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Build Your Own Clone Classic Brit 50

Kit Instructions (Revision 1.0)

WARNING!!! HIGH VOLTAGE!!!! Tube amplifiers contain high voltage that can cause injury and even death. Please use extreme caution and common sense when building this kit. Do not attempt to do anything to your amp while it is plugged in other than take voltage readings as necessary or actually playing an instrument through it as it was intended. Don't just turn the power off!!! Always unplug the power cord from the socket before working on your amp!!! The mains supply can still electrocute you AND the power filter capacitors can still retain a charge powerful enough to kill you. Always unplug the power cord from the socket before working on your amp.

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DISCLAIMER Build at your own risk!!! BYOC, Inc. is not liable or responsible for any damages, injuries, or deaths that may incur from or while building this kit. It is your own responsibility to follow proper safety precautions. Never attempt to build, modify, repair, or perform any sort of maintenance on your amplifier while the power cord is plugged into an AC power source. This kit contains only the amplifier chassis. It is intended to be housed in a non-conductive, electrically insulated cabinet or enclosure. This kit does not come with any such cabinet or enclosure and is not intended to be used without one. It is your responsibility to house this amplifier kit in a proper cabinet or enclosure before attempting to use it. Warranty: BYOC, Inc. guarantees that your kit will be complete and that all parts and components will arrive as described, functioning and free of defect. Soldering, clipping, cutting, stripping, or using any of the components in anyway voids this guarantee. BYOC, Inc. guarantees that the instructions for your kit will be free of any majors errors that would cause you to permanently damage any components in your kit, but does not guarantee that the instructions will be free of typos or minor errors. BYOC, Inc. does not warranty the completed kit as a whole functioning unit, nor do we warranty any of the individual parts once they have been used. If you have a component that is used, but feel it was defective prior to you using it, we reserve the right to determine whether or not the component was faulty upon arrival. Please direct all warranty issues to: sales@buildyourownclone.com This would include any missing parts issues. Return: BYOC, Inc. accepts returns and exchanges on all products for any reason, as long as they are unused. We do not accept partial kit returns. Returns and exchanges are for the full purchase price less the cost of shipping and/or any promotional pricing. Return shipping is the customer’s responsibility. This responsibility not only includes the cost of shipping, but accountability of deliver as well. Please contact sales@buildyourownclone.com to receive a return authorization before mailing. Tech Support: BYOC, Inc. makes no promises or guarantees that you will successfully complete your kit in a satisfactory manor. Nor does BYOC,

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Inc. promise or guarantee that you will receive any technical support. Purchasing a product from BYOC, Inc. does not entitle you to any amount of technical support. BYOC, Inc. does not promise or guarantee that any technical support you may receive will be able to resolve any or all issues you may be experiencing. That being said, we will do our best to help you as much as we can. Our philosophy at BYOC is that we will help you only as much as you are willing to help yourself. We have a wonderful and friendly DIY discussion forum with an entire section devoted to the technical support and modifications of BYOC kits. www.byocelectronics.com/board When posting a tech support thread on the BYOC forum, please post it in the correct lounge, and please title your thread appropriately. If everyone titles their threads “HELP!”, it makes it impossible for the people who are helping you to keep track of your progress. A very brief description of your specific problem will do. It will also make it easier to see if someone else is having or has had the same problem as you. The question you are about to ask may already be answered. Here is a list of things that you should include in the body of your tech support thread: 1. A detailed explanation of what the problem is. (Not just, “It doesn’t work, help”) 2. Photo that clearly shows your circuit board. 3. Photo that clearly shows the tube-side of inside of the chassis. 4. Photo that clearly shows the inside of the front of the chassis. 5. Photo that clearly shows your wiring going from the circuit board to the pots and any other switches (only if your kit has non-PC mounted pots and switches). 6. Does the indicator light come on? Also, please only post photos that are in focus. You're only wasting both parties' time if you post out of focus, low-resolution photos from your cell phone. Credits: Written by: N.W. Kenning & K. Vonderhulls Artwork & Photography by: N.W. Kenning Revision Notes: None All material in this document is copyrighted 2016 by BYOC, Inc.

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CLASSIC BRIT 50 KIT INSTRUCTION INDEX

Parts Checklist…………………………………………………page 5 - 8 Chassis Assembly………….………...…………………….…...page 9 - 20 Wiring (Power Section)…………….………………………….page 21 - 50 Populating the Circuit Board……………..…………………..page 51 - 66 Wiring ………………………………………………………….page 67-75 Wiring(Tube Side)……………………………………………..page 76 - 93 Wiring (Potentiometer Side)………..…………………………page 94 – 111 Wiring Layouts/Diagrams……………………………………..page 112 - 113 Turning Your Amp on for the First Time……………………page 114 – 117 Biasing…………………………………………………….…….page 118 Operating Overview……………………………………….…...page 119 -120 Diagrams and Schematic………………………………….…...page 121 - 125

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Parts Checklist for Classic Brit 50 Kit

Resistors: 1/2watt (4th color band will either be silver or gold): 1 – 470 ohm (Yellow/Purple/Brown) 2 – 820 ohm (Gray/Red/Brown) 1 - 2.7K (Red/Purple/Red) 1 – 10K (Brown/Black/Orange) 1 – 15K (Brown/Green/Orange) 1 – 33K (Orange/Orange/Orange) 2 - 47K (Yellow/Purple/Orange) 4 – 68K (Blue/Gray/Orange) 1 – 82K (Gray/Red/Orange) 5 – 100K (Brown/Black/Yellow) 3 – 220K (Red/Red/Yellow) 2 – 470K (Yellow/Purple/Yellow) 4 – 1M (Brown/Black/Green) 1watt: 2 – 1 Ohm (Brown/Black/Black/Silver/Brown) 2 - 5.6K (Green/Blue/Black/Brown/Brown) 2watt: 2 – 8.2K (Gray/Red/Black/Brown/Brown) 2 - 10K (Brown/Black/Black/Red/Brown) 5watt: 2 – 1K (Brown/Black/Black/Brown/Brown or just say “1k” on them)

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Diode: 5 – 1n4007 (or byv26ev) Capacitors: 1 – 47pF (Red or black with ‘47’ on the body) 2 – 500pF (Red or black with ‘500’ on the body) 2 – 0.1uF axial leaded polyester film 7 – 0.022uF axial leaded polyester film 2 - .68uF axial leaded polyester film 2 – 10uF/150V Electrolytic 1 – 220uF/25V Electrolytic 2 – 32+32 Electrolytic (Really big with three terminals) 1 - 33+33 Electrolytic (Somewhat big with three terminals) Potentiometers: 3 – A1M (Bass, Loudness 1, and Loudness 2) 1 – B5K (Presence) 1 – B25K (Middle) 1 – B250K (Treble) Hardware: 1 - Chassis 1 - Circuit board 3 - Circuit board hex standoffs 1 – Rotary Switch 2 – ON/OFF SPST Toggle switch 2 - 8 pin tube sockets 2 – Octal Tube Retainer Clips 3 - 9 pin tube socket w/shield

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6 – ¼” Shorting Mono Jacks 1 - Indicator Lamp 1 - 6' 3-conductor power cord 1 - Power cord socket 2 – black screws for power cord socket 1 - Panel mounted fuse holder 1 - Flat-Mount Fuse Holder 1 - Mains Fuse (3A Slow-Blow for 120V, 2A Slow-Blow for 220V or 240V) 1 - HT Fuse (500mA) 3 - Rubber Grommets 25 – M3 screws 12 – M3 nuts 6 - #4 lock washer 6 - Wire nuts 6 – M4 screws 6 – M4 nuts 6 – M4 flat washers 6 - #8 internal lock washers (for the M4 screws/nuts) 4 - #10 nut 4 - #10 flat washer 2 - #10 internal lock washer 2 – lock washer w/solder terminal 2 - mounting rings for large electrolytic capacitors Wire: 3’ – Green 20AWG 4' - White 20AWG 3' - Black 20AWG 4' - Yellow 20AWG 4' - Brown 20AWG 2' - Red 20AWG 3.5' - Bare Bus

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Save the wire you clip from the transformers as well. This will provide you with more than enough wire to complete your kit. Tubes: 3 – ECC83 2 – EL34 Transformers: 1 – Power Transformer (Classic Tone 40-18033) 1 – Output Transformer (Classic Tone 40-18025) 1 – Choke (Classic Tone 40-18058)

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Chassis Assembly

Step 1: Add grommets

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Step 2: Mount the transformers. Orient the power transformer so that the side with the green wires is towards the “tube side” of the chassis. Orient the output transformer so that the side with the black/yellow/purple/orange wires is towards the “tube side” of the

chassis. Orient the choke so that the side with the wires is over the grommet hole. The power transformer will already have mounting screws attached. Use #10 nuts and flat washers for the power transformer. Use the two #10 lock washers for the screws closer to the outside of the chassis. Use the two lockwashers with solder terminals on the screws closer to the inside of the chassis. Use the M4

screws, M4 nuts, M4 flat washers, and #8 lock washers to mount the output transformer and choke.

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Step 3: Add the tube sockets (red arrows)

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3a: Adding the 9 pin sockets - First crimp pins 4 & 5 of the 9-pin sockets. You don’t really have to do this. When you hook up the heater wires, you will need to connect pins 4 & 5. Some people think crimping these two pins together makes it easier, but if you

don’t want to do this, you can just use wire to jump the two pins together.

Orient the 9 pin sockets so that pins 4 & 5 are closer to the back side of the chassis. Use M3 screws to mount the 9 pin sockets. The

chassis will have braze-on nuts already build in.

3b: Add the Octal Sockets. Orient the sockets as shown below. The notch in the socket should be pointed towards the back side of the

chassis. Follow the exploded diagram on page 14 for the order in which to mount the various parts.

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Only add the ring terminal to the power tube sockets. Do not add a ring terminal to any other tube socket

Use M3 screws and M3 nuts. See next page for exploded diagram.

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Step 4: Mount the two 32uF x 32uF capacitors to the outside of the chassis. Use the mounting rings to mount to chassis. Use M3 screws to mount to chassis of the left capacitor (Green arrow). Use M3 screw and nut to tighten clamps. Use M3 screw, M4 flat washer, and M3 nut to attach mounting ring of the right capacitor (Red arrow). Orient them so the silver lug is facing towards the

panel mounted fuse holder.

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Step 5: Add flat mount fuse holder. Use 1 x M3 screw and 1 x M3 nut.

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Step 6: Add the rear plexi panel and rear panel mounted parts !!!!The plexi panels are EXTREMELY DELICATE!!!!

6a: Mount the AC Power Cord Receptacle. Use black flat head screws for power cord receptacle.

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6b: Mount the rotary switch. Bend the rotary switch tab flat before mounting to the panel.

6c: Mount the two speaker jacks and the panel mounted fuse holder. After these are in place, use an M3 screw to secure the far end

of the rear plexi panel.

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Step 7: Add the front plexi panel and panel mounted parts

7a: Add the Switches and lamp. Orient the toggle switches so that the “ON” arrow is pointing in the same direction as the “ON” label on the plexi panel. The lamp is not mounted with any nuts or bolts. You simply push it through its hole and it will lock in place. The

lamp may be loose fitting. You can use a thick glue (i.e., a glue that is not runny) to hold it in place better once you have finished building your amp.

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7b: Mount all the potentiometers and the four remaining ¼” jacks.

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Wiring (power section)

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Step 1: Solder the High Voltage Center Tap (red/yellow) and Heater Center Tap (green/yellow) wire to ground via the lower lock washer w/ solder tab.

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Step 2: Cut the orange, gray, white, and both yellow wires. Cut the brown wire if you are using 120V. Cut the black wire if you are using 240V. These are you mains wires for the power transformer. Leave them long enough

so that you can switch them if you need to at a later date. Put a wire nut on each of the wires, and tie them together with a cable tie.

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Step 3: Connect the OFF side of the MAINS switch to the center lug of the panel mounted fuse holder.

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Step 4: Attach the remaining terminal on the panel mount fuse holder to the ‘L’ terminal of the AC receptacle.

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Step 5: Attach the Black wire from the transformer (Or brown if using 240V) and one lamp wire to the ON side of the MAINS switch.

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Step 6: Connect the remaining lamp wire and the blue wire from the transformer to the “N” terminal of the AC receptacle.

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Step 7: connect the OFF side of the STANDBY switch to the red lug of the first 32 +32 capacitor. At the same time, make a jump connection between the positive lugs. Only solder at the green arrows, not the red arrow yet.

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Step 8: Connect the silver lug of the first 32 + 32 capacitor to the silver lug of the second 32 + 32 capacitor. Connect the “E” terminal of the AC receptacle to the silver lug of the second 32 + 32 capacitor, and then connect to

ground.

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Step 9: Connect ON side of the STANDBY switch to one end of the flat fuse holder.

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Power Wiring Drawing

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Step 10: Add bus wire to the speaker jacks. Solder on the green arrows, not on the red arrows yet.

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Step 11: Connect the black wire from the OT secondary (Common) to the Sleeve bus and solder.

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Step 12: Connect the yellow, orange, and purple wires to the rotary switch as shown.

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Step 13: Using a piece of white wire, connect the tip bus to the pole terminal of the rotary switch as shown. Solder the tip bus.

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Step 14: Connect the Output Transformer primaries to their respective sockets. Blue to pin 3 of the V5 power tube, which is closest to the power transformer. Red to pin 3 of the V4 output tube as shown.

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Step 15: Connect a 1 ohm 1 Watt resistor from pins 1 & 8 of the V5 power tube (tube closest to the power transformer) to the terminal ring (page 13) and solder. It is difficult to see in the picture, but one end of the resistor

is threaded through both pins 1 & 8.

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Step 16: Repeat the previous step for the V4 power tubes, but this time, also add a black wire to the terminal ring. Connect the other end of the black wire to the remaining unsoldered lug on the speaker jacks. You should now

have all of the lugs on the speaker jacks soldered.

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Step 17: Connect the 6.3V heater wires from the power transformer to the filament pins of the power and preamp tubes. Start with the power tubes. One green wire goes to pin 2, the other to pin 7 of each power tube. It does not

matter which green wire goes to which pin. Insert the wires into the their solder terminals. Before you solder, insert another length of green wire into those same solder terminals to connect to the next tube. The heater wires

will “daisy chain” to all the tubes.

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Step 18: Continue daisy chaining the heater wire to the pre amp tubes. Pre amp tube filament pins are 9 and 4/5. You will need to jumper pins 4 and 5 if you elected not to crimp them together earlier.

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Step 19: Connect 1k 5W resistors between pins 4 and 6 of V4 and V5 as shown. Only solder on pin 4 of both sockets for now.

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Step 20: Using a length of brown wire, make a jump between pins 6 of each power tube. Only solder pin 6 of V5 (closest to the transformer).

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Tube Side Wiring

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Step 21: Connect a bare bus wire to the back of the potentiometers as shown. We will refer to this as the “ground bus”. If you are having trouble connecting the bus wire to the back of the potentiometers, you can rough up the

backs with some emery cloth or a file, this should help with solder adhesion.

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Step 22: Connect a .1uF capacitor between lugs 1 and 2 of the B25K Presence potentiometer. Thread the extra lead through lug 1 and solder it to the back of the potentiometer as shown.

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Step 23: Prepare the bottom row of input jacks. Connect a 1M 1/2Watt resistor between the tip and sleeve terminals of each jack, threading the extra lead through the sleeve terminal to the tip disconnect terminal as shown. Connect a 4” piece of black wire to each sleeve terminal. Solder the sleeve terminal only. They should look like the

picture above.

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Step 24: Use ¾” of bus wire to connect the sleeve terminal of the other input jacks to the tip disconnect terminal as

shown. Only solder the terminals with green arrows.

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Step 25: Mount the input jacks and connect the black wires to the ground bus at the green arrow.

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Step 26: Connect the ground bus to the last terminal washer mounted to the power transformer and solder at the green arrows.

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Chassis Wiring Layout

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Populating the Circuit Board

Step 1: Run bus wire along turret lugs as shown. Solder the bus wire jumps.

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Step 2: Insert trimpot so that one wiper is not inserted into a turret lug as shown.

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Step 3: Insert all components into circuit board except for the large 32uF + 32uF capacitor, and two large .68uf capacitors. Insert leads into openings of turret lugs. DO NOT solder the red arrows for now. Solder all the other

turret lugs and bus wires. It is easier to solder the bus wire connections first. Do not use too much solder. It will fill up the turret lugs and run out through the other side. If you are having problems with this, tilt the circuit board

slightly or on its side so that you are not fighting against gravity as hard.

NOTE: If your kit came with byv26ev diodes (gray with black stripe), they will be oriented so that the black stripe is in place of the gray stripe on the 1n4007 diodes.

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Drawing of component placement so far. DO NOT solder the red arrows yet.

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Step 3a: Add the large capacitors that were left out of the previous step, and solder all connections.

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Completed Board Component Placement Picture

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Step 4: Make bare bus connection on underside of board between the “potentiometer side” of the 8.2k 2W and 100K/82K junction. Make a 2nd connection between 82K/100K and “potentiometer side” of the 10K 1W. Make a

3rd connection between 820Ohm/220uF/2.7k/.68uF junction and 820Ohm/100K/.68uF junction as shown.

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Step 5: Make a jumper connection on the underside of the board between the 15K/10uF junction and the 200k/200k junction.

Add a 2nd jumper connection between the “potentiometer side” of the 47K and the 10K/.1uF junction. Add a 3rd jumper connection between the left 10K 2W/33uF + 33uF capacitor and the 100K/100K junction as shown.

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Top-side picture with component values and the underside wires. Top of pic is the potentiometer side. Bottom of pic is the tube

side.

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Example of wire connections to top tier of turrets.

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Step 6: Connect off-board wires to top tier of turret lugs on the board. Start with the “potentiometer side”. Use 10” of red wire

off the 8.2K 2W resistor. Use 8” of brown and yellow wires off each 200K/.022uF junctions. Use 8” of white wire off the 10K/.1uF junction. Use 4” for all other wires. Here we are using black wires for all ground connections and we are alternating

brown, yellow, white with all others. We are only doing this to make it visually easier to differentiate the wires.

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Step 7: Connect off board wires to the two 68K/68K junctions and 500pF/470K/470K junction. Thread the wires through the board as shown at the red arrows use 6” of wire for these connections.

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Step 8: Add the rest of the off-board wires to the “tube side” of the circuit board. Use 7” of red wire from the currently unused turret lug. Use 7” of green wire off the “tube side” of the 8.2K 2W resistor. Use 6” of orange wire from the “tube side” of the

47K resistor. Use 4” for all other wires.

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Step 9: add the 3 hex standoffs at the red arrows. Use M3 screws.

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Top-side component picture showing the location of the standoffs in green.

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Step 11: Mount the circuit board. 11 a: Run the brown and yellow wires from the two 220K/.1uF junctions under the board so they stick out on the “tube side”

(red arrows). Also run the red wire coming from the “potentiometer side” of the 8.2K 2W resistor under the board. (green arrows)

11 b: Make sure you can get to the remaining choke wire and 1K 2Watt resistor (blue arrow), and the remaining white OT primary wire (orange arrow)

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Wiring

Step 1: Connect the red wire from the empty turret lug to the previously unsoldered lug of the first 32uF + 32uF capacitor. Solder the

capacitor lug. (shown at green arrows).

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Step 2: Twist the red wires from the transformer together and attach to the rectifier diodes as shown. Solder both connections.

WARNING!! A: DO NOT make wires/leads so long that they go through the turret lug and out of the other side. They may touch the

chassis and cause a short. B: DO NOT use too much solder. It may drip out the bottom and cause a short.

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Step 3: Attach the green wire from the “tube side” of the rectifier diode junction to the remaining lug of the flat fuse holder.

(green arrows)

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Step 4: Connect the red wire from the “potentiometer side” of 8.2K 2W resistor to the YELLOW terminal of the 32uF+32uF electrolytic capacitor (red arrows). Also connect the green wire from the “tube side” of the 8.2K 2W resistor to the RED terminal

of the 32uF+32uF capacitor (green arrows) Solder both connections.

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Step 5: Connect the remaining white OT wire and one of the choke wires (it doesn’t matter which choke wire) to the previously empty turret lug. (green arrow) solder.

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Step 6: Using a short piece of brown wire, connect the unsoldered pin 6 of V4 to the “tube side” of the 8.2K 2W resistor. At the same time, connect the remaining choke wire to the same turret lug (green arrows). Solder all the connections.

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Step 7: Prepare the 5.6K 1W resistors as shown. The straight piece will go into pin 5 of V4 and V5 in the next step.

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Step 7a: Attach the brown and yellow wires from the “potentiometer side” of the 220k/.022uF junctions to pin 5 of V4 and V5 using the 5.6K 1W resistors prepared in the previous steps. Attach the brown wire to V5, and the yellow wire to V4 (shown at

green arrows). Solder all connections.

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Step 8: Attach the orange wire from the ‘tube side” of the 47K resistor to the orange OT wire that is already attached to the

rotary switch (green arrows).

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Tube Socket Wiring

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Step 1: Attach the first white wire from the 47pF/100K/.022uF junction to pin 6 of V3.

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Step 2: Attach yellow wire from 47pF/82K/.022uF junction to pin 1 of V3.

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Step 3: Attach brown wire from .1uF/1M junction to pin 7 of V3.

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Step 4: Attach the white wire from the 470Ohm to pin 8 of V3. Make sure you either strip enough to make a jump to pin 3, or

use a piece of bus wire to make the jump. Shown with green arrows, solder both pins of V3.

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Step 5: Connect the 2nd yellow wire from the 1M/.022uF junction to pin 2 of V3.

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Step 6: Add the 100k resistor and jumper to V2. Thread one end of a 100K 1/2W resistor through pin 1 of V2. Bend the lead around and thread through pin 7. Insert the other end into pin 6. Solder pins 1 & 7 (Green arrows) DO NOT solder pin 6 (red

arrow).

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Step 7: Connect brown wire from 10K 2W/32uF+32uF capacitor to pin 6 of V2 (green arrow) solder pin 6 of V2 now.

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Step 8: Attach white wire from the 100K/33K/500pF junction to pin 8 of V2.

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Step 9: Connect yellow wire from .68uF/820Ohm junction to pin 3 of V2.

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Step 10: Connect brown wire from 470K/470K junction to pin 2 of V2.

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Step 11: Connect white wire from .022uF/100K junction to pin 6 of V1.

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Step 12: connect yellow wire from 68K/68K junction to pin 7 of V1.

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Step 13: Connect brown wire from .022uF/100K junction to pin 1 of V1.

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Step 14: Connect white wire from 68K/68K junction to pin 2 of V1.

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Step 15: Connect the yellow wire from .68uF/2.7K junction to pin 8 of V1.

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Step 16: Connect remaining brown wire to pin 3 of V1.

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Wiring diagram for Tube Side

For high-Res image click here: http://byocelectronics.com/brit50tubesidewiring.pdf

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Wiring (Potentiometer Side)

Step 1: Attach the first black wire to the ground bus (green arrows).

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Step 2: Connect the white wire from the .1uF/10K junction to lug 3 of the PRESENCE potentiometer (green arrows).

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Step 3a: Make a jump between lug 1 of the BASS pot and lug 3 of the MIDDLE pot (green arrows). Solder both lugs.

Step 3b: Make a second jump between lug 2 of the BASS pot and lug 1 of the Treble pot. Only solder on the green

arrow. DO NOT solder on the red arrow yet.

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Step 3c: Connect a piece of black wire from lug 1 of the MIDDLE pot to the ground bus.

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Step 4: Connect the brown wire from .022uF to lug 2 of the TREBLE pot.

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Step 5: Connect next black wire to ground bus as shown.

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Step 6: Connect yellow wire from .022uF to lug 2 of the MIDDLE pot.

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Step 7: Connect white wire from .022uF to lug 1 of the TREBLE pot. Solder the connection now.

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Step 8: Connect brown wire from 500p to lug 3 of the TREBLE pot.

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Step 9: Attach next black wire to the ground bus.

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Step 10: Connect lug 1 of both LOUDNESS pots to the ground bus.

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Step 11: Connect yellow wire from 470K/500p junction to lug 2 of the LOUDNESS 1/BRIGHT TREBLE pot.

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Step 12: Connect the white wire from 470k to lug 2 of the LOUDNESS 2/NORMAL pot.

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Step 13: Connect the brown wire from .022uF to lug 3 of the LOUDNESS 1/BRIGHT TREBLE pot.

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Step 14: Connect the final brown wire from .022uF to lug 3 of the LOUDNESS 2/NORMAL pot.

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Step 15: Using two 2” pieces of wire, make a jumper between the tip connection of the LOWER input jacks, and the disconnect

connection of the UPPER jacks. Solder the LOWER jacks at the green arrows. DO NOT solder the red arrows for now.

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Step 16: Connect the yellow wires to the tip terminals of the upper jacks, and the white wires to the disconnect terminal of the

upper jacks. Solder all connections now.

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Diagram for Potentiometer Side Wiring

For High-Res image click here: http://byocelectronics.com/brit50potsidewiring.pdf

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120V Layout

Go to http://www.byocelectronics.com/brit50-120layout.pdf for high-res PDF.

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240V Layout

Go to http://byocelectronics.com/brit50-240layout.pdf for high-res PDF

Note: The difference between 120V and 240V wiring is using the brown wire on the transformer instead of the black, and a 2Amp fuse for the Mains Fuse.

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Turning your amp on for the first time

Step 1: Make sure your AC power cord is NOT plugged in. Do NOT install any of the tubes yet. Do not plug a speaker into the speaker jack. Do not plug any instruments into the input jacks. If at any point in this process, you smell smoke, see sparks, or hear any loud electrical hum noises, immediately pull the AC power cord from the wall socket.

Step 2: Do not test your amp on a metal table or any surface that can conduct electricity. Situate yourself and your amp so that the AC power outlet you will be using is within arm's length.

Step 3: Install your amplifier chassis into the cabinet or enclosure that you should have. You should never apply power to the amplifier while it is not inside its cabinet or enclosure. If you insist on supplying power to the amplifier while it is not inside its cabinet or enclosure, the safest way to do so is with the chassis laying on a non-conductive, flame retardant surface with the transformer side facing down and the open side of the chassis facing up, making sure that no foreign objects (especially any of your body parts) are touching any part of the amp.

Step 4: Install the 3A (120v) or 2A (240v) fuse into the panel mounted fuse holder on the back of the chassis. You can tell the 2A or 3A fuse apart from the 500mA fuse because the 2A or 3A fuse will have a small “2” or “3” printed on it and the 500mA fuse will have “500” printed on it somewhere. You can also tell because the the 2A or 3A fuse will have a thicker conductive wire running through the middle of it than the 500mA.

Step 5: Turn the amplifier's power switch on, but still do not plug the power cord in yet. Step 6: Orient the amp so that you can see the indicator light. When you plug the power cord into the AC power supply, you should be able to see the indicator light come on immediately. This means, at the very least, AC power is getting to the power transformer and that the power transformer is working.

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Step 7: Turn the mains switch off and unplug the power cord from the wall socket.

Step 8: With the mains switch off and the AC power cord unplugged from the wall, now install the 500mA fuse into the flat mount fuse holder. When testing your amp voltages, always keep one hand in your pocket and wear shoes with rubber soles. This doesn't reduce the risk of electrocution, but it will reduce the amount of damage that will be done if you get do electrocuted. It won't make you impervious to electrocution, but the less “grounded” you are, the less the amount of current that will be able to flow through your body. Doing things like going barefoot or holding onto a metal drain pipe with your free hand while working with electricity won't increase the risk of electrocution, but they will increase how well you conduct current to ground, and that increases the amount of damage you can do to yourself if you are electrocuted.

32uF+32uF

EL34 ECC83

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Step 9: Plug the AC cord into the wall socket. Make sure the standby switch is in the “standby” position. Turn the mains switch on. The tubes should start to warm up and glow. Hopefully you know that vacuum tubes get very hot once they are warmed up. You must allow adequate time to pass for them to cool off before you attempt to touch them. If you measure the voltage at the red terminal of the first 32uFx32uF electrolytic capacitor, you should read approximately 490VDC. To test the rectified DC voltage, first set your meter to test DC voltage 500V or greater. Then connect the black probe to chassis ground. Then touch the red probe to the various test points Step 10: Turn the standby toggle switch to the on position. You should read 480VDC at position B (red terminal of the second 32uFx32uF capacitor), 355VDC at position C (yellow terminal of the second 32uFx32uF electrolytic capacitor), 305VDC at position D (the right positive lead of the 32uFx32uF electrolytic capacitor on the circuit board), and 280VDC at position E (the left positive lead of the 32uFx32uF electrolytic capacitor on the circuit board). These are approximate voltages and the circuit isn’t actually under full load yet, so don’t be alarmed if your actual readings are +/- 20V. Step 11: Unplug the AC power cord from the wall and turn the toggle switches to their off positions. Step 12: VERY IMPORTANT BEFORE YOU ADD THE EL34 TUBES!!! Be sure to plug a speaker into the speaker jack. You should never turn your amp on when the power tube is installed without the proper speaker load. Doing so will damage your output transformer. Plug a speaker into the speaker jack. Make sure the impedance rotary switch is set to the correct impedance for the speaker you are using. The speaker should be able to handle 30watts. Step 13: Install the EL34 tubes into their sockets. Plug the AC power cord into the wall. Turn the mains toggle switch on. You should see the EL34s begin to heat up and glow.

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Step 14: Unplug the AC power cord from the wall and turn the toggle switches to their off positions. Step 15: Install the ECC83 tubes. Plug the AC power cord into the wall. Turn the mains toggle switch on. Keep the standby switch off. You should see all the tubes start to heat up and glow. Step 16: Turn all the knobs down and take the amp out of standby. You should hear a soft white noise start to come out of the speaker. Step 17: Return the amp to standby.

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BIASING Step 18: OK. You need to bias your amp correctly before you start playing. This is very important. If you have it biased too “hot” you can damage the EL34 tubes or burn out one of the resistors. If you have it biased too “cool”, it just won’t sound very good. You adjust the bias by turning the trimpot on the circuit board. You will need a very small hex wrench or screwdriver (depending upon the type of trimpot supplied with your kit). When calculating bias, you will need to follow a simple equation. The EL34 tubes have 25 watts maximum dissipation. We want the bias point to be 70% of the max dissipation or 17.5 watts. To do this you will first measure the plate voltage of the EL34s. On one of the EL34 tubes, measure the voltage on pin 3. To do this, Place your multimeter on the maximum VDC setting, place the black lead into a screw hole, or any other ground connection. Then touch the red lead to pin 3 of one of the EL34s. Write the number down. Now take your plate voltage and divide it by 17.5. As an example, say you have a plate voltage of 480VDC. Your equation would be (17.5/480). This gives us a value of .036, or 36mV. You would then set your bias to that value. If you can’t be exact, don’t worry, as long as you are close to your final value (within .5mV or so, you will be okay) Test the bias voltage by taking a reading at pin 1 or 8 of either power tubes. You’ll probably want to set your meter to its lowest voltage range if it isn’t an auto-ranging meter…probably the 200mVDC setting. Step 19: Plug a guitar in. Take the amp out of standby. Take her for a test drive.

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Operating Overview

Front Panel

This should be pretty standard stuff for the most part, but the JTM45 does have some peculiarities.

You probably won’t ever want to use the HIGH TREBLE channel unless you are jumpering it with the normal channel. It will typically be much too bright for most peoples’ taste.

Loudness 1 only works if you have an input in either of the two “1” inputs. Loudness 2 only works if you have an input in either of the two “2” inputs.

Jumpering: You can use a patch cable to connect one of the “1” inputs to one of the “2” inputs. Plug your instrument into either of the open “1” or “2” inputs. This will allow you to blend both channels. Many people think this is how you should always run a JTM45. That’s a matter of opinion, but it is certainly the best way to get the most gain out of the amp.

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Back Panel

Power Cord Socket: Plug your power cord in to this. Fuse Holder: This is where the fuse goes. It says 2AMP, but be sure to use a 3A if you are in a 120VAC country. Impedance Selector: Set this 3 position switch to match the impedance of the speaker(s) you are using. Speaker Jack: Insert speaker cable here. Use speakers rated for 30 watts or higher.

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Diagrams and Schematic

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Circuit board (top side)

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Circuit Board Wiring (showing from top side)

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Power Section and Heater Wiring for hi res pdf go to http://www.byocelectronics.com/brit50powerwiring.pdf

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Schematic For hi res pdf go to http://www.byocelectronics.com/brit50schematic.pdf

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For technical support, visit www.byocelectronics.com/board

Written by: N.W. Kenning & K. Vonderhulls

Artwork & Photography by:

N.W. Kenning

Copyright BYOC, Inc. 2016