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  #1  
Old 08-19-2018, 12:25 PM
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AlanInSitges AlanInSitges is offline
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Old vs. New Scopes

Well I made it back to Spain with two huge suitcases packed full of vintage Murrican test gear, all with no damage (though the TSA went through them both), including a new-in-the-box Sencore CR161.

One thing I didn't buy back home was an oscilloscope, since there are plenty for sale used online here in Europe. As I'm browsing around what's on offer I'm seeing plenty of Tektronix, HP and Hameg scopes like I want in the 250€ range. There are cheaper ones, but I think it'll be worth it to have one new enough to display voltage and frequency measurements on the screen. The thing is, none of these come with probes, and the Textronix-or-HP-branded probes I see for sale cost almost as much as the scope does.

So this leads me to start thinking:

- Is there an operational difference between the 100+€ Textronix-branded probes on ebay and the 7€ Chinese ones I can buy on Amazon? Consider I'd be using them with something like a Textronix 2445 or TDS420A.

- Given that one of these cheap-o probes will work OK, and knowing that the scope I'm buying is probably 20 years old and hasn't been calibrated in a decade, would I be better off just spending the money on a new one of the many cheap Chinese scopes like a Rigol, Hantek, Siglent, or UNI-T?

My interest in the older Tek scopes was that I understand for certain uses (like IF alignments that need a sweep/marker) they are more useful. I am aware that I'm unlikely to spend much/any time doing said alignments but still.

What do you guys think?
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Old 08-19-2018, 02:24 PM
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Scopes vary in the input capacitance, I've seen 20pf to 50 pf or more. The input resistance should be the standard 1 M ohm. Make sure that the compensation adjustment on a 10X probe can cover you scope input capacitance. Some cheap 1X probes might add a lot of capacitance. I would think the cheap probes wouldn't be as durable. Some of the more expensive probes have accessory adapter tips, ie. different kinds of points or hooks.
For alignment you really don't have to have a very fancy scope. The scope is used in the X-Y mode (make sure the scope has that) and the horizontal sweep is only 50-60 Hz in most cases. You would want to use a demodulation probe or connect to the demodulation signal in the set, that means that the scope bandwidth can be very low (audio range). For TV work you can get by with as little as 5 MHz bandwidth since that is the bandwidth of the video. Looking at RF or IF you would use a demodulation probe, and in some cases a meter. A good scope will have a stable and reliable trigger circuit, I'm not sure a cheap scope would. Input sensitivity is another important spec.
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Old 08-19-2018, 03:02 PM
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I wouldn't waste anything on a Chinese scope (or Chinese anything if I can help it). I have a BK Precision 1479A; apparently the original owner got it in 1976 and it was stored for who knows how long before I got it. It worked fine right out of the box. Its bandwidth is a pretty healthy 30MHz, more than enough for most TV work. I don't really know anything about trigger circuits but this one allows the user to select variable or automatic triggering. I know others here use scopes that are at least similar to mine.
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Old 08-19-2018, 06:14 PM
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I wouldn't hesitate to have a cheap probe...Even if only as a cheap knock around spare or a beater...Granted I tend to go for the cheapest test gear that will do the job.
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Old 08-19-2018, 09:58 PM
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Quote:
Originally Posted by AlanInSitges View Post

- Is there an operational difference between the 100+€ Textronix-branded probes on ebay and the 7€ Chinese ones I can buy on Amazon? Consider I'd be using them with something like a Textronix 2445 or TDS420A.
For TV and radio work, you'll be far better off the with the 2445 than the TDS420. Early digital scopes (like the TDS420) don't capture many waveforms per second, and can't produce any brightness gradients on the trace. The result is that complex signals like a composite video signal, or modulated carrier will look like a mess with no recognizable features. Also, they're not very good at an X-Y display, which you'll need when using a sweep generator for alignment.

Be aware that the auto frequency and voltage measurement features of the 2445 (or any analog scope) are of limited usefulness. They won't display a continuous measurement like a digital scope, and they can be easily tripped up and give wildly inaccurate results.

If you want everything in one scope, you'll need an older high end digital scope (like a Tektronix with "digital phosphor") or a more modern one. If you're willing to have two, then you can get away with a TDS420 plus an analog scope.
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Old 08-20-2018, 01:43 AM
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For everyday work (I do much more design than repair) you'd have to wrench my 400MHz Tek 2465B out of my cold dead hands. For TV/video related repair work just about any decent 20MHz+ dual trace scope will work well. Secondhand Hameg scopes are usually a good bet in this segment of the market. Often under GBP50.

A digital scope needs to have digital phosphor or equivalent to make any sense of analogue video waveforms. Best value in digital scopes I reckon is from Rigol. I have their DS1054 which is a lot of scope for under GBP300.
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Old 08-20-2018, 10:24 AM
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Had many scopes thru the years, still have a few Tektronx in the attic storage. Current bench use is a Siglent 200M, 2G sample, digital SDS1202CNL+, does everything I need. I still have a Tec. 475 as a backup but almost never use it.
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  #8  
Old 08-20-2018, 01:28 PM
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Another option is to get an analog scope and a separate digital frequency counter, maybe a sin wave generator with a wide frequency range too... That is what I do since I basically never sink more than $50 into any single piece of test gear. For clean sin waves or square you can feed the counter directly, but on complex waveforms like synchroguide h osc waveforms one can match an outboard sin osc to the number of divisions on the scope (dual channel makes it easier) and feed the matched sin osc to the counter.
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Old 08-20-2018, 05:40 PM
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Quote:
Originally Posted by Electronic M View Post
Another option is to get an analog scope and a separate digital frequency counter, maybe a sin wave generator with a wide frequency range too... That is what I do since I basically never sink more than $50 into any single piece of test gear. For clean sin waves or square you can feed the counter directly, but on complex waveforms like synchroguide h osc waveforms one can match an outboard sin osc to the number of divisions on the scope (dual channel makes it easier) and feed the matched sin osc to the counter.
Some good tips here. To blazes with a fortune in test gear, most of which won't get a lot of use, push what you have right to the edge.

What would be considered a wide frequency range in a sine wave generator? I picked up a Hewlett-Packard 652A a couple of months ago for free, apparently in working condition, the only catch being the meter is loose and slapping about in there. Its frequency range is 10Hz to 10MHz. I had no idea what I might be able to do with the thing, I just thought it was kind of neat.
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Old 08-20-2018, 06:07 PM
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Quote:
Originally Posted by Jon A. View Post
Some good tips here. To blazes with a fortune in test gear, most of which won't get a lot of use, push what you have right to the edge.

What would be considered a wide frequency range in a sine wave generator? I picked up a Hewlett-Packard 652A a couple of months ago for free, apparently in working condition, the only catch being the meter is loose and slapping about in there. Its frequency range is 10Hz to 10MHz. I had no idea what I might be able to do with the thing, I just thought it was kind of neat.
You got a good generator. I had one about 7 years ago that I managed to damage (was doing some tube RF experiments and messed up) and later sold it. Those are useful for audio and you can get interesting video patterns feeding them into a tube set past the detector. You could use it with a scope and counter...Heck if you build or find an outboard AM or FM modulator you could use it as a test generator for radio work*.

*You can without it by tuning for minimum noise (generator carrier swamping ambient noise), but a modulator with tone is more fun to use.
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Old 08-21-2018, 07:04 PM
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Originally Posted by Electronic M View Post
You got a good generator. I had one about 7 years ago that I managed to damage (was doing some tube RF experiments and messed up) and later sold it. Those are useful for audio and you can get interesting video patterns feeding them into a tube set past the detector. You could use it with a scope and counter...Heck if you build or find an outboard AM or FM modulator you could use it as a test generator for radio work*.

*You can without it by tuning for minimum noise (generator carrier swamping ambient noise), but a modulator with tone is more fun to use.
Sweet, it's well worth fixing up then. I really need to open it and secure that meter, I'm concerned about it shorting something.

So I would need a tube set to create the video patterns? I wish I could find a later model tube colour to mix things up a little.

What would you recommend for a counter? Good to know my HP is good for radio work as well, could be handy for whenever I'm able to resume work on that Pye. I'd prefer to resurrect ready-made AM and FM modulators but if I need to build them so be it.
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Old 08-22-2018, 01:00 AM
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You could probably do the same on most early SS sets. Anything too computerized that mutes it's video if it does not see sync will fight attempts to make patterns by feeding in sinewaves. I had one of those HP generators before I had a good TV test pattern generator or scope, and I had a TV set that had audio but no video so the HP was the best way to inject SOMETHING recognizable into the 1st video stage for diagnosis...And it did help me figure out that my video amp worked.

My only counter is a Triplet 7000 that I picked up for $15 at a hamfest a couple years ago. It is a good(enough for me) counter. I also had some other counter for a while that was less accurate (and thus I got rid of it).

My college had some nice HP digital scopes when I was there...If those ever drop below a C-note I may have to grab one.
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Last edited by Electronic M; 08-22-2018 at 01:06 AM.
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  #13  
Old 08-22-2018, 07:30 PM
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Quote:
Originally Posted by Electronic M View Post
You could probably do the same on most early SS sets. Anything too computerized that mutes it's video if it does not see sync will fight attempts to make patterns by feeding in sinewaves. I had one of those HP generators before I had a good TV test pattern generator or scope, and I had a TV set that had audio but no video so the HP was the best way to inject SOMETHING recognizable into the 1st video stage for diagnosis...And it did help me figure out that my video amp worked.

My only counter is a Triplet 7000 that I picked up for $15 at a hamfest a couple years ago. It is a good(enough for me) counter. I also had some other counter for a while that was less accurate (and thus I got rid of it).

My college had some nice HP digital scopes when I was there...If those ever drop below a C-note I may have to grab one.
Oh, so that's what triggers the "no signal" screen on newer SS sets. Those are much too recent for my liking, my newest is a JVC-built Sears from '84. I still need to crack that one open to track down the cause of the "tick tick tick" sound from the HV.
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Old 08-26-2018, 02:35 PM
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Originally Posted by Jon A. View Post
Oh, so that's what triggers the "no signal" screen on newer SS sets. Those are much too recent for my liking, my newest is a JVC-built Sears from '84. I still need to crack that one open to track down the cause of the "tick tick tick" sound from the HV.
Are you sure JVC built the Sears set?
In the states, Sanyo built most of the Sears products, with a sprinkling of Gold Stars, RCA's and Toshiba.
Maybe the Canadian products are a little different.
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Old 08-26-2018, 08:24 PM
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Are you sure JVC built the Sears set?
In the states, Sanyo built most of the Sears products, with a sprinkling of Gold Stars, RCA's and Toshiba.
Maybe the Canadian products are a little different.
Oh snap, I mixed up the Japanese suppliers. Yes the set I spoke of is a Sanyo under the hood. However, I briefly had a worn-out 1978 Electrohome with a JVC-built chassis, the first model year they used them. It wasn't built nearly as well as the earlier models. It had vertical interval reference though, I kept the module as a curiosity.
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