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OT: Oscilloscope Purchase

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  • rcaffin
    replied
    That 200a SOB gave me the worst shock ever. 450VDC on the ball of my thumb.... blew 3 or 4 little pits in it.
    Yeah, happens, but 450 VDC is not that much.

    I was making up an electrostatic deflection amplifier for an experimental electron microscope long ago. Things got a bit messy.

    It was a 1 Million volt electron microscope, and the electrostatic deflection amplifier had a 6,000 V supply. (Those are not typos.)

    We were using beam tetrode valves rated at only 600 V, but if you pushed the tetrode grid into fairly hard cut-off you could put 6kV on the plate at the top of the bottle.
    So, we wired it up and switched it on. Big flash.
    We never found the anode resistors: they were instantaneously totally vaporised. The 'amplifier' had turned into an RF oscillator.

    The solution was to put some grid-stoppers on the grid pins, and then stand back some distance. It worked.

    Cheers
    Roger
    (And the resident spell-checker has never heard of 'tetrodes'.)

    Leave a comment:


  • Paul Alciatore
    replied
    Sorry, but they are both too late. I have posted them before that I have them beat by a factor of about 100.



    Originally posted by nickel-city-fab View Post

    [crowd cheering] B+! B+! B+! B+! B+! [crowd cheering] "... and in the other corner we have Mr Plate-voltage man!!" [crowd goes wild]

    Leave a comment:


  • Paul Alciatore
    replied
    Well, most ANALOG scopes do have some response beyond their advertised bandwidth. But you must be aware that they usually do not specify anything in that range. So, KNOWING just what you are seeing can be hard. Believe me, I have been there in situations where it did make a difference. There is a difference between knowing that there is a 200 MHz swiggle on your 100 MHz scope and knowing just how large (Voltage swing) that swiggle actually is. And the amplitude can be all important. Or what about it's harmonic content? 400 MHz, 800 MHz, etc.

    And digital scopes with their sampling artifacts just gets us into another whole bucket of worms. And digital scopes DO have an analog front end. The signal goes through a LINEAR amplifier either before the ADC or inside of it.

    Just saying that a scope can show things beyond it's specified bandwidth does not say that we can automatically know what it is actually showing us.



    Originally posted by macona View Post
    Most scopes will go way past their rated frequency anyway. I had a 100mhz Tek TDS series and it would do 250mhz no problem with some attenuation. My lecroy is rated for 600 and does 1ghz before attenuation starts to happen. Though that one is rated 10GS/s. Pretty overkill for home use, I don’t know the last time I looked at anything over a couple hundred kHz. At work we have rf drivers on stuff that’s over 100mhz though.

    we do use the spectrum analyzers from signal hound, they work pretty well.

    Leave a comment:


  • nickel-city-fab
    replied
    Originally posted by Jim Stewart View Post

    Once when I was working at Tektronix I got across +450 VDC. Once was enough, much more careful after that.

    -js
    [crowd cheering] B+! B+! B+! B+! B+! [crowd cheering] "... and in the other corner we have Mr Plate-voltage man!!" [crowd goes wild]

    Leave a comment:


  • nickel-city-fab
    replied
    Originally posted by J Tiers View Post

    I sold mine...... after I got a 200CD.

    That 200a SOB gave me the worst shock ever. 450VDC on the ball of my thumb.... blew 3 or 4 little pits in it. That happens when you forget to turn off power.
    I have one of those little holes in my left index finger from a Sony Trinitron HV section (cap on the flyback dumped thru my finger....) after I woke up I didn't care so much about getting the red out of the picture.... I took the whole thing apart for parts.

    Leave a comment:


  • Paul Alciatore
    replied
    Not sure as to which "that" you are referring to.

    My purchase? Ha,ha!

    The wait time? Just a joke on my part. I can hardly wait for it to arrive. Promised delivery date is next Thursday.

    The included arbitrary waveform generator? It is on their site.

    ???



    Originally posted by dian View Post

    Leave a comment:


  • Jim Stewart
    replied
    Originally posted by J Tiers View Post

    I sold mine...... after I got a 200CD.

    That 200a SOB gave me the worst shock ever. 450VDC on the ball of my thumb.... blew 3 or 4 little pits in it. That happens when you forget to turn off power.
    Once when I was working at Tektronix I got across +450 VDC. Once was enough, much more careful after that.

    -js

    Leave a comment:


  • J Tiers
    replied
    Originally posted by nickel-city-fab View Post

    somewhat OT but one of my deepest regrets in life was scrapping a working HP 200a oscillator during a need to move....
    I sold mine...... after I got a 200CD.

    That 200a SOB gave me the worst shock ever. 450VDC on the ball of my thumb.... blew 3 or 4 little pits in it. That happens when you forget to turn off power.

    Leave a comment:


  • nickel-city-fab
    replied
    Originally posted by J Tiers View Post
    I had a 130 as well. I believe the bandwidth was around 250 kHz........ Made with differential inputs from biological instrumentation, IIRC.
    somewhat OT but one of my deepest regrets in life was scrapping a working HP 200a oscillator during a need to move....

    Leave a comment:


  • J Tiers
    replied
    I had a 130 as well. I believe the bandwidth was around 250 kHz........ Made with differential inputs from biological instrumentation, IIRC.

    Leave a comment:


  • PStechPaul
    replied
    My Hitachi VC-6025 2-channel DSO that I bought around 1990 has served me well for the past 30 years. It uses a CRT and can operate as analog or DSO. I paid about $2000 for it and now they are on eBay for about $300. It is rated for 60 MHz with 20 MSample/sec. It displays a warning if it detects possible aliasing at higher sample rates on signals with high frequency components.
    Click image for larger version

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    My previous scope was an HP 130A of late 1950s vintage.

    Click image for larger version

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    I still like the clean and logically designed front panel controls, and I still have it, although it is need of repair. It has a bandwidth of only 300 kilocycles, but has a very sensitive 1 mV/cm low range.

    Leave a comment:


  • J Tiers
    replied
    Some do go past their limits, but as noted, it is not that useful unless you have sky high sample rates like your 10GS/s. You end up with very little detail, if any, and things just do not look as they should. You end up pushing further toward the basic Nyquist sampling limit, let alone being able to see details.

    The response is "there" but not very useful.

    The equivalent with an analog 'scope is very useful. You have a "sampling rate" that is very high.

    [QUOTE=psomero;n1939155]

    You saw a scopemeter in the < $500 range? You should have bought it.

    ............../QUOTE]

    I did buy it.... it cost me $300 for a 196B, the bigger screen type, and I got some other stuff with it at that price. Took it in to work, where the standard 'scopes" were the similar portable Tek unit, and the Scopemeter was actually considerably more versatile.
    Last edited by J Tiers; 04-18-2021, 04:33 PM.

    Leave a comment:


  • macona
    replied
    Most scopes will go way past their rated frequency anyway. I had a 100mhz Tek TDS series and it would do 250mhz no problem with some attenuation. My lecroy is rated for 600 and does 1ghz before attenuation starts to happen. Though that one is rated 10GS/s. Pretty overkill for home use, I don’t know the last time I looked at anything over a couple hundred kHz. At work we have rf drivers on stuff that’s over 100mhz though.

    we do use the spectrum analyzers from signal hound, they work pretty well.

    Leave a comment:


  • psomero
    replied
    Originally posted by J Tiers View Post
    Do you demand "brand new"?

    Because used ones do offer a far lower price. I bought a Fluke "Scopemeter" portable a few years ago for well within your budget. It is the larger type, with a big screen, digital, with built-in meter, true RMS, the whole nine yards.

    The trigger options on it are better than the equivalent Tek, and it is isolated for up to 600VAC on each channel, depending on the voltage "category" you need.

    Far more oscilloscope than I would otherwise have obtained at that price. Only downside is the screen is not color, so you need to keep better track of which trace is what.
    You saw a scopemeter in the < $500 range? You should have bought it.



    The thing with the Rigols/Siglents/Hanteks/Whatevers is that they don't have the same level of design rigor, so they will generally have known issues with measurement integrity or performance in some situations. You get extra bells and whistles, but they come with that caveat. Many forums for EE stuff are devoted to documenting the use of these kind of scopes.

    I want to buy one for myself, but haven't been using my old tek CRT 4-channel scope enough to justify it. If I was going to really buy one, I'd go find a used good condition TDS-2024B, but I do BLDC motor stuff, so having the four isolated channels is a big plus. If there was a store left who sold them locally, I would have bought a Rigol by now. Before they closed, I had gone to Fry's three separate times with cash in hand to buy whatever they had, but they had no stock at the time. Oh well.

    Leave a comment:


  • dian
    replied
    Originally posted by Paul Alciatore View Post
    Well, I finally pulled the trigger. I ordered a Hantek DSO2D15 plus two 200 Mhz probes from Amazon. I think the included arbitrary function generator took me over the finish line. Now comes the infinitely long wait for delivery. That's OK because I need to clear some space on one of my electronic benches.
    why dont i see that on their site?

    https://www.hantek.eu/oscilloscopes/
    http://www.hantek.com/products/List/3
    Last edited by dian; 04-18-2021, 12:10 PM.

    Leave a comment:

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