Mojotone TMB User Manual

THE MOJOTONE

BRITISH STYLE

WATT

18WATT TMB

1X 12 COMBO AMP / AMP HEAD

ojotone’s 18watt TMB Amplifier Kit addresses a

M

common mod made to a classic circuit, but with a few

new avors of our own. The 18watt TMB is based on the
circuit used in vintage Marshall models 1958, 1973, and
1974 (more affectionately known as the ‘18-watters’.)

These original Marshalls were only produced between the years
1965 and 1967, but were highly sought-after for having massive
sounding JTM-45-like tones in a smaller, more manageable
package. Because they were produced in comparatively low
quantities, these amps still remain a ‘lost ark’ today.

18-watters became popular studio amps for many players
and were used, at times, by everyone from Gary Moore, to
The Pretenders, to AC/DC. Over the years, some players have

reported having no use for the amp’s original tremolo channel
and have opted to replace the tremolo controls with a 3-band
EQ, since the original amps were only equipped with a
single tone control for each channel. In the Mojotone version,
we have done just this. We have integrated the entire preamp
section and the tone stack from our British 800 kit (based on
the original Marshall JCM 800 circuit) for a lean and mean,
hot-rodded gain sound. We have also integrated a master
volume control so this monstrous sound can be harnessed
and used in any size room.

Two EL84s give the amp’s normal channel a warm and
round character which, when the volume is pushed higher,
begins to break up into a smooth grind perfect for blues rock
and classic rock rhythm sounds. On the dirty channel, one
can access screaming lead tones perfect for everything from
dim dirty grunge all the way to saturated hair metal sustain!

With our TMB mod in place, this take on a classic beast
now has a normal channel with high sensitivity and low
sensitivity inputs as well as a single volume and single
tone control; the second channel has a single input with
volume, treble, middle, and bass controls. And don’t
forget about the master volume!

CONTENTS

SECTION 1: SAFETY PG.3

SECTION 2: TOOLS PG.3

SECTION 3: PARTS INVENTORY PG.4

SECTION 4: COMPONENT IDENTITY & ORIENTATION PG.5

SECTION 5: CHASSIS ASSEMBLY PG.6

SECTION 6: TRANSFORMER WIRING PG.8

SECTION 7: COMPONENT WIRING PG.10

SECTION 8: BOARD ASSEMBLY & INSTALLATION PG.10

SECTION 9: WIRING THE SOCKETS, JACKS & POTS PG.12

SECTION 10: Rear panel component installation & wiring PG.14

SECTION 11: SPEAKER WIRING & INSTALLATION PG.15

SECTION 12: INITIAL CHASSIS TESTING PG.15

SECTION 13: CHASSIS INSTALLATION & final assembly PG.16

SECTION 14: SOUND TEST PG.17

SECTION 15: TROUBLESHOOTING PG.17

MORE FROM MOJOTONE PG.18

All content included in this book including text, graphics and images is the property of Mojotone, LLC and protected by U.S. and international copyright laws. The collection, arrangement and assembly of all
content in this book is the exclusive property of Mojotone, LLC and protected by U.S. and international copyright laws. You may not copy, reproduce, distribute, publish, display, perform, modify, create deriva­tive works, transmit, or in any other way exploit any part of copyrighted material without permission from Mojotone, LLC .

Copyright © 2019 Mojotone, LLC

SECTION 1:

SAFETY

SAFETY FIRST! ELECTRONICS CAN BE DANGEROUS AND MUST BE TREATED WITH RESPECT. ANY CIRCUIT THAT WORKS WITH 120 VAC POWER FROM AN

ELECTRICAL OUTLET IS ESPECIALLY DANGEROUS AND COULD POTENTIALLY KILL YOU. HERE ARE SOME SAFETY GUIDELINES TO KEEP YOU SAFE AS YOU WORK:

Never work on a circuit while power is applied.

Do not connect power to a circuit until the circuit

is nished and you have carefully checked your
work (twice).

If you smell anything burning, immediately

disconnect the power and examine your circuit to
nd out what went wrong.

Keep your work area dry and organized.

Be careful around large capacitors. They can

continue to hold voltage long after they are discon­nected from power. Discharge electrolytic capaci­tors if power has been applied to the unit.

SECTION 2:

Be especially careful when you solder. A hot

soldering iron can easily burn you.

Always work in a well-ventilated space.

Have safety equipment such as a re extinguisher,

a rst-aid kit and a phone nearby.

Be Patient! Rushing through any type of techni-

cal work just leads to frustration and compounds
issues that can easily be avoided.

Tools

CERTAIN TOOLS ARE REQUIRED TO SUCCESSFULLY BUILD YOUR AMP. THE FOLLOWING TOOLS ARE RECOMMENDED TO COMPLETE YOUR PROJECT:

½” Nut Driver

Set of needle nose pliers (one with no grip and

one with serrated edge)

Wire Cutters

Wire Strippers

Soldering Iron & Solder

Adjustable Wrench

Phillips Head Screwdriver

Multimeter

NEED A TOOL? DO YOU SEE SOMETHING ON THIS LIST THAT YOU DON’T HAVE? TURN TO PAGE 20 FOR A FULL LIST OF TOOLS, PARTS AND KITS TO ADD TO YOUR WORK BENCH.

www.mojotone.com

3

ECC83S

EL 84 EZ 81

SECTION 3:

PARTS INVENTORY *optional based on order

(1) Void Free Birch Head Cabinet*

(1) Faceplates (front & back)*

(1) Void Free Birch Combo Cabinet*

(1) Mojotone British Vintage
30w, 12“, 8Ω Speaker*

(2) (1)

(3)

Vacuum Tubes*

(1) British Style 18 Watt

Power Transformer

(6) 9 pin Tube Socket

(1) Aluminum Chassis

(1) British Style 18 Watt
Output Transformer

(3) Tube Shield for ECC836

(1) Turret Board

(3) Spring Retainer for
EL84 & EZ81

(3) Impedance Selector Switch

w/ hardware

4

Potentiometers

(1) 1MA (vol. / tone), (1) 250kl (treb.)
(1) 25kb (mid.), (4) 500ka (vol. / tone)

BUILD. MODIFY. REPAIR.

(1) Indicator Lamp

w/ hardware

(1) 10‘ Removable Power Cord

(1) A/C Power Jack

(8) Knobs

(1) 1/4'' Mono Plug

(1) Fuse Holder & Fuse

w/ hardware

(2) Toggle Switch

w/ hardware

Jacks w/ hardware
(4) J1 4-Lug Jack
(1) J2 2-Lug Jack

(2) Four-Lug Terminal

(2) Rubber
Grommets

(2) Ground

Tabs

RESISTORS CAPACITORS

Carbon Composite

(2) 1/2W 1M
(1) 1/2W 2.7k
(2) 1/2W 5.1k
(1) 1/2W 10K
(1) 1/2W 47k
(3) 1/2W 68k

(7) 1/2W 100k
(7) 1/2W 470k
(3) 1/2W 820Ω
(2) 1W 100Ω

Metal Oxide

(2) 2W 10kΩ
(2) 2W 2.7k

Wire Wound

(1) 3W 130Ω

Silver Mica

Mojotone Dijon

HARDWARE

Standoffs for Turret Board

(20) 4-40 1/4'' Screw & Keps Nuts

(2) 8-32 1/4’’ Screw & Keps Nuts

(2) 6-32 1/2’’ Screw & Keps Nuts

(4) 10-32 11/2’’ Screw & Keps Nuts

(1) 47pf @ 500V

(2) 500pf @ 500V

(1) 4.7nf @ 630V

(4) 10nf @ 630V

(5) 22nf @ 630V

(1) 680nf @ 160V

WIRES

20 gauge Pre-Tinned PVC Coated Wire (4‘ of each color)

Copper Bus Wire (2‘)

(2) Sprague Atom
25µf @ 50V

(1) Mojotone
Electrolytic KingCap
16µf @ 475V

(2) Can Capacitor
32µf + 32µf
@ 500v

(2) Can Capacitor

Clamps

Red

Blue

Yellow

Green

Gray

Black

SECTION 4:

COMPONENT IDENTITY & ORIENTATION

ENSURE ALL POLARIZED CAPS ARE IN THE CORRECT ORIENTATION WHEN INSTALLING ONTO THE BOARD. THIS IS TYPICALLY DENOTED BY AN ARROW POINTING TOWARDS THE NEGATIVE
SIDE, OR A SMALL INDENTION ON THE POSITIVE SIDE.

SAFETY FIRST! A CAP IN THE WRONG ORIENTATION CAN EXPLODE! SO FOLLOW YOUR WIRING DIAGRAM AND PAY CLOSE ATTENTION WHEN ORIENTING YOUR POLARIZED CAPS.

POLARIZED

www.mojotone.com

NON-POLARIZED

5

500 K 25 K 250 K 500 K 500 K

1 M

500 K

SECTION 5:

Chassis ASSEMBLY

PLEASE NOTE: ALL PARTS LISTED IN THE CHASSIS PREP SECTION STARTS AT ONE END OF THE CHASSIS AND COMPLETES ON THE OPPOSITE END, BOTH TOP AND BOTTOM.

FLATTENED VIEW OF INSIDE OF CHASSIS

INDICATOR

LAMP

MAINS SWITCH

STANDBY

J1 JACK

J1 JACK

POTENTIOMETERS

POWER TRANSFORMER

OUTPUT TRANSFORMER

RUBBER

GROMMETS

4 LUG

TERMINAL

CAN CAPACITOR

GROUND

TAB

9-PIN SOCKET

Mount the power transformer using its

pre-assembled hardware and your adjust­able wrench. The transformer will be re­cessed through the rectangular cutout in the
“belly” of the chassis.

9-PIN TUBE SOCKETS

GROUND

TAB

J1 JACK

FOR TURRET BOARD MOUNTING

Install rubber grommets in holes for output

transformer leads.

Mount the output transformer using the (2)
8-32 x 1⁄4” screws and corresponding keps
nuts onto the outside of the chassis next to

the power transformer (output transformer
is not recessed). Install the transformer so

that the Red, Blue and Brown wires go

through the grommet furthest from the pow­er transformer. The Yellow, Black, Green
and Orange go through the grommet clos­est to the power transformer. The screws
will go through the outside of the chassis,
and the nuts will be installed in the inside.
Use a screwdriver and adjustable wrench
to tighten.

6

BUILD. MODIFY. REPAIR.