Did I buy a decent oscilloscope?

[Frankentronics]

Greetings,

I just bought a used Tektronix 2246 100MHz from eBay seller alltest_instruments. The total with shipping and tax was $187.18.

I only have some limited experience with a 20MHz scope and the one thing that I noticed was that the Tektronix might have some issue with the screen. But I do not know if it's an issue, I just see that the CRT behaves differently than the 20MHz scope.

So, if I keep a trace in place for 5 seconds or so, and then I move the trace up or down, there is a faint ghost image of where the trace was, prior to moving it, that takes a second or two to fade away. Nothing is burned into the screen. It just that the phosphors that were lit take a little bit of time to fade.

I tried to take a video and am posting a still to kind of show what it looks like. But things do look different on a picture.



It doesn't really bother me. I just want to make sure the CRT is not at the end of it's life. I can vary the intensity of the trace from very faint to very bright, though.

Thanks...

[WattsThat]

It’s the persistence of the phosphor, a necessary thing in an analog scope.

It’s scanning the crt in real-time so with the time base at its minimum 20ns and the x10 function on, that beam is wizzing across the crt in 200ns. If not for the persistence of the phosphor, you’d never see the trace. Keep the trace as dim as you can reliably see things and that’s as good as it gets.

It was a very capable service bench scope thirty years ago. It’s fine until you need to look at one time event waveforms and then you realize today’s digital scopes are far more capable without the size, heat and most times, the noise.

[nigelwright7557]

A scope needs to show a trace even at very slow speeds so uses a phosphor coating with a long time lag.
If it didnt you wouldnt be able to see slow waveforms.

[Frankentronics]

Definitely thank you for your replies.

One question, tough. How come this is not how the CRT on my 20MHz scope behaves? Is it because it uses a different scan rate?

Thanks...

[WattsThat]

Yes, different write speeds and different phosphor persistence.

http://w140.com/tekwiki/wiki/Phosphor

Be sure to download the user and service manuals if you haven’t already done so. You might have to search a bit for the service manual but they’re out there.

[tautech]

Definitely thank you for your replies.

One question, tough. How come this is not how the CRT on my 20MHz scope behaves? Is it because it uses a different scan rate?

Thanks...

Reduce the trace Intensity and the trace persistence is much reduced.
Like with any CRO use just enough intensity and no more.

[Cubdriver]

The 2246 is a nice scope - I've had mine for close to 20 years now.



As for the persistence, that's normal for the scope.  Different scopes use different phosphor formulations, so comparisons between very different models are next to meaningless.

Congrats on getting it, and enjoy your new gear!

-Pat

[james_s]

Definitely thank you for your replies.

One question, tough. How come this is not how the CRT on my 20MHz scope behaves? Is it because it uses a different scan rate?

Thanks...

Different phosphors have different characteristics. There are at least 3 or 4 different ones that were commonly used in scopes, each has different tradeoffs of brightness, visibility, writing speed, persistence, durability and other factors. Many Tek (and other brand) higher end scopes had several optional phosphors available as an option at the time of purchase. Probably the most common special order was the blue one optimized for use with scope cameras.

[Electro Fan]

Maybe post some more photos showing various signals and some of the readouts.  The 2246 is a very nice model.  It’s an analog scope but it used digital technology to display a fair amount of measurement info.  Try the cursors if you haven’t already. 

[Frankentronics]

Thank you all for your replies.

The most important thing is that the CRT is in fact behaving normally. Of course, I had to make sure about that while the item is still newly acquired, in case I need to return it.

I really like the scope and I did in fact already download both manuals. I bought some cheap 100MHz probes. They are a bit stiff but seem to work fine.

Is there a way to hack generic probes so that they act like Tektronix probes, with that little 10x sensing peg on the BNC connector?

Perhaps the only thing that I wish was better about this model is the fact that the measurements section does not have RMS. I didn't realize that until I got the unit.

And the part that I don't quite understand, yet, is the A and B mode capability. I have not been able to understand, yet, what that's for.

But like I said I am very happy with the scope and I also like that seller's handling of the sale (the communication and the truly expert packaging).

At this time I do not have a function generator but I can still rig up some tests signals to post images.

Thanks...

[Johnny10]

Might also help to take focused pics if you want us to give complete answers.
Difficult to see if brightness is turned too high.

[Electro Fan]

As Johnny10 said posting better photos will help folks give better info and advice.

On the A and B question, here is a video that might help:

https://youtu.be/54roz8IUoVI

The video shows the controls on a 24xx model which work somewhat different than the controls on the 22xx models but the scope functionality is similar, just not using the same controls in the exact same way - the concepts are pretty similar.

https://download.tek.com/manual/070608300web.pdf

Here is another on the 400 models:

https://youtu.be/0enuruGWYk8

The 400 model controls are different (they were predecessors to the 22xx and 24xx scopes, of course) but again similar functions in terms of the intended capability.

Basically, Tektronix provided ways to show two views (A and B) of the same signal, each with their own time base setting.  This allows you to see more detail in a selected part of the signal and let’s you navigate, measure, and even trigger based on the second view (in addition to the first view).  The trace separation control can be useful in addition to the vertical control.  Overall “A and B” (often referred to as a delayed time base function) is similar to the zoom function on a digital oscilloscope. 

w2aew has made a bunch of great videos in case you haven’t already discovered them - tons of tremendous Tektronix and overall test equipment and electronics videos - highly educational.

[rstofer]

You just got the deal of a lifetime on a scope!  Even if you decide to get a DSO later on, you will still want to keep the CRO.  I have a Tek 485 that I have had for quite a while ($200 used on eBay) and it still stands up under my bench for the time when I need the extra bandwidth or I'm just feeling nostalgic.

If you want probes that support the Tek ring features, I suspect you are going to have to buy Tek probes.  Finding the right probe will be a challenge.

My 485 has the feature, I don't bother with it.

[Cubdriver]

You just got the deal of a lifetime on a scope!  Even if you decide to get a DSO later on, you will still want to keep the CRO.  I have a Tek 485 that I have had for quite a while ($200 used on eBay) and it still stands up under my bench for the time when I need the extra bandwidth or I'm just feeling nostalgic.

If you want probes that support the Tek ring features, I suspect you are going to have to buy Tek probes.  Finding the right probe will be a challenge.

My 485 has the feature, I don't bother with it.

Probemaster also makes scope probes with the readout actuator pin.  It adds about $10 to the cost of a fixed 10X probe; more to a switchable one.  (I don't have any of their probes, but they seem to be well regarded from what I've seen.)

https://probemaster.com/4900-oscilloscope-probe-basic-kit-150-300-mhz/

-Pat

[Frankentronics]

Thank you all again for your informative replies.

I already watched many videos by w2aew (some even more than once). I'll definitely be watching more of them as I learn.

Thank you also for the basic A/B mode explanation. Now at least I know what it's all about. The manual doesn't really explain it clearly. I'll study those resources tonight.

Those ProbeMaster probes look nice. Perhaps down the line I'll upgrade to that. Thanks for the info.

The photo I initially posted was a still grab from a video. I had to make a video recording to grab a still of the exact time I wanted to show.

Here are some photos of the scope in XY mode. I breadboarded a transistor curve tracer circuit so I could test the XY mode. What is odd, as you can see on the photos, is that I get a diagonal line coming from CH 1, when the CH1 button is pressed. My 20MHz scope doesn't do that.

I'm sure the Tek scope is not malfunctioning but I can't understand why it does that when I press the CH1 button. Any ideas?

Thanks...

[engrguy42]

You just got the deal of a lifetime on a scope! 

But...it's, like 30+ years old...

And, y'know, there's this "bathtub curve" thing. And, it's from eBay. I mean, did someone spill Coke on it 16 years ago? Did they cross their leads while measuring high voltage 22 years ago? Did they open it up and change components 7 years ago? 

I dunno, I can't see why someone would buy something like this. Seems like a huge risk. And nobody can look back and say "Hey, I've had mine for 43 years and it works fine, no sweat". Because it hasn't been around that long.

Good luck.

[Frankentronics]

You just got the deal of a lifetime on a scope! 

But...it's, like 30+ years old...

And, y'know, there's this "bathtub curve" thing. And, it's from eBay. I mean, did someone spill Coke on it 16 years ago? Did they cross their leads while measuring high voltage 22 years ago? Did they open it up and change components 7 years ago? 

I dunno, I can't see why someone would buy something like this. Seems like a huge risk. And nobody can look back and say "Hey, I've had mine for 43 years and it works fine, no sweat". Because it hasn't been around that long.

Good luck.

What is a bathtub curve?

I like buying old stuff and I know there's a risk. But even if you buy a new scope you don't know if anything got rattled when the UPS handlers dropped the box from the conveyor belt, from 3 feet high. We also don't know if there are any cold solder joints in a new one, that will crack after a few months due to thermal expansion.

I am actually planning to open it up and look at the components and at the solder joints.

Thanks...

[wizard69]

You just got the deal of a lifetime on a scope! 

But...it's, like 30+ years old...

So?   In less than half a year I will be 60 and I still believe I'm useful!!!

These old analog scopes do have a few advantages and frankly it is good to have one around.   I liken this to work where we have several instruments that get used occasionally.   A long as they work there is no real reason to replace them.    Does better tech exist, almost certainly.    Is it needed to do the job - nope.

The same argument often comes up when talking about analog VOM's on the bench.   Yeah a digital is better in 99% of the cases.   However if you want to demo decay of a charge in the classroom an analog meter makes it far more obvious what is going on.

And, y'know, there's this "bathtub curve" thing. And, it's from eBay. I mean, did someone spill Coke on it 16 years ago? Did they cross their leads while measuring high voltage 22 years ago? Did they open it up and change components 7 years ago? 

In a way you kinda have to expect that instruments of this age have had work done on them.   It is sort of like buying a used car, at some point they all go into the shop.

I dunno, I can't see why someone would buy something like this. Seems like a huge risk. And nobody can look back and say "Hey, I've had mine for 43 years and it works fine, no sweat". Because it hasn't been around that long.

Good luck.

And yet I've had tools that I've literally have had since my teen years.   I probably would of had instruments from that era but I couldn't afford them so no instruments 40 some years old.   If somebody can save a few bucks buying used and gets started with good instrumentation early I'd say go for it.    Buying used is a gamble no doubt there, but that is the case even if you are buying a home.   Buy used you take on the responsibility for maintaining the device, it can be a good trade off if you have good tech skills.

To look at this another way when do you give up on old tech.   Back in 1984 I walk into a new job in a factory that I imagined was fairly modern.   Some of the machinery in that plant was relay based or running on old 5TI PLC's with 256 bytes of RAM if I remember correctly.   Ended up maintaining those old 5TI's for a long time!    In tech school I literally had one teach suggest that I didn't need to worry about tubes when asking about them.   Yet that first job introduced me to an RF amplifier that needed a forklift to move ( I was most happy when it was replaced).    just because something is old doesn't mean there isn't value in it.    Frankly a quality built bit of instrumentation can have a very long life compared to some of the more harshly used industrial electronics.

[Cubdriver]

You just got the deal of a lifetime on a scope! 

But...it's, like 30+ years old...

And, y'know, there's this "bathtub curve" thing. And, it's from eBay. I mean, did someone spill Coke on it 16 years ago? Did they cross their leads while measuring high voltage 22 years ago? Did they open it up and change components 7 years ago? 

I dunno, I can't see why someone would buy something like this. Seems like a huge risk. And nobody can look back and say "Hey, I've had mine for 43 years and it works fine, no sweat". Because it hasn't been around that long.

Good luck.

What is a bathtub curve?

I like buying old stuff and I know there's a risk. But even if you buy a new scope you don't know if anything got rattled when the UPS handlers dropped the box from the conveyor belt, from 3 feet high. We also don't know if there are any cold solder joints in a new one, that will crack after a few months due to thermal expansion.

I am actually planning to open it up and look at the components and at the solder joints.

Thanks...

A bathtub curve is the normal failure pattern for well designed electronics and mechanical systems.  It refers to the plot of the failure rate over time, which looks like the cross section of a bathtub.  When the things are new, there may be a relatively high 'infant' failure rate, where marginal components with manufacturing defects will fail right out of the gate.  Once these early failures have occurred, the rate of failure drops to something very low for a long time.  Eventually, things start simply wearing out from old age and use, and the failure rate rises again at end-of-life of the instrument or machine.

I wouldn't worry about it WRT to your new scope - ignore the troll.  He likes to stir things up.

-Pat

[wizard69]

Used instruments can be good buys.   Often they become available after going off lease or a project shuts down, these can be kinda expensive but still a bargain.   Older equipment suffers will certainly have had a different life experience but that is where careful shopping comes in.    For many of use it comes down to either having a hobby or not, quality bench instruments cost a lot, so carefully considering them for the bench should be part of the plot.   

That came out of nowhere.

You just got the deal of a lifetime on a scope! 

But...it's, like 30+ years old...

And, y'know, there's this "bathtub curve" thing. And, it's from eBay. I mean, did someone spill Coke on it 16 years ago? Did they cross their leads while measuring high voltage 22 years ago? Did they open it up and change components 7 years ago? 

I dunno, I can't see why someone would buy something like this. Seems like a huge risk. And nobody can look back and say "Hey, I've had mine for 43 years and it works fine, no sweat". Because it hasn't been around that long.

Good luck.

What is a bathtub curve?

I like buying old stuff and I know there's a risk. But even if you buy a new scope you don't know if anything got rattled when the UPS handlers dropped the box from the conveyor belt, from 3 feet high. We also don't know if there are any cold solder joints in a new one, that will crack after a few months due to thermal expansion.

I am actually planning to open it up and look at the components and at the solder joints.

Thanks...

[wizard69]

You just got the deal of a lifetime on a scope! 

But...it's, like 30+ years old...

And, y'know, there's this "bathtub curve" thing. And, it's from eBay. I mean, did someone spill Coke on it 16 years ago? Did they cross their leads while measuring high voltage 22 years ago? Did they open it up and change components 7 years ago? 

I dunno, I can't see why someone would buy something like this. Seems like a huge risk. And nobody can look back and say "Hey, I've had mine for 43 years and it works fine, no sweat". Because it hasn't been around that long.

Good luck.

What is a bathtub curve?

I like buying old stuff and I know there's a risk. But even if you buy a new scope you don't know if anything got rattled when the UPS handlers dropped the box from the conveyor belt, from 3 feet high. We also don't know if there are any cold solder joints in a new one, that will crack after a few months due to thermal expansion.

I am actually planning to open it up and look at the components and at the solder joints.

Thanks...

A bathtub curve is the normal failure pattern for well designed electronics and mechanical systems.  It refers to the plot of the failure rate over time, which looks like the cross section of a bathtub.  When the things are new, there may be a relatively high 'infant' failure rate, where marginal components with manufacturing defects will fail right out of the gate.  Once these early failures have occurred, the rate of failure drops to something very low for a long time.  Eventually, things start simply wearing out from old age and use, and the failure rate rises again at end-of-life of the instrument or machine.

I wouldn't worry about it WRT to your new scope - ignore the troll.  He likes to stir things up.

-Pat

For electronic instruments that belly in the curve can be extremely wide compared to say high power RF equipment.   This especially when it comes to the higher quality manufactures.   In some cases stability and drift can even get better with age.

People seem to like to knock old analog scopes and frankly I'm not sure why.   A new digital scope can certainly be a good investment, especially if one is heavy into digital electronics.   However analog scopes are fine for many and are at price points that are hard to dismiss.   Even if you had to buy three to get one working you likely have saved money over a digital scope.

[engrguy42]

Interesting how someone can clearly define a well known engineering description of the likelihood of failure (which is a standard consideration by real companies in the real world), and in the next sentence wave their hands and tell someone to ignore it, and then follow that with a personal attack.

As usual in this forum, no facts explaining WHY it's reasonable to ignore the bathtub curve in a 30+ year old device (which anyone on the planet would consider FAR beyond its service life and at high risk of failure).

[Gyro]

As usual in this forum, no facts explaining WHY it's reasonable to ignore the bathtub curve in a 30+ year old device (which anyone on the planet would consider FAR beyond its service life and at high risk of failure).

Oh, will somebody please give him some scientific measurements of the bath!

[engrguy42]

Let's be honest. People here like these things for nostalgia reasons. No facts involved. And they can't accept anyone who questions that.

Fine. Just try not to recommend that others buy these things solely because YOU like them.

[Electro Fan]

Ok, you are at the beginning of a fun and great journey.  Nice curve tracer.

Regarding the diagonal line, my guess is that it is related to X-Y.  Take a look at post 36 in this thread:
https://www.electro-tech-online.com/threads/x-y-scope-mode-diagonal-line.139864/page-2
Try playing with the buttons over to the right under Mode and Source; there are lots of combinations

As for the probes, I have a couple/three-ish Tek scopes and early on I bought some Probemaster probes.  They were/are very good in terms of both price and performance, no doubt.  They have the feature that let's the probe sense the 1x/10x ring.  No reason not to try Probemaster but I've also found over the years that there are still good Tek probes available on eBay - some vintage but gently used/well cared for, and occasionally some that look like they came from the factory with little or no use.  You can't be 100% sure what you will be getting (until you get it) but if you go slow and take the time to read lots of eBay ads and study the photos and do some Q&A with the sellers you can improve the good to surprise ratio, and you will likely be able to find some good Tek probes.  If you are still more selective and only go for purchases that will allow returns you are probably doing all you can do.  At some point everything that has potential reward probably has some risk but the risk can be mitigated with good study.

This site (along with others and Tek manuals) will help you piece together what probe models to look for.
http://www.barrytech.com/tektronix/probes/tekprobes.html

Enjoy the 2246.

---

Edit:  Mode and Source might not be part of the matter.  It's been awhile since I used XY.  Here is a good explanation:
https://www.keysight.com/main/editorial.jspx?cc=US&lc=eng&ckey=2838609&nid=-32110.1203274.02&id=2838609

I could be wrong (often am) but I think what it's saying is that with XY the scope is effectively using the inputs of both channels to make the trace - even when one channel is set to Off.  When you turn both channels on the scope is making two XY traces.  You can see this by making ovals or circles with two inputs (2 channels) from a function generator.  With two channels from the function gen connected to the scope inputs for channel 1 and channel 2 but just one scope channel set to on you will get one oval or circular trace; with both scope channels set to on you will get two oval or circular traces.

Another excellent w2aew video (on Lissajous patterns and XY):