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Trimmer pots and resistance values

Discussion in 'Electronic Basics' started by max-man, Oct 29, 2005.

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  1. max-man

    max-man Guest

    I need to get hold of a 1.5K trimmer pot for an old arcade game
    monitor but cannot find one of this value anywhere. Seeing as it's
    essential that I use 1.5K but the closest that I can find is 1K or
    2.5K, is there any way that I could modify, for example, a 1K pot with
    a 0.5K resistor to give the correct value, or won't that work seeing
    as it would be external to the pot and wiper?
     
  2. John Fields

    John Fields Guest

    ---
    Depends.

    If you need one end of the control to look like zero ohms and the
    other end to look like 1.5k, and the pot is wired like a rheostat,
    that's one requirement.

    If it's wired like a voltage divider, that's another.

    However, if all you need is a trimpot and all you can get is a
    2.5kohm unit, and you need a rheostat, solder it in and trim it up
    until it looks like 1.5K and you should be fine.

    If not, post back and I'm sure at least one of us will be happy to
    help you out.
     
  3. max-man

    max-man Guest

    Thanks. I should have said that all three pins of the pot are used so
    I assume that makes the pot value even more critical?
     
  4. Chris

    Chris Guest

    Hi, Max. I kind of wish you'd have given some more information on the
    circuit, and how your trimmer is being used.

    Anyway, there are a number of things you can do. First, 2K is actually
    very common for trimmers -- check the Digi-Key catalog. Since many
    pots are rated at +/-20%, the high end of the tolerance might be close
    enough. You might want to try it.

    Another thing you can do if it's being used as a voltage divider is to
    put a 5.6K 5% resistor across the legs of the pot. The total
    leg-to-leg resistance will then be almost 1.5K, and the wiper will
    scroll across the right voltage range.

    .-----o
    | |
    | |
    .-. .-.
    5.6K | | | |<--
    | | | |
    '-' '-'2K
    | |
    | |
    '-----o
    created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de


    If you don't need the top 1/3 of the range, you might want to put a 510
    ohm resistor in series with a 1K pot. This would have some value for
    some applications.


    o
    |
    .-.
    510| |
    | |
    '-'
    |
    |
    .-.
    1K| |<--
    | |
    '-'
    |
    o
    created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de


    If you absolutely, positively have to have exactly 1.5K, and nothing
    else will do, you might want to contact some manufacturers' reps, and
    ask for a couple of samples. You'd be amazed at what a well-placed
    request from a one-man engineering firm needing a sample for a
    potentially good volume prototype can do.

    Good luck
    Chris
     
  5. Guest

  6. max-man

    max-man Guest

  7. max-man

    max-man Guest

    <snip>

    Excellent, many thanks. :)
     
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