Fender Super Bassman Tube Layout

[negativefx]

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

 

[B-string]

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.

 

[tombowlus]

Tom Lees included a full schematic in his Link Removed.

 

[B-string]

Didn't find a full schematic, only a block diagram?

 

[negativefx]

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.

 

[negativefx]

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

 

[jeffmaxwell]

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."