), I found some scanned 465B manuals, so I know the probe is P6105. The only scanned manuals I found including the DM44 were for the 475.
Now for the questions:
1) Can I assume the 475+DM44 will work fine for my 465B+DM44 in regards to just the DM44 part? I ask, because I understand after 465B/466 the scope's circuits changed a good deal. So my worry is that affects the DB44 part somehow.
2) Can I depend on the probes stated in that 475+DM44 document for the DM44 section's current probe and temperature would work for my 465B+DM44, as far as the DM44 is concerned ?
3) What other probes would work for me -- say high voltage probes if I do work with Tubes in the future -- for the 465B, or what probes will work that may have come with later models?
Is there a cross-reference anywhere? It's not on Tektronix's site as far as I could find; at least not one that covers the 465B in it if it exists?
4) And finally, can I 'trust' non-original-Tektronics , aftermarket, probes I find being sold new on eBay? Like this:
http://cgi.ebay.com/For-HP-Tektroni...1QQihZ013QQcategoryZ25415QQrdZ1QQcmdZViewItem
Thanx very much again!
Continuing this extraodinarily useful thread to us newbz (as I've been away from school, DIY, and associated tools used in both for a few decades now) ... What about probes?
Thanx everyone for the input so far. I settled on a decent looking (I have to see once it's delivered) Tek 465B with DM44 multimeter that I won for a good price on eBay. But no probes. As the seller wants something like 60$ for the 465B manual that he's selling in another auction (but not convering the DM44 ; forget about it either way), I found some scanned 465B manuals, so I know the probe is P6105. The only scanned manuals I found including the DM44 were for the 475.
Now for the questions:
1) Can I assume the 475+DM44 will work fine for my 465B+DM44 in regards to just the DM44 part? I ask, because I understand after 465B/466 the scope's circuits changed a good deal. So my worry is that affects the DB44 part somehow.
2) Can I depend on the probes stated in that 475+DM44 document for the DM44 section's current probe and temperature would work for my 465B+DM44, as far as the DM44 is concerned ?
3) What other probes would work for me -- say high voltage probes if I do work with Tubes in the future -- for the 465B, or what probes will work that may have come with later models?
Is there a cross-reference anywhere? It's not on Tektronix's site as far as I could find; at least not one that covers the 465B in it if it exists?
4) And finally, can I 'trust' non-original-Tektronics , aftermarket, probes I find being sold new on eBay? Like this:
http://cgi.ebay.com/For-HP-Tektroni...1QQihZ013QQcategoryZ25415QQrdZ1QQcmdZViewItem
Thanx very much again!
Try this HP1707B. The seller made an error in his description that an astute buyer will probably be able to take advantage of- it is a 75 MHz scope, not a 1 MHz BW scope as he states in the description. If you're lucky, none of the potential bidders will realize the error and it will sell cheap. Has service/operations manual, too!
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=280070546820&ssPageName=ADME:L:DBS:US:11
This scope is solid state except for the CRT, so it is relatively small and light weight.
I have the military version of this scope (AN/USM-338) and it is very nice! Delayed sweep! If you don't know what that is or why it is useful, look it up. I can tell you it is very handy for looking at rising or falling edges of digital waveforms, for example. You can see photos of the guts of my scope here:
http://mark.rehorst.com/AN_USM_338/index.htm
I_F
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=280070546820&ssPageName=ADME:L:DBS:US:11
This scope is solid state except for the CRT, so it is relatively small and light weight.
I have the military version of this scope (AN/USM-338) and it is very nice! Delayed sweep! If you don't know what that is or why it is useful, look it up. I can tell you it is very handy for looking at rising or falling edges of digital waveforms, for example. You can see photos of the guts of my scope here:
http://mark.rehorst.com/AN_USM_338/index.htm
I_F
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=280070546820&ssPageName=ADME:B:WNA:US:12
Someone got a great deal. I told you!
I_F
Someone got a great deal. I told you!
I_F
m8o said:To all those in the know...
Continuing this extraodinarily useful thread to us newbz (as I've been away from school, DIY, and associated tools used in both for a few decades now) ... What about probes?
Thanx everyone for the input so far. I settled on a decent looking (I have to see once it's delivered) Tek 465B with DM44 multimeter that I won for a good price on eBay. But no probes. As the seller wants something like 60$ for the 465B manual that he's selling in another auction (but not convering the DM44 ; forget about it either way), I found some scanned 465B manuals, so I know the probe is P6105. The only scanned manuals I found including the DM44 were for the 475.
Now for the questions:
1) Can I assume the 475+DM44 will work fine for my 465B+DM44 in regards to just the DM44 part? I ask, because I understand after 465B/466 the scope's circuits changed a good deal. So my worry is that affects the DB44 part somehow.
2) Can I depend on the probes stated in that 475+DM44 document for the DM44 section's current probe and temperature would work for my 465B+DM44, as far as the DM44 is concerned ?
3) What other probes would work for me -- say high voltage probes if I do work with Tubes in the future -- for the 465B, or what probes will work that may have come with later models?
Is there a cross-reference anywhere? It's not on Tektronix's site as far as I could find; at least not one that covers the 465B in it if it exists?
4) And finally, can I 'trust' non-original-Tektronics , aftermarket, probes I find being sold new on eBay? Like this:
http://cgi.ebay.com/For-HP-Tektroni...1QQihZ013QQcategoryZ25415QQrdZ1QQcmdZViewItem
Thanx very much again!
Congratulations on getting the Tek 465B! That's a very good scope!
I don't know if I can answer your questions. But I'll give it a try:
1. You need to get the correct manual for your scope model and serial number range. Try looking at http://bama.edebris.com/manuals/tek/ .
2. Maybe. But look in the correct manual for your scope model and serial number range.
3. Many probes will work, as long as their bandwidth is high-enough and their input impedance and capacitance-compensation range match/include the impedance and capacitance printed next to your scope's inputs, on its front panel.
You would probably usually want probes that have at least a slightly higher bandwidth than your scope has, so you're not seeing 6-dB-down when at f=BW (i.e. 3 dB down from scope BW plus 3 dB down from probe bandwidth). (So you might want to check whether or not a P6106 or P6106A would work with your scope.)
P610X probes, and Tek 400-series inputs, are typically spec'd for 500V peak. You'll usually use 10X probes, anyway. So 400v would look like 40v to your scope.
For higher voltages, you _might_ be able to use a Tek P6009 100X 120 MHz probe, which is spec'd up to 1.5 kV. And there's a P6015 1000x probe that's spec'd up to 15 kV (assuming it still has enough of the special fluid that goes inside, or you have a refill can). Or, you might be able to "roll your own" and make a resistive divider that could go ahead of a regular probe's tip, or that replaces a regular probe. But you'd have to do some homework, for that, since it might be different than doing it for, say, a multimeter. And it can be dangerous and/or destructive, even if done properly. You can find more information about that by searching at http://groups.google.com (which now has the searchable archive of all text-only message-traffic from all Usenet newsgroups, from about 1981 to the present! It's a GOLDMINE!)
There's a list of older Tektronix oscilloscope probes, with specs, on Stan Griffiths' excellent Tek scope website, at: http://www.reprise.com/host/tektronix/reference/voltage_probes.asp .
The official Tektronix website's now-somewhat-abbreviated list of matching probes for discontinued scopes is at:
http://www.tek.com/site/ps/0,,60-15264-INTRO_EN,00.html .
There is a very useful archive of older test equipment manufacturers' CATALOGS, which also contains all of this information (and much more), at: http://www.testmart.com/advice/advicetmp.cfm .
I have quite a few good links to Tektronix Oscilloscope information, on my links page, at: http://www.fullnet.com/~tomg/links.htm . (A few of them may be too old to work any more. Sorry.)
Here is a list of sources for low-cost non-Tek probes that should work well (and also some info about selecting probes): http://www.slack.com/probes.html .
4. Usually you CAN trust non-Tek probes. But review all of the information in my answer to question 3, above, and at some of the links provided, such as this sub-link: http://www.reprise.com/host/tektronix/reference/choosing_a_probe.asp .
As mentioned by another poster, there is a truly-excellent discussion group, called TekScopes, at http://www.yahoogroups.com . It's probably THE highest-quality discussion group that I've ever been involved with. There are some highly-esteemed ex-Tektronix guys who are regulars, there, as well as many other Extremely-Knowledgable (and helpful) people. (So be sure to "tiptoe", at least at first. ;-) )
Good luck!
- Tom Gootee
http://www.fullnet.com/~tomg/index.html
-
Tektronix "XYZs of Oscilloscopes"
I forgot to mention that the well-regarded Tektronix "XYZs of Oscilloscopes" primer is at: http://www.tek.com/Measurement/cgi-...rement/App_Notes/XYZs/&FrameSet=oscilloscopes .
There is also a "Oscilloscopes FAQ" type of website, which I have not reviewed, at: http://www.qsl.net/wd1v/scopefaq/index.html .
- Tom Gootee
http://www.fullnet.com/~tomg/index.html
-
I forgot to mention that the well-regarded Tektronix "XYZs of Oscilloscopes" primer is at: http://www.tek.com/Measurement/cgi-...rement/App_Notes/XYZs/&FrameSet=oscilloscopes .
There is also a "Oscilloscopes FAQ" type of website, which I have not reviewed, at: http://www.qsl.net/wd1v/scopefaq/index.html .
- Tom Gootee
http://www.fullnet.com/~tomg/index.html
-
Mark A. Gulbrandsen said:
In the HP scopes of the 1960's and 1970's they had problems getting the triggers to synch correctly.
Don't neglect to look at the Heath scopes -- put Heath* wildcard in the EBay Business/Test Equipment search engine.
FWIW, I have fewer scopes than Mark -- I now have 3
1) 5223A -- a low bandwidth very low noise digitizing scope -- it has two differential amplifiers and storage -- you can get a good look at what's going on in a power supply with this one. I bought one for next to nothing, gave it to a University, then had to get another -- if you can get a good clean one with 5A22N and 5A28 plug-ins they are a good investment. Do not buy this scope without plug-ins.
2) 2465B -- probably one of the best-ever all analog scopes -- 400 MegaHertz bandwidth -- it will lock onto anything.
3) TDS0312B -- this is the one I use most of the time -- very convenient -- has FFT and can do things like phase measurement and you can put a floppy disk in and get a picture of the display to dump into PhotoShop -- but it isn't as quiet as the 5223.
Most likely an older TEK scope can be fixed, and a TDS style, if it is broke, is a write-off.
My goal - to spend less than $1,000 on ebay for a scope. My needs are a scope that is probably less than 100mhz it might be nice to have higher, but I don't need it. Most of what I look at are power supplies and low speed serial data.
I am having a hard time figuring out where the different obsolete TDS scopes fit in the hierarchy. I don't need high Mhz, and the LCD display of the TDS200/ 1000/2000 series is appealing to me (because of size), but I don't know how they compare to the older higher number TDS series scopes like the 300,400,500,600 etc.
I have not used a digital scope in the past, always analog. I understand that these newer digital scopes have the ability to display realtime waveforms much like an analog scope (if this is incorrect please let me know).
I see that the newer low mhz scopes have higher sampling rates than the older high mhz scopes. Is this relevant? I also have noticed that the LCD scope only has a display resolution of 320x240 where the CRT scopes were 640x480. Is this something that would noticeable? Seems like it would be. Again I am used to perfectly smooth analog scopes. I don't know if one of these newer ones would look grainy, or if it matters.
I am leary of buying a 22xx or 24xx vintage machine due to just generally being afraid of buying 15-20 year old sensitive electronics that I can't repair.
So it would seem my options are the TDS 200 series or the TDS 300-600 series.
any suggestions?
I am having a hard time figuring out where the different obsolete TDS scopes fit in the hierarchy. I don't need high Mhz, and the LCD display of the TDS200/ 1000/2000 series is appealing to me (because of size), but I don't know how they compare to the older higher number TDS series scopes like the 300,400,500,600 etc.
I have not used a digital scope in the past, always analog. I understand that these newer digital scopes have the ability to display realtime waveforms much like an analog scope (if this is incorrect please let me know).
I see that the newer low mhz scopes have higher sampling rates than the older high mhz scopes. Is this relevant? I also have noticed that the LCD scope only has a display resolution of 320x240 where the CRT scopes were 640x480. Is this something that would noticeable? Seems like it would be. Again I am used to perfectly smooth analog scopes. I don't know if one of these newer ones would look grainy, or if it matters.
I am leary of buying a 22xx or 24xx vintage machine due to just generally being afraid of buying 15-20 year old sensitive electronics that I can't repair.
So it would seem my options are the TDS 200 series or the TDS 300-600 series.
any suggestions?
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.