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

  1. #1
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    Time to get an O-scope...tips?

    I think it's about time I got an o-scope. I've seen some threads here where folks have taken pix of a handheld Fluke device that appears to have o-scope capabilities. Is this the best route? Or should I look for an older (and much larger) used o-scope? I don't know enough to make a good decision...I don't need it have a bunch a features/capabilities that I'll never use while working on guitar amps (pretty much the only thing I intend to use it for). But I also don't mind spending a little extra for something newer and much smaller.

    Is there anything else I'll need? Do I need a signal generator...or is that part of the o-scope? Any special leads or anything?

    Any products/features I should avoid?

    Thanks for any suggestions.

  2. #2
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    You dont need to get too extravagant,dual channel is nice.I've been using a Tektronics T922 for about 10 years,paid about $100 used.Before that I had an old RCA tube unit along with an electronic switch to give it 2 channels.The Fluke Scope-meter you mention is quite expensive,I've never had one,couldnt see spending that much.Check eBay,you'll see some of the costlier ones with 100MHZ inputs,but a 10MHZ is fine.You will need a signal generator to inject a signal for testing.Get one that will give you a sine wave,the RF type are not for guitar amp use,they are for radio.You can find some older tube units that will give you a sine wave and square wave at a wide range of frequencies,but all you need is something that will give you a 1K signal at a 1/4 volt or less.You will also need a couple of "dummy loads" to check your output.I have 2 8ohm 50 watters that I can use individually or in series/parallel to get 4 or 16ohm.

  3. #3
    Better Tone thru Mathematics bob p's Avatar
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    I've been on a test equipment buying spree over the past few weeks, so I'll offer my two cents on the subject. There are a few important topics that should factor into your decision:

    1. Analog vs. Digital

    Don't buy a ditgital sampling scope unless you have special needs for that type of equipment, ie: interfacing the scope iwth a PC. Otherewise, buy an analog scope.

    2. Bandwidth

    If you plan on audio work and only audio work on amps, that tremendously diminishes the bandwidth of the scope that you will need. Just about any scope that you are likely to find in working condition is going to have bandwidth that is far in excess of what you will actually need. So the first decision that you need to make is whether or not you want a mulltipurpose scope for audio, TV, radio type stuff (or even logic circuits), or just a plain old audio band scope.

    If all that you want to do is to work on tube amps, then don't feel the need to buy a high bandwidth scope as it would be money wasted. For exampke, I bought an old 500 KHz Heath 0-10 vacuum tube scope on eBay for $0.99 that needed trivial repair work. Its a single channel scope, but its still plenty of scope for tracing audio signals in guitar amps. You read that right -- the bandwidth is only 1/2 MHz.

    3. Number of Channels

    Most people recommend a dual trace (two channel) scope for tube amp work. In some respects, its more of a luxury than a necessity. If you can remember what a sine wave looks like, its easy enough to do your circuit tracing with a single channel scope. A second channel is helpful for direct comparison between two signals, but I think of it as more of a luxury than a necessity for audio work. 4-channels scopes are fun to work with, but those extra channels are nothing but an expensive luxury for tube audio work.

    4. Delayed Sweep/Dual Sweep Time Base, External Triggering, Y-Mode Alternate Triggering, Signal Summing, etc.

    More advanced scopes offer these features. If you're just doing audio work, you may never use the features.



    In a nutshell, then, a single trace or a dual trace scope of just about any bandwidth will be fine for tube audio work. You don't have to spend a lot of extra money on a scope with features that is primarily intended for repairing TV, radio, or logic circuits.

    There are lots of brands to choose from in old gear. Some of the vacuum tube scopes are becoming costlier because of collectability. I have both solid state and tube 'scopes, and for reliability, I'd recommend an inexpensive solid state scope.

    Your best bang for the buck is problably and older solid state scope that's in good operating condition. Tek scopes tend to cost more than other equivalent scopes because people are willing to pay a premium for the brand name. The same appears to be true for BK, though the premium appears smaller.

  4. #4
    Better Tone thru Mathematics bob p's Avatar
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    As an example of buying used scopes, I bought a 60 MHz, dual trace, delayed dual/sweep timebase scope on eBay for $54. It was made by Hitachi, who I think did the ghost manufacturing for BK. Looking at other eBay auctions, the equivalent Tek scope would have cost at least twice as much.

    Watch out for buying scopes on eBay. If the scope doesn't come with the full compliment of probes and manuals, its either military surplus that may or may not have been trashed, or it could be stolen merchandise. There is no shortage of disreputable people selling dead/untested gear on eBay. Beware of gear that is "untested but pulled from a working environment" or offered for sale "As-Is."

    I have also encountered no shortage of people selling perfectly good working scopes without their manuals and probes included in the deal. Making matters worse, these people have absolutely no idea how to use the equipment or to demonstrate that it works. Caveat emptor, as their wares could be stolen merchandise. I would only buy from a reputable seller who offers a money back guarantee.

    If you don't want to hassle with shopping for used gear and your budget allows for it, buy an inexpensive new scope. I found someone on the web that was giving deep discounts on BK's entry level scope: BK-2120B. I almost bought one, but ended up buying something else.

    Personally, I don't like the portable scopes by Fluke. For one, they're incredibly pricey. Second, I just can't stand to look at an image of an analog sine wave that is poorly approximated on a low-resolution LCD display. To me, a real CRT is preferable. YMMV.

    HTH.

    Don't forget, when you buy a scope, that's only the first step in your gear acquisition. After buying the scope you'll need some sort of signal generator (see my thread in music electronics). You might also want to buy a frequency counter. As @stokes mentioned, you'll need load resistors, etc. ... Just in case you haven't thought about it, somebody should warn you that the decision to buy a scope is just the beginning...

  5. #5
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    Thanks so much for the responses.

    bob - Scope GAS? Say it ain't so!

  6. #6
    Lifetime Member Ray Ivers's Avatar
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    Matt,

    What's your budget?

    My B&K 2120 'scope died about a month ago (after almost 20 years of service), so I've been using my first-generation Fluke ScopeMeter until I figure out what I want to replace it with; I'm leaning towards a Tektronics 2004B right now. FWIW, I favor a bright, rock-solid presentation down to 0Hz, low latency, two or more channels, wide input sensitivity range, etc. - but your budget will be the biggest determinant of what 'scope to look at IMO.

    Ray

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    Senior Member Satamax's Avatar
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  8. #8
    Member bulldogguitars's Avatar
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    I purchased a Tenma 20Mhz dual trace scope from MCM in one w/a built in sig gen for under $300. You might want to check them out. www.mcminone.com

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    Thanks for the links/suggestions. I like the fact that that one has a built-in signal generator.

    Ray,
    I hadn't set a strict budget but I didn't want to spend more than a few hundred. It appears that I have options at or below that price point.

  10. #10
    Better Tone thru Mathematics bob p's Avatar
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    If you're willing to spend a few hundred, here's the link for brand-new BK 2120B for only $350. That's a smokin' deal on a new brand-name scope. (Ray, this might interest you too!)

    http://www.testequipmentdepot.com/b+...sion/2120b.htm

    I've seen one fellow on eBay that sells used 2120 (and similar) scopes with a 30-day warranty for about $125. That's not a bad price, considering the merchandise is warranted for 30-days. And it makes the idea of buying a used scope on eBay a less dangerous proposition.

    I dedided to watch ebay because I wanted to find a killer deal. It took me a couple of weeks, but I picked up a 60 MHz multi-channel scope with two probes, manual, and all the bells and whistles including dual time bases and delayed sampling, and a big CRT for all of $54 or so. That just goes to show that if you're willing to do your homework, there are good deals to be had. The bad news? The scope was such a good deal that I had to pay almost as much for my HP dual channel frequency counter/timer and my HP function generator as I paid for my scope!
    Last edited by bob p; 01-25-2007 at 10:23 PM.

  11. #11
    Supporting Member Mark Lavelle's Avatar
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    I'll second all of the above, but I'm surprised that nobody mentioned that you must get "10x" probes for high-voltage amp work. That's what most scopes come with, but you'll want to be sure.

    And while I agree that two channels aren't absolutely necessary I would also say the odds are good that some day you'll want that 2nd channel (unless your scope and your sig. generator both have an additional trigger/sync input & output, respectively). That's the only way to see the phase differences at different points in your circuit...
    Murky Mark, Minister of Musical Mischief
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  12. #12
    Noodle of Reality Steve Conner's Avatar
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    I would go one step further than Mark, and say that a x100 high voltage probe is well worth having. The voltages in tube amps are towards the upper end of what regular x10s can stand: if you try scoping the power tube plate voltage of a SVT cranked into a dummy load, you could get a very nasty surprise indeed. A x100 should be safe with any voltage in any tube musical instrument amp.

    What's more, the input impedance of a x10 probe can load tube circuits enough to change the very waveform you're trying to measure. For example, if you scope a grid circuit with 1M impedance, the x10 probe will change things by 10%, the x100 by only 1%, and clipping direct to the scope would cut the signal to half its original amplitude, and that's not counting the capacitance of whatever lead you clip it with.

    I have a few scopes, and a lot of other test equipment, since I'm an EE and often do consulting work from home, besides messing with guitar amps. I used to use a little battery powered 20MHz scope that I was given as a freebie since it was broken. Later I got an old Tektronix R7603 from a military surplus dealer on eBay.
    Last edited by Steve Conner; 01-26-2007 at 12:09 PM.
    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

  13. #13
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    The good news is this stuff is very cheap nowadays.
    I used to work on test equipment long before (well a few years before) I got into working on tube stuff, you can get a good Tek scope for $100 that listed new for $1000!
    if I'd only known.....we literally had boxes of thousands of tubes! I got some for my amps, but I could have had the mother lode!

  14. #14
    Better Tone thru Mathematics bob p's Avatar
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    Mark's comments about probes are good points. (Mark, I don't know how I managed to overlook probes when I made that earlier post -- it completely slipped my mind!)

    Steve's post has me seriously rethinking my decision to use a pair of 1:10 probes. Darn. More stuff to buy...

    When I was shopping for a scope I asked for guidance from a friend who is a retired tube-era design engineer from Motorola. He told me that as a rule of thumb, test gear has always sold on the used market for about 1/10 of what it costs new. That's been my observation on eBay as well. The biggest exception seems to be when you buy used gear where the model is still in production. Prices for gear that is still in production tend to be higher. Once a piece of gear is no longer in production, its price on the used market really drops, and it seems to follow the 10% rule.

    HTH.

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    Well I did a little shopping. I've found that the prices can be all over the place and the issue of "fully tested/fully functional" doesn't always mean you're paying way more...although that often seems to be the case.

    I've found some e-bay sellers that have a ton of feedback with no negatives and are selling older SS 'scopes for reasonable and the auction says "fully functional...price refunded if DOA" or words to that effect...but they have no probes (maybe arouses some suspicion). It also has a cal sticker that was only a few years old. So I decided to take a chance and try one...it's only 20MHz but it's a dual...after shipping it'll be $90.

    All the Tektronics scopes that were "fully tested, fully functional" were in the $300s and rising...I never saw a Tek that was cheap except for the ones where it seemed very likely to get a non-functional unit.

    So I needed probes. It was extremely uncommon to see a 10x/20MHz probe so I assume I can just go higher in bandwidth? My bandwidth will be whatever the 'weakest link' is...correct? Then I noticed that many of the 10x/100MHz probes I was looking at were only rated for 300v...but I found some rated for 600v and got them (I got the 1x/10x combo...I didn't know if I'd need the 1x for pedals but it wasn't much more for the 2-pack than just a single 10x probe). See, bob is already right about the 'scope-GAS'.

  16. #16
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    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

  17. #17
    Senior Member Enzo's Avatar
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    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.

  18. #18
    Senior Member Satamax's Avatar
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    Question

    Quote Originally Posted by Mark Black View Post
    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.

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    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!

  20. #20
    Senior Member Satamax's Avatar
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    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.

  21. #21
    Old Timer Tom Phillips's Avatar
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    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

  22. #22
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    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.

  23. #23
    Better Tone thru Mathematics bob p's Avatar
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    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.

  24. #24
    Senior Member Enzo's Avatar
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    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.

  25. #25
    Member Alexander's Avatar
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    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

  26. #26
    Better Tone thru Mathematics bob p's Avatar
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    Helpful stuff that Enzo posted in another thread:

    Quote Originally Posted by Enzo View Post
    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.

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