Time to get an O-scope...tips?

[Mark Black]

I've already got two functional Tek scopes, but I'm STILL kicking myself for letting this one slip by recently. Had it in my ebay watched items & spaced out the end of the auction:

http://cgi.ebay.com/ws/eBayISAPI.dll...9433&rd=1&rd=1

[Enzo]

It is common to sell scopes without probes. I would not send my probes off with a scope unless they were old beaters. Brand new probes can be had for $30-40 anyway. You can spend a ton on probes, but frankly I have always got good life and service from cheapo generic probes. SOmetimes I get the house brand at MCM, or maybe I call Probemaster. Or what's the other one? TPI or something like that? (Test Probes International)

X10 only probes would not likely get in the way, but the switchable X10/X1 are the most useful. It is really seldom you need to go to X1.

You do not have to match the probe to the scope in bandwidth. Obviously if you plug a 20MHz probe into a 100MHz scope, you will be limiting the scope. But nothing wrong with using a 100MHz probe with a 20MHz scope.

But yes indeed please do pay attention to voltage.

20MHz is plenty for audio. In fact, about any scope that works will be fine, even an old 500KHz. If your scope works, it will be a great addition to your bench.

[Satamax]

I've already got two functional Tek scopes, but I'm STILL kicking myself for letting this one slip by recently. Had it in my ebay watched items & spaced out the end of the auction:

http://cgi.ebay.com/ws/eBayISAPI.dll...9433&rd=1&rd=1

Mark, are thoses 475 good, any better than the 465, or should i keep looking at a 465? I have a 564B and a tekmeter for the moment.

[Mark Black]

Mark, are thoses 475 good, any better than the 465, or should i keep looking at a 465? I have a 564B and a tekmeter for the moment.

I have never owned either a 465 or 475, but I understand they are built very ruggedly and perhaps more importantly may be the last Tek scopes which do not use proprietary custom IC's which are largely no longer available for some of the later scopes. The DM44 multimeter option on the 475 I missed looked kind of attractive too.

I own a 2235 and a 2335, which have been pretty good and both have protective front covers making them easy to transport for field work. The 2335 did develop a problem at one point with one of those aforementioned custom IC's in the vertical amplifier circuit, but luckily with some careful microsurgery I was able to remove enough of the conformal coating to access and repair the problem.

Tek service manuals are very elaborate and pretty well written, which I consider a plus.

One thing for sure - after you get a decent scope & get used to using it daily having it fail is like going to a gig and finding out you forgot your guitar - kind of a sick & helpless feeling. I started with a big old Tek tube-based scope (still have it somewhere actually but forget the model number). It worked OK but was a little cranky and sometimes I would have to give it a little smack. Made a heck of a space heater too. One day one of those 66 tubes went bad and that led to the purchase of the 2335, followed by the 2235 when the 2335 had its problem. I figure you have to have at least 2 scopes, since you will need one to troubleshoot the other at some point - nothing lives forever.

Happy hunting!

[Satamax]

Thanks a lot Mark!

Well, my 564 is a tube based scope, i like it enough, but the time base is acting up and i hate moving it around, which i have to do, since the workshop is also used for woodworking As well, there's a chanel missing since last time i used it So i'm on the lookout for something reliable to replace it. And with a green trace, as i don't like too much the digital display of my tekmeter, thought i'd may be give a shot to the new ones like the 210/310 if i had the money, they're realy portable. I'd love a phosphor display, but that's out of my league and need for the price.

Realy it gonna be a 465 i think. I'm used to old tek paint and red knobs.

[Tom Phillips]

The Tek 465 & 465B are my current bench scopes. They do have proprietary parts inside but that has not been a problem so far. Good support is available through the newsgroup discussions. I love the bright green trace.

Someday it would be nice to have a good digital scope with an LCD screen. I'd like to be able to store traces and output screen shots to the computer. However, that stuff is expensive and I HATE the display quality for audio work. The traces always look noisy like a line of marching ants.

Tom

[Steverino]

The 465 is/was the industry standard. I used to calibrate scopes, and although a real challenge to repair, they rule the roost.

I also have one at home, and I paid 250 for it including reapir manual and two probes. You get what you pay for.

[bob p]

My take on the old iron in the Tek line is a bit different.

Because I wanted to spend my time using a scope rather than working on it, I wanted a solid-state scope. I wanted to focus my repair work on amps not on scopes, so I committed to buy a SS design. Besides, Tek tube scopes are heavy, collectible, and expensive to ship if you can't find one locally.

Looking at the SS Tek scopes then, there's the problem of repairing a scope that uses proprietary circuits that may no longer be available. The majority of of the Tek SS scopes use proprietary Tek ICs that are hard to find, and are often expensive. Finding what you need might require cannibalizing an old scope to get them. I wanted to avoid falling into that trap. Having "tek" on my bench wasn't worth the potential headache.

That decision left me with two options -- buying a newer, more expensive Tek scope that's less likely to be in imminent need of repair, or going farther back in time to find an older SS scope that didn't use proprietary ICs.

As it turns out, there are two great/classic Tek scopes that are 100% SS in design, but were made in the era before Tek started designing their own proprietary ICs. These scopes are the Tek 453 and 454. Both of these scopes use 100% generic SS components, so if you had to repair them, chances are you wouldn't have too much trouble finding parts. If you bought one of these, you could probably maintain it yourself. It might last for your entire lifetime and you might never need to buy another scope. These scopes are pretty easy to find in need of repair, at a reasonable cost, but they're very heavy and expensive to ship. Because of the collectability/desirability, a 100% working/restored model 453 is likely to cost you just as much as a brand-new discounted BK-2021B. Personally, I think that the new BK is the better deal.

If you're really interested in old Tek stuff, there are 3 Yahoo! groups dedicated to Tek scopes. Lots of Tek experts there.

In sumary then there are a number of reasons why some people would consider the Tek 453 and 454 to be the "ideal" hobbyist scopes:

* The 453 (50Mhz) has more than enough bandwidth for audio
* The 454 (150Mhz) is sufficient to work on most hobby oriented digital logic
* Both are sturdy, rock solid, and reliable.
* both are commonly available
* Both are relatively inexpensive
* Both easily meet or exceed their performance specs.
* Both have excellent triggering circuits
* Both are easy to use.
* They do not contain any Tektronix-made IC's.

Knowing this, why did I decide NOT to go with one of these Tek scopes? As inexpensive as they are, they're still way too expensive relative to other quality used scopes on the market. To get one of these fully restored or in mint condition, with all of the probes, accessories and manuals, I would have had to have paid about $300, or 6x as much as I paid for my 60 MHz Hitachi. If my Hitachi dies, I'm only out $50 and I can afford to throw it away and buy a better scope in the future for relatively less money. In some respects, the disposable philosophy isn't such a bad idea.

Its true that if you buy a Tek scope, you will get what you pay for. They're good quality pieces of gear. The other way to look at this is that you will have to pay more to own a Tek than you have to pay for an equivalent scope, even though you don't really have to. Its all a matter of personal preference.

[Enzo]

I think we obsess too much over it. I have gotten great service from B&K scopes over the last 25 years or so, and they are not high end by any means. We had one of the Hitachi scopes and it worked well in our commercial shop, adn that was inexpensive when bought new.

Of course I do have a couple ancient Tek space heater tube scopes in the back.

[Alexander]

Just another vote for a 20mhz 2-channel Tenma- mine was bought new in '91 and still works great (with 10x probes even!!) But I bought a nice B&K bench meter at Test Equip.Depot and they're great folks to deal with too. Either the B&K or the Tenma at around 350.00 and that's some piece of mind you don't have with Ebay gear.

Happy Trails,
Alexander
Retrodyne Amplification

[bob p]

Helpful stuff that Enzo posted in another thread:

In my opinion, you don't NEED a signal genny, but they are very handy. That said, you can MAKE a simple one with a chip or two and a 9V battery. For basic repairs, mostly any signal will do. Having a sine wave generator where you can adjust the level and freq to anything in the audio band will be more of a necessity when you get into characterizing performance. My main bench genny sits on 100Hz almost all the time. I use music more than I use the genny. With music I can hear a hole in the response curve faster than I can find it with sweeps. And of course I use the guitar.

I am not suggesting signal generators are bad or useless, I do use mine a lot. Crossover distortion settings would be hard without one. But the scope will widen your horizons substantially without one. With one would be better, yes. The purchase of a scope is not wasted without one is what I am trying to say. Any more than your voltmeter is wasted without a scope. Plenty of good work was done with just that meter, right?

A scope is like a visual voltmeter. You can watch the voltage in a circuit vary continuously. It lets you see gross distortion. A missing half a waveform is pretty obvious on a scope, but unless your ear is experienced to recognize that particular form of distortion, not as easy without it. A symptom like that instantly tells you one side of a p-p amp is not running. A scope can help see frequency response, but since guitar amps are pretty well out of it over 5kHz, this is not so helpful, to me anyway. CLipping is easy to see, even clipping you can't hear. Crossover distortion becomes obvious.

SInce the bandwidth of guitar amps is so limited, there is no need for a 100MHz scope. Certainly one will work just fine, but so will a 10MHz scope or even a 500kHz scope. Oh, someone can come up with some arcane procedure that will only work with a whiz bang scope, but by the time you REALLY need something like that, then you will be ready for a scope upgrade anyway.

Unless it is some fine old piece of history, I doubt you will even find a scope under 10MHz. Don't worry about the MHz, you will have enough no matter what. Get as much as you like, just don't pay a lot extra for more scope than you need. A working 20MHz scope next to a working 100MHz scope - if they are priced the same, sure I'd take the 100, but when the one is $100 and the other is $300, then I'd take the slow one all day.

Yes, the scope freq rating is the max it will reliably respond to, it will always work at lower speeds. Other than DC, audio is about as slow as it gets. SOme applications require higher speed, like computer circuits and other high speed digital stuff. Or microwave and UHF radio.

ALmost all scopes these days are triggered sweep. All that means is the trace on the screen will synchronize with the signal so it appears stable. Like a strobe light makes a spinning fan appear stable if it blinks at the same speed as the fan turns. if a scope triggers the trace to sweep across the screen at the same point of each waveform, then the picture will appear in the same position. Some older scopes had "recurrent" sweep, which mean the trace just swept at whatever speed you set the knob to. A little tweaking and the waveform can be fairly steady, so even those old dinosaurs will still serve you well. These might be the scopes you can find for $20 at a ham fest. Working even. Triggering is preferred, but not essential.

Vertical sensitivity. A scope is really just an amplifier - or maybe a preamp - and instead of pushing a speaker back and forth, it pushes a beam of electrons back and forth on the scope screen. That is the glowing line. The vertical knob is just a volume knob. The moer you turn it up, the more sensitive it becomes. Some scopes are VERY sensitive. All the way up might need only 1 millivolt or even less to move the screen trace a whole division on the screen. Turn your scope up that far, and you get nothing useful, just the same noise and crap a guitar cord picks up without a guitar. Older scopes often went up as high as 10 or more volts per screen division. Many newer scopes only go up to 5 volts/div. I prefer the larger voltages. Let me detour for a moment

By the way division merely means the little cross lines on the screen. They are usually about a centimeter apart. They divide the screen. 5v/div means if your probe encounters 5 volts, it will move the screen trace one division - one centimeter - on the screen. My scope here is typical at 8 divisions tall and 10 wide.

Probes. Scopes, especially used ones, are often sold without probes. You will need at least one. You want a 10x (10 times) probe, or better yet, a switchable 10x/1x probe. You can spend $1000 on a probe, but the common cheap $30 probes have always worked fine for me.

A 10x probe just has some high value resistors in it as a voltage divider. What ever voltage the tip of the probe encounters, it will be divided by 10, so the scope itself sees 1/10 as much. So a 100v test point will seem like 10v to the scope. This way I can probe 550V and teh scope will see 55v. As long as the probe is rated for a higher voltage, a lower voltage scope can view it.

When I have a high voltage ar a large signal, I would like to have it fit on my scope screen. If the lowest sensitivity on the scope is 5v/div, then on my 8 division screen, I am limited to 40 volts. I can move the trace around, so centered i can then see 40v peak to peak on a signal, or set the trace to the bottom, and I can see 40 volts of DC. Even on my 10x probe, that still limits me to 400v. If my scope goes down to 10v/div, then I have no problem fitting 600v on my screen. Usually there are other ways around this, but you get the idea. SO I prefer a scope with a 10k/Div scale.

By the way, when you use the 10x probe, you set the scope to 5v/div, but assume 50v/div while looking at the trace.

Most modern scopes are dual trace, meaning you can watch two different inputs, either switching between them, or superposing them together on the screen. It can be handy sometimes, but mostly I use just one channel. I do keep my second channel connected to my bench speaker/load panel. DOn't turn down a single channel scope if it otherwise suits just for that one quality. And that 100MHz scope that can be a four channel? I am sure you could come up with some application to use all four traces, but really, no one needs that to service guitar amps.

My old old B&K has been a workhorse for me, certainly Tektronix scopes are first rate, but inexpensive Hitachi scopes worked well for us, and others report success even with things like the MCM house brand Tenma.