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AMP MAKER WF-55 Construction Manual

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A M P
WF-55
Construction guide
Your WF-55 amplifier kit contains all of the
electronics and hardware parts needed to
make a vintage 4W Tweed-voiced classic.
M A K E R
ww w. am pm ake r.c om
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 off one by one.
If this is your first 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
1

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Summary of Contents for AMP MAKER WF-55

  • Page 1 A M P M A K E R WF-55 Construction guide Your WF-55 amplifier kit contains all of the Before jumping in, clear a space on your workbench. Unpack all of the electronics and hardware parts needed to components. make a vintage 4W Tweed-voiced classic.
  • Page 2 WF-55 4W Tweed-style amplifier: Kit contents 1MΩ 0.5W UF4007 Miscellaneous: 68kΩ 0.5W UF4007 Turret board 100kΩ 0.5W UF4007 Chassis (optional) 1.5kΩ 0.5W UF4007 Control panel (optional) 100kΩ 0.5W 1N5357B Approx 10m insulated wire (2m for 1.5kΩ 0.5W each of red and green, 1m for each 22kΩ...
  • Page 3 Capacitors are usually printed with their The WF-55 includes a pair of Orange values, and their polarity is shown by Drop capacitors that have no polarity. use of a minus sign (-) to indicate the The value is printed as ‘223’, meaning position of the negative terminal 22000pF or 22nF.

  • Page 4: Block Diagram

    Block diagram 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. 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 first build.
  • Page 5 Second amplification 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 amplification stage to create some mild preamp distortion (see How the amp distorts box, right).
  • Page 6 Schematic 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 off-board components. All components are numbered on the There are many ways to tweak the...
  • Page 7 www.am pma ker.c om...

  • Page 8: Chassis Assembly

    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 Output transformer The mains (or power) transformer The output transformer runs across the mounts through the large rectangular chassis, behind the power transformer.
  • Page 9 The octal socket mounts in the layout with space to write in the mains 28mm hole. The socket and mounting voltage, fuse rating (0.5A for the WF-55 ring go on the inside of the chassis, and whether your local mains is 110-120V or...

  • Page 10: Turret Board Assembly

    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. 2020 UPDATE: Your kit comes with The top picture shows the components there are three 100k resistors, one of three 16uF and one soldered in position.
  • Page 11 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.
  • Page 12 Some people alter the circuit at a later date. WF-55 Construction guide...
  • Page 13 MF spacers to mount the turret the turret board to the chassis. Add board in the WF-55 chassis four M3 screws and M3 spacers to the holes circled in red in the photo (right).
  • Page 14 The result will look like lugs on the On/Off switch. Twist them this example (below). The wiring for 240V mains uses a short piece of red wire to connect the two 120V windings in series. WF-55 Construction guide...
  • Page 15 USA and other 110-120V mains European 220/230V mains The same power transformer also works For European 220/230V mains, the wiring is with North American mains. There's just a even simpler - there’s a dedicated very simple wiring change. First, connect 220/230/240V power transformer supplied the two red wires from the Power switch to with your kit.
  • Page 16 Check power valve. that each connection is present before continuing. The schematic is always the definitive guide to amplifier connections, but this diagrams is a quick guide for the wires connected directly to the turret board WF-55 Construction guide...
  • Page 17 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 fitting R1, the 1M resistor on the socket itself (you may find it easier to do the first bit of wiring with the socket out of the chassis).
  • Page 18 The original series of Fender Champ amplifiers had only a 4- ohm output, but your WF-55 can work with 4/8/16-ohm speakers. For a 4-ohm speaker •...
  • Page 19 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.
  • Page 20 Solder the brown wire to the 275V lug and the white wire to the 0V lug. Your amplifier wiring should now look like the WF-55 shown on the opposite page. The last pair of connections to make is for the 275V output of the mains transformer.
  • Page 21 ww w. am pm ake r.c om...

  • Page 22: Initial Testing

    DC voltage across each of the following capacitors: C4, C5, C6 and C7. Each figure should be under 10V. If not, wait a few moments and remeasure. WF-55 Construction guide...
  • Page 23 Careful testing of the continuity between adjacent pins of the valve socket wiring can reveal mistakes that might prove costly. the input socket and check that there's continuity from the sleeve of the guitar cable to the Earth pin board to the valve sockets and other on the mains plug components.

  • Page 24: Final Testing

    • If you have a guitar plugged in, normal unplug it Your amp Typical Mains (AC) 110-240V pin 2 - 7 (AC) 6-7V Test point A - B (AC) 280-290V Test point C - D (DC) 380-390V WF-55 Construction guide...
  • Page 25 4. Set your multimeter to its high DC voltage range and check the voltage from C to D. You should get a reading of around 380-390V. Contact Amp Maker if not. Powering down Turn the S1 Power switch off. But keep measuring the C-D voltage and you will see it fall as the capacitors slowly discharge.
  • Page 26 • If you have a guitar plugged in, perhaps from the ground continuity tests, you should unplug it • Connect a speaker/cabinet of the correct impedance to the WF-55’s speaker output socket • Turn the amp's Volume knob to zero •...
  • Page 27 Test procedure (with valves installed) Set your multimeter to the high DC voltage range 2. Measure C-D 3. Measure E-D 4. Measure F-D 5. Measure G-H 6. Measure the voltage between pin 3 of V2 (the 6V6) and point D on the turret board, being extremely careful to touch the multimeter's probe to pin 3 alone.
  • Page 28 2 - 6V6 cathode current Divide the 6V6 cathode voltage (I-D) by the value of R9 (470 ohms). A typical result is around 38mA. Contact Amp Maker if it's more than 45mA. 3 - Combined preamp and screen current Divide the E-F figure by the value of R11 (10k) to get a combined screen and preamp current (typically 4mA or so).
  • Page 29 Champ’s Then check out the forthcoming “Create your characteristic voice and response should be clear: own tone” pages on the Amp Maker website. The • very mellow at low volumes most popular tweaks for the Champ circuit will be •...