Download Mojotone Tweed Champ Style Amp Kit

Mojotone® Tweed Champ Style Amp Kit
Tools needed for build: (Picture 1)
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40 watt soldering iron
Wire cutters/ stripper
Needle nose pliers
Phillips head screwdriver
Small flat head screwdriver
AC/DC multimeter with resistance reading
44 Rosin core solder
Picture 1
1. Lay out parts for a quick inventory.
Compare physical inventory to the included bill of materials.
(Packaging mistakes are fortunately rare for Mojo but double check us before you start your build.)
2. Install chassis mounted hardware
a. Tube Sockets: Install so that they all face the same direction, noting pin #1 orientation
b. Power Transformer: Make sure to mount the PT so that the label faces toward tube sockets.
This will be helpful for anyone looking at the transformer model number without having to take
the chassis out of the amp
c. Output Transformer: Feed wires through grommets and note wire locations
d. Off/On 1 Meg Potentiometer
e. Install Input and Ouput Jacks
f. Fuse Holder: Install fuse at the same time so you won’t forget!
g. Pilot Light Assembly
© Mojotone® Tweed Champ Style Amp Kit 2012
Picture 2
Picture 3
© Mojotone® Tweed Champ Style Amp Kit 2012
3. Fiberboard Assembly (Picture 4)
Picture 4
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Always try and rely more on the schematic than the wiring diagram in any circuit.
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(2) ½ w 100 Ohm Resistors - solder from the pilot light to ground.
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1/2w 1 Meg resistor from Input 1 to ground tied to Input 2. This accomplishes the noise back
to ground when unplugged.
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Be sure of component placement and orientation, especially capacitors (positive, negative).
If you plan on doing modifications such as “hot-rodding”, adding a bright switch etc. or have
never put a kit together before, it is suggested that you assemble the basic amp and have it
functioning properly, to have an understanding of how the amp works before you start
modifying it.
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Check and double check the traces on the back of the fiberboard. (this is one of the most
common areas that mistakes are made. (Picture 5)
Picture 5
© Mojotone® Tweed Champ Style Amp Kit 2012
4. Internal Wiring
(Picture 6)
Picture 6
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Follow the color coded wiring diagram closely, remember to twist filament wires (6.3
heater lines) together, to reduce hum from AC voltage.
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Have enough of the power cord inside chassis to reach fuse, switch and ground.
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Affix the floating fiberboard, noting it is held in place by the wires, attach backing with
rubber cement if necessary (or mount directly to chassis).
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Place entire fiberboard inside the chassis noting the orientation (see schematic).
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Connect corresponding wires to hardware, try to keep wire short and runs as neat as
possible. This will help make future troubleshooting and repair easier.
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Always use a clean tip on your soldering iron to make positive, clean solder joints,
(“cold” solder joints can be a major problem in hand-wired amps).
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Try to avoid crossing wires over each other.
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Before you plug the amp in check and re-check your wiring. If you are not clear on any
part of the circuit, ask someone.
© Mojotone® Tweed Champ Style Amp Kit 2012
5. Testing the Amp
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*WARNING* Never stick your hands inside amplifier especially while power is on!
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Test tube socket voltage with a multimeter to ensure correct operation.
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Plug in speaker
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Turn amp on without tubes installed first, checking transformers and components for shorting,
excessive heat, arcing, smoking, etc.
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Turn amp off before putting tubes in proper location, and allow tubes to heat up for approx. 30
seconds before playing at volume.
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Listen! The best way to tell if there any problems with the circuit of the amp and/or tubes is just
to listen.... excessive noise, popping/ crackling, hum, loud squeals, as well as ghost- echo
sounds. These are all symptoms of many common problems in tube amps.
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If you need to service the amp after having it on, you must “discharge” the capacitors. This is
done by unplugging the amp, turning the power and standby to the on position and letting it sit
for 30 mins. or so. If you do not have a standby switch, you will need to short the capacitor
positive leads to ground with a pair of pliers or an insulated wire. It is common to hear a pop
when this is done. This is just the cap discharging itself. Always use a multimeter to check the
residual voltage in the cap to make sure it is fully discharged.
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Feel free to call Mojo at 1-800-927-Mojo (6656) at any time if you have any questions regarding
your kit.
Thanks for choosing Mojo and don’t forget to crank it up!!
**WARNING**
THE VOLTAGES FOUND INSIDE YOUR AMP CAN CAUSE SERIOUS HARM
OR EVEN DEATH. NEVER ATTEMPT TO SERVICE YOUR AMP WHILE A
POWER SOURCE IS CONNECTED.
Online Resources
Grounding principles: www.aikenamps.com/StarGround.html & www.el34world.com/charts/grounds.htm
Signal Flow Diagram: www.el34world.com/charts/currentflow.htm
Printed Resources
"The Tube Amp Book" by Aspen Pittman
"A Desktop Reference of Hip Vintage Guitar Amps" By Gerald Weber
"All About Vacuum Tube Guitar Amplifiers" By Gerald Weber
© Mojotone® Tweed Champ Style Amp Kit 2012