Bias Adj Pot Help

Discussion in 'The Projects Forum' started by dubs0587, Sep 10, 2013.

  1. dubs0587

    Thread Starter New Member

    Sep 10, 2013
    I have a Fender Hot Rod Deville. I installed new power tubes so I needed to adjust this bias. As I began to turn the trim pot, the guts fell out.

    The internal pad just fell apart.
    The trim pot removed.
    The underside of the pcb where the trim pot is located.
    PIN Layout.jpg

    The #2 terminal of the trim pot is connected to two circuit points, as shown in the image. Why? Is it for heat dissipation? The design of the circuit for the desired trim pot? Could a 3 terminal device be used in place of the poor quality 4 terminal trim pot? I appreciate any input!
  2. bountyhunter

    Well-Known Member

    Sep 7, 2009
    The #2 terminals provide the physical mounting of the device, hence they are as shown. Pot should not need a heatsink.

    I believe you could substitute any similar value pot, make sure you know whether it's linear or log type.
    dubs0587 likes this.
  3. apprenticemart2


    May 7, 2013
    dubs0587 likes this.
  4. dubs0587

    Thread Starter New Member

    Sep 10, 2013
    It's linear type. I can't seem to find anything with similar dimensions. I could jimmy rig something with long enough leads, but that's proving to be very challenging.
  5. MrChips


    Oct 2, 2009
    That is a common type of trim pot. The two solder tabs are for mounting to the PCB.

    How the heck did all four solder connections come loose?

    1) It was not so soldered in properly in the first place?
    2) Heat from the tubes caused the solder to melt?

    You need to try and figure out why the trim pot came off.
  6. dubs0587

    Thread Starter New Member

    Sep 10, 2013
    I unsoldered the trim pot from the pcb. I was simply using the images as a reference to my question. My issue is finding a higher quality trim pot, preferably within 1% tolerance, that I can jimmy rig it onto the pcb since I can't find anything similar to the stock trim pot.