Fender Super Bassman Tube Layout

Discussion in 'Amps [BG]' started by negativefx, Nov 27, 2013.


  1. negativefx

    negativefx complete hack Gold Supporting Member

    Joined:
    Feb 18, 2013
    Location:
    Fort Collins
    Does anyone have specifics on the function that V3 (AX7) and V4 (AT7) serve in the Super Bassman? I'm guessing the AT7 is a phase inverter but what about V3? According to the block diagram, the loop is not tube buffered. Block diagram shows an out arrow from the autobias to V4 but not to V3.

    Here's what I have so far:

    V1 - First gain for overdrive channel, first and 2nd gains for vintage.
    V2 - 2nd gain for overdrive channel
    V3 - ???
    V4 - phase inverter?
    V5-10 - power
  2. B-string

    B-string Supporting Member

    Joined:
    Nov 21, 2008
    Location:
    Lake Havasu City, Az USA
    Just from Fender's description on tube use I would hazard the guess V3 is the driver tube.
    "power amp (one 12AX7, one 12AT7, six 6550s)" V4 being used only as the PI not a combo Driver/PI.
  3. tombowlus

    tombowlus If it sounds good, it is good Gold Supporting Member

    Joined:
    Apr 3, 2003
    Location:
    North central Ohio
    Disclosures:
    Editor-in-Chief, Bass Gear Magazine
  4. B-string

    B-string Supporting Member

    Joined:
    Nov 21, 2008
    Location:
    Lake Havasu City, Az USA
    Didn't find a full schematic, only a block diagram?
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  6. negativefx

    negativefx complete hack Gold Supporting Member

    Joined:
    Feb 18, 2013
    Location:
    Fort Collins
    That's the block diagram out of the Fender manual. Doesn't explain the function of V3 and V4 but I suspect you're right that it's the driver tube.
  7. negativefx

    negativefx complete hack Gold Supporting Member

    Joined:
    Feb 18, 2013
    Location:
    Fort Collins
    According to the BGM article, both V3 and V4 are phase inverters.

    V1 - First gain for overdrive channel, first and 2nd gains for vintage.
    V2 - 2nd gain for overdrive channel
    V3 - Phase inverter
    V4 - Phase inverter
    V5-10 - power
  8. jeffmaxwell

    jeffmaxwell Gold Supporting Member

    Joined:
    Oct 8, 2007
    Location:
    San Diego, CA
    Disclosures:
    owner, Silver Hammer Designs
    here's what the manual says

    "The tube front end is comprised by tube V3
    (12AX7) which receives signal from the preamplifier
    at grid of V3-B and global feedback signal to the
    grid of V3-A. This push-pull amplifier stage drives
    cathode follower V4 (12AT7) which drives the grids
    of the six (6) 6550 power output tubes operating as
    3 parallel push-pull pairs V5&V6 (1A/1B), V7&V8 (2A/2B),
    and V9&V10 (3A/3B). The output tube bias
    (automatically controlled by Fender Automatic Bias)
    is fed through R219-221 to the grids of V4-A and
    V4-B."

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