StewMac '81 BRIT-800 Assembly Instructions Manual Download Page 1

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A S SE M B LY I N S T RU C T I O N S

With loads of

helpful tips!

’81 BRIT-800

50W

A M P L I F I E R K I T

ORIGINAL BRITISH CIRCUIT

The king of shred

Summary of Contents for '81 BRIT-800

Page 1: ...ASSEMBLY INSTRUCTIONS With loads of helpful tips 81 BRIT 800 50W AMPLIFIE R KIT ORIGINAL BRITISH CIRCUIT The king of shred ...

Page 2: ...nd troubleshooting 41 Final assembly 44 Tips for using this amp 44 Photograph of completely wired chassis 45 Learning more secrets revealed in the schematic 46 Circuit schematic 47 More iconic amp kits from StewMac 48 Full page wiring diagram 50 Tube replacement chart 51 COPYRIGHT WARNING This material is protected by copyright and has been created by and solely for the purposes of StewMac You may...

Page 3: ...erythingthatmakestheoriginalssosought after Build it with StewMac These immersive instructions walk you through every step of creating your 81 Brit 800 And you ll learn a lot gaining a deep knowledge of your amp s inner workings Follow our steps closely for safety too we ve carefully laid out a path that even newcomers can follow in handling electrical components Building an amp can seem daunting ...

Page 4: ...t need to read the schematic but it s fun See how your guitar s signal gets processed into sound on page 47 Sort your components by type using the parts list Quick look Output Gain Processing Gain Gain Processing Negative feedback See page 9 10735 2019 StewMac Ground Jack Transformer Preamp tube plate grid cathode Power tube grid plate cathode screen Capacitor Electrolytic Cap Diode Resistor Poten...

Page 5: ...rs r 1 470Ω 5W carbon composite r 2 820Ω 5W carbon composite r 1 2 7K 5W carbon composite r 1 4 7K 5W carbon composite r 2 5 1K 5W carbon composite r 1 10K 5W carbon composite r 1 15K 5W carbon composite r 1 33K 5W carbon composite r 1 47K 5W carbon composite r 1 56K 5W carbon composite r 1 82K 5W carbon composite r 6 100K 5W carbon composite r 2 220K 5W carbon composite r 3 470K 5W carbon composi...

Page 6: ...r r 1 5K control pot L linear taper r 1 25K control pot L linear taper r 1 250K control pot L linear taper r 1 Impedance selector switch r 1 Voltage selector switch r 1 Power switch 5 lugs r 1 Standby switch 4 lugs r 6 Knob r 2 Three lug terminal strip r 2 Ground tab r 1 Power cord Wire r 1 White wire r 1 Green wire r 1 Shielded wire r 1 White heater wire r 1 Black heater wire r 1 Bare copper bus ...

Page 7: ...5 32 bit For mounting turret board and filter cap Ruler Item 4905 StewMac Shop Rule Digital multimeter Item 3618 Fieldpiece Pocket Multimeter Snuffer stick bleed resistor Item 1552 Snuffer Stick Pencil Wooden chopsticks Glue Wood glue white glue or contact cement for gluing a paper label inside the cabinet Butane lighter or matches For heating heat shrink tubing Contact cement Helpful Round nose b...

Page 8: ... to call 911 can be a lifesaver How to use a snuffer stick To discharge a capacitor clip the snuffer stick lead to ground preferably a mounting bolt on the power transformer Hold the tip of the stick to the cap s positive lead and use your multimeter to watch the voltage drain to less than 18V Take breaks and stop when you re tired Fatigue leads to mistakes and no one can afford mistakes when work...

Page 9: ...f a farad called microfarads μF or trillionths of a farad picofarads pF The voltage spec for a cap refers to how much DC voltage it can handle at any given time A unique property of capacitors is that they don t allow DC current to flow past them only AC current This is important in parts of an amplifier circuit such as the path between a preamp stage and a power amp stage Here a coupling capacito...

Page 10: ... 3 6 5 2 1 4 4 2 3 1 4 2 3 1 1μF 5W 1K 5W 1K 001μF 510K 1 29 2 26 3 4 5 6 7 20 21 22 23 24 27 25 28 8 9 10 11 12 13 14 15 16 17 18 34 35 36 37 38 39 40 44 45 46 33 32 31 19 30 41 42 43 022μF 022μF 68μF 5 0 0 p F 500p F 022μF 022μF 022μF 5W 10K 5W 10K 022μF 022μF 01μF 47 8µF 8µF 1 0 Complete wiring diagram Our diagrams show a flat view of the metal chassis Here s the complete Brit 800 50 wiring Whe...

Page 11: ...n the con nection for a second longer to allow time for all of the flux to cook out of the joint n Don t ever blow on the hot solder or touch anything until the joint is completely cool A good solder joint is shiny a sign that it was left to cool undisturbed 1 29 2 26 3 4 5 6 7 20 21 22 23 24 27 25 28 8 9 10 11 12 13 14 15 16 17 18 34 35 36 37 38 39 40 44 45 46 33 32 31 19 30 41 42 43 n Trim away ...

Page 12: ...SE V3 12AX7 V2 12AX7 V1 12AX7 SPEAKER EXTENSION SPEAKER VOLTAGE SELECTOR IMPENDANCE SELECTOR MAINS FUSE FILTER CAP 3 FILTER CAP 2 FILTER CAP 1 MAINS INPUT OUTPUT TRANSFORMER Mounted outside POWER TRANSFORMER Mounted outside FILTER CHOKE Mounted outside 1 M A 1 M A Solder three lugs to make them a common ground 3 Solder 1 Snip 2 Wrap ...

Page 13: ...igher voltage which is output by the secondary coil This voltage can be as high as 500V and is referred to as high tension H T The leads connecting to these two coils are called primary and secondary leads STEP 5 Mount the power transformer The power transformer has ten leads Separate these into color coded pairs and twist these sets together Two solid red leads Thick solid black Thick solid orang...

Page 14: ... VOLUME PREAMP VOLUME INPUT NORMAL H T FUSE V3 12AX7 FILTER CAP 3 FILTER CAP 2 FILTER CAP 1 V2 12AX7 V1 12AX7 SPEAKER EXTENSION SPEAKER VOLTAGE SELECTOR IMPENDANCE SELECTOR MAINS FUSE MAINS INPUT B A B A B A 4 3 2 1 8 7 6 5 4 3 2 1 8 7 6 5 6 4 3 2 1 9 8 7 5 6 4 3 2 1 9 8 7 5 6 4 3 2 1 9 8 7 5 ...

Page 15: ...Orient these eight pin tube sockets so that pin 1 is closest to the rear panel of the chassis Use 4 40 x 3 8 machine screws and locknuts to mount these sockets on the outside of the chassis Include a spring retainer on the bottom of each socket to provide support for these three tubes when they re installed later STEP 13 Install the three small tube sockets Position these nine pin sockets so pin 9...

Page 16: ...R EXTENSION SPEAKER VOLTAGE SELECTOR IMPENDANCE SELECTOR FILTER CAP 3 FILTER CAP 2 FILTER CAP 1 MAINS FUSE MAINS INPUT 4 3 2 1 8 7 6 5 6 4 3 2 1 9 8 7 5 6 4 3 2 1 9 8 7 5 6 4 3 2 1 9 8 7 5B A B A B A 1 2 4 3 1 M A 2 5 0 K L 2 5 K L 1 M A 5 K L 4 3 2 1 8 7 6 5 1 2 4 3 L O H I STEP 00 Enlarged to show detail Mount jacks outside on the front panel 1 2 4 3 1 2 4 3 L O H I ...

Page 17: ... 8 white jumper and wrap one end to lug 4 of the low sensitivity jack Wrap the other end to lug 3 of the high sensitivity jack Solder this jumper in place on both lugs and trim any excess leads Cut a 2 1 2 white jumper and wrap one end to lug 2 of the low sensitivity jack Wrap the other end to lug 4 of the high sensitivity jack Solder this jumper in place on lug 2 of the low sensitivity jack and t...

Page 18: ...MAL H T FUSE V3 12AX7 V2 12AX7 V1 12AX7 SPEAKER EXTENSION SPEAKER VOLTAGE SELECTOR IMPENDANCE SELECTOR FILTER CAP 3 FILTER CAP 2 FILTER CAP 1 MAINS FUSE MAINS INPUT 4 3 2 1 8 7 6 5 6 4 3 2 1 9 8 7 5 6 4 3 2 1 9 8 7 5 6 4 3 2 1 9 8 7 5B A B A B A 1 2 4 3 1 2 4 3 1 M A 2 5 0 K L 2 5 K L 1 M A 5 K L 4 3 2 1 8 7 6 5 L O H I 1μF ...

Page 19: ...d to the back of the presence pot and then to the left lug of the presence pot Wrap the other lead of this resistor to the right lug of the presence pot but don t solder it yet STEP 25 Add a 1μF capacitor Solder one lead of a 1μF cap to the middle lug of the presence pot Solder the other lead of this capacitor to the back of the presence pot Trim away all excess leads from the components on the pr...

Page 20: ...AMP VOLUME INPUT NORMAL H T FUSE V3 12AX7 V2 12AX7 V1 12AX7 SPEAKER EXTENSION SPEAKER VOLTAGE SELECTOR IMPENDANCE SELECTOR FILTER CAP 3 FILTER CAP 2 FILTER CAP 1 MAINS INPUT MAINS FUSE 6 4 3 2 1 9 8 7 5 6 4 3 2 1 9 8 7 5 6 4 3 2 1 9 8 7 5B A B A B A 1 2 4 3 1 2 4 3 L O H I 4 3 2 1 8 7 6 5 4 3 2 1 8 7 6 5 ...

Page 21: ...s and then bend the black and white pair at a 90 angle toward socket V4 STEP 30 Connect to socket V4 Cut two 6 heater wires one white and one black Twist them tightly together Twist the end of the white wire to the white jumper coming from V5 Twist the black wire with the black jumper coming from V5 Solder the white pair onto pin 2 of V4 Solder the black pair onto pin 7 Bend the wires into the bac...

Page 22: ...PUT NORMAL H T FUSE V3 12AX7 V2 12AX7 V1 12AX7 SPEAKER EXTENSION SPEAKER VOLTAGE SELECTOR IMPENDANCE SELECTOR FILTER CAP 3 FILTER CAP 2 FILTER CAP 1 MAINS INPUT MAINS FUSE B A B A B A 1 2 4 3 1 2 4 3 L O H I 4 3 2 1 8 7 6 5 4 3 2 1 8 7 6 5 6 4 3 2 1 9 8 7 5 6 4 3 2 1 9 8 7 5 6 4 3 2 1 9 8 7 5 3 6 5 2 1 4 3 6 5 2 1 4 ...

Page 23: ...d push your heater wires into the floor of the chassis and into the back corner of the chassis as much as you can STEP 34 Install the voltage switch Using two 4 40 x 3 8 screws and locknuts mount the voltage selector switch as shown in the diagram with the lug attached to the middle shaft facing the power inlet STEP 35 Connect the voltage switch The voltage selector switch allows you to set the am...

Page 24: ... H T FUSE V3 12AX7 V2 12AX7 V1 12AX7 SPEAKER EXTENSION SPEAKER VOLTAGE SELECTOR IMPENDANCE SELECTOR FILTER CAP 3 FILTER CAP 2 FILTER CAP 1 MAINS INPUT MAINS FUSE B A 1 2 4 3 1 2 4 3 L O H I 4 3 2 1 8 7 6 5 4 3 2 1 8 7 6 5 6 4 3 2 1 9 8 7 5 6 4 3 2 1 9 8 7 5 6 4 3 2 1 9 8 7 5 3 6 5 2 1 4 3 6 5 2 1 4 B A B A 5 W 1 K 5 W 1 K 1 0 ...

Page 25: ...Solder the lead wrapped to pin 4 Wrap one lead of the second 1K 5W resistor to pin 4 of V4 and wrap the other lead to pin 6 of V4 standing it up off the tube socket 1 2 Solder the lead wrapped to pin 4 STEP 42 Add two white jumpers Cut one 3 white jumper Solder one end of the jumper to V4 pin 6 with the resistor lead already in place Wrap the other end to V5 pin 6 but don t solder it yet Cut one 4...

Page 26: ...AL H T FUSE V3 12AX7 V2 12AX7 V1 12AX7 SPEAKER EXTENSION SPEAKER VOLTAGE SELECTOR IMPENDANCE SELECTOR FILTER CAP 3 FILTER CAP 2 FILTER CAP 1 MAINS INPUT MAINS FUSE B A B A B A 1 2 4 3 H I 4 3 2 1 8 7 6 5 6 4 3 2 1 9 8 7 5 6 4 3 2 1 9 8 7 5 4 3 2 1 8 7 6 5 3 6 5 2 1 4 3 6 5 2 1 4 6 4 3 2 1 9 8 7 5 1 M A 1 2 4 3 L O 001μF 510K ...

Page 27: ...d the leads of the 470k resistor and solder them together Solder one of the resistor leads to the right lug of the preamp volume pot along with the capacitor lead already in place Solder the other resistor lead to lug 1 of the low input jack Trim away any excess leads STEP 50 Add three jumpers Cut a 16 white jumper and solder one end to the middle protruding lug of the voltage selector switch Cut ...

Page 28: ...stewmac com 26 2019 StewMac 1 29 2 26 3 4 5 6 7 20 21 22 23 24 27 25 28 8 9 10 11 12 13 14 15 16 17 18 34 35 36 37 38 39 40 44 45 46 33 32 31 19 30 41 42 43 022μF 022μF 68μF 5 0 0 p F 500pF ...

Page 29: ...28 STEP 55 Add two resistors two capacitors Add one 100k resistor between turrets 24 and 44 Add another 100k resistor between turrets 24 and 43 Add a 022μF 22nF capacitor between turrets 16 and 44 This and the following yellow capacitors are not polarized so you can install them in either direction We recommend facing them all in the same direction making their printed specs easy to read Add anoth...

Page 30: ...wmac com 28 2019 StewMac 1 29 2 26 3 4 5 6 7 20 21 22 23 24 27 25 28 8 9 10 11 12 13 14 15 16 17 18 34 35 36 37 38 39 40 44 45 46 33 32 31 19 30 41 42 43 022μF 022μF 022μF 5W 10K 5W 10K 022μF 022μF 01μF 47 ...

Page 31: ...3 1 2 white jumper to turret 37 Add a 3 1 2 white jumper to turret 36 STEP 65 Add four resistors Add a 220k resistor between turrets 8 and 20 Add another 220k resistor between turrets 7 and 20 Add an 82k resistor between turrets 27 and 35 Add a 100k resistor between turrets 27 and 34 STEP 66 Add three capacitors two jumpers Add a 022μF capacitor between turrets 8 and 35 Add another 022μF capacitor...

Page 32: ...stewmac com 30 2019 StewMac 1 29 2 26 3 4 5 6 7 20 21 22 23 24 27 25 28 8 9 10 11 12 13 14 15 16 17 18 34 35 36 37 38 39 40 44 45 46 33 32 31 19 30 41 42 43 8µF 8µF ...

Page 33: ...rret 26 Add a 1N5408 diode between turrets 2 and 29 Connect the negative lead to turret 2 and the positive lead to turret 29 Add another 1N5408 diode between turrets 1 and 29 Connect the negative lead to turret 1 and the positive lead to turret 29 STEP 71 Add one resistor three jumpers Add a 220k 2W resistor between turrets 2 and 26 Add a 7 white jumper to turret 29 Cut two 10 white jumpers and tw...

Page 34: ...stewmac com 32 2019 StewMac 1 29 2 26 3 4 5 6 7 20 21 22 23 24 27 25 28 8 9 10 11 12 13 14 15 16 17 18 34 35 36 37 38 39 40 44 45 46 33 32 31 19 30 41 42 43 Behind board view ...

Page 35: ... the back of turret 25 Cut a 2 1 2 white jumper and solder one end to the bottom of turret 9 Route the free end up toward the top of the board turn it at a 90 degree angle to the right until you reach the back of turret 6 and then bend it at another 90 degree angle and solder the lead in the back of turret 6 Cut a 12 white jumper and solder one end to the bottom of turret 5 Route the free end of t...

Page 36: ...ELECTOR IMPENDANCE SELECTOR FILTER CAP 3 FILTER CAP 2 FILTER CAP 1 MAINS INPUT MAINS FUSE B A B A B A 4 3 2 1 8 7 6 5 6 4 3 2 1 9 8 7 5 6 4 3 2 1 9 8 7 5 4 3 2 1 8 7 6 5 3 6 5 2 1 4 3 6 5 2 1 4 1 2 4 3 1 2 4 3 L O H I 6 4 3 2 1 9 8 7 5 1 M A 1 M A 2 5 0 K L 2 5 K L 5 K L 1 29 2 26 3 4 5 6 7 20 21 22 23 24 27 25 28 8 9 10 11 12 13 14 15 16 17 18 34 35 36 37 38 39 40 44 45 46 33 32 31 19 30 41 42 43...

Page 37: ...lder the white jumper from turret 17 to lug 1 of the high sensitivity input jack Solder the white jumper from turret 16 to lug 4 of low sensitivity input jack STEP 82 Solder the master volume pot Solder the green jumper from turret 14 to the back of the master volume pot Solder the white jumper from turret 10 to the middle lug of the master volume pot STEP 83 Solder the treble pot Solder the jumpe...

Page 38: ... SPEAKER VOLTAGE SELECTOR IMPENDANCE SELECTOR FILTER CAP 3 FILTER CAP 2 FILTER CAP 1 MAINS INPUT MAINS FUSE B A B A 3 6 5 2 1 4 1 2 4 3 L O 1 2 4 3 H I B A 4 3 2 1 8 7 6 5 4 3 2 1 8 7 6 5 6 4 3 2 1 9 8 7 5 6 4 3 2 1 9 8 7 5 6 4 3 2 1 9 8 7 5 3 6 5 2 1 4 1 29 2 26 3 4 5 6 7 20 21 22 23 24 27 25 28 8 9 10 11 12 13 14 15 16 17 18 34 35 36 37 38 39 40 44 45 46 33 32 31 19 30 41 42 43 ...

Page 39: ... a 5 1k resistor attached to the end to V4 pin 5 You want to solder this resistor very close to the tube socket as pictured in the diagram To determine which jumper is connected to turret 8 take a resistance reading from turret 8 to the two resistors in question The one that has roughly 5 1K resistance is the one you are looking for STEP 92 Solder the jumper to V5 Solder the jumper from turret 7 r...

Page 40: ... VOLTAGE SELECTOR IMPENDANCE SELECTOR FILTER CAP 3 FILTER CAP 2 FILTER CAP 1 MAINS INPUT MAINS FUSE B A B A 3 6 5 2 1 4 1 2 4 3 L O 1 2 4 3 H I B A 6 4 3 2 1 9 8 7 5 6 4 3 2 1 9 8 7 5 6 4 3 2 1 9 8 7 5 4 3 2 1 8 7 6 5 4 3 2 1 8 7 6 5 3 6 5 2 1 4 4 2 3 1 4 2 3 1 1 29 2 26 3 4 5 6 7 20 21 22 23 24 27 25 28 8 9 10 11 12 13 14 15 16 17 18 34 35 36 37 38 39 40 44 45 46 33 32 31 19 30 41 42 43 ...

Page 41: ...ack and lug 4 of the main speaker jack Solder this jumper to lug 1 of the main speaker jack Cut a 3 green jumper and solder one end to lug 4 of the main speaker jack along with the jumpers already in place Solder the other end of this jumper to pin 8 of socket V4 Cut a 1 1 2 white jumper and solder one end to lug 3 of the extension speaker jack Wrap the other end to lug 3 of the main speaker jack ...

Page 42: ...for testing STOP DON T INSTALL THE TUBES YET DON T PLUG THE AMP IN YET The next page is going to keep you out of trouble STEP 100 Set the chassis on chassis stand or on blocks for testing Set your chassis up for final testing Chassis stands are extremely useful for this If you do not have a chassis stand a couple of blocks of wood can work just fine STEP 99 Install the six control knobs Turn the s...

Page 43: ...afe and easy STEP 101 Perform a safe power up Atthispoint thereshouldbenotubes installed and the speaker should be disconnected Before plugging the amp in turn the power switch to ON Switching the amp on before the first power up protects you from shock if a mistake in your wiring has created a short to the chassis If this short exists an indication would be that the pilot light will not turn on s...

Page 44: ...te this number in Box 2 of the calculation in Step 106 It ll be needed if you use a bias meter to set your bias Set your multimeter to read 50V DC andtestforvoltageatturret20 Adjust the bias pot until this voltage reads around 38V If all of these voltages come within approximately 10 of their expected values turn the power switch OFF Afterafewmomentsturnthestandby switch OFF as well and unplug the...

Page 45: ...as probes and taking it for a test drive if the amp is stable and your tests match the voltagesspecified feelfreetoletitrip STEP 106 Improved method of setting the bias using a bias meter The more accurate way to set the bias is by using a bias meter such as the VHT Bias Tester StewMac 1580 This method starts with a simple calculation to find your bias setting thenyouadjustthebiaspotuntilyour bias...

Page 46: ... think of 80s metal guitar this is the amp you are hearing This amp is based on the JCM800 2204 but with a twist Marshall never released hand wired versions of the 800s so this is not exactly a replica but more of a boutique style build Ourversionhasslightlymoregainand soundsalittlebitsweeterthanitsPCB predecessor but make no mistake the sound is 100 JCM800 World renowned for that sizzling in your...

Page 47: ...stewmac com 45 2019 StewMac Top view of wired chassis ...

Page 48: ...frequency to the signal this can be heard as more bite to the naked ear But don t be surprised if the sound engineer at your next gig asks you to turn down the presence it can be extremely abrasive when mic d up The signal is then sent to the phase inverter which uses all of V3 The phase inverter then sends the signal to the output section The power supply stage provides power to the other circuit...

Page 49: ... cathode Power tube grid plate cathode screen Capacitor Electrolytic Cap Diode Resistor Potentiometers Rectifier tube plate cathode filament plate Shielded cable 81 BRIT 800 50W O R I G I N A L B R I T I S H C I R C U I T Output Gain Gain Gain Power Processing Processing Power Negative Feedback ...

Page 50: ...y clean with enough guts to gig Perfect for recording as well as performing the D Reverb produces stinging clarity that absolutely refuses to get lost in the mix One of the most popular designs ever this amp lives in the happy middle between bright clarity and rich distortion It excels in the studio and on the stage While capable of crystal clear tones at good volume you can push this one into bea...

Page 51: ...800 50W AMP KIT This hairy monster lives to shred The defining British circuit that dominated the 80s This 50W giant created your favorite heavy rock and metal albums Used by Slayer and Pixies and recorded on early Metallica albums this circuit produces that screaming guitar tone that your mother despises With solid state rectification there s no sag and the distortion created by this circuit is w...

Page 52: ... 1 2 4 3 1 M A 1 M A 2 5 0 K L 2 5 K L 1 M A 5 K L 4 3 2 1 8 7 6 5 4 3 2 1 8 7 6 5 3 6 5 2 1 4 6 4 3 2 1 9 8 7 5 6 4 3 2 1 9 8 7 5 6 4 3 2 1 9 8 7 5 D D D A B 3 6 5 2 1 4 4 2 3 1 4 2 3 1 1μF 5 W 1 K 5 W 1 K 001μF 510K 1 29 2 26 3 4 5 6 7 20 21 22 23 24 27 25 28 8 9 10 11 12 13 14 15 16 17 18 34 35 36 37 38 39 40 44 45 46 33 32 31 19 30 41 42 43 022μF 022μF 68μF 5 0 0 p F 500pF 022μF 022μF 022μF 5W...

Page 53: ...2AX7 ECC83 V3 V2 81 BRIT 80050W A M P L I F I E R K I T O R I G I N A L B R I T I S H C I R C U I T StewMac I C O N K I T S DANGER Unplug the amp before changing tubes Tube locations from left to right EL34 EL34 12AX7 ECC83 V5 V4 V1 12AX7 ECC83 12AX7 ECC83 V3 V2 Cut this label on the dotted line with a razor knife and metal straightedge Fasten it inside the cabinet using thinned wood glue or conta...

Page 54: ...stewmac com 52 2019 StewMac ...

Page 55: ...stewmac com 53 2019 StewMac ...

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