Fender Princeton Vibrato - Weak?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by vds5000, Dec 22, 2009.

  1. vds5000

    vds5000 Member

    Messages:
    2,009
    Joined:
    Mar 6, 2008
    Does anyone know if the vibrato on a vintage Princeton is supposed to be significantly more subtle than the vibrato on a Vibro Champ? Or is there something wrong with the amp?
     
  2. TweeDLX

    TweeDLX Member

    Messages:
    3,778
    Joined:
    Mar 24, 2008
    Location:
    Port Angeles, Washington
    My SFP(NR) doesn't seem "subtle", but I don't have a VC to compare it to. :)
     
  3. mbratch

    mbratch Member

    Messages:
    2,390
    Joined:
    Nov 3, 2003
    Location:
    Webster, NY
    The NR Princeton probably has the weakest tremolo of the whole Fender line. It should be fairly sweet, and moderately decent at 10, but it's not as deep as a Vibro Champ. There are after market mods that richen the tremolo.
     
  4. vds5000

    vds5000 Member

    Messages:
    2,009
    Joined:
    Mar 6, 2008
    Well, maybe 'weak' is a bit of an understatement. I'd say the Intensity on 10 (Princeton) is comparable to the Intensity on 2 (VibroChamp). Any ideas? I wonder if it's a tube issue?
     
  5. mark norwine

    mark norwine Member

    Messages:
    15,953
    Joined:
    Jul 25, 2005
    Location:
    NJ...GSP135
    A simple glance at the schematics clearly show that the bias schemes for these 2 amps are totally different: VC modulates bias on the driver tube while the PR modulates the bias on the power tubes. To hypothesize "what might be wrong" with one or the other because they sound different is silly. They're entirely different circuits!

    If you want to pulse the PR harder, decrease the 1M resistor that bridges the oscillator plate to the intensity control. You may get "helicopters", though. A back-biased diode spanning the intensity pot can help that [if needed]. It functions to shunt the positive oscillations to ground; this allows the power tubes to be driven to cutoff, but not saturation. As a habit, I do this to most bias-trem amps.

    edit: The above suggestion assumes your amp to be healthy in the first place. If the oscillator's cathode bypass cap is old & dry, you'll loose gain....eventually you won't oscillate at all. Is your cap new(er)?
     
    Last edited: Dec 23, 2009
  6. mbratch

    mbratch Member

    Messages:
    2,390
    Joined:
    Nov 3, 2003
    Location:
    Webster, NY
    As pointed out in the referenced thread, it could be due to a weak tremolo tube or indicate a need for power tube bias adjustment.
     

Share This Page