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    Multiple turn trimpots

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    j beede

    Posts : 458
    Join date : 2011-02-07
    Location : California

    Multiple turn trimpots

    Post by j beede on Sun Apr 22, 2018 3:29 pm

    I wonder why multi-turn PCB trimpots aren't commonly used to set cathode bias current? Cost, physical size and power dissipation don't seem to be issues. I suspect it has to do with their failure modes. What has your experience been?
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    Peter W.

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    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: Multiple turn trimpots

    Post by Peter W. on Mon Apr 23, 2018 8:46 am

    j beede wrote:I wonder why multi-turn PCB trimpots aren't commonly used to set cathode bias current? Cost, physical size and power dissipation don't seem to be issues. I suspect it has to do with their failure modes. What has your experience been?

    A couple of things:

    a) Cost: For us, the hobbyist, the difference between a $0.90 part and an $1.95 part is negligible. Times 1,000 units, not so much.
    b) And, here is a good example of the difference between 'accuracy' and 'precision'. Setting bias need only be accurate. Precision is wasted. So, a pot that has enough range to be accurate is all that is required.

    If we wish to populate our equipment with "better" parts, that is a great idea, and I am as guilty as anyone else along those lines. But, let's be sure that those parts we use are appropriate to the use and do not introduce needless complexity instead.
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    tubes4hifi
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    Re: Multiple turn trimpots

    Post by tubes4hifi on Mon Apr 23, 2018 11:25 pm

    in my experience, a $2 or $3 multi-turn pot will very often fail after being turned to one extreme or the other, and where is the end of turning???
    I've never had a $1 single turn pot fail, and it has the same adjustment range, and I'd rather turn one 10 degrees than 4 or 5 360 degree turns.
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    j beede

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    Join date : 2011-02-07
    Location : California

    Re: Multiple turn trimpots

    Post by j beede on Tue Apr 24, 2018 1:19 am

    My application would benefit from the narrow width of four multi turn pots mounted side-by-side. My suspicion is that there is a reason why these pots are not commonly used. tubes4hifi addressed the issue that I was trying to raise.
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    CletusB

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    Join date : 2018-02-11
    Age : 63
    Location : Trinidad & Tobago

    Re: Multiple turn trimpots

    Post by CletusB on Tue Apr 24, 2018 5:34 am

    tubes4hifi wrote:in my experience, a $2 or $3 multi-turn pot will very often fail after being turned to one extreme or the other, and where is the end of turning???  
    I've never had a $1 single turn pot fail, and it has the same adjustment range, and I'd rather turn one 10 degrees than 4 or 5 360 degree turns.
    Yup!

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