50K RA Vibrato pot with On-Off switch?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Figaro, Mar 28, 2020.

  1. Figaro

    Figaro Supporting Member

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    Where can I buy an 50K RA pot with an On-Off switch in the USA to disconnect the Vibrato on a Fender for a slight gain boost? The only one I’ve found online is From Tube Amp Doctor in Europe.
     
  2. Jeff Gehring

    Jeff Gehring Silver Supporting Member

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    Why bother with chasing unicorns? Since the effect of lifting the tremolo is a gain boost, why not implement it as a pull switch on the 1M audio taper volume pot? You can find those easily, like this CTS one at Antique Electronic Supply.
     
  3. Figaro

    Figaro Supporting Member

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    It’s a later silverface VR so could I just used the stock 1M volume pot that has the on-off switch for the boost? Thanks
     
  4. Jeff Gehring

    Jeff Gehring Silver Supporting Member

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    Sure, all you need is an available SPST switch contact closure. You'd need to remove the existing pull-boost wiring to the switch of course.
     
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  5. pdf64

    pdf64 Member

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    And hard wire it closed or open, according to your preference :)
    ie short out that 1k resistor for the boost to be off.
     
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  6. Figaro

    Figaro Supporting Member

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    I will disconnect the boost. It sounds terrible and very thin.

    Thanks for the help!
     
    Last edited: Mar 28, 2020
  7. doctorx

    doctorx Member

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  8. Figaro

    Figaro Supporting Member

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    What did you use it for in a blackface Bassman?
     
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  9. doctorx

    doctorx Member

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  10. Figaro

    Figaro Supporting Member

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    A Bassman does not have vibrato (tremolo).
     
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  11. gerrickreidenbach

    gerrickreidenbach Member

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    That's one hell of a Bassman.
     
  12. doctorx

    doctorx Member

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    My bad, you're right, I meant Bandmaster.
     
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  13. gldtp99

    gldtp99 Member

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    Ok, now that makes sense---- :cool::cool::cool:

    I just ran into the other room to see if my '66 BF Bassman had suddenly grown a Tremolo circuit.

    It hadn't but the Tremolo circuits were still in place on my BF Bandmasters and Showman (Showmen?) amps.

    Even my '64 Blonde Blackface AA763 Showman (w/7355 output tubes) still had a Tremolo circuit----- but it still has no Mid pot unlike the much more common BF 6L6GC Showman amps.

    Yes, i'm pretty bored--- :rolleyes:o_O
     
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  14. Roe

    Roe Member

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    I replaced the 50ka pot (with switch) and got a 100k instead. the switch is very abrupt. a 100ka is better
     
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  15. Roe

    Roe Member

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    the difficulty is finding a 100KRA pot. A linerar pot works but isnt ideal
     
  16. Figaro

    Figaro Supporting Member

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    Does the 100K pot gradually remove the ground and if so, do you still need the switch?
     
  17. pdf64

    pdf64 Member

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    Doubling the trem depth pot value halves the load on the preceding stage, thereby allowing it to develop another ~3dB gain. That pretty much removes the need / benefit of switching the pot out.
     
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  18. Figaro

    Figaro Supporting Member

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    So is a 100K pot at maximum exactly the same as disconnecting the vibrato (tremolo)?
     
  19. pdf64

    pdf64 Member

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    No, but following the Pareto principle, it's probably near enough for most.
    It's a while since I took comparative measurements but roughly, switching the 100k pot out would provide about another 1db gain, thereby making a switch there somewhat too subtle in its effect for most folk.
    If going to the bother of making something switchable, it's usually seen to be necessary for the different switch modes to make a noticeable difference. That may usefully be approximated to a 3dB change in a significant parameter / characteristic.
     
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  20. Figaro

    Figaro Supporting Member

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    Would a higher value pot (250K?) at maximum be the same as disconnecting the trem?
    If not, I’ll probably just use a switch. Disconnecting it really doesn’t make a big difference. I might make it footswitchable since my late silverface Fender VR already has a footswitch jack for the boost. I think this boost will be better than the original. ;)
     
    Last edited: Mar 29, 2020

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