Weak Tremolo on AA964 Princeton

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by mbratch, Mar 4, 2006.

  1. mbratch

    mbratch Member

    Messages:
    2,390
    Joined:
    Nov 3, 2003
    Location:
    Webster, NY
    Just picked up a 64 Princeton amp, and the tremolo (vibrato) is very weak. Up to 10 intensity it's just on the edge of usable. Is this typical of these amps? If not, what do you think the cause of the problem is?

    Here's a sound clip illustrating the problem. The first sequence is my 64 Princeton with intensity at 10, speed at 1. The second sequence is my 68 Vibro Champ with the same settings.
     
  2. mbratch

    mbratch Member

    Messages:
    2,390
    Joined:
    Nov 3, 2003
    Location:
    Webster, NY
    Added a clip sample.
     
  3. brad347

    brad347 Member

    Messages:
    4,814
    Joined:
    Feb 8, 2006
    Location:
    Brooklyn, NY
    open it up... can you see the neon bulb flashing inside the black bulb/photoresistor assembly?
     
  4. Blue Strat

    Blue Strat Member

    Messages:
    30,036
    Joined:
    Aug 2, 2002
    Location:
    Sterling, VA (not far from Washington DC)
    The PRs with weak tremolos that I've seen were due mostly to VERY "hotly" biased power tubes. If you back off the bias to around 20mA the trem intensity will likely increase.
     
  5. Blue Strat

    Blue Strat Member

    Messages:
    30,036
    Joined:
    Aug 2, 2002
    Location:
    Sterling, VA (not far from Washington DC)
    There's no "bug" in Princetons. They use a bias modulation technique instead.
     
  6. brad347

    brad347 Member

    Messages:
    4,814
    Joined:
    Feb 8, 2006
    Location:
    Brooklyn, NY
    Cool. I wondered that when I saw your previous post. Thanks for the tip.

    That's why I like this board, an amp novice like me learns a lot. If I've never owned an amp, I sure don't know what's inside it.

    :BEER
     
  7. mbratch

    mbratch Member

    Messages:
    2,390
    Joined:
    Nov 3, 2003
    Location:
    Webster, NY
    I was looking at schematics and noticed the the trem in Vibro Champs and Deluxe Reverbs use two triodes. The Princeton only uses one triode. Never noticed that before.
     
  8. Blue Strat

    Blue Strat Member

    Messages:
    30,036
    Joined:
    Aug 2, 2002
    Location:
    Sterling, VA (not far from Washington DC)
    Neither did anyone else. There are no diodes in any of these circuits.

    There's a diode in the bias power supply which feeds the trem circuit in Princeton's Deluxes and larger Fenders with Trem.

    I'm trying to figure out where you're seeing a 2nd diode in any Fender amp with a tube rectifier.
     
  9. mbratch

    mbratch Member

    Messages:
    2,390
    Joined:
    Nov 3, 2003
    Location:
    Webster, NY
    That's TRIODE (1/2 12AX7) not DIODE. :)
     
  10. Blue Strat

    Blue Strat Member

    Messages:
    30,036
    Joined:
    Aug 2, 2002
    Location:
    Sterling, VA (not far from Washington DC)
    D'OH! Time for an eye (and brain) exam. Sorry 'bout that!:D
     

Share This Page