Fender Super Bassman, Owner'S Manual

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The Super Bassman® uses the following types of tubes:
Pre-Amplifier: Two 12AX7A tubes (V1, V2)
(Upper Chassis, bottom view)
Power Amplifier: One 12AX7A tube (V3), One 12AT7 tube (V4), and Six
6550C power tubes (V5, V6, V7, V8, V9 and V10)
(Lower Chassis, top view)
If your amplifier is not performing as it should, refer to the
Troubleshooting section below. Generally speaking with most tube
audio amplifers the tubes are the most likely thing to fail and may
be replaced without taking your amplifier to a qualified service
technician. If any tubes need replacing, carefully read and follow
these steps. If you do not feel comfortable replacing your amplifier's
tubes, take it to an authorized Fender service center. All other service
needs should be refered to an authorized Fender service center. There
are no user serviceable parts inside the electronics chassis. Lethal
voltages exist inside your tube amplifier! Tube amplifier components
get very hot! Failure to follow all these instructions may result in
damage to your amplifier, or personal injury!
How to Replace the Tubes on your amplifier:
1) If Fender Automatic Bias indicated a tube failure, make a note of
which tube(s) failed. NOTE: Bad tubes will remain displayed as
bad until they are replaced, even if the power is cycled on/off.
2) Turn off the amplifier and remove the power cable from the IEC
inlet {O}. You might also want to disconnect other cables (such as
the speaker, line-out, effects loop, etc) so that they are not in the
way.
3) Caution! The tubes and transformers get very hot during
operation, and may cause burn injuries. Wait for the amplifier to
cool down before proceeding to step
4 .
4) After the amplifier has cooled down, to gain access to the
preamp tubes use a #2 Phillips screw driver to remove the 4
nickel screws holding the front grille underneath the front panel
controls. Power amp tubes can be accessed by using a Phillips
screwdriver to remove the 5 black screws holding the rear metal
grille. Remove the grille slowly and disconnect the connector for
the FAN wires.
5) You now have access to all of the tubes. Preamp tubes have metal
shields that must be twisted and pulled down to remove them.
Pull the tubes straight down to remove them. The small driver
tubes near the power tubes have no shields and may simply be
pulled straight up to remove them. The power tubes each have
a top retainer ring (and insulating washer) held down by springs.
Gently lift each retainer up pull it over the tube and off to the
side. Pull the tubes straight upward to remove them and avoid
rocking them side-to-side to prevent breakage. They should be
somewhat difficult to remove.
Caution: Excessive side-to-side
motion could cause the Locator-Pin on the bottom of the tube
to fracture in the socket, which will not be covered by the Fender
Electronic Product Warranty to remove. If you are uncomfortable
in performing this process please seek the assistance of an
Authorized Fender Electronics Service Center.
6) Refer to the tube chart for tube type and
location. Fuse holders are marked to
indicate the corresponding tube pairs.
7) Replace faulty tubes with tubes of the same
type. Refer to the note below about proper
tube handling methods. Any output tube should be replaced
with the same type (6550C) and grade.
8) Replace all the necessary fuses. NOTE: The type of fuses used
for the tubes can be blown without showing any visible signs of
failure. If Fender Automatic Bias indicated that one or more tubes
have failed, you should replace the fuse for the corresponding
pair(s) of tubes, even if it looks okay.
9) Replace the front grille and install the four nickel mounting
screws if necessary. Replace the rear metal grille and install the
five black mounting screws. Don't forget to reconnect the FAN
wires before installing the rear metal grille.
10) Reconnect the speaker cable and any other signal cables you
disconnected in step 2 .
11) Reconnect the power cable.
12) Turn on the amplifier, but keep it in standby for at least 1 minute.
13) Press & hold the up/down adjust buttons for 2 seconds to reset
the Automatic Bias settings.
14) Take the amplifier out of standby and wait for the Fender
Automatic Bias display to update (10-15 seconds). If the display
still indicates that the tubes are bad, either the fuse or tubes used
as replacements were not good. Repeat steps
1 – 14 , with new
tubes or fuses.
Note on Handling Tubes:
It is important not to leave fingerprints, grease, or
other foreign substances on the glass surface of the
tubes. This is especially important for the power
output tubes. If fingerprints or other substances are
left on the surface of the tube, they will cause the
tube to become hotter than normal in that spot, which can lead to
cracks in the glass and premature failure of the tube. Some people
recommend not touching the tubes with bare hands at all. However,
it this is usually impossible to avoid. Take the following steps to ensure
that the tubes are clean and will have the maximum possible life:
1) Wash your hands before handling the tubes.
2) Avoid excess handling of the tubes.
3) After installation of the tubes, wipe them with a clean cloth to
remove any fingerprints or foreign substances.
Tube Replacement Tube Replacement
Front face of chassis
Front face of chassis
Fuses and corresponding tube pairs