Circuit Description; Power Amplifier - Fender BASSBREAKER 007 Combo Service Manual

PCB EXCHANGE POLICY
Parts marked with a single asterisk (
Lists are not field replaceable. If a failure due to
one of these components is detected, please con-

CIRCUIT DESCRIPTION

This section provides concise information about
new or unusual circuit designs incorporated into this
amplifier model. The purpose is to aid the service
technician by providing insight into the design areas
most likely to become obstacles in troubleshooting.
Information is focused for its effective use while
maintaining the security of Fender® proprietary in-
formation wherever possible.
PRE-AMPLIFIER
The guitar input signal is injected into INPUT jack
J5 on the CONTROL PCB. Via a coax, this signal
is fed to the TUBE PCB to a tube gain stage (V1-A).
Note that plate & cathode resistors are non-typical
values for Fender tube amps. Its cathode bypass
cap C27 is switched in and out of the cathode cir-
cuit by JFET switch Q3. This switching provides
part of the control for the TREBLE BOOST function
that offers increased gain and an emphasis on the
guitar's treble frequency range.
AC coupling cap C19 feeds the GAIN control via a
coax. GAIN control R56 is on the CONTROL PCB.
Its wiper feeds a coax to send the signal back to the
TUBE PCB to the second tube gain stage (V1-B).
Its cathode circuit (C22 & Q2) is apart of the TRE-
BLE BOOST's gain switching function.
The signal flow continues on the TUBE PCB to the
third tube gain stage (V2-A). AC coupling cap C18
feeds a coax to send the signal to the TRE-
BLE/BASS/MID tone control circuit (R59, R57, R58
respectively) found on the CONTROL PCB.
The wiper of the VOLUME control (R60) is coupled
through coax to the fourth gain stage (V2-B) on the
) in the Part tact the FMIC Customer Service Department to or-
*
der the complete PCB Assembly.
TUBE PCB. Its cathode circuitry is the POWER
AMPLIFIER's feedback control loop network.
The Power Amplifier is a single-ended Class-A de-
sign using one EL84 (V3-A). Its cathode bias is set
at approximately 40mA using the 5W power resistor
R29. Screen grid bias is set through R16.
The plate drives a custom designed single-ended
output transformer (T1 – FMIC # 7706163000) to
provide an impedance match with the specified 8
Ohm speaker load. T1's primary is connected to
the TUBE PCB and its secondary is connected to
the REAR PANEL PCB.
For the COMBO version, the internal speaker is
connected to T1's secondary thru terminals P35 &
P36. The internal speaker is disconnected when
the SPEAKER OUT jack (J3) is connected to an 8
Ohm speaker load.
For the HEAD version, the amplifier can only drive
an 8 Ohm rated speaker through the SPEAKER
OUT jack (J3).
Voltage divider R6 & R5 creates the signal reduc-
tion for the LINE OUT feature offered on the
Bassbreaker 007 for interconnection to other guitar
amps or sound reinforcement equipment. Use of
the LINE OUT does not mute any speaker output
capability. (NOTE: this feature does not work with-
out a speaker installed on the head.)
BASSBREAKER™ 007
(This is the model name for warranty claims)

POWER AMPLIFIER

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