PRINCETON RECORDING AMP®™
(This is the model name for warranty claims)
5
PCB EXCHANGE POLICY
Parts marked with a single asterisk (
*
) in the Part
Lists are not field replaceable. If a failure due to
one of these components is detected, please con-
tact the FMIC Customer Service Department to
order the complete PCB Assembly.
CIRCUIT DESCRIPTION
This section provides concise information about new
or unusual circuitry 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.
TUBE PCB
The Tube PCB contains all of the vacuum tube cir-
cuitry in 4 breakaway PCBs. These subassemblies
are the Main PCB (includes the tubes & sockets), the
Control PCB, the Power Supply PCB, and the Pri-
mary PCB.
The Tube PCB’s wire set is extensive with signals
coupling through coax. Power & ground interconnect
between the Power Supply PCB through wires. The
soldered ends of the power wires are generally found
on the power supply PCB with FASTON connections
found at their receiving end at the Main PCBs. Care
must be taken to ensure good connections at the
faston and soldered end.
Please refer to the service diagram & drawing –
0068621000 -Wire Set, PCB Assy, PRA, Tube. They
contain the details regarding the wiring.
The input signal couples through J1 or J2 through a
high-impedance op-amp buffer (U1-A & B) on the
Control PCB. It exits to the compressor & overdrive
circuits on the TZ/FX/IO. The signal exits out of the
Control PCB through ribbon connector P26. Follow-
ing these circuits, the signal couples via coax A to
the tube input amplification stage (V1-B).
The amplified signal output by V1-B is fed via coax to
and from the Control PCB (Coax B & C respectively)
along with a supporting ground lead (T). Signal
equalization (Treble & Bass) and volume can be ad-
justed with their respective controls. The signal level
is reduced through this passive tone control circuit.
With a fixed Midrange resistor, there is output when
the Treble & Bass are set to minimum.
Once back on the Main PCB via Coax C, the signal
is amplified using V1-A. R14 & 15 act as a voltage
divider to reduce the signal to levels compatible to
the solid-state effects loop found on the IO PCB.
The signal to the effects loop is sent and returned via
the D & E coax. V3-A boosts the signal level back
up and sends it to the reverb loop and the power
amp.
The reverb driver uses both sections of the 12AT7
(V2-A & B) which are plate coupled to the reverb
transformer. Note the 2 grids & plates are tied to-
gether. The secondary of the reverb transformer
connects to the reverb tank input through a coax
terminated with the RED RCA jack.
The reverb tank output couples to the reverb recov-
ery tube (V3-B) by a similar coax terminated with an
RCA jack. Q1 & Q2 (J111 JFETs) allow the reverb
signal to be switched off by footswitch control. The
plate signal of V3-B is routed back and forth through
the reverb level control (found on the control PCB)
through coax F & G along with a supporting ground
lead (U).
The reverb wet/dry mix is performed at the grid of
V4-B. The cathode circuitry of this tube allows the
summation of the negative feedback signal taken
from the speaker output. The power amp feedback
