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http://www.GuitarAmplifierPCBs.com 1. Introduction This manual contains instructions to convert an Epiphone Valve Junior guitar amplifier to a roaring 18Watt amp modeled after the famed Marshall 1974X circuit. The heart of it all is the “Baby Will”, a simplified version of Marshall’s 1974X amp known as the LiteIIb. The Baby Will takes the LiteIIb circuit and conveniently lays it out in a printed circuit board, PCB, package. This manual provides instruction for the assembly of version 2.
http://www.GuitarAmplifierPCBs.com Here’s a look at the Baby Will PCB if you haven’t purchased yours yet. Version 2.
http://www.GuitarAmplifierPCBs.com 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.
http://www.GuitarAmplifierPCBs.com Table of Contents 1. 2. 3. 4. Introduction ............................................................................................................................. 2 Electrical Shock Warning ........................................................................................................ 4 Disclaimer of Liability .............................................................................................................. 4 Project Overview...................
http://www.GuitarAmplifierPCBs.com 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 “Baby Will” circuit board Misc.
http://www.GuitarAmplifierPCBs.com 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.
http://www.GuitarAmplifierPCBs.com 5.2 Remove the EVJ’s Stock Components A few of the stock EVJ parts have to be replaced. The tubes, tube retainers, stock circuit board, and output transformer 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.
http://www.GuitarAmplifierPCBs.com Unscrew the output jacks from the chassis and separate the board from the chassis. The board will be glued to the chassis. It may require some extra work to pick the glue off. Be careful not to damage the board or the output jacks. They will be reused later. Flow the solder to each transformer lead on the output jack board and pull the lead out. Remove the fastening nut at the star grounding post and remove the output board’s ground wire.
http://www.GuitarAmplifierPCBs.com Here’s the output board and the output transformer after removal. Set the output board aside. It will be used later in the build. The output transformer can be discarded. It will NOT be used later in the build. 5.2.3 Clean 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.
http://www.GuitarAmplifierPCBs.com 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 Circuit Board Disconnect these four (4) leads from the stock EVJ circuit board. Lift the ground wire from the star ground post.
http://www.GuitarAmplifierPCBs.com 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.
http://www.GuitarAmplifierPCBs.com 6. Prepare the Chassis 6.1 Layout and Drill The Baby Will circuit board, tone potentiometer, and the new output transformer require some drilling in the chassis. 6.1.1 Layout the Drill Plans Always verify you are using the latest version of the drill plan posted on GuitarAmplifierPCBs.com. If you can not print onto 11x17” paper, you can take an electronic version of the drill plan to Kinkos. They will print it professionally for under $1.
http://www.GuitarAmplifierPCBs.com 6.1.2 Drilling the Chassis Start by setting the center of each hole to be drilled. A center punch is often used. Here, a 1/16” drill bit was used as shown in the picture. Use the appropriate drill bit size as prescribed by the drill plan. Here, a unibit was used to drill out the 7/8” hole for the two (2) additional tube socket holes. Deburr or countersink each hole to ensure no sharp edges will cause injury or component failure.
http://www.GuitarAmplifierPCBs.com Version 2.3 of the Baby Will circuit board was designed to use most of the stock chassis mounted pcb standoffs. However, you need to remove one (1) standoff for the board to fit. Drill out and remove the stock standoff as shown in the picture below.
http://www.GuitarAmplifierPCBs.com 7. The Baby Will 7.1 Assemble the Baby Will Circuit Board The anticipation has been killing you, hasn’t it? Finally, the assembly of the Baby Will begins. Did you check you make sure you have all of the parts you’ll need to complete the assembly? I wish I did. 7.1.1 Tube Sockets The tube sockets get installed on the back side of the board. I repeat the back side of the board. Insert the tube sockets as shown. They only go in one way (on the back side).
http://www.GuitarAmplifierPCBs.com 7.1.2 PCB Standoffs Install the one (1) PCB standoff on the back side of the board in the location shown. 7.1.3 The Power Grid Install the four (4) rectifier diodes. Orient the diodes as indicated on the circuit board. Bend the leads over, insert them into the board, and bend them to the side as shown. Solder them to the board.
http://www.GuitarAmplifierPCBs.com Trim the leads off at the top of each solder pool. Install, solder and trim all of the resistors in the power grid as shown. Refer to the latest version of the schematic on GuitarAmplifierPCBs.com, the Baby Will circuit board, and the component package to identify, locate and position component values. The filtering capacitors are not installed at this time. The height of these capacitors interferes with the installation of the other components.
http://www.GuitarAmplifierPCBs.com 7.1.4 Signal Path and Cathode Resistors Install, solder and trim all of the signal path and cathode resistors as shown. Don’t bother with the input section. We’ll get to that later. 7.1.5 Sag Resistor Install, solder and trim the sag resistor as shown.
http://www.GuitarAmplifierPCBs.com 7.1.6 Signal Path and Cathode Capacitors Install, solder and trim all of the signal path and cathode capacitors as shown. Make sure the 47uF cathode bypass capacitors are oriented with the polarities indicated on the circuit board. 7.1.7 Hum Balance Version 2.3 of the Baby Will circuit board is equipped with a DC elevated artificial center tap.
http://www.GuitarAmplifierPCBs.com 7.1.8 Filter Capacitors and Ground Wire We can install the filter caps now that we have most of the components installed on the board. Insert the three (3) filter capacitors in their locations as indicated on the board. These capacitors are polarized. Be careful to install them by inserting the positive lead (the longer one) into the square pad and the negative lead (as indicated by the downward arrow and “-“ symbol) in the round pad.
http://www.GuitarAmplifierPCBs.com 7.1.10 Input Jack Hookup The input section of the Baby Will is designed to accommodate a variety of configurations. The VJ Conversion only calls for one input jack. This requires a jumper to tie the two input leads together so the two halves of V1 (12AX7) work in parallel. The lead from R19 will be used to jumper the two inputs. Bend the leads of the 1Meg resistor over as usual and insert it into the R19 location.
http://www.GuitarAmplifierPCBs.com Prepare the stock input jack by cutting off the stock connector. Cut off the connector that plugged into the stock EVJ circuit board. Leave the input connector plugged into the input jack board. Strip the insulation from the leads. Insert the white lead into the input #1 (“IN-1”) pad and the black lead into a ground pad. Solder and trim. The input section is done.
http://www.GuitarAmplifierPCBs.com Here’s what everything should look like so far - minus the input jack wiring. Oops, this picture is missing the ground wire, too.
http://www.GuitarAmplifierPCBs.com 7.1.11 Volume and Tone Controls To better understand how the volume and tone controls are wired, we recommend that you study the VJ Conversion Chassis Layout and Schematic. Cut the tab off of each of the pots with a pair of cutters (side cuts). A pair of pliers can also be used to bend the tab over and break it off. We like to install the controls on the outside of the chassis for better access.
http://www.GuitarAmplifierPCBs.com 8. Putting it All Together 8.1 Install the New Components Now that everything is out of the chassis that we don’t need, the chassis has been drilled, and the Baby Will has been assembled, we can prep the chassis and install all of the new components. 8.1.1 The New Output Transformer Relocate the extra power transformer grommet from the left-front to the new hole drilled for the output transformer.
http://www.GuitarAmplifierPCBs.com Cut and solder the output transformer leads onto the output jack board. Refer to the GuitarAmplifierPCBs.com layout diagram, transformer hookup diagram, and output jack board for hookup details. Re-Install the output jack board into its stock location. Guide the ground wire from the output jack board to the star grounding stud. This will be secured to the stud later.
http://www.GuitarAmplifierPCBs.com 8.1.2 The Baby Will PCB and Tube Hardware Lay the Baby Will down into the EVJ chassis with the tube sockets toward the chassis and the diodes toward the power rocker switch. Align the standoffs with their respective holes and fasten a screw into the standoff(s) near the power transformer. Do not tighten them down. Install and fasten the volume and tone controls and the input jack into the chassis.
http://www.GuitarAmplifierPCBs.com 8.1.3 Hookup the Leads to the Baby Will The board is installed in the chassis, but we still need to hook the high voltage supply, heater element supply, and output transformer. Guide the high voltage secondary leads to the T1 and T2 locations on the board. Add some extra length (½” or 12mm) and cut the wires. Strip ¼” of the insulation from the wire, twist the wire ends, and tin the end of the wire with some solder. Insert one of the leads into T1.
http://www.GuitarAmplifierPCBs.com Here’s how it should look when everything is hooked up. Good Job! You’re almost done. But, before you start celebrating, you still have to review your work, start it up and test the voltages.
http://www.GuitarAmplifierPCBs.com 9. Turn on the Power 9.1 Check Your Work 9.1.1 Take a Break Now is a good time to take break. Rest your mind and gather your thoughts. You don’t want to be tired or rushed while performing the following steps. 9.1.2 Visual Inspection When you are ready, step through the instructions in this manual again and verify each step was performed and completed properly.
http://www.GuitarAmplifierPCBs.com 9.2 Power Up without Tubes 9.2.1 The First Power Up Make sure you are working is a safe area free of any flammable chemicals or vapors. An assembly error may result in the emission of sparks. The tubes should NOT be installed during the initial power up. Plug the amplifier into a speaker cabinet. Match the speaker impedance with the appropriate output jack. Failure to connect a speaker will cause harm and eventual failure of the output transformer.
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http://www.GuitarAmplifierPCBs.com 9.3 Power Up with Tubes 9.3.1 The Real Test Install the tubes! Aren’t they pretty? These measurements WILL match those on the schematic. Verify the amp’s power switch is in the “OFF” position. Insert the mains power cord in the IEC mains connector. Secure the black ground lead of your voltmeter to the chassis star ground lug. Plug the amplifier into a speaker cabinet. Match the speaker impedance with the appropriate output jack.
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http://www.GuitarAmplifierPCBs.com 11. Finish Things Up 11.1 Re-Assemble the Amp Slide the chassis back into the stock cabinet. Fasten the chassis to the cabinet with the stock screws. Insert the screw caps into the sockets. Press them in until they are flush with the cabinet surface. Attach the back panel with the stock screws. Congratulations! Your Valve Junior is complete. Plug in a guitar and enjoy the legendary tone of your 18 Watt LiteIIb “Baby Will” guitar amplifier.
