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  • Differential Probes

    Can anyone make a couple of recommendations for general purpose differential probes? Im using it for audio so an output impedance of 1M is preferred.
    Are they usually active, or no?
    If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

  • #2
    Originally posted by SoulFetish View Post
    Can anyone make a couple of recommendations for general purpose differential probes? Im using it for audio so an output impedance of 1M is preferred.
    Are they usually active, or no?
    The Tektronix P6055 Differential Probe set is a good selection for this. These are X10 Probes (a pair of course), with matching adjustments at the connector end, which always worked well with Tektronix Differential Input Amps like the 7A13, 7A22, R5030, R5031 differential Input amps on those dual beam scopes, as well as the TM 500's AM502 Differential Amplifier Plug-in.

    Click image for larger version

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    tek_p6055_1971_cat.pdf
    P6055 Operating Instructions.pdfP6055 Operating Instructions.pdf

    These are Passive Probes. I have a set of them for use with my differential input scope plugins, and have had good success with them. I found the above information here: http://w140.com/tekwiki/wiki/P6055

    Other mfgr's Differential Probes found are active AND EXPENSIVE! I used to have a Tektronix P6046 Active differential probe set, but was troublesome to keep running. Sold it decades ago. I haven't looked on recent years to see what has appeared on the market.
    Last edited by nevetslab; 04-21-2020, 10:54 PM.
    Logic is an organized way of going wrong with confidence

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    • #3
      Are they usually active, or no?
      Maybe it should be mentioned that connecting a pair of probes (like the P6055) to two channels of a standard scope in subtract mode typically won't allow precise scoping of floating signals. Reasons are that the 2 channels might not be exactly identical and the CMRR will be poor.

      For floating measurements an additional high CMRR differential amplifier is needed, either external or in the scope.

      So one might say that the whole differential probe system/setup will always active.
      Last edited by Helmholtz; 04-22-2020, 01:46 AM.
      - Own Opinions Only -

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      • #4
        Originally posted by Helmholtz View Post
        Maybe it should be mentioned that connecting a pair of probes (like the P6055) to two channels of a standard scope in subtract mode typically won't allow precise scoping of floating signals. Reasons are that the 2 channels might not be exactly identical and the CMRR will be poor.

        For floating measurements an additional high CMRR differential amplifier is needed, either external or in the scope.

        So one might say that the whole differential probe system/setup will always active.
        Absolutely correct. Unless you're using a scope that HAS differential inputs (which I have in my Tektronix 7000 series vertical amp plugins, or in my LF dual beam scopes (R5030, R5031), or Tek 1A7A, TM 500-AM502 Diff Amp, etc), you won't get the perfomance with the traditional 2-channels, putting one out of phase. I don't think you'll get any better balance by tweaking the adjustments on the two probe connector bodies than you would tweaking the gain of either channel for best CMRR.
        Logic is an organized way of going wrong with confidence

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        • #5
          I've been familiarizing myself with the Diff. probe market. Wouldn't you know that the first one I looked into (as it was first in my browser search) happened to be around $1200. So, pretty quickly, I was seeing my chances of getting one vanish very quickly if that was the kind of money I was looking at.
          While the low end market starts around $150, they can run into the several thousand dollar range too. I've been reading through some threads over at eevblog to get a sense of peoples experiences with different products, and get some suggestions. Newark has some different options I wanted to get some thoughts on:
          They sell a Testec 5101 SI9001 differential Probe, 25 MHz bandwidth, 1.4 kV, 10:1 & 100:1 options for $316.20.
          Also, They have a PicoScope TA041 - Oscilloscope Probe, 25 MHz, Differential, 700 V, 10:1 & 100:1 options for $325.49 .
          Do any of you have any experience with these manufacturers? what do you think about these?
          If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

          Comment


          • #6
            Originally posted by SoulFetish View Post
            I've been familiarizing myself with the Diff. probe market. Wouldn't you know that the first one I looked into (as it was first in my browser search) happened to be around $1200. So, pretty quickly, I was seeing my chances of getting one vanish very quickly if that was the kind of money I was looking at.
            While the low end market starts around $150, they can run into the several thousand dollar range too. I've been reading through some threads over at eevblog to get a sense of peoples experiences with different products, and get some suggestions. Newark has some different options I wanted to get some thoughts on:
            They sell a Testec 5101 SI9001 differential Probe, 25 MHz bandwidth, 1.4 kV, 10:1 & 100:1 options for $316.20.
            Also, They have a PicoScope TA041 - Oscilloscope Probe, 25 MHz, Differential, 700 V, 10:1 & 100:1 options for $325.49 .
            Do any of you have any experience with these manufacturers? what do you think about these?
            You've done more research into the current products available now than I have. I've only used the Tektronix P6046 Active FET Diff Probe years ago, which wasn't well behaved, having bought it used, and did my best to calibrate it. Sold it off. So, it's just been the Tek P6055 probes that I've used since then, use on both the 7A13 100MHz BW Diff Plugin (7000 series scope), as well as with the 7A22 and the R5031 Dual Beam Diff inputs (same front end as used in the 7A22).

            I'll have to take a look at the Testec and the PicoScope probes. I like the high voltage range on the Testec, with both 10:1 & 100:1 Never hard of either company, so no opinions. Thanks for the information.
            Logic is an organized way of going wrong with confidence

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            • #7
              another one is Probe Master. Here is the comparable item to the Testec:
              Probe Master 4232 Differential- Probe
              If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

              Comment


              • #8
                Originally posted by SoulFetish View Post
                another one is Probe Master. Here is the comparable item to the Testec:
                Probe Master 4232 Differential- Probe
                After looking at these three probes, it looks like the same unit being produced by one mfgr, and marketed with different brand names. I own a number of Probe Master DMM probes, and have always liked their products, though I've never known them to manufacture electronic assemblies like this. All of these are very similar in price.

                What I've always liked about the Tektronix Differential Amplifier plugins is their ability to apply a wide range of DC voltage to offset the potential being measured, allowing DC coupling and much higher gain applied. They began that principal with the Type W plugin, as well as adding that to the 1A7A plugin, and to the 7A13 and 7A22. They also did that on the 5000 series scopes, though I wasn't a big fan of that series' CRT resolution.
                Logic is an organized way of going wrong with confidence

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                • #9
                  Originally posted by nevetslab View Post
                  After looking at these three probes, it looks like the same unit being produced by one mfgr, and marketed with different brand names. I own a number of Probe Master DMM probes, and have always liked their products, though I've never known them to manufacture electronic assemblies like this. All of these are very similar in price.

                  What I've always liked about the Tektronix Differential Amplifier plugins is their ability to apply a wide range of DC voltage to offset the potential being measured, allowing DC coupling and much higher gain applied. They began that principal with the Type W plugin, as well as adding that to the 1A7A plugin, and to the 7A13 and 7A22. They also did that on the 5000 series scopes, though I wasn't a big fan of that series' CRT resolution.
                  I've looked at the 7- series on the used market a couple of times. It's a bulky unit, but if you had a couple of different plugins that you could make use of often, it seemed worth the size. The unit must be a nightmare to lift though. I had a.. I can't remember. 556, maybe? it was a huge dual beam scope with a tube vertical amplifier if I remember correctly.
                  I just checked the tekWiki site, it was the 556. What a behemoth! It needed a lot of work, but I found a taker who wanted to buy it. It was early on in my electronics adventure, and I had 2 extra plugins for it that I absolutely destroyed to raid for parts. I was dumb and didn't know the value, even if it was just for posterity. Those are where I saw Nuvistors for the first time. One thing I will say for it was what an awesome display of physical craftsmanship. The wiring was a sight to behold. no leaded solder used in the unit at all due to the ceramic terminals. Check out this site to see some really nice photos of one of the units:
                  Tektronix Type 556 Dual-Beam Oscilloscope

                  I just realized that the whole site is in German
                  still has some great photos.
                  If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

                  Comment


                  • #10
                    Originally posted by SoulFetish View Post
                    I've looked at the 7- series on the used market a couple of times. It's a bulky unit, but if you had a couple of different plugins that you could make use of often, it seemed worth the size. The unit must be a nightmare to lift though. I had a.. I can't remember. 556, maybe? it was a huge dual beam scope with a tube vertical amplifier if I remember correctly.
                    I just checked the tekWiki site, it was the 556. What a behemoth! It needed a lot of work, but I found a taker who wanted to buy it. It was early on in my electronics adventure, and I had 2 extra plugins for it that I absolutely destroyed to raid for parts. I was dumb and didn't know the value, even if it was just for posterity. Those are where I saw Nuvistors for the first time. One thing I will say for it was what an awesome display of physical craftsmanship. The wiring was a sight to behold. no leaded solder used in the unit at all due to the ceramic terminals. Check out this site to see some really nice photos of one of the units:
                    Tektronix Type 556 Dual-Beam Oscilloscope

                    I just realized that the whole site is in German
                    still has some great photos.
                    The Tek 7000 series scopes ARE typically 24" deep, but not that wide. At least the 3-plug-in mainframes. Their CRT's have the crispness much like your 556 had, but the full 8 x 10 CM screen, rather than the 6CM height those hybrid scopes were limited to. And, these aren't that heavy. Granted, much heavier than the small current technology digital scopes, which have a much smaller footprint overall.

                    Tektronix never did create a dedicated mainframe product similar to the TM500 series, that would allow the use of their 7000 series plug-ins in stand-alone or support roles to the 7000 series scopes. They do design those instrument to be packaged either horizontal (rack mount) or vertical. I've never looked into what it would take to turn a discarded 7000 series scope mainframe into such a product. The plug-ins are considerably deeper than the 5000 series/TM500 series plug-ins (both the same depth). Stand-alone 7A13 & 7A22 Differential Amplifiers would be a handy amplifier. They aren't a lot of money these days, so buying spares for parts is a good back-up plan.

                    YEP.....the build factor and quality of the 500 series scopes WAS something to behold. One of the reasons I held onto a few plugins and stand-alone power supplies. That 556 was their flagship. Twice what a 547 was, which is what I had owned, until the tunnel diode assembly failed, and I never tracked down a replacement to cure it. Mine had a 1A4 installed most of it's working life, and occasionally the Type W when I needed the differential probes/DC offset. Lifting a 556 is mus like lifting my LeCroy 7200A Digital scope, one of my stay-at-home projects, as it doesn't power up now.
                    Logic is an organized way of going wrong with confidence

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                    • #11
                      I would definitely go mainframe, if I came across a 7104 in great shape (at a great price). It would be cool to own the piece of gear that reached the analog/1GHz benchmark.
                      If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

                      Comment


                      • #12
                        Look at the speed of this op-amp Analog Devices LTC6268. In that package, almost makes you want to design a differential probe project, doesn’t it nickb?
                        .....what’s this? LTC6268_isoSPI_DiffAmp.asc
                        If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

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