Power Supply - Fender SUPER-SONIC 22 Service Manual

to properly measure the amount of bias current for
each output tube (V6 and V7). The Optimal bias
setting for each tube in this amplifier is 22mA-
26mA. The bias current for V6 can be derived by
measuring the voltage across R140, which in this
case will measure 22mV-26mV. The same proce-
dure can be used for V7 by measuring the voltage
across R141. The bias current for both output
tubes is controlled by potentiometer R156, found on
the Main PCB assembly.
The Feedback network consists of feedback resis-
tor R132 and shunt resistor R133.

POWER SUPPLY

The Power Supply is typical of a Fender tube ampli-
fier. The secondary side of the Power Transformer
consists of 3 windings: high-voltage winding, low-
voltage winding and heater winding. The high volt-
age winding is used to generate the high voltage
.
SUPER-SONIC™22
(This is the model name for warranty claims)
DC power supplies in the amplifier. The high volt-
age DC power supply consists of a standard bridge
rectifier configuration. The "voltage-drop" resistors
R148 thru R151 set the DC plate voltages used at
various tube stages throughout the design. The low
voltage winding is used to generate the low voltage
+/-16V DC power supply, as well as the output tube
bias supply. The low voltage DC power supply also
consists of a standard bridge rectifier configuration.
Three-Terminal regulators are used to regulate the
+/-15VDC power supplies. A voltage doubler circuit
(C85-C86 and D43-D44) is used on ½ of the low
voltage winding to generate a negative DC power
supply for the bias control potentiometer R156. The
heater winding produces a 6.3VAC power supply
that is used for the heater filament in all of the tubes
in the amplifier, as well as illuminating the pilot light.
7