Fender blues jr. Reverb & master volume 50k audio taper pot DISCONTINUED? HELP!

Discussion in 'Amp Central Station' started by jonmichael02302, Sep 11, 2016.

  1. jonmichael02302

    jonmichael02302 TDPRI Member

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    I'm in the middle of modifications on my FBJR 2003 cream board & it's calling for swapping out the master volume & reverb pots to 50k audio taper. Only problem is, the brilliant and lovely technical genius' at Fender discontinued 50k audio taper pots. Now you can only get them in 250k & 1m.... (unless you want to pay $27 plus shipping per pot from some generous gentleman in London, which... WILL NEVER HAPPEN).
    Could somebody please tell me which, if any, of the two audio taper pots available i can substitute for the 50k? Could i use a 250k or 1m instead? Will either of the two suffice?
    Thank you guys!
     
  2. Darkness

    Darkness Tele-Afflicted

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    Are you trying to replace a pcb mounted pot? Can you not get a panel mounted 50k audio taper and use flying leads to the pcb? I'm asking because a quick Google search showed several sources for through hole mounted pots in the spec you need.
     
  3. jonmichael02302

    jonmichael02302 TDPRI Member

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    Yes, the Blues Jr has cheap pots that mount directly to the board. Two large connections on the outer ends with 3 smaller ones in the middle. I thought about wiring it to the board but a lot of people & on billm site he advises against it.
     
  4. muchxs

    muchxs Doctor of Teleocity

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    Read the entire post 'cuz I'm thinkin' out loud.


    I checked Antique Electronics Supply first. Quick searched "50k" 'cuz I don't feel like lookin' at eight pages of pots.

    https://www.tubesandmore.com/search/node/50k?cats[0]=147

    AES P/N

    R-VSN-50KLD-DS

    is close. It's a 50k linear snap- in style pot. It's AES item #

    003926

    https://www.tubesandmore.com/products/potentiometer-50k-linear-d-shaft-16mm-snap-w-detent

    At $1.25 each you're not gonna go broke. Order half a dozen of them.

    Here's the thing: When you identify the manufacturer via the EIA code on the part you can dismantle one and re- load it with a 50k audio taper element. For that matter you could re- load one of your stock pots.

    It's like jewelry. Carefully bend the little tabs and take it apart. Bend 'em back when you put it back together.


    I checked Mojotone's three pages of pots and came up dry. No "snap in" style pots there.


    Returning to AES's site, I found AES item #

    R-VSN-100KA-SS

    That's a 100ka snap- in style. You could try that.

    https://www.tubesandmore.com/products/potentiometer-audio-solid-shaft-snap-16mm


    Oooh, waidaminnit. Here we go!

    https://www.tubesandmore.com/products/potentiometer-audio-d-shaft-16mm-snap-w-bracket

    AES Item #

    R-VSN-50KA-DS

    is 50k audio snap- in D-shaft.

     
    Last edited: Sep 12, 2016
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  5. jazzguitar

    jazzguitar Tele-Afflicted

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    If that is unavailable you could always use a 100k audio pot and a 100k resistor in parallel.
     
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  6. MatchlessMan

    MatchlessMan Tele-Holic

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    Also a 47k pot will work just as well, so that's another option.
     
  7. jonmichael02302

    jonmichael02302 TDPRI Member

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    It amazes me the kindness shown in this group. The time people take from their lives to reach out to help total strangers.
    As far as taking these pots apart, I don't trust myself but hopefully that last link will work! I can't thank you guys enough for all of your help.
     
  8. jonmichael02302

    jonmichael02302 TDPRI Member

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    How would I do this? Meaning, how &/or where do I solder the resistor?
     
  9. jazzguitar

    jazzguitar Tele-Afflicted

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    You connect the control pot as usual, the resistor then goes to the two outer terminals of the pot, one wire each.
     
  10. jonmichael02302

    jonmichael02302 TDPRI Member

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    AWESOME! And this would make it a 50k audio taper? No difference in performance either?
    Just to reconfirm, blues jr pots solder directly to the pcb and there's 5 solder joints, two bigger joints to the rear & 3 smaller in front. I'm focusing on the three smaller joints & solder to the two terminals i drew the red arrows to (see attached photo)? [​IMG]
     
    Last edited: Sep 18, 2016
  11. jonmichael02302

    jonmichael02302 TDPRI Member

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    Nevermind guys, I guess fender is a bigger joke than I thought. Why they would discontinue a 50k audio taper pot is beyond me but I guess they don't have 100k audio either. I did find a place that has a few 50k audio taper but they're asking $15 plus shipping each. No way am I paying $20 for a $3 pot. I guess I'll scratch the audio taper reverb and only do the master volume. Any suggestions?
     
  12. edvard

    edvard Tele-Afflicted

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    This may be a bit too much reading, but whenever anybody asks a question like this, I always point them to this article, and it's never let me down:
    Geofex: The Secret Life of Pots
    http://www.geofex.com/Article_Folders/potsecrets/potscret.htm

    Basically he breaks down what an audio taper pot REALLY is (it's not quite what you think unless you shell out some serious cash), and the best way to make do (better) with a linear pot and a resistor. Doing things this way is going to have a different load on the driving circuit, but here's the method I've used many times for getting the best approximation:

    Take the original pot value (in your case 50k) and multiply by 1.5 to 2; that's the value of your tapering resistor. Now, multiply that by any number between 4 and 6 that gets you closest to the resistance of a readily-available linear pot. Connect the resistor between the left lug (with the shaft pointed towards you) and the middle lug. So for your case, connect any resistor between 75k to 100k to a 500k linear pot, and you have a 50k audio taper (or at least a reasonable facsimile).
     
  13. jonmichael02302

    jonmichael02302 TDPRI Member

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    So amazing you posted this link, i started to read this article last night but got unexpected company & forgot to finish reading it! But I took a screen shot of your suggestion so i can memorize it. Just SIMPLY BRILLIANT! I LIVE FOR THIS KIND OF STUFF! So very nice of you to share this. Thank you!
     
  14. jonmichael02302

    jonmichael02302 TDPRI Member

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    Edvard, looks like fender only makes 250k linear pots so just to be sure I get this right, in order to make this a 50k audio taper, take the same values from the 500k and divide that by 2? Basically cut it in half.... so instead of soldering a 100k resistor, I use a 50k resistor on a 250k pot?
    Sorry if I'm confusing anyone, I'm just desperately trying to learn & most importantly, get this amp put back together. I haven't played in a week & I'm having withdrawals. Lol
    Thank you edvard
     
    Last edited: Sep 21, 2016
  15. edvard

    edvard Tele-Afflicted

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    That would get in the ballpark, yes. Not optimal, but might do the trick anyway. The curve will be right, but when it's full up, you might lose some volume; here's why:

    When you have the volume up all the way on a 'real' 50k pot, the pot is a 50k load to ground. When using a tapering resistor, it'll be 50k in parallel with the 250k, which works out to roughly 42k, give or take the tolerance. What that means is you may or may not have as much volume as before, but it's probably close enough. If there is a substantial volume reduction, then try a larger value tapering resistor; somewhere between 50k and 75k. Keep in mind that the larger the tapering resistor, the shallower the "logarithmic" effect.
     
  16. jonmichael02302

    jonmichael02302 TDPRI Member

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    This is all so fascinating to me, thank you. It might behoove me to try a 60k resistor then, just to get closer to that 50k mark? Makes sense to me but man, what an AWESOME learning experience this has been.
    Now that I think of it, what if I only try this on the reverb control & go ahead & pull the trigger & spend the $15 bucks & buy the 50k audio taper for the master volume pot only. This way I'm not sacrificing any volume.... Worst case scenario, I'll switch the reverb control back to linear if need be.
    I can't thank you enough for all of your help Edvard.
     
    Last edited: Sep 22, 2016
  17. edvard

    edvard Tele-Afflicted

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    Hey, don't thank me until the solder is cool. Then fiddle with it a bit and let your ears be the judge.

    I'd probably buy the 50k pot as well, just to have peace of mind that I'm not losing anything. Have you tried some of the surplus electronics outlets? There are folks out there that buy up manufacturer's batch remainders and blow them out. I used to have a list on a piece of paper somewhere, but nowadays, I just search for "surplus electronic parts" and then search from the sites that come up. Individual components don't stay in their stores long enough to show up on Google.
     
  18. jonmichael02302

    jonmichael02302 TDPRI Member

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    Oh man that hurt.... $23 for one 50k audio taper pot. Worth the piece of mind i guess. I'll skip doing the reverb control pot for now. I can always go back and do it if need be. Way too many road blocks any other way. STORY OF MY LIFE! LOL. I just want to get this thing put back together. The last two things needed now are a new set of tubes.. & a speaker... Any suggestions? What a journey this has been but i have to admit, i learned a lot & loved every minute of it! I'll let you know the end result asap!
     
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