AMP MAKER WF-55 Instructions for use

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Before jumping in, clear a space on
your workbench. Unpack all of the
components.
Your kit's contents
Start by checking the Kit contents
listing (overleaf). Look through the
electronic components and check
them o one by one.
If this is your rst electronics
build, familiarise yourself with the
component values. In some cases, it's
as simple as reading the value from
the body of component (most
capacitors, for example). However,
most resistors are too small to have
printed values, and instead they have
colour coded bands on the resistor
Your WF-55 amplier kit contains all of the
electronics and hardware parts needed to
make a vintage 4W Tweed-voiced classic.
AMP MAKER
WF-55
Construction guide

2 WF-55 Construction guide
indicate their resistance value. You can
decipher the code using the Resistor
colour codes diagram (right). If you’re
not sure (or if you nd the colours hard
to tell apart), just use your digital
multimeter to check each one.
Don’t worry if you see small
discrepancies; there’s a 5% tolerance
for these resistors and so a 100kΩpart
could measure from 95-105kΩ.
Component polarity
Some of the components have a
polarity, meaning that the component
needs to be inserted in one particular
direction for the circuit to work. For
R1 1MΩ0.5W
R2 68kΩ0.5W
R3 100kΩ0.5W
R4 1.5kΩ0.5W
R5 100kΩ0.5W
R6 1.5kΩ0.5W
R7 22kΩ0.5W
R8 220kΩ0.5W
R9 470Ω2W
R10 22kΩ0.5W
R11 10kΩ1W
R12 100Ω1W
R13 100kΩ2W
C1 22nF 400V
C2 22nF 400V
C3 22uF 25V
C4 16uF 450V
C5 16uF 450V
C6 16uF 450V
C7 47uF 450V
VR1 1MΩlog
WF-55 4W Tweed-style amplier: Kit contents
D1 UF4007
D2 UF4007
D3 UF4007
D4 UF4007
D5 1N5357B
SW1 DPDT (On/O)
V1 ECC83 (socket + shield)
V2 6V6 (socket + clip)
T1 Power transformer
T2 Output transformer
L1 Neon (220-240V)
F1 500mA fuse + holder*
J1 1/4" mono jack socket
J2 1/4" mono jack socket
J3 IEC chassis plug*
* (integrated)
Miscellaneous:
Turret board
Chassis (optional)
Control panel (optional)
Approx 10m insulated wire (2m for
each of red and green, 1m for each
of black, blue, brown, grey, orange,
white, yellow)
Approx 15cm of solid bare wire
Approx 5cm of heatshrink tubing
Hardware:
M2.5 screw+nut x2
M3 shakeproof washer x10
M3 countersunk screw x2
M3 screw x6
M3 nut x8
M3 M-F spacer x4
M4 screw+nut+washer x4
M4 ground lug x2
M6 screw x4
M6 cagenut x4
Rubber grommet x1
example, if you look closely at the larger
capacitors, you'll see a small '-' (minus)
mark close to (or pointing at) one of the
capacitor's two leads. This marks the
negative terminal. In the WF-55,
all of the capacitors' negative
terminals point towards ground.
The rectier (D1-D4) and
zener (D5) diodes also have a
polarity, indicated by a silver
band around one end of the
diode's black body. Where the
Resistors are frequently
colour-coded to indicate
their value

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diodes are used to rectify AC voltage
into DC voltage (D1 to D4) the silver
band points away from ground.
The zener diode (D5) is a special
case, and in this amplier, the silver
band points towards ground. Don't
worry if you're not clear of the reasons -
the turret board photos and diagrams
on the following pages show exactly
which way to use these components.
Go through the components in the
WF-55 Kit contents list and tick them
o. Get in touch with Amp Maker if
there's any discrepancy or confusion.
Capacitor voltage ratings
All components have a voltage rating -
a maximum working voltage for the
component. All of the resistors supplied
in your kit are rated at well over the
maximum voltage present inside this
amplier. It's a dierent story for the
capacitors, however. They are rated
according to their place in the circuit
and voltages present at that position.
For example, the large power
supply capacitors will be faced with the
highest voltages in your amp - up to
360V. So they must be rated for at least
this voltage; the parts supplied with
your kit are rated at 450V. Likewise,
there are some signal caps inside the
amplier that are rated at 600V - more
than enough to do their job safely and
reliably.
Look closely and you will see that
one capacitor is rated at a much lower
voltage: 25V. Capacitor C3 is in the
cathode of the 6V6 power valve. It
never sees the high voltages that the
other capacitors do. The Kit contents
box (opposite) lists the voltage rating
requirements for each capacitor.
Resistor power ratings
For resistors, the signicant rating is
their power handling. As electrical
current passes through them, they heat
up. So they are designed with a rating,
and the amplier designer species a
power rating so that the resistor
doesn’t overheat. The Kit contents list
shows the (minimum) rating required
for each part. Most are 0.5W, but a few
have higher ratings, and are
consequently larger in size.
Capacitors are usually printed with their
values, and their polarity is shown by
use of a minus sign (-) to indicate the
position of the negative terminal
The WF-55 includes a pair of Orange
Drop capacitors that have no polarity.
The value is printed as ‘223’, meaning
22000pF or 22nF.

4 WF-55 Construction guide
The block diagram here shows the stripped-down schematic (a diagram that shows how
the electronic components are connected together to form a circuit). It’s a good place to
start if this is your rst build. Here's an explanation of each sections.
The WF-55 (like its inspiration, the Fender Tweed Champ 5F1) has
about as simple a circuit as you can get, and it's very easy-to-follow.
Block diagram
First amplication stage
The guitar input is shown at the left,
and it feeds into the light green section.
This is the rst stage of the amp, using
one half of the ECC83 preamp valve to
amplify the low-level guitar signal. This
section also includes the amplier’s
Volume pot, which lets you control how
much of the boosted signal is fed into
the second stage.
Valve heater supply
All valves used in guitar amps need a heater supply (the
heater is the part of the valve's internal electrodes that
glows dull-orange when an amplier is switched on). The
light orange section shows this part of the circuit. It uses
one of the windings on the power transformer - the one
that provides approximately 6.3V - and there's a simple
connection to minimise hum levels.
High voltage supply
The power transformer provides a high voltage in addition to the low voltage supply that
heats the valves. This high voltage winding is shown in the light blue section. It feeds
into four rectier diodes which work together to turn the AC voltage into the DC voltage
required by the valves. The fth diode, a type known as zener, acts to lower slightly the
supply voltage to get it into the desired range.
The large power supply capacitors and resistors lter out mains hum and pass the
DC voltage on to each of the amplication stages (shown by the dotted vertical lines).

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Second amplication stage
The guitar signal - still fairly clean so far - is now fed into the
second part of the amp. This uses the other half of the ECC83
preamp valve. If the Volume control is set high, the incoming
signal will overdrive the second amplication stage to create
some mild preamp distortion (see How the amp distorts box,
right). The output of this stage then runs straight through to
the input of the power stage.
Power stage
The power stage includes the 6V6 power
valve and the output transformer. The valve
operates in what's known as "single-ended
Class A" mode. Typically, this creates a guitar
tone with a fast attack.
The power valve works with high
voltages and low currents, and the output
transformer transforms this into a low
voltage, high current signal that's suitable for
driving the speaker (which is connected to
the jack socket on the right).
Mains circuit
The light grey section shows the part of the
amp that operates directly from the mains
supply. It includes the fuse, On/O switch and
a neon indicator. Just as important is the
connection of the Earth wire from the IEC lead
to the amp's metal chassis (bottom right)
How the amp distorts
To add distortion to the incoming guitar
signal, the amplier is designed so that each
stage can be overdriven by the previous
stage. So, when the Volume control is at
maximum, the output of the rst amplication
stage is 'too hot' for the second stage to
reproduce accurately. The result is that the
guitar signal is amplied, compressed and
clipped at the same time, and it's this
distortion (= indelity) that produces the
harmonics that fatten up the guitar tone.
Distortion also comes from the power
valve - because the already fattened-up
signal is also too hot for the 6V6 valve to
reproduce accurately. So it also distorts as it
tries to amplify the signal. That leads to an
even richer distortion tone.
In reality, there's a modest amount of
distortion available from the Champ circuit.
Add a clean boost pedal to overdrive the
amp’s rst stage, too.

6 WF-55 Construction guide
Schematic
All components are numbered on the
schematic (R1, C3, D4, etc), so that you
can relate this schematic to the Kit
contents listing (earlier) and the turret
board layout (later).
It's the specic values in the circuit
that combine to make the amplier
work and sound the way that it does.
For example, capacitor C1 does two
jobs. The rst is to block the high DC
voltage (supplied to the rst stage of
the preamp via resistor R3 and R10)
from feeding into the input of the
second amplication stage; any value
of capacitor would work for this task.
The second job that the capacitor does
is to control the amount of lower
frequencies in the amplied guitar
signal that are passed from the rst
amplication stage to the second -
higher values allow more bass through,
lower values allow less.
Build now, tweak later
It's the ease with which you can alter
individual components in an amp
circuit that makes hand-wired amps so
appealing. For example, you can swap
in components with the same ratings
but dierent values to change the
response of part of the circuit. This is
the real beauty of building your own
amp - you can ne-tune it to the tone
you like.
It's best to get your amp up and
running rst, by sticking to the
components specied on the
schematic and supplied with your kit.
There are many ways to tweak the
vintage 5F1 Champ circuit, and you can
decide if you want to try that when the
amplier is working properly as
standard. While it may be tempting to
leap ahead and increase the bass
frequencies by using other capacitor
values, for example, doing this in the
wrong part of amp circuit may
inadvertently cause your amp's
distortion tone to become 'muddy'.
Solder lug numbering
Look closely at the schematic and you'll see numbering for
the solder lugs of certain components. For example, the jack
sockets, pot and mains input socket each have 3 solder lugs.
To help avoid confusion, your schematic
includes numbers next to each
connection for these components, and
at the bottom left of the schematic
there's also an annotated photo
reference for each.
Valve sockets have even more
solder lugs. There are nine solder lugs for
the preamp valve, numbered clockwise,
starting at the gap (below). The second
and larger valve socket is an 8-pin type
(for the 6V6 power valve). It has a small
keying 'notch' in the central round hole -
which you can just see here at the 3-
o'clock position. The pin numbers (1 to 8)
are moulded in the underside next to
each solder lug, working clockwise
from this keying notch. However,
they're almost impossible to see in
anything other than the brightest
light, so I've added annotations here
for reference.
The picture opposite shows the WF-55's full schematic - the same
circuit as the block diagram and with all component values added
and with numbered lugs for all o-board components.

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8 WF-55 Construction guide
8
Chassis assembly
Here’s how to use the WF-55’s pre-punched chassis (optional). If you are
using your own donor chassis, use these pictures as a general guide.
Mains transformer
The mains (or power) transformer
mounts through the large rectangular
cut-out. To t it, undo the four nuts and
remove the xing hardware from the
transformer. Mount it on the chassis'
top surface, sliding it at an angle
through the cut-out. Fix the hardware
in the same order: red bre washer
against the chassis, then the plain steel
washer, then the steel locking washer
and nally the nut. Tighten the four
nuts fully.
The power transformer can go
either way around, but it's probably
best to have the mains-related solder
lugs closer to the side of the chassis (as
shown above). This makes for slightly
neater cable runs later on.
Output transformer
The output transformer runs across the
chassis, behind the power transformer.
Use M4 screws, shakeproof washers
and nuts, and make sure that this
transformer's lugs face towards the
power transformer, as shown in the
photo (above). Then t a rubber
grommet to the 10mm hole near this
transformer.
Valve sockets
Add the 9-pin valve socket
to the 22mm hole near the
front panel. Use M2.5
screws and nuts with M3
shakeproof washers to
secure the base of the
valve shield.
Front panel
The full WF-55 kit comes with a plain mahogany
front panel. Before mounting, decide what sort
of look you want, and how you want to nish it.
You have a huge range of options. At the
simplest, your local DIY shop has simple oil-
based nishes, such as Danish oil and Tung oil.
If you're feeling more adventurous, you can use
one of the many nishes that guitar makers use,
such as Gibson cherry red. The example here uses a
subtle red dye shading and Danish oil.
Fit the ceramic 9-
pin socket to the
chassis with the
aluminium skirt of
the valve shield.

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The octal socket mounts in the
28mm hole. The socket and mounting
ring go on the inside of the chassis, and
the retaining clip goes on the outside of
the chassis (see below). Use M3
hardware to mount this socket - it can
be a bit ddly to align the mounting ring
and retainer but persevere!
Solder lugs for grounding
Both grounding lugs are secured with
M4 screw, shakeproof washer and nut.
The rst is close to the mains socket,
and the second is close to the rubber
grommet you've already added.
For each solder lug, bend them so
that the 'arm' is pointing upwards -
Controls, switches and sockets
Once your front panel is prepared, mount it on the chassis
using the input jack socket, Volume pot and neon indicator.
Make sure you can get to the lugs for soldering later!
The pot is a general purpose type, and there are two
adjustments to make. First, bend back the small forward-
projecting tab (A) so that the pot sits ush against the
chassis. Then trim the soft nylon shaft (B) of the pot. Use a
Dremel-type tool or junior hacksaw to cut it down to about 8-
10mm. Now, t the chickenhead knob; rotating it so that
when the pot is turned fully clockwise, the pointer is at about
5-o'clock. Fix it by tightening the knob's set screw.
Finally, add the power switch, mains socket and speaker
jack socket to the chassis’ back panel. For the On/O switch,
align it so that the 'On' label on the switchplate is uppermost.
And for the combined IEC/fuseholder, make sure the Earth
lug is uppermost. Insert the 500mA fuse into the holder in
the fuse tray and slide it into place (you'll feel it click into the
socket's internal fuse contacts).
you'll use this to solder when you add
the wiring.
For the chassis' back panel, your kit
comes with a simple pre-printed sticker
that ts between the mains socket and
speaker socket. It shows the rear panel
layout with space to write in the mains
voltage, fuse rating (0.5A for the WF-55
whether your local mains is 110-120V or
220-240V) and your chosen speaker
impedance. Make sure to add this
information. Even if you know these
values by heart, you may sell or lend the
amplier out to someone who isn’t as
knowledgeable.
The 8-pin socket with
its spring retainer and
ring (out of sight under
the chassis in this
photo) are ddly to t.
The pot (above) needs trimming before
you mount it on the chassis. Orient the
Power switch so that ‘On’ is up (below).

10 WF-55 Construction guide
Turret board assembly
Your WF-55 kit contains a turret board, staked with turrets. Add and solder the
board-based components before putting the board into the chassis.
The top picture shows the components
soldered in position. The lower photo is
annotated with component numbers
(C1, R4, etc). Use that as your guide to
component layout.
Resistor notes
Make sure to use the larger resistors -
which are rated at 1W or 2W - in the
appropriate position. For example,
there are three 100k resistors, one of
which is substantially thicker than the
other two. The smaller pair are R3 and
R5 in the preamp, and the larger one is
R13, connecting across C7 in the high
voltage part of the power supply.
Side-mounted components
Most of the components are best
mounted using the holes in the top of
2020 UPDATE:
Your kit comes with
three 16uF and one
47uF capacitors
instead of the four
22uF capacitors shown
in these photos. This
was forced by
manufacturing
changes but makes no
dierence in operation
or tone.

11www.ampmaker.com
the turrets. However, it's best to side
mount the rectier diodes, D1-D4 (as
shown above). This leaves the top holes
ready for connecting the power
transformer later.
Ground and other connections
Once all of the components are in place
on the turret board, use some of your
kit's uninsulated solid-core wire to
make three short connections along
the edge of the board - as shown in the
picture below, left.
First, solder two ground bus wires:
the rst to connect turrets A-B-C-D,
and the second to connect turrets E-F-
G-H-I. These wires will connect all of
these components to ground once you
have completed the chassis wiring.
Finally, connect the three turrets J-K-L
at the top of the board. Now you're
ready to start wiring in the next stage.
Note: At the end of this process,
there will be a pair of resistors left over
(R1 and R2). This is normal; put them to
one side for the moment.
Turret board soldering tips
• Do a 'dry run' before you solder. Line up the parts in
their correct order, from left to right. This helps you to
avoid having to desolder components.
• Even if you can read resistor colour codes easily, use
your multimeter to check their resistance, just in case.
• Check twice and cut once. Extending a lead that
you've trimmed too short is a pain, so double-check
that you've got the correct component before cutting.
• Aim for solder joints that are shiny and gently domed.
Solder should 'ow' around the component leads and
turret surface - almost seamlessly.
• If a solder joint looks 'lumpy' or dull, you may have a
poor joint, which can cause the amp not to work, or to
work intermittently. If in doubt, resolder the joint.
• If a turret's top hole is crowded, use the side of the
turret. There are side-ridges for this purpose - wrap
the new lead around the turret's side and solder it in
position. As long as there's a good contact to any part
of the turret, the circuit will work.
Polarity notes
Five of the capacitors have a polarity that you need to
follow/ So mount C3-C7 so that their negative terminals
connect to the bottom row of turrets.
In addition, the diodes (D1-D5) must also be inserted
the correct way around. Follow the component layout
diagram, paying close attention to the orientation of the
grey-silver bands at one end of each diode.

12 WF-55 Construction guide
Turret board wiring
Once your turret board is tted with components, ip it over so that it's face
down with the ground bus towards you (it will look identical to the top photo).
In this step, you will add much of the
hook-up wire. Most of the wires from
the turret board fan out from the turret
board, but at this point, you're only
adding the wire to the turrets - not any
other component. Note that I’ve shown
the wires connected to the hole in the
underside of the turrets. Some people
prefer to connect them to the top of the
turrets, wrapping them around the
turret shaft. It’s partly a matter of
personal preference: it looks neater
with wires connected under the board,
but it is a pain in the neck to x one if
you have made a mistake or want to
alter the circuit at a later date.

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Estimating wire length
Before you start, do some 'dry runs'. To
do this, add the mounting hardware for
the turret board to the chassis. Add
four M3 screws and M3 spacers to the
holes circled in red in the photo (right).
Now you can place the board in the
chassis and use the diagram below to
see where each wire runs.
Your kit contains plenty of wire, so
err on the side of having slightly-long
leads and trim to length later The
longest wire is the red one that runs to
the output transformer (T2) - make
that wire approx 30cm (12-in) long.
Adding the wiring
I strongly suggest you use the colour
scheme shown in the photos and
diagrams to avoid any confusion. Every
amp builder has their own preference,
and some just go with what Fender or
Marshall has used in the past. I've seen
some amps which use the same colour
for every single wire!, Which must make
troubleshooting a bit of a challenge.
Working with stranded wire
If you’ve built circuits with stranded
wire before, you can skip thi section.
If not, here’s a quick run-through of
how to prepare the stranded wire
supplied with your kit for soldering to
turret and lugs.
Practice makes perfect. The idea is
that you create tinned wires that go
exactly where you want, with no wire
‘whiskers’ making it harder than
necessary, or risking short circuits
against nearby objects.
Use M3 screws, shakeproof washers,
nuts and MF spacers to mount the turret
board in the WF-55 chassis

14 WF-55 Construction guide
Chassis wiring part 1
Put the turret board to one side while you start to wire up the rest of the
components, starting with the mains side of the amplier.
By now, you have a chassis with almost
everything in place: both transformers,
a pair of valve sockets and all front and
rear panel controls.
Connecting the mains input
First, solder a short piece of green wire
to connect the Earth lug of the
integrated IEC/fuseholder to the solder
lug that's closest to the back panel.
Then use some brown and blue wiring
to connect the IEC/fuseholder (brown
wire for Live, blue for Neutral) to the
centre pair of lugs on the On/O switch
(S1). The result will look like the photo
(above, right).
UK/Oz/etc 240V mains
If your mains supply is 240V (the UK,
Australia and some other countries),
the following section shows how to
connect the power switch to the mains
transformer and neon indicator. (If your
local mains supply is 110-120V, as in the
USA, or 220/230V as in mainland
Europe, see the blue and red boxes
opposite.)
Take two pieces of red wire and
solder them to the upper pair of solder
lugs on the On/O switch. Twist them
together and run them along the side of
the chassis to the primary side of the
power transformer. Connect - but don't
yet solder - these two red wires to the
outer pair of lugs labelled 0V and 120V.
Connect another pair of red wires to
this same pair of lugs and run this pair
up to the neon indicator on the front
panel - one wire to each of the neon’s
solder lugs. Now solder all four solder
lugs (two on the transformer and two
on the neon indicator).
Finally, make a short connecting
wire (about 2cm long) and solder it to
the centre pair of lugs (labelled 120V
and 0V). This puts to the transformer’s
two 120V windings in series for 240V
mains and completes the wiring for the
mains circuit. The result will look like
this example (below).
The wiring for
240V mains
uses a short
piece of red wire
to connect the
two 120V
windings in
series.

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Adding the valve heater wiring
Solder three long lengths of wire (two
green and one black) to the three 6.3V -
CT - 0 solder lugs on the power
transformer: green to the 0 and 6.3
lugs and black to the centre lug (CT).
Twist them together. These wires need
to be long enough to run to the back of
the chassis, along the chassis edge and
around to the power valve, V2. Attach a
green wire to each of pins 2 and 7 of V2
(either way round is ne) and the black
wire to pin 8.
Now take two more pieces of green
wire and attach one each to the same
pair of pins as the rst pair of green
wires. Twist these wires together and
run them along to the preamp valve, V1.
Strip the ends of these wires and
European 220/230V mains
For European 220/230V mains, the wiring is
even simpler - there’s a dedicated
220/230/240V power transformer supplied
with your kit. Solder and run two red wires
from the On/O switch to the power
transformer, as usual. But connect one red
wire to the 0V lug and the other red wire to
whichever of the 220V or 230V lugs
matches your local supply (don’t solder
them yet). Then connect another pair of red
wires to this same pair of lugs and run these
two wires up to the neon indicator - one
wire to each solder lug. Now solder all four
solder lugs (two on the transformer and two
on the neon indicator).
USA and other 110-120V mains
The same power transformer also works
with North American mains. There's just a
very simple wiring change. First, connect
the two red wires from the Power switch to
the rst pair of lugs labelled 0V and 120V.
Now connect another pair of red wires to
this same pair of lugs and run them to the
second pair of 0V and 120V lugs: 0V to 0V
and 120V to 120V. Now solder the rst pair
of lugs, but not the second pair. Finally,
add another pair of red wires from the
second pair of 0-120V lugs, and run them
to the neon indicator. Now solder all four
solder lugs (two on the transformer and
two on the neon indicator).
attach one of them to pin 9 of V1, and
the other to BOTH pin 4 and pin 5.
Now you can solder all of these
pins. The pins are quite tightly packed
on these 9-pin valve sockets, so be
very careful to avoid 'whiskers' from
these wires shorting against adjacent
pins. When you've completed this
stage, your chassis should look like this
(centre).
Add the power valve's plate wire
There's one more wire to add before the
board goes in. Take a 30cm (12-in)
length of brown wire and solder it to pin
3 of the V2 socket . Run the other end
of it over to and through the rubber
grommet in the centre of the chassis
(photo below).

16 WF-55 Construction guide
Chassis wiring part 2
Mount the turret board in the chassis, using the remaining M3 harrdware
and the M3 MF spacers to keep the board clear of the chassis surface.
The schematic is
always the
denitive guide to
amplier
connections, but
this diagrams is a
quick guide for the
wires connected
directly to the
turret board
Two pairs of
red+yellow wires
connect the turret
board to the
preamp valves,
and three wires
connect to the
power valve.
Be sure to mount your turret board the
right way round. The ground bus must
be more or less in the centre of the
chassis, and the ve diodes should be
close to the back of the chassis.
Now you can start making the
connections shown in the wiring
diagram below. First: check that you
have 11 wires sprouting from your
board. Carefully trim each of them to
length. As always, check twice and cut
once! Experienced amp builders might
get it right rst time, but there’s no
harm in leaving a couple of centimetres
of extra wire to trim later.
Start with the four wires to the
preamp valve, V1, and then connect the
three wires to the power valve, V2. At
this point, the two valve sockets will
look like the photo on the right. Check
that each connection is present before
continuing.

17www.ampmaker.com
Wiring the Volume control
Before wiring the Volume pot, complete
the input socket wiring (see above). The
Volume pot has four connections:
• the black wire you've just added to
the input jack socket - this one
connects to solder lug 3 of the pot,
but don't solder it yet.
• the black wire that comes from the
board (the turret that connects to
the negative terminal of C4). This
also connects to lug 3 of the pot.
Now you can solder the two black
wires to this lug.
• the blue wire that comes from the
board (the turret at the
unconnected end of C1). Trim,
connect and solder this wire to lug 1
of the pot.
• the nal connection is a new blue
wire. Solder one end to lug 2 of the
pot and solder the other end to pin
7 of the preamp valve (V1).
With this wiring done, the volume pot
will look like this photo.
Input jack socket wiring
The input jack socket has three contacts, which
allows it to short the V1 input to ground when
there's no guitar plugged in (to lower noise). Start
by tting R1, the 1M resistor on the socket itself (you
may nd it easier to do the rst bit of
wiring with the socket out of the
chassis). This resistor connects to all
three solder lugs, so you must bend
one of the legs of the resistor so that it
goes through lug 2 and connects to lug
3. The body of the resistor sits between
lugs 1 and 2 (right).
Solder the resistor into place at lug
2, but don't solder the other lugs for the
moment. Mount the socket on the front panel. Now trim a piece of
black wire so that it's long enough to run from lug 3 of this jack socket
to lug 3 of VR1, the Volume control. With this wire in place, you can
solder lug 3 of the jack socket.
Finally, use your last resistor, R2, to connect directly from lug 1 of
the input jack socket to pin 2 of the preamp valve, V1. Solder it in place
at both the valve socket and the jack socket. Now, all lugs on the jack
socket are connected and soldered (left).

18 WF-55 Construction guide
Chassis wiring part 3
The nal connections include the output transformer and speaker socket,
before connecting the mains transformer to the turret board’s diodes.
Start with the last ground connection
from the turret board, the black wire
that runs from the turret at the bottom
end of C6. Trim, connect and solder it to
the ground lug that's next to the rubber
grommet (right).
This wire grounds the power supply
section, including all of the capacitors,
resistors and diodes connected to that
part of the ground bus. The preamp
ground bus is grounded at the metal
input socket, via it’s direct contact with
the chassis.
Output transformer - secondary
The output transformer has two
windings and two rows of lugs. The
primary is connected to the valve
circuit and the top row, and the
secondary is connected to the speaker
output and the bottom row.
Wire the speaker side rst. For the
speaker output, the rst decision you
need to take is which impedance you
want to use. The original series of
Fender Champ ampliers had only a 4-
ohm output, but your WF-55 can work
with 4/8/16-ohm speakers.
For a 4-ohm speaker
• Solder an orange wire to the 0 lug
• Solder a yellow wire to the 4-ohm
lug.
That’s all at this point. Both wires
should be long enough to travel
through the grommet, and over to the
speaker output socket. Now go to the
Output transformer - primary box
(above right).
For an 8-ohm speaker
• Solder an orange wire to the 0 lug
• Solder a yellow wire to the 4-ohm
lug
• Solder a green wire to the 8-ohm
lug.
All wires should be long enough to
travel through the grommet to the
speaker output socket. Twist and
The WF-55 output
transformer has
two rows of solder
lugs; the lower row
provides the
secondary
(speaker)
connections

19www.ampmaker.com
thread them through the grommet.
This is how the 8-ohm option looks
when soldered (right). Now go to the
Output transformer - primary box
(above).
For a 16-ohm speaker
• Solder an orange wire to the 0 lug
• Solder a yellow wire to the 4-ohm
lug
• Solder a grey wire to the 16-ohm
lug.
All three wires must be long enough to
travel through the grommet to the
speaker output socket. Twist the wires
together and thread them through the
grommet. Now go to the Output
transformer - primary box (above).
Speaker socket wiring
There are just a few 'loose ends' left.
First, complete the speaker output and
negative feedback wiring. Inside the
chassis, take the twisted bundle of
wires from the output transformer and
run them to the speaker socket.
First, trim, connect and solder the
orange wire to lug 3 of the socket. This
connection is the same no matter what
speaker output impedance you have
decided to use. Then connect but do
not solder the wire for your chosen
speaker output (yellow for 4-ohms,
green for 8-ohms, grey for 16-ohms) to
lug 1 on the speaker socket. What you
do next depends on the speaker output
you've chosen.
For an 8/16-ohm speaker
If you chose 8- or 16-ohms, you can
solder lug 1 now. The photo (next page)
shows an 8-ohm speaker output
completed. You have a yellow wire left
over: solder it to the turret at the end of
Output transformer - primary
You now have two sets of wires passing through the
rubber grommet. Take the red and brown pair that come
from the inside of the chassis. These connect to the
unused (top) row of the output transformer’s solder lugs.
When the amp is running, these lugs carry a high DC
voltage, so they must be properly insulated against
accidental touch. Use the insulating sleeve provided with
your kit.
First thread the brown wire through the left-most
wire guide in the sleeve and the red wire through the
right-most wire guide. Add some heatshrink to each wire
and then solder the wires in place. With the wires soldered,
move the heatshrink up the wire to cover the joint. Apply
heat so that the tubing shrinks around the joint (below).
Do the same for the unused centre lug.
Now you can slide the insulating sleeve up to cover
the row of solder lugs. Once the wiring and insulating is
done, the fully wired-up transformer will look like the one
below (depending on the speaker impedance you chose).

20 WF-55 Construction guide
Chassis wiring part 3 (cont’d)
R7 that's closest to the mains socket.
This provides the negative feedback
connection that’s part of the Champ’s
distinctive tone.
For a 4-ohm speaker
The nal bit of wiring for a 4-ohm
speaker is slightly dierent. First make
a short yellow connecting wire and
solder one end to the turret at the end
of R7 that's closest to the mains socket.
Now run this over to the speaker output
socket to lug 1, where you already have
a yellow wire from the output
transformer. Attach the new wire to lug
1 and solder both wires in place.
High voltage supply
The nal connections for your WF-55
are the high voltage supply wires. Take
some brown and white wire and solder
one each to the two turrets at the
junctions of the rectier diodes: one to
D1+D3 and the other to D2+D4 (as this
is an AC connection, either way around
is ne).
Twist these two wires together and
run them around the back of the
chassis and over to the power
transformer. Solder the brown wire to
the 275V lug and the white wire to the
0V lug. Your amplier wiring should now
look like the WF-55 shown on the
opposite page.
The above photo shows the negative feedback wiring for 8/16-
ohm speakers. For 4-ohm speakers, the yellow wire goes
straight to the speaker socket (see text, left).
The last pair of connections to
make is for the 275V output of
the mains transformer. It feeds
the four rectire diodes on the
turret board.
Completed wiring
on an 8-ohm
speaker output
socket - just two
wires to the
socket, the yellow
wire goes to the
turret board.