Epiphone Plexi SE PCB Handbuch
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Plexi SE PCB Valve Junior Conversion Version
Build Manual 3 August 009
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Plexi SE PCB
Valve Junior Conversion
Build Manual
http://www.GuitarAmplifierPCBs.com
Plexi SE PCB Valve Junior Conversion Version
Build Manual 3 August 009
of 34
1. Introduction
This manual contains instructions to convert an Epiphone Valve Junior into a 5
watt single ended tube amplifier modeled after the legendary Marshall 1 5
Super Lead (Plexi). The heart of the amp is the Plexi SE PCB, which
conveniently lays out the circuit in a printed circuit board, PCB, package.
This manual provides instruction for the assembly of version 1.0 of the Plexi SE
PCB.
To simplify things,
• The Epiphone Valve Junior will be referred to as EVJ, and
This manual guides you through the conversion which includes:
• removing the stock EVJ chassis from its cabinet,
• extracting the stock EVJ pcb,
• drilling the chassis,
• assembling the Plexi SE PCB,
• installation and hookup of the Plexi SE PCB into the EVJ chassis,
• initial power-up and testing, and
• reinstalling the chassis back into the EVJ cabinet to finish up the job.
Here’s a look at the Plexi SE PCB if you haven’t purchased yours yet.
Version 1.0
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2. Electrical Shock Warning
Building tube amplifiers involves working with, or around, high voltages. Working
inside a tube amplifier can be dangerous if you don't know the basic safety
practices. Building, modifying, or repairing tube amplifiers should only be
performed by trained personnel.
3. Disclaimer of Liability
GuitarAmplifierPCBs.com assumes no liability or responsibility, under any
circumstance, for personal injury or damage to property or personal property.
GuitarAmplifierPCBs.com reserves the right to make design changes or
improvements without obligation to revise prior versions.
All specifications are subject to change without notice.
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Plexi SE PCB Valve Junior Conversion Version
Build Manual 3 August 009
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Table of ontents
1. Introduction ............................................................................................................................. 2
2. Electrical Shock Warning........................................................................................................ 3
3. Disclaimer of Liability .............................................................................................................. 3
4. Project Overview..................................................................................................................... 5
4.1 Here’s what you’ll need: ................................................................................................. 5
4.1.1 Parts: ..................................................................................................................... 5
4.1.2 Tools: ..................................................................................................................... 5
4.1.3 Supplies: ................................................................................................................ 5
5. Let’s get started…................................................................................................................... 6
5.1 Remove the EVJ chassis ............................................................................................... 6
5.2 Remove the EVJ’s Stock Components .......................................................................... 7
5.2.1 Remove the Tubes and Tube Retainers ............................................................... 7
5.2.2 Remove the Output Transformer from the Chassis .............................................. 7
5.2.3 Clean Up the Power Transformer.......................................................................... 8
5.2.4 Remove the Volume Potentiometer ......................................................................
5.2.5 Remove the Stock EVJ Circuit Board....................................................................
6. Prepare the Chassis ............................................................................................................. 11
6.1 Layout and Drill ............................................................................................................ 11
6.1.1 Layout the Plexi SE PCB for Drilling ................................................................... 11
6.1.2 Layout the Faceplate for drilling .......................................................................... 12
6.1.3 Drilling the Chassis.............................................................................................. 13
7. Plexi SE PCB ........................................................................................................................ 13
7.1 Assemble the Plexi SE PCB ........................................................................................ 13
7.1.1 PCB Standoffs ..................................................................................................... 14
7.1.2 Tube Sockets....................................................................................................... 14
7.1.3 Spade Connectors............................................................................................... 15
7.1.4 Diodes.................................................................................................................. 16
7.1.5 The “Plexi Preamp”.............................................................................................. 17
7.1.6 The “Cascade Preamp” ....................................................................................... 18
7.1.7 Wiring the Heaters............................................................................................... 1
7.1.8 Filter Capacitors .................................................................................................. 21
7.1. Bypass Capacitors............................................................................................... 22
7.1.10 Install the Remaining Components ..................................................................... 23
7.1.11 Input Jack ............................................................................................................ 24
7.1.12 Control Leads ...................................................................................................... 25
8. Putting it All Together............................................................................................................ 26
8.1 Install the New Components ........................................................................................ 26
8.1.1 Hookup the Plexi SE PCB ................................................................................... 26
. Turn on the Power ................................................................................................................ 2
.1 Check Your Work ......................................................................................................... 2
.1.1 Take a Break ....................................................................................................... 2
.1.2 Visual Inspection ................................................................................................. 2
.2 Power Up without Tubes .............................................................................................. 30
.2.1 The First Power Up.............................................................................................. 30
.3 Power Up with Tubes ................................................................................................... 32
.3.1 The Real Test ...................................................................................................... 32
10. Finish Things Up............................................................................................................... 34
10.1 Re-Assemble the Amp ................................................................................................. 34
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Build Manual 3 August 009
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4. Project Overview
You’ll find that this is a fun project that can be completed by an inexperienced
builder in a day or two. We at GuitarAmplifierPCBs.com wrote this manual
specifically for the novice builder. So, anyone can do it. Really, it’s simple and it
doesn’t require expensive tools or complex equipment.
4.1 Here’s what you’ll need:
4.1.1 Parts:
• The Plexi SE PCB
• Misc. parts and components (refer to the Plexi SE PCB parts list
document for a full listing of what parts are needed and where you
can buy them)
4.1.2 Tools:
• Phillips head screw driver
• Standard screw driver
• Needle nose pliers
• Adjustable wrench
• Power drill (corded or cordless)
• 3/16”, 5/16”, 7/16”, 1/2" Metal cutting drill bit
• Unibit or punch (one 1¼ in. holes)
• Soldering iron (30-40 watt power rating)
4.1.3 Supplies:
• Fluxed solder
• Roughly 6 ft. 600v rated wire (22-18 AWG)
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5. Let’s get started…
OK. So you have all the parts and are ready to start. Let’s get that EVJ chassis
out of the cabinet.
5.1 Remove the EVJ chassis
Take off the back panel by removing the seven (7)
screws using a Phillips head screw driver.
Be careful pulling off the back panel.
They are typically stuck onto the chassis.
Slowly pull from each side to prevent the
tolex from lifting off the panel.
Locate the screw caps on the top of the EVJ. Using
a standard screw driver, the smaller the better, pry
up the caps until you can pull them out of their
sockets.
Remove the four chassis screws and pull out the
chassis.
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Build Manual 3 August 009
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5.2 Remove the EVJ’s Stock omponents
A few of the stock EVJ parts have to be replaced. The tubes, tube retainers, and
stock circuit board need to be removed.
5.2.1 Remove the Tubes and Tube Retainers
It’s as simple as:
• lift the tube retainer off the power tube,
• turn the retainer shield until the spring lifts the shield off the per-amp tube,
• pull the tubes out, and
• unclip the power tube retainer.
These items can be discarded. They will not be used later in the build.
Now that the tubes and their hardware have been
removed we can take a look inside. This is a version 2
EVJ. You can tell by the green board and the rectified
DC heater supply. Version 3s have a black board.
5.2.2 Remove the Output Transformer from the hassis
One mounting location for the circuit
boards falls near the edge of the stock
output transformer. So, the output
transformer needs to be unscrewed
from the chassis and pushed aside.
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Build Manual 3 August 009
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5.2.3 lean Up the Power Transformer
The stock EVJ’s power transformer provides leads for various mains supply
voltages. The extra leads are fastened to dead posts on the stock circuit board
for storage. We are going to clean up the inside of the chassis by pulling any
unused power transformer leads outside of the chassis cavity.
Disconnect these three (3) leads from
the stock EVJ circuit board.
Version 1 and 2 EVJ will
have 12v secondary taps
tied off and tucked inside the
chassis. These need to be
pulled outside and secured
as well.
After the leads are all pulled outside
the chassis, bundle them together and
tie them off.
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Build Manual 3 August 009
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5.2.4 Remove the Volume Potentiometer
Unscrew the fastening nut from the volume
potentiometer.
Pull the volume pot back into the chassis. Leave it
connected to the stock EVJ circuit board.
The volume pot will be glued to the
chassis. This part will NOT be used later
in the build, so use whatever force you
need.
5.2.5 Remove the Stock EVJ ircuit Board
Disconnect these four (4) leads from
the stock EVJ circuit board.
Lift the ground wire from the star
ground post.
Unplug the input jack wire at the circuit
board.
Remove the six (6) screws fastening
the circuit board to the chassis.
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Plexi SE PCB Valve Junior Conversion Version
Build Manual 3 August 009
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Remove the stock circuit board and
pull all of the power transformer leads
to the rim of the chassis.
Salvage the ground wire from the
stock circuit board for use later.
Unscrew the input jack and remove it
from the chassis. Set it aside for use
later.
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