Hi welcome to the Eev blog an Electronics Engineering Video Blog of interest to anyone involved in electronics design. I'm your host Dave Jones Hi look what? I Just scored a Tech25 50 MHz dual Channel Analog oscilloscope Beauty Always wanted one of these because it is one of only three oscilloscopes I think it is that I know of on the market that has a 500 microvolt per division vertical scale and that's great for um, measuring real low noise stuff the output of power supplies and things like that. So I thought it'd be just a real nice scope to have always got. Always wanted one and I was lucky enough to pick one up here local.

These are quite rare to find these in Australia here, but in in the US they're fairly common. It's a really nice 50 MHz um late 80s kind of vintage. uh Tectronics scope and I've mentioned it before. you should have an analog scope in your lab.

You can get them for 50 or 100 bucks under 100 bucks 50 MHz Duel Channel Like this one. Very handy analog scope to have. You know if you're just relying on your riyo, you know, digital scope. It's not too bad, but they're noisy and you know they're just not as real time as a good analog scope.

Highly recommend you get one. So I thought we'd just uh I'll do a tear down. Everyone wants to see a tear down. of course vintage tear down do that as a separate video cuz people like the separate tear down videos and but for this one, I will just uh uh basically uh Power It Up Did I get a DT or not? I don't know.

Um, we'll Power It Up Check it out. Um, check out all the basic functions so this will be a reasonably, uh, basic guide on how to test a secondhand scope like this if you pick one up on eBay cheaply. I Got this one for 100 bucks Australian which is pretty darn good. uh, value? You can pay more than this in the Us I Was pretty lucky to get this.

Um, but this should be a reasonable guide to just what to uh, check once you get it, is it within calibration? Do all the functions work and stuff like that? So let's power it up. Give it a go. now. one thing I Like about the tech? uh, 2200 uh series.

There's a whole bunch of them. This one. the the specific triple 25 I've got here is um I think there's only one other which has the 500 microvolts uh, per division vertical scale. but but, um, the thing is, they're quite small and they're quite lightweight.

This one only weighs about 6 kilos. So if you're buying a secondhand analog scope on eBay weight can be a big factor cuz you'll pay shipping costs, especially if you're buying it from uh, the Us or some other country. and you're shipping it overseas. It can be a big deal, so this one's reasonably, uh, lightweight in the scheme of things.

Um, unfortunately, this one didn't have a um, this one doesn't have the actual bail on it, the the tilting bail or the tilting handle which comes over because it was a rack mount uh unit. So, but that's not a big deal. You know, if if you need it really portable, then the tilting bail is important, but some you can pick up a bit cheaper because uh, they don't have the tilting bail on them. they come out of a rack uh system or something like that.

Now it's a good basic layout. dual Channel Analog scope I Really like it. You got your dual Channel inputs here. you've got your horizontal, you've got your Uh triggering totally separate.

Over here this has got Auto full auto uh, peak-to Peak triggering on it which is really nice. It's got um it instead of a dual uh time base. This is only a single time base, but it does actually have um, a * 5, * 10, and * 50 mag. So it works like a dual time base, but it doesn't have the full Uh capability as you get on a full dual time base analog scope.

Now let's take a look at the vertical here and uh, you'll see that The reason I like this one is is because it has a Time 10 magnification. Most scopes on the market will only have time 5 ver vertical mag so it says up pull cow for times uh 10 mag. so if you pull this here and you get this yellow, you can notice the yellow there on there so you can tell if it's pulled out at a glance there which is a really nice uh feature of this. Now conveniently, it's got uh two different uh two different positions here for you Time 1 and your X 10 probe.

Uh, because this doesn't have like an automated probe detection for x 10. it doesn't have menus and all that other stuff where you can and onscreen display of the volts per division. Uh, if you're using a times 10 probe which you will be most of the time then you take this position over here so you don't have to multiply it in your head. you just look at the one that you're using and I find that really quite uh handy.

And of course it's got all the basic stuff on your vertical that you want. It's got AC and DC and ground coupling on uh, both channels. it's got uh Inver It's got an ad uh mode where you can add both channels and it's got a subtract mode as well cuz that's what this channel 2 invert thing here does. If you want to subtract them, well, you invert Channel 2 so you're adding Channel 1 plus minus Channel 2 which means that you're subtracting them.

so it's got subtract mode and it's got alt and chop as well. And um, my almost most Scopes have these because it's not a this is not an old school dual beam oscilloscope. This is a dual Trace oscilloscope and the difference is actually quite significant, which a lot of people don't understand. This only has one, um, one beam inside, so it can only project one uh beam of electrons at once onto the screen.

So um, if we put it into if we display both channels here and we, uh, here we go I've got it turned on here. It does actually work. By the way, it seems to at least power up Now we've got the Dual uh channels here and we can adjust those like this and that's just uh fine. Now it's on alt mode at the moment.

What it means is that the A Jeel Trace oscilloscope can only draw one Trace at a time. so it can only draw that one and then that one. And this is what alternate means. Al means it.

Al It alternates between these two traces. it draws this one. Then it draws that one and back at that one. and that's really good for higher timebase settings.

Now you'll see this effect. If we turn it down to 1 millisecond per division, 2 milliseconds. you'll start to see it very shortly. There you go.

10 milliseconds per division. You really start to see it. 20 milliseconds. You'll see it draws that one.

Then it draws that one. There we go. So that's why you need chop mode. Because what chop does? instead of alternating between the two? it? um, it slices it it well.

It still alternates between the two, but it does it. Uh, not for a whole sweep. It does it. uh, like this.

it just jumps between them like this, you can't actually see it cuz it. you can't see it vertically cuz it disables the Uh Trace during that. But um, it does. Actually, it chops between the two like that all the way across.

so even at very slow timebase speeds, you can get both traces on the screen at once. And of course that that works up at higher frequencies as well, but it won't be as bright. And really, you should, uh, switch to alt motor if you're up on the higher settings like that. As I said, one of the great things I love about this scope is that it has 500 micr volts per division.

Uh, vertical scale. Now as as you can see on the dial here, it only goes down to 5 m volts per division. but it's got a Time 10 uh time 10 vertical amplifier here and most scopes on the market will only have a times five so they'll typically might go down. A good oscilloscope will get down to 1 molt per division vertical scale.

but this one does better. does twice as good as that at 500 microvolt. So if you put on five five M volts vertical scale and you pull that knob Bingo Now have got 500 microvolts per division, which is absolutely fantastic. Uh, vertical scale? It is absolutely awesome.

I Love it! Now we're going to check out this thing. uh, just just to make sure what its, um, noise floor is like. to make sure it's actually uh, good. Make sure it's in the vertical scales are within cow.

That's the first thing we want to check. Then we'll move on to the horizontal and move on to the triggering and things like that. But uh, let's see. um if this thing basically uh, works.

So let's give it a basic checkout. First thing we're going to do is make sure we get both traces on the display here. So we're going to put it into uh, dual Channel position. uh, alt is a good one, just sort of mid-range on your uh, horizontal time base.

Here, you know, one volt per division or something like that doesn't really matter. and uh, yes, we are getting two tracers here now. We want to test the focus of the traces. As you can see, it really goes out of focus it both.

Oh, it's more towards one end, but as long as you can actually get that reasonably sharp. now that's a pretty good sharp. Trace I Really like that. No problems at all.

And next, you want to test the intensity of it. The intensity is really, it goes up really really bright. I like that. And basically you want to turn that up to the fastest time base um, setting you can get.

in this case it is uh, 500 sorry 50 micros sorry 50 nond per division. um and that is at full brightness with jeel channels up so that's really good. and I can't see any uh screen burning in here cuz these CRT displays. Um, if if people have just left them on at full intensity then they can get burned in.

but there's no signs of of burning there at all and we'll uh check the horizontal course and fine here. So we move it across like that. it looks all right. There's a little bit of a there's a little bit of a wiggle there I don't know if you can see that.

let's turn the vertical right up. No, it doesn't seem to matter, but there's a little little slight wiggle there I'm not sure what that is, but uh, make sure you can get the full horizontal uh trace on the screen like that and you can do fine and Co adjust so it looks like both fine and coar work just fine. You want to be able to center it on the screen like that? No problems at all. Uh, next thing you want to do is you want to test the trace rotation when you buy it.

Um, if it comes from a different uh part of the world, you may have to, uh, do some Trace rotation So you want to make sure that works. Line it up with uh one of the lines on the screen there one of the cules and uh, it's spot spot on I like it. So our Focus intensity Works our horizontal position Works our vertical position works. You want to, uh, make sure that the line is nice and flat and it doesn't curve.

You can see it starts to curve when it gets down to the bottom of the scope down there, but that's of the display down there. but that's fine. So both uh uh, so that's the Channel 2 position and the channel one position goes all the way up as well. No problems, it looks like it's working.

An absolute treat so far. and the next thing we want to do is plug in our function generator now. I'm using my Um Agilant 3000x series oscilloscope the Wave Gen module from that cuz that's the highest frequency. Uh, general Purpose function generator I've got Um here in the lab so uh, what I've done is I fed in a 1 khz uh sine wave.

There it is. There's my My Uh scope up there and I've got it set to a 1 khz uh sine wave at 400 m Peak to Peak Now the reason it's 400 MTS is because that will give us a full scale down here on our Um scope. You can do it at other values but it's just uh I just like to get um, full scale here now. Uh, this thing is supposed to Output 400 Ms per division.

My vertical scale here on Channel 1 is 50 Ms per Division and as you can see if I put it right down there on the bottom. it's just shy of the Um upper Um marker there. So really, it's um, slightly out of cow on the vertical Channel there. not a huge amount I'm not, um, overly concerned about that.

Now let's try Channel 2 as well. Let's uh, it's 50 Mt per division. Once again, it hasn't triggered from there cuz it's still triggering off uh. channel one over here.

So we need to uh, the source to be uh, trigger two? Bingo! So so we're now testing our trigger capability from Channel 1. Channel 2 works just a treat. We'll have to test external later, but uh, vertical mode will? uh, just uh. select select between the two of them basically.

and we selected the Channel Two. There There we go. Not a problem. It's uh, it's reasonably clean and nice.

I Like it and look, you can actually see if you look in there, you can actually see the step response of the deck inside the Agant 3000 Series function generator. You can let me try and turn that oh sorry, wrong. Channel There we go There we go. Look at that.

You can see, you can see the deck, you can see the steps in the output deck cuz it's a digital function generator, not an analog. See the steps in it. Look at that. Beautiful.

I Like it. So anyway, let's turn it back and wh really high intensity there. and Channel 2. once again, it is short.

Um, it's It's slightly out of cow, but at least it's consistently out of cow on both channels. So uh, we'll have to, uh, pop it open later, find the adjustment uh, pot and uh, adjust the vertical. but that's good enough I wouldn't uh, complain about that too much at all. And I've changed the function chin to 4 volts per division.

So um, now I'm at 0.5 volts per division on Channel 2 and it's exactly the same. It's out by the same amount. so I really like that. Plug it into Channel One here and uh, trigger off Channel One Let's turn it up and bingo.

it's out by once again, the same amount. It's very consistent across there. so uh, really? I'm I'm quite happy with that and you can test all the scales in the same way. You can see that that one is uh, uh, half of the value we had before and so forth.

so it looks to work a treat on all ranges. Really? I'm quite happy with that. And one more check right down at the low end. I've set the function gen to 40 MTS Peak to Peak and we've got on 5 Mt per Division and once again, out by the same amount.

Beautiful! I Love it! It's working a treat and it's relatively uh, well, it's it's very Noise free down at 5 Ms per division. Now let's try and uh, take it down a bit further and try this uh time 10 magnification gain. Now unfortunately, my function generator only goes down to 10 MTS Peak to Peak and that's not low low enough to test. uh, the 500 microv volts per division range which this thing's capable of.

So I have built this little Contraption here which is uh 4 50 ohm Terminators and it wired in parallel onto the Uh coax here and I've set my function generator to 50 ohms output and just so happens I've got a little Dave CAD drawer in here which shows what's going on. The function Gen is set to 10 MTS Peak to Peak and that's into a 50 ohm load because I've turned on the internal 50 ohm load in the function generator. So if we had a single 50 ohm Terminator here, we've actually got four. but if we had a single one then we would get our 10.

We would get that value 10 m volts Peak to Peak into 50 ohms. But because we got four in parallel like this, it's 12.5 uh ohms total and if you do the math it comes out to drops it down to 4 Ms Peak to Peak Which is great because we've got eight divisions on our screen here. 500 microvolts per division gives us 4 Mill volts Peak to Peak Full scale. Fantastic.

And here it is it. This is not on uh x 5 uh sorry time 10 mag. but if we pull it Bingo there's the there's our uh S Wave in on x 5 mag. Now you notice that it's actually more than 4 MTS Peak to Peak And that is not because of the scope.

that's an error in our function generator. If we go up here and we plug it into our Ulin up here, check it out. We actually get no. You probably can't see it there, but it's actually 4.7 Ms Peak to Peak So the function generator isn't actually spot on.

If we're go to the wave generator there, it is 10 ms Peak to Peak. There's obviously uh, some error in that. as you'd expect when you get down that low and uh, basically we are getting 4.7 MTS Peak to Peak I've got the average in uh turned on there. If we, uh, turn the average in off, we can actually see that it's a bit noisier than that.

but uh, you turn the average in on and bingo. So this thing is uh, our Tech triple 25 is is working A treat I Love it! Now You can actually see when we've got no input down here. it's actually picking up a whole bunch of noise on time. 5.

Um, times 10 mag. sorry I'm so used to saying Time 5 uh, magnification for vertical? this is time 10. So uh, that's the same on Channel one. Or let's try Channel two.

Oh, it's not as bad on Channel 2, so if we turn them both on there, you'll uh, notice that. um, oh, what have we got here? we've got. add there we go. That's the problem.

There's your problem, right? We've got alt mode and look. Channel one is a bit. Channel one is a lot noisier. It's got something on there, so something's going on there.

It's not the best. when you turn it down, you can notice a bit more noise, but you turn the time base up. it's definitely got something something on that. So I'm going to actually apply a uh Terminator to that and see if we can get that go away.

Yes, it certainly does. If we terminate that, it's gone. So likewise, on Channel 2 or so, I'm not sure where that's coming from. Maybe something internally.

Of course, if I put my hand near it or my hand on the control something like that. So when you're measuring low noises like this, just, uh, it. noise pickup is a major issue. but um, I Do deem that to be uh, pretty decent and uh, working reasonably well.

Right down at this 500 microvolts per division. Now we have to check out our horizontal as well. Now I'm feding in my 1 khz signal and I've got it set to1 milliseconds per division, 100 micros per Division and you'd expect to get 10 divisions there, but you don't It's actually short of that. So uh, the horizontal isn't uh, isn't really uh, spot on that needs to be uh adjusted as well if you want to calibrate this thing.

I mean you know if if you just want to get Uh signals on there, then you know it's it's good enough, but uh yeah, I would I would be tempted to go in there and uh, tweak that just so that's that's a bit too far out. I think I'm not happy with that. so we have to uh C that internally and we need to check our trigger as well. of course.

now. so we'll take our trigger level here and we just, uh, adjust it and make sure it goes uh, make sure it goes between pretty close to the positive and negative um values there and it certainly does. and uh, if we uh, choose the negative slope trigger and do the same thing. Yep, that's working perfectly.

No problems at all and that's in the peak to Peak Auto triggering mode. We also want to test the uh normal mode as well. So we move it over to normal and we turn it back to peek to peek and you see it. Boom it uh goes straight in there.

But if we go to normal mode, once we get past that trigger threshold up there, it should vanish. So yep, it does. There you go, and likewise on the bottom side. once we reach that, just past the negative, uh, bottom of that waveform down there.

Bingo. Gone. And once again, then positive and negative and it works. A treat.

So normal mode works as well and we'll check the single sweep mode over here. So take it all the way over and we get nothing on the screen. This is where you're probably going to want to turn your intensity up like this and then press the trigger button. There It is.

bang, No problems at all. and a very simple way to test your trigger hold off down here is to set it to minim Minum and note the brightness of the trace here. and as you turn your hold off, control up. It should dim like that.

And that's a very basic test that indicates that the trigger hold off is working as well and we're going to want to do a quick test on the external input to make sure it works as well. Um, now it's triggering off channel one at the moment up there. but if I turn it down to external here and external and the source actually to our external cuz this external mode you can choose between the 50 HZ it's line frequency or external divide by 10 or external or uh Z input. but there you go.

it's uh TR and triggering stable and if I disconnect that, of course it loses its trigger Works a treat and we'll just check our line triggering here as well. This means that it actually gets the trigger Source uh from the 50 HZ Mains or if in the US it'll be 60 HZ uh Mains but it's 50 here. So I've set my function generator to 50 HZ and I if I go below 50 HZ you'll see it scroll in One Direction going across like that and if I go above 50 HZ it'll go back in the other direction. And of course, if you had the ex, if you had it exactly the same frequency as the main frequency, it would actually be stationary.

but I can only adjust my function generator in 0.1 Hertz increments. So my Mains here in Sydney at the moment is somewhere between 50.0 That's 50.0 it's going in One Direction and 50.1 Herz There you go. So it's somewhere in between there. so the Main's frequency in sitting at the moment is probably 50.0 5 Herz or thereabouts give or take and we'll do a quick functional check on our Um trigger coupling up here.

I've got the AC uh coupling and it should work on DC in Peak to Peak Auto Now if I turn it over to normal mode here. okay, in AC coupling, it should uh trigger but on low frequency at my 1 khz Test signal. Um, it should actually, uh, completely attenuate that so there's nothing to trigger on so it should disappear and high frequency it should work a treat. And if you keep it in uh, auto mode, then it's pretty much it's still going to try and get a trigger there even with the low frequency uh, filter on.

But if we put on low frequency reject filtering and we increase our uh frequency here, then it should eventually trigger. At what have we got way up there. it's way up there. It's uh, we're in the megahertz region at the moment.

Let me turn that back. Frequency Gem was a bit overzealous there. but uh, if I put that down to you know that's 90 khz 50. That's 10.

That's 10 khz roughly. and it's just starting to trigger at 10 khz. There you go. So it's an order of magnitude.

uh thing. really. So anything over 10 khz, this thing's going to trigger on nicely. And likewise, with the high frequency reject filter, it's uh, 8 khz at the moment.

If I turn up the frequency on that thing, it should eventually not trigger at all. Let's see what frequency it stops triggering at 50 khz 60, 70, 80, 130 khz. still got 70 160, 170 khz. There you go.

It's barely triggering now. 180 khz and it stopped triggering completely. That works a treat. And if you're a really Keen TV Service Tech you might go in and test your TV line in your TV field modes, but I'm not going to bother now.

let's go back to the horizontal here. I'm feeding in 100 khz sine wave and uh, let's put it onto the alt horizontal mode sh and it hasn't displayed anything at the moment. That's and it's on x 5. uh.

magnification. Uh, time base. That's because we haven't done the trace separation. There it is.

Bingo, there is our magnified. There's our magnified waveform. So if we turn that down, we can actually, uh, separate the tracers like that and actually get both of them on the screen at once. So that's our time.

5. Uh, that? that looks like Time 5 to me. I won't go in there and measure it, but it looks looks pretty good and that's time 10 There it is. Okay, so that looks like it works.

An absolute treat and we can even go to Time 50 here and Bingo there it is. That's the time 50 magnification. And of course, if we just go over to mag here, it'll just display the magnified waveform like that. but you can do both or just the one.

So there you go, that looks like it works fine. I like it and we should actually check that that value is spot on. I've got times 10 mag at the moment with 100 khz so I'd expect uh, that to be 10 divisions across and it's not. It's slightly out, just like it is with the Um main time base as well, but that should come back in once we calibrate the main time base.

Another thing we haven't checked is the probe adjust here. So I've got a x 10 probe so we're actually going to use the time 10 uh, setting over here, not the time 1. So we're on .1 Vols per division. It says we should be getting 500 uh, M volts Peak to Peak at 1 Kilz Are we Well, not quite five divisions there so it's a little bit out.

Um, but not a problem and uh, we should be getting basically 1 khz. but once again, the time base is out just like it was before, so looks like our probe adjust is working fine. Let's have a quick check of the high frequency bandwidth here. I've uh Fe I'm feeding in the highest frequency I've got from my function gen which is 20 mahz at 4 vs Peak to Peak Now um, this, uh on the problem with this Tectronics triple 25 is if you use it on Standard Time base.

It's just really, it's not fast enough. that's as fast as it goes. Okay, so you know I can see the 20 MHz signal there, but you can't easily get in there and measure its frequency and stuff like that. So it really forces you to use your Uh forces you to use the Mag mode, which is okay.

There's nothing inherently wrong with that, it's just not as nice as um. some other Scopes which I have the main time base which uh, goes down to that. but anyway, that's okay and you'll notice that it. it's a bit fuzzy here.

Once again, if we go here, our frequency is, uh, slightly out again. Of course because our main time base is out as we've verified before. but uh, as you can see, the amplitude has dropped a bit from um, uh, where it was before. so uh, really, you know it's um, it's it's starting to roll off there I think now.

One thing I didn't mention with the vertical channels is, uh, that, um, the bandwidth. The quota bandwidth 50 MHz is only for uh, basically all of your um basically from your 5 Molt range and up. Once you engage this x 10 magnification here, you will actually drop the bandwidth in. In the case of this oscilloscope, it's bandwidth.

With the time 10 gain on any either of these vertical channels, the bandwidth drops to about 5 mahz so it drops by an order of magnitude. Uh, basically. so just something to watch out for. You don't get the full 50 MHz quoted bandwidth down at your very low um, uh, volts per division settings.

Just a little trap to watch out for Now as you can see, my 20 MHz signal looks a bit fuzzy there. That's because my Intens is right up and it's causing a bit of a blooming effect on that signal now. I You know I don't know if um, uh, the you know if there's actually something wrong with here and the and there and the triggering is, you know there is a bit of trigger Jitter or its performance at the high frequency isn't as good as it should be I'm not sure I'd need a reference uh, triple 25 scope to actually uh, compare its True Performance there. but anyway, that's more than good enough for for my purposes.

I'm not fussed with the high frequency, uh performance of this thing. anyway. so um, now if you wanted to actually test the bandwidth I've mentioned this before of um, any scope. uh, really.

but in particular, these um, analog ones is you can feed in a square wave and if you don't have a 50 mahz, um, uh. function generator. That's fine. Just feed in a 1 khz square wave with a very fast rise and fall time and you'll be able to, um, see, you'll be by measuring the that's a square wave I'm feeding in now.

it's not terminated properly and all that sort of stuff. but um, you'll be able to measure the rise time. The uh rise and fall time of the oscilloscope uh will basically be equal to um, uh, the well, the bandwidth will be equal to 0.35 On The Rise time. So um, that's a way to actually calculate the Uh bandwidth of your analog oscilloscope if you don't have a function generator to go to that height.

Me: I've demonstrated that and mentioned that in one of my Ryol blogs if you want to check it out. And the last thing I'm not fussy about, but the beam find. Yep, beam find works. Now there you go.

Um, that's uh. I've done some basic tests on this thing and apart from, um, some slight calibration issues with the uh vertical, Channel and the horizontal, they've drift a bit. I should be able to, uh, bring those back into uh Cow by uh, tweaking, uh, some pots inside or something like that. but um, yeah, I'm quite happy with this.

it. uh, it works. Um, it was advertised as working, but uh, I took a bit of a risk I don't think there were it was actually showing any waveforms in the actual ad for it, but um, I deem that to be a winner. There you go, So you know, don't be uh, too scared to buy these analog scopes on eBay But one tip, if you are going to buy it and you really want to be sure that it's working at least, um, buy one that actually shows both way forms on both channels.

Um, like hooked up to just the probe adjust signal or something like that if you can. If you got both signals on there um and showing a basic waveform, then you can be pretty sure that, uh, it's going to do uh, most of its basic uh functions and um, if it is slightly out like this, uh, then you can just, uh, tweak it back into calibration. get the service manual and do that. So there you go.

This is fun and I really like this. It seems to perform reasonably well. I'm quite happy with it. I'm going to download the Uh surfice manual for it and uh, get in there and tweak the pots and have some fun I Think see you.