Analog versus digital oscilloscopes 2

[james_s]

As far as collectable status, I suspect something more general is going on because used test equipment of all types has become much rarer and more expensive over the past couple of years.

I, and I suspect others, would also like to understand that phenomenon.

I have wondered if it is the fact that so much of the electronics industry has moved overseas that all the used gear is in China now, or perhaps it's a generational thing where gear gets replaced in cycles as new waves of technology appear. For a while the market was flooded with stuff like analog scopes and 70s-80s gear as businesses upgraded to DSOs and other 90s-2000's gear. Then there was a wave of that gear as businesses upgraded and now we are at a point where the last round of high end gear that was purchased is still working. Or maybe the pandemic has resulted in enough people taking up hobbies or getting more into the hobbies they have and buying up supplies of gear leading to shortages. Either way it has been well over a year since I've seen anything resembling a deal on any sort of used test equipment I watch for. Thankfully I have just about everything I really need at this point.

[Trader]

As far as collectable status, I suspect something more general is going on because used test equipment of all types has become much rarer and more expensive over the past couple of years.

I, and I suspect others, would also like to understand that phenomenon.

I have wondered if it is the fact that so much of the electronics industry has moved overseas that all the used gear is in China now, or perhaps it's a generational thing where gear gets replaced in cycles as new waves of technology appear. For a while the market was flooded with stuff like analog scopes and 70s-80s gear as businesses upgraded to DSOs and other 90s-2000's gear. Then there was a wave of that gear as businesses upgraded and now we are at a point where the last round of high end gear that was purchased is still working. Or maybe the pandemic has resulted in enough people taking up hobbies or getting more into the hobbies they have and buying up supplies of gear leading to shortages. Either way it has been well over a year since I've seen anything resembling a deal on any sort of used test equipment I watch for. Thankfully I have just about everything I really need at this point.

If you have (for example) a $350 Rigol DS1054Z 100MHz, you can do almost everything you need as a hobbyist and also do a lot of professional experiments and debugs.

To have a 2nd ~$350 "low-end" scope, 200/250Mhz, 2CH won't add so much to you. (my opinion).

A ~$1,350 Rigol MSO5074 (hacked to 350MHz) or a ~$1,400 Siglent SDS2104X Plus (hacked to 500MHz) (plus 4*500MHz probes $ $ $) will add much more certainly, a better FFT, etc.

On eBay you can find a (for example) 4CH Tektronix 2465A 350MHz for ~$150, and at least, bring more quality to your waveform analysis, since it performs well even at 750MHz.

Single-shot capture below 125Mhz, you can use the low-end DSO, for high frequencies waveforms you can use the CRO, and now you have 4 more channels to play, costing 90% Less (I excluded the Keysight and Tek DSOs from the same range, that costs at least 2X the Rigol/Siglent).

In summary: I think these CROs fill this gap between $350 and $1,350 scopes, as a 2nd scope.

[tggzzz]

That's a considered, nuanced, balanced, rational argument.

Shame too many people don't think in those terms!

[bdunham7]

On eBay you can find a (for example) 4CH Tektronix 2465A 350MHz for ~$150, and at least, bring more quality to your waveform analysis, since it performs well even at 750MHz.

In summary: I think these CROs fill this gap between $350 and $1,350 scopes, as a 2nd scope.

If you can find (or have found) a good condition 2565/A/B for $150 and you have room on the bench and a specific need for its capabilities, then go for it.  Most of the ones I've seen for $150 on eBay are broken or even incomplete.  I have several (2445, 2465B, 2221A, and more) that I have fixed up and the specific reasons I might drag one out are usually related to vector graphics or a specific need for the Z-axis input.  Also, on one occasion I needed something with better input overload recovery, but I also have two other DSOs that would suffice. If I had room to keep one on the bench, I might use it sometimes just because it was there.  IMO the gap that an old high-performance CRO would fill is small and waning, but YMMV.  What do you use yours for?

[tggzzz]

On eBay you can find a (for example) 4CH Tektronix 2465A 350MHz for ~$150, and at least, bring more quality to your waveform analysis, since it performs well even at 750MHz.

In summary: I think these CROs fill this gap between $350 and $1,350 scopes, as a 2nd scope.

If you can find (or have found) a good condition 2565/A/B for $150 and you have room on the bench and a specific need for its capabilities, then go for it.  Most of the ones I've seen for $150 on eBay are broken or even incomplete.  I have several (2445, 2465B, 2221A, and more) that I have fixed up and the specific reasons I might drag one out are usually related to vector graphics or a specific need for the Z-axis input.  Also, on one occasion I needed something with better input overload recovery, but I also have two other DSOs that would suffice. If I had room to keep one on the bench, I might use it sometimes just because it was there.  IMO the gap that an old high-performance CRO would fill is small and waning, but YMMV.  What do you use yours for?

Undoubtedly many Tek 24x5 and similar machines on fleabay are suspect, and need a little work. But not all. 
Undoubtedly digitising scopes will be the way of the future
But...
A good working analogue scope is a joy to use and is very capable, and can be used for many purposes.
100MHz was fine for digital logic 40 years ago, but modern jellybean logic requires far more than that.

Anybody that declares that only digitising scopes should be considered and that working analogue scopes should be ignored is, IMHO, a twit.

For most of my purposes, a sufficient combination is a 2 channel >300MHz analogue scope (assure signal integrity), plus cheap logic/protocol analyser and printf statements. If those aren't sufficient then you need serious thought or money.

[Trader]

If you can find (or have found) a good condition 2565/A/B for $150 and you have room on the bench and a specific need for its capabilities, then go for it.  Most of the ones I've seen for $150 on eBay are broken or even incomplete.

Everything on eBay is suspicious, even a new product.  A while ago I bought a "Used" power supply and the seller sent a totally broken device, I returned it, simple.

But if the seller is honest, he/she will put real pictures, and inform, as best possible, the device status, etc...

Any used scope requires a certain examination and maybe calibration (yearly). A good CRO costing 80% less than a "medium-end" chinese DSO, I think it's a good deal.

[radiolistener]

Analog and digital oscilloscopes  both have pros and cons. So this is just a choice of user.
For a noob, it's better to select a new model of digital oscilloscope from a known brand, like Rigol or Siglent.

[TimFox]

A related question, relevant to new students of the art:
In my education, during the previous century, my schools were careful to have us start with traditional equipment (stopwatches, thermocouples with potentiometers, analytic balances, analog voltmeters, etc.) to learn the basics, knowing that when we went on to "real work", we would use more modern equipment, but needed to know what they did (instead of treating them like a black box) and what limitations were important.
In that regard, it is easier to understand what a CRO is doing, since you can slow it down to see the trace moving in real time.  Going from there to a fashionable DSO, you can then learn how to deal with aliasing, finite resolution, latency, etc. while appreciating the measurement, storage, and mathematical capabilities.

[Trader]

I guess, these are the "cheap" basic and "hackable" scopes from 350MHz to 1GHz.

* Rigol MSO5074 # $1,000 (long FFT) # (hack up 350 MHz)
* Siglent SDS2104X Plus # $1,400 + 4 new probes (more default features, cheap options, long FFT) # (hack up 500 MHz)
* Tektronix MDO34 # >$4,800 # (up to 1GHz, hackable?)
* Keysight DSOX3014T # >$4,800 # (up to 1GHz, hackable?)

My preference will be a Tektronix or Keysight of 1GHz, but the "basic" model costs $5K. And any scope, if hacked, will void the (3-5 years) warranty...

IMHO, as the 2nd scope for a hobbyist that already has some decent DSO and has some budget restriction, could be a good CRO.

[bdunham7]

A related question, relevant to new students of the art:
In my education, during the previous century, my schools were careful to have us start with traditional equipment (stopwatches, thermocouples with potentiometers, analytic balances, analog voltmeters, etc.) to learn the basics, knowing that when we went on to "real work", we would use more modern equipment, but needed to know what they did (instead of treating them like a black box) and what limitations were important.
In that regard, it is easier to understand what a CRO is doing, since you can slow it down to see the trace moving in real time.  Going from there to a fashionable DSO, you can then learn how to deal with aliasing, finite resolution, latency, etc. while appreciating the measurement, storage, and mathematical capabilities.

I agree totally with the importance of the 'historical' aspect of science and technology, learning why things are done the way they are by learning how they were developed.  I also enjoy going back and seeing things that I missed--how and when they were developed, etc.  Technoanthropology perhaps.  But my interest is in the details, the little tidbits that make up device, as well as the general progression.  A DSO seems like a natural evolution of the oscilloscope, but fundamentally it is an entirely different sort of machine.  The only reason it strongly resembles an analog oscilloscope is because is because that is the format that users expect to see, from a graticuled screen to knobs for vertical sensitivity and horizontal timebase.  Behind the scenes it is an entirely different beast, eliminating many of the issues that older types had while introducing new ones.  Understanding things like analog triggers, phosphors, delay lines, etc helps you understand why a DSO is configured the way that it is and in a limited way, how to use one, but that historical understanding actually tells you very little about what it is actually doing inside, nor what it is actually capable of in its best form.

[TimFox]

This is not only for historical interest, but to give the novice student a feeling for how measurement works and what it means.
For example, nobody uses analog voltmeters anymore (although I own a few), since DVMs are more convenient and accurate.
However, if a novice starts with a Simpson 260 VOM, he can see a physical needle move and understand the resolution of the measurement (between marks on the dial), and watch it change in quasi-real time.
If he starts with a DMM, all he sees is a number pop up--many consider a readout to be inherently perfectly accurate (like on a pocket calculator) because it's digital, innit?
Operating a traditional analytic balance manually gives far more insight than the modern digital-readout scales, that again just pop up a number like magic.
But, once the student progresses past basic understanding, then on with the modern units and understanding what their capabilities and limitations are.

[tggzzz]

A related question, relevant to new students of the art:
In my education, during the previous century, my schools were careful to have us start with traditional equipment (stopwatches, thermocouples with potentiometers, analytic balances, analog voltmeters, etc.) to learn the basics, knowing that when we went on to "real work", we would use more modern equipment, but needed to know what they did (instead of treating them like a black box) and what limitations were important.
In that regard, it is easier to understand what a CRO is doing, since you can slow it down to see the trace moving in real time.  Going from there to a fashionable DSO, you can then learn how to deal with aliasing, finite resolution, latency, etc. while appreciating the measurement, storage, and mathematical capabilities.

Precisely.

If you understand the basics, you can apply them to any equipment that will be developed in the future. That's a solid engineering education.

If you spend a lot of your time puzzling over a consequence of a setting hidden two levels down in a menu system, you will know how to use that instrument. That is fine for technicians .

I was lucky I learned that from Asimov's story " Profession ", available on the web and just as relevant now as in 1957.

To avoid misunderstandings, we need both engineers and technicians, of course, just as we need both doctors and nurses.

[TimFox]

My favorite gadget from that time in my life was the traditional "analytical balance", with two pans and standard weights.  I remember the final (least-significant) part of the balancing involved turning a knob that moved the end point of a metal chain to change the balance.  A quick Google for "analytical balance" only turned up the modern units (one pan and digital innards), but I found one source in India that still sels the older kind (for roughly $200 USD), https://www.indiamart.com/proddetail/chainomatic-analytical-balance-7916098133.html?pos=1&pla=n
As a youngster, we visited a friend of the family who worked at Lincoln Labs at MIT.  I remember the sign on a door:  "Balance room.  Do not slam door."

[tggzzz]

My favourite is from school physics lessons, measuring voltage to 0.1% when the best available analogue meters were 2%.

Tools: a not very stable NiFe cell, an uncalibrated but sensitive meter, a Weston Standard Cell, a 1m rule and 1m of resistance wire. Plus imagination and understanding, of course.

[bdunham7]

However, if a novice starts with a Simpson 260 VOM, he can see a physical needle move and understand the resolution of the measurement (between marks on the dial), and watch it change in quasi-real time.
If he starts with a DMM, all he sees is a number pop up--many consider a readout to be inherently perfectly accurate (like on a pocket calculator) because it's digital, innit?

What I'm pointing out is that a DMM operates on an entirely different principle than a Simpson 260 and having 'the basics', or even a thorough understanding of an analog VOM does not inform you as to the internal operation of the core a DMM -- and thus does not give you any insight into its capabilities nor its potential shortcomings.  Some fundamentals carry through, from Archimedes to Newton and so on, but others don't.  An advanced engineer that specialized in taut-band meters and VTVMs will not have any clues about how a dual-slope ADC might work unless they learn that anew.  Of course they would understand precision voltage dividers and amplifiers, so their previous education wouldn't be totally wasted. 

[TimFox]

tggzzz:
I remember one of those, a true "potentiometer", where the wire was supplied mounted on a meter stick.  1 mm resolution was 0.1% of full-scale.
Here's one, made by Central Scientific Co. of Chicago, now in Constantinople:  http://www.hasi.gr/instruments/ele66
We also had some of the original-style Wheatstone bridges, where the resistive legs were varied by placing tapered metal pegs into mating sockets between the wire-wound resistors inside the box.

[TimFox]

However, if a novice starts with a Simpson 260 VOM, he can see a physical needle move and understand the resolution of the measurement (between marks on the dial), and watch it change in quasi-real time.
If he starts with a DMM, all he sees is a number pop up--many consider a readout to be inherently perfectly accurate (like on a pocket calculator) because it's digital, innit?

What I'm pointing out is that a DMM operates on an entirely different principle than a Simpson 260 and having 'the basics', or even a thorough understanding of an analog VOM does not inform you as to the internal operation of the core a DMM -- and thus does not give you any insight into its capabilities nor its potential shortcomings.  Some fundamentals carry through, from Archimedes to Newton and so on, but others don't.  An advanced engineer that specialized in taut-band meters and VTVMs will not have any clues about how a dual-slope ADC might work unless they learn that anew.  Of course they would understand precision voltage dividers and amplifiers, so their previous education wouldn't be totally wasted.

I'm not referring to learning how to design and build a DMM, I'm referring to measuring voltage as a new concept for the novice student.  The guts of a DMM are additional to the guts of a VOM, and should be learned later.

[tggzzz]

tggzzz:
I remember one of those, a true "potentiometer", where the wire was supplied mounted on a meter stick.  1 mm resolution was 0.1% of full-scale.
Here's one, made by Central Scientific Co. of Chicago, now in Constantinople:  http://www.hasi.gr/instruments/ele66
We also had some of the original-style Wheatstone bridges, where the resistive legs were varied by placing tapered metal pegs into mating sockets between the wire-wound resistors inside the box.

That's it I suspect the school made their own rather than buy one, though.

The other trick at school was to use a sensitive but slow ammeter to measure charge. Understanding the principles behind such ballistic galvanometers neatly ties together the concepts and practical aspects of current, charge, time constants, and integration. Won't get that from a DMM, no matter how many digits it has.

The nearest I have to a wheatstone bridge is a 7-decade Kelvin-Varley divider plus a nice stable 9.999571V voltage source. Sounds like the internals of some of the Fluke voltmeters from the 1960s I also have a couple of working saturated Weston cells, one of which dates from 1949

[james_s]

On eBay you can find a (for example) 4CH Tektronix 2465A 350MHz for ~$150, and at least, bring more quality to your waveform analysis, since it performs well even at 750MHz.

In summary: I think these CROs fill this gap between $350 and $1,350 scopes, as a 2nd scope.

If you can find (or have found) a good condition 2565/A/B for $150 and you have room on the bench and a specific need for its capabilities, then go for it.  Most of the ones I've seen for $150 on eBay are broken or even incomplete.  I have several (2445, 2465B, 2221A, and more) that I have fixed up and the specific reasons I might drag one out are usually related to vector graphics or a specific need for the Z-axis input.  Also, on one occasion I needed something with better input overload recovery, but I also have two other DSOs that would suffice. If I had room to keep one on the bench, I might use it sometimes just because it was there.  IMO the gap that an old high-performance CRO would fill is small and waning, but YMMV.  What do you use yours for?

Undoubtedly many Tek 24x5 and similar machines on fleabay are suspect, and need a little work. But not all. 
Undoubtedly digitising scopes will be the way of the future
But...
A good working analogue scope is a joy to use and is very capable, and can be used for many purposes.
100MHz was fine for digital logic 40 years ago, but modern jellybean logic requires far more than that.

Anybody that declares that only digitising scopes should be considered and that working analogue scopes should be ignored is, IMHO, a twit.

For most of my purposes, a sufficient combination is a 2 channel >300MHz analogue scope (assure signal integrity), plus cheap logic/protocol analyser and printf statements. If those aren't sufficient then you need serious thought or money.

Just about the *only* reason to consider an analog scope outside of a few specialized niche uses like XY mode is price. If you find a good deal on a *working* one or just want the experience of using one then by all means go for it, they are still useful instruments. The key there is finding a working one that is a good deal, these are getting harder to find all the time and they're only going to keep getting harder to find as time goes on. Nobody is making them anymore and every one that gets worn out, blown up, destroyed in shipping, or otherwise scrapped is one less available for someone to buy. A working >300MHz analog scope is a specialized item, they were always expensive and never all that common, I've never even seen one in the flesh, much less actually owned one. Most people are not suggesting ignoring working analog scopes, but it is not really realistic to assume that most people can just go out and find a good deal on one. It's like suggesting someone go out and buy a 30 year old car, I have one, I love it, it gets me around just fine and I wouldn't trade it for anything, but it's still a 30 year old car, some of the parts are hard to come by these days, and if I didn't know how to work on it myself and didn't enjoy working on cars it would be a hassle. A 30 year old scope is the same way.

[Trader]

If you find a good deal on a *working* one or just want the experience of using one then by all means go for it, they are still useful instruments. The key there is finding a working one that is a good deal, these are getting harder to find all the time and they're only going to keep getting harder to find as time goes on. Nobody is making them anymore and every one that gets worn out, blown up, destroyed in shipping, or otherwise scrapped is one less available for someone to buy. A working >300MHz analog scope is a specialized item, they were always expensive and never all that common, I've never even seen one in the flesh, much less actually owned one. Most people are not suggesting ignoring working analog scopes, but it is not really realistic to assume that most people can just go out and find a good deal on one.

I agree, it's not easy, but still possible, these screenshots are just some scopes sold in the last 3 months, there are much more.

https://www.eevblog.com/forum/beginners/analog-versus-digital-oscilloscopes-2/msg3617766/#msg3617766

If you want a 350-500 MHz scope those are the DSO basic models [70-100 MHz], costing 6X more, and you need to "upgrade it", losing the 3-years warranty.

https://www.eevblog.com/forum/beginners/analog-versus-digital-oscilloscopes-2/msg3617782/#msg3617782

The Tek 350MHz has an effective bandwidth (-3db) at 430MHz. Image shows 2 equal amplitude signals fed into CHs 1 & 2, 1 at 40MHz, the other 400MHz. On a 400MHz scope it is normal for the 400MHz signal to have 30% less vertical deflection (70.7% of the real amplitude), CH 2 lost ~18% (-1.7db) at 400MHz.

[bdunham7]

Just about the *only* reason to consider an analog scope outside of a few specialized niche uses like XY mode is price.

While I agree with most of what you said, I have to point out that even XY mode is a questionable issue.  Although it doesn't look quite as good as a lower frequency XY display on an analog scope, I can display a 99.999999MHz X and 50MHz Y pattern, see the attachment for a very short video.

You can't do that on any analog scope that I've ever seen, certainly not on any with a fixed delay line.  Not that I typically find this feature useful...

[bdunham7]

I agree, it's not easy, but still possible, these screenshots are just some scopes sold in the last 3 months, there are much more.

Of the scopes you listed, the fourth is obviously broken and I think the third is as well, but I couldn't find the auction and the picture shown isn't clear enough.  The other three I can't be sure, but I'd give you 50-50 odds at best of getting a properly working scope.  And calibration is another story on these.   

[Trader]

I agree, it's not easy, but still possible, these screenshots are just some scopes sold in the last 3 months, there are much more.

I'd give you 50-50 odds at best of getting a properly working scope.  And calibration is another story on these.   

As I said: "Everything on eBay is suspicious, even a new product."

See the "Sold" scopes, I selected this model, there are many.  My opinion is just related to the budget for the 2nd scope, if possible get a better DSO.

[james_s]

Just about the *only* reason to consider an analog scope outside of a few specialized niche uses like XY mode is price.

While I agree with most of what you said, I have to point out that even XY mode is a questionable issue.  Although it doesn't look quite as good as a lower frequency XY display on an analog scope, I can display a 99.999999MHz X and 50MHz Y pattern, see the attachment for a very short video.

You can't do that on any analog scope that I've ever seen, certainly not on any with a fixed delay line.  Not that I typically find this feature useful...

I just know I've tried several different Tektronix DSOs connected to a vector arcade game board and none of them have displayed a usable picture, my 465B on the other hand displays a beautiful sharp image that looks just like it does on a proper vector monitor. Testing vector game boards is definitely a niche application though.

[james_s]

If you want a 350-500 MHz scope those are the DSO basic models [70-100 MHz], costing 6X more, and you need to "upgrade it", losing the 3-years warranty.

Warranties are meaningless to me, unless something is DOA it isn't worth the effort to pack it up and ship it in for service. Besides, you can easily undo the hack and the manufacture will never know. I got my 1GHz TDS784C for around $500 and my TDS3000 that I upgraded to 500MHz was about the same price. Today both would probably cost more but they're still modestly priced for what you get. The only downside of the TDS700 is it's a boatanchor, but it's still smaller and lighter than the high end Tek analog mainframes.