Circuit Description; Power Amplifier - Fender SUPER-SONIC 22 Service Manual

This section provides concise information about
new or unusual circuitry designs incorporated into
this amplifier model. The purpose is to aid the ser-
vice technician by providing insight into the design
areas most likely to become obstacles in trouble-
shooting. Information is focused for its effective use
while maintaining the security of Fender® proprie-
tary information wherever possible.
PRE-AMPLIFIER
The guitar input signal flows through a tube gain
stage (V1-A) before it is split into two signal paths,
the "Vintage" path or the "Burn" path. The "Vintage"
channel, consisting of passive 2-band tone stack,
volume control and subsequent tube sections, can
also be split into two paths within the channel,
known as "Normal" and "Fat". The path selection
will depend upon the selection of the "Vintage/Fat"
front panel switch (or via Footswitch).
The "Normal/Fat" switch controls relays K3 and K4
in order to activate the desired path. When the
"Normal" path is selected, relay K3 thru K4 will be in
the "normally closed" state. When the "Fat" path is
selected, relay K3 thru K4 will be in the "normally
open" state. The "Normal" path provides a tone that
is similar to the '65 Fender Vintage blackface ampli-
fier. The "Fat" path provides a tone that is similar to
the '66 Fender Fat Head blackface amplifier.
The "Vintage" channel remains active until the "Vin-
tage/Burn" front panel switch (or via Footswitch) is
selected. This will change relay K1, K2, K6 and K7
to reconfigure the "Vintage" channel to become the
"Burn" channel. When the "Vintage" path is se-
lected, relays K1, K2, K6 and K7 will be in the
"normally closed" state. When the "Burn" path is
selected, they will be in the "normally open" state.
The "Burn" channel provides a new tube distortion
tone that is more versatile than past Fender tube
drive circuits. The "Burn" channel consists of two
Gain controls, a passive 3-band tone stack, volume
control and an extra tube stage, V2-A
"Gain 1" (R31) to "0" will provide no signal through
this channel. "Gain 1" provides the high gain to the

CIRCUIT DESCRIPTION

Setting
SUPER-SONIC™22
(This is the model name for warranty claims)
signal, while "Gain 2" (R35) provides harmonic
overtones to the signal,
2" in tandem can provide many distortion tones,
ranging from standard clean rock "crunch" tones, to
"Texas Blues" tones to "lo-fi" fizz tones, to "plays-
itself" ultra-high gain tones.
The signal is directed back to the summing point at
V4-B and amplifier stage at V3-A the input to the
reverb circuit at V3 and V4. The amount of reverb
is controlled by potentiometer R166. The reverb
signal is summed at the input of V4-B. The output
from V4-B is split into two paths: The "Dry" path and
the "Effects Loop" path. This path selection is con-
trolled only by the footswitch. When the "dry" path
is selected, relay K5-A/B is "normally closed".
When the "Effects Loop" path is selected, relay K5-
A/B is normally open". When the footswitch is not
used, K5-A/B will default to "normally closed". The
"Effects Loop" will not be in operation unless the
"Send" and "Return" jacks are connected to either
an outboard Effects system or if a jumper cable
connects the two jacks together. If a plug is con-
nected only to the "Return" jack, the signal of the
Pre-Amp will be broken, thus not allowing signal to
flow to the "Pre-Amp Out" jack and the power ampli-
fier. The output from the desired path ("dry" or
"Effects Loop") is directed through K5-A, pin 13.
From here, the signal is sent to the power amp.

POWER AMPLIFIER

The Power Amplifier is a discrete, Class AB push-
pull topology with feedback.
sections include a phase-splitter stage (12AT7 at
V5) and a pentode push-pull output stage (6V6's at
V6 and V7). The output signal is directed through
an output transformer capable of driving 8 ohm
speaker loads. The output is wired to the External
Speaker
The phase splitter circuit is a "long-tailed" configura-
tion commonly found in Fender Tube amplifiers.
The output circuit consists of two 6V6 tubes in a
push-pull configuration, again, commonly used in
Fender Tube amplifiers.
(R140 and R141) are can be used by the technician
Using "Gain 1" and "Gain
The basic amplifier
The 1 ohm Resistors
6