5F11 tweed Vibrolux - tremolo question

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Figaro, Apr 2, 2015.

  1. Figaro

    Figaro Supporting Member

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    On my 5F11 tweed Vibrolux, you can still hear the tremolo a little even when the intensity control is turned all the way down. The only way I can get it off is to connect the footswitch and turn it off. Is this normal for this circuit?
     
  2. RiftAmps

    RiftAmps Member

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    Yes, the trem on these amps (same goes for the VibroChamp and Princeton Reverb) is always 'ON', you need to disconnect it with a footswitch.
     
  3. Figaro

    Figaro Supporting Member

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    With a PR and VC the tremolo is available, but it does not function when the Intensity control is turned all the way down. Why do I still hear it on this 5F11 Vibrolux?
     
  4. pdf64

    pdf64 Member

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  5. swiveltung

    swiveltung Member

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    I think that is a tube bias tremolo, that's why you hear it a little if not using a switch right?
     
  6. Figaro

    Figaro Supporting Member

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    Yes, tube bias tremolo, like the later brown Princeton, blackface Princeton Reverb, etc... so I'm thinking it shouldn't work when the Intensity control is turned all the way down.

    pdf64, thanks but it's a 2013 clone so a cap shouldn't be the problem.
     
  7. Jeff Gehring

    Jeff Gehring Silver Supporting Member

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    That cap determines how close to signal ground the impedance at the low side of your trem pot gets, for the tremolo waveform. If it's not a near-zero ohms impedance, the cap will act as another impedance "under" the trem pot low side, and you'll get tremolo when the pot is at its minimum setting...

    If the clone was built in slavish adherence to the original schematic, that's a 25uF/25V cap there. As has pdf64 mentioned, the voltage rating should be bumped up to 50V or so, and it wouldn't hurt to increase the capacitance to at least 50uF to help the problem you mentioned.
     
  8. Figaro

    Figaro Supporting Member

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    Thanks! That's the info I needed. I will check that cap and replace it with a 50/50 it's a 25/25.

    Also, which power transformer should a 5F11 have? This clone has a Mojotone model 760EX PT, which the description says is for a BF Princeton/Champ. This amp just seems a little underpowerd. Is that the correct one? If not, what would be the best one for a 5F11?
     
    Last edited: Apr 3, 2015
  9. RiftAmps

    RiftAmps Member

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    Your transformer is 330-0-330v whereas I use a 325-0-325v for my 5F11. Your one is slightly overpowered if anything.
     
  10. Figaro

    Figaro Supporting Member

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    But the Mojotone tweed Vibrolux model 757 PT is 350-0-350v? The original 5F11 layout shows 340v on the plates so I wonder how many volts the original PT had?
     
    Last edited: Apr 4, 2015
  11. RiftAmps

    RiftAmps Member

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    The originals used the same transformer as a Tweed Harvard which was a 275-0-275 (I seem to remember, could be wrong).

    The 5F11 works better with around 370v on the plates so that's why people are now using higher voltage transformers.
     
  12. Figaro

    Figaro Supporting Member

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    Thanks Riftamps! I checked it's plate voltage and it's 380v so the Mojotone 757 PT would make it over 400v. Closer to a Deluxe, which I don't think would be a bad thing.
     

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