The Dynaco Tube Audio Forum

Would you like to react to this message? Create an account in a few clicks or log in to continue.
The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all Dynakitparts.com products


4 posters

    Multiple turn trimpots

    j beede
    j beede


    Posts : 473
    Join date : 2011-02-07
    Location : California

    Multiple turn trimpots Empty Multiple turn trimpots

    Post by j beede 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?
    Peter W.
    Peter W.


    Posts : 1351
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Multiple turn trimpots Empty Re: Multiple turn trimpots

    Post by Peter W. 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.
    Roy Mottram
    Roy Mottram
    Admin


    Posts : 1840
    Join date : 2008-11-30

    Multiple turn trimpots Empty Re: Multiple turn trimpots

    Post by Roy Mottram 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.
    j beede
    j beede


    Posts : 473
    Join date : 2011-02-07
    Location : California

    Multiple turn trimpots Empty Re: Multiple turn trimpots

    Post by j beede 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.
    CletusB
    CletusB


    Posts : 234
    Join date : 2018-02-11
    Age : 68
    Location : Trinidad & Tobago

    Multiple turn trimpots Empty Re: Multiple turn trimpots

    Post by CletusB 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!

    Sponsored content


    Multiple turn trimpots Empty Re: Multiple turn trimpots

    Post by Sponsored content


      Current date/time is Thu Mar 28, 2024 6:33 am