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Re: [regenrx] Re: 10-turn Pots

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  • Paul Martin
    All, The problem with 10 turn pots (at least, the ones I’ve found) is that they are not truly linear. The resistance value has steps instead of a smooth
    Message 1 of 13 , Jul 1, 2011
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      All,
      The problem with 10 turn pots (at least, the ones I’ve found) is that they are not truly linear. The resistance value has steps instead of a smooth change in value as you turn the shaft. Still, it’s worth a try.

      From: Larry Beaty
      Sent: Thursday, June 30, 2011 9:37 AM
      To: regenrx@yahoogroups.com
      Subject: RE: [regenrx] Re: 10-turn Pots


      Bear,

      Great idea. Thinking outside the box. Now isn't that much better than a
      flame about this high?

      Larry

      From: mailto:regenrx%40yahoogroups.com [mailto:mailto:regenrx%40yahoogroups.com] On Behalf Of
      qrpbear
      Sent: Thursday, June 30, 2011 1:57 AM
      To: mailto:regenrx%40yahoogroups.com
      Subject: [regenrx] Re: 10-turn Pots

      Looking around at some of the projects I have built lately it's apparent the
      greatest cost factor has been air variables and vernier dials. I am
      seriously considering using varactors with 10 turn pots for tuning and
      regeneration control in my next project. Rather than using turns counting
      dials I am drawn to the idea of using one of the inexpensive 3-1/2 digit 20V
      LCD panel meters that are abundantly available on Ebay for about $10.
      Certainly not traditional but I can buy the varactors, 3 pots and a panel
      meter for about the same price that 70 year old National type B dials go for
      these days. For the price of a couple of air variables of indeterminate
      vintage and condition I can buy some really nice, new, large knobs and most
      of the other parts.

      Hmmm.... I can smell the solder melting already!!!

      73,

      'Bear' NH7SR

      [Non-text portions of this message have been removed]





      [Non-text portions of this message have been removed]
    • N1BUG
      I ve used my share of 10 turn pots in other applications... instrumentation, position sensor, etc. They have a linearity rating which can range from poor to
      Message 2 of 13 , Jul 1, 2011
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        I've used my share of 10 turn pots in other applications...
        instrumentation, position sensor, etc.

        They have a linearity rating which can range from poor to excellent.
        Pots with 5% linearity are likely to be disappointing in any
        precision application or where very smooth adjustment is required.
        Even 1% can be annoying or an outright disaster in precision
        instrumentation applications. 0.25% and 0.1% linearity units are
        much better, though somewhat more costly. I found a box of 10 turn
        pots with these better linearity ratings at a hamfest once for a
        very attractive price.

        73,
        Paul N1BUG


        On 7/1/2011 7:54 AM, Paul Martin wrote:
        > All, The problem with 10 turn pots (at least, the ones I’ve
        > found) is that they are not truly linear. The resistance value
        > has steps instead of a smooth change in value as you turn the
        > shaft. Still, it’s worth a try.
      • Graeme Zimmer
        Pail, ... I think you are confusing Linearity with Resolution (also refered to as Granularity ). The element in most 10 turn pots consists of very fine
        Message 3 of 13 , Jul 1, 2011
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          Pail,

          >The problem with 10 turn pots (at least, the ones I’ve found) is that they
          >are not truly linear.

          I think you are confusing Linearity with Resolution (also refered to as
          "Granularity").

          The element in most 10 turn pots consists of very fine resistance wire wound
          on a long insulating inner core, which itself is wound into a 10 turn coil.
          Because of this construction, it is pretty much impossible to make a 10T pot
          which is anything but highly linear. The wiper does however hop from wire to
          wire, which causes incremental jumps in resistance or "granularity".

          The best 10t pots are the old style ones which are physically much larger.
          These old pots were about 2 inches in diameter and about 3 inches long. They
          were often used in analog computers and similar. The larger size allows for
          much smaller steps (finer resolution).

          Many of the modern multi-turn trimmers are actually a single-turn pot fitted
          with an internal worm-gear drive.

          I'm being a bit pedantic about this because the term "Linearity" is normally
          reserved for the "taper" of the pot (e.g. Log v/s Linear, etc).

          ................. Zim.
        • N1BUG
          You re correct, of course. Linearity wouldn t really matter for his application, granularity might. My comments earlier are thus mostly irrelevant, although my
          Message 4 of 13 , Jul 1, 2011
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            You're correct, of course. Linearity wouldn't really matter for his
            application, granularity might. My comments earlier are thus mostly
            irrelevant, although my experience has been the 10 turn pots with
            better linearity also have less granularity. I'm quite fond of the
            older, larger ones with 0.1% linearity ratings. They are very smooth
            with minimal granularity - at least, all the ones I've encountered
            so far were.

            I once bought some new, smaller 1% rated linearity pots (1" diameter
            by 1 inch long, approximately) for a project and had to give up on
            using them. The granularity was horrible.

            73,
            Paul


            On 7/1/2011 9:46 AM, Graeme Zimmer wrote:
            > I think you are confusing Linearity with Resolution (also refered to as
            > "Granularity").
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