Oldfield Amplifiers Dual 40 User manual

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Oldfield Amplifiers
User Guide
Dual 40 - 6740

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Thank You
Welcome to the Oldfield family and thank you for putting your trust in
Oldfield Amplifiers. We value that trust as much as we feel confident
you will enjoy your new Oldfield amplifier.
Your new Oldfield amplifier is built to provide you with the best tonal
experience and durability available in a guitar amplifier. As with all
Oldfield’s, it is hand built with you, the player, as the central focus of
our efforts. By using the highest grade components, point-to- point
vacuum tube circuitry and fine craftsmanship, your amplifier will
inspire many hours of musical satisfaction and lasting enjoyment.
Thanks,
The Oldfield Team

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Table Of Contents
Important Safety Instructions.............................................................4~5
Overview................................................................................................6
Front Panel Controls And Features.......................................................7
Rear Panel Controls And Features………………………………….……8
Tube Layout…………………………………….……………………………9
Warranty…………………………………………………………..….…….10
Operational Notes………………………………………………..….…….11

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Important Safety Instructions
ΔFor your safety read, retain, and follow all instructions. Heed all warnings.
ΔOnly connect the power supply cord to an earth-grounded AC receptacle. This amplifier is designed to
operate on standard North American 115V AC and should only be plugged in to a receptacle meeting
those specifications.
ΔWARNING: To prevent damage, fire or shock hazard, do not expose this unit to rain or moisture.
ΔUnplug the power supply cord before cleaning the unit exterior (use a damp cloth only). Wait until the
unit is completely dry before reconnecting it to power.
ΔMaintain at least 6 inches (15.25 cm) of unobstructed air space behind the unit to allow for proper
ventilation and cooling of the unit.
ΔThis product should be located away from heat sources such as radiators, heat registers, or other
products that produce heat.
ΔThis product may be equipped with a polarized plug (one blade wider than the other) or a three-prong
grounded plug. This is a safety feature. If you are unable to insert the plug into the outlet, contact an
electrician to replace your obsolete outlet. Do not defeat the safety purpose of this plug.
ΔProtect the power supply cord from being pinched or abraded.
ΔThis product should only be used with a cart or stand that is recommended by the manufacturer.
ΔThe power supply cord of this product should be unplugged from the outlet when left unused for a long
period of time, or during electrical storms.
ΔThis product should be serviced by qualified service personnel when: the power supply cord or the plug
has been damaged; or objects have fallen, or liquid has been spilled onto the product; or the product has
been exposed to rain; or the product does not appear to operate normally or exhibits a marked change
in performance; or the product has been dropped, or the enclosure damaged.
ΔDo not drip or splash liquids, nor place liquid filled containers on the unit.
ΔCAUTION: No user serviceable parts inside, refer servicing to qualified personnel only. Do not expose
the circuit of the amplifier under any circumstances.

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ΔCAUTION: By nature vacuum tubes get very hot during operation. Do not touch vacuum tubes until
they have sufficiently cooled.
ΔOldfield amplifiers are capable of producing very high sound pressure levels which may cause
temporary or permanent hearing damage. Use care when setting and adjusting volume levels during
use.
ΔFailure to comply with any of these safety precautions could result in damage to the amplifier and in
worst cases bodily harm. Non-compliance with any safety precaution may void any stated warranties.

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Overview
Congratulations on your purchase of a new Oldfield Dual 40 amplifier. The Dual 40 is capable of
producing a vast array of tones with its two channels and expanded functionality. The Dual 40 is
well suited for just about any style of music and any playing situation.
This amplifier is all tube and hand-wired using the best quality components available for guitar
amplification. It is built to last a lifetime and give the owner countless hours of enjoyment whether
on stage, in the studio, or in the home.
The Dual 40 has two very distinctly voiced channels. Channel One leans towards the British style
tones and Channel Two is purely American. Each channel has its own gain and full tone controls.
The master volume is global to the amplifier. Channel switching and certain functions are controlled
either through panel switches or the supplied foot controller.
Feature summary:
Two channels
40 watts output power into 8Ω
All tube, hand-wired circuitry
(2) EL34 Power Section
(4) 12AX7 Preamp Section
5AR4 Tube / Solid State Selectable Rectifier
Full Power / Half Power Option
Fully Bypassed Effects Loop
Finger–jointed Cabinet

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Front Panel: Controls And Features
(Reference the front panel viewing left to right)
1. Amplifier Input: Connect your instrument
with a proper instrument cable to the Amplifier
Input jack.
2. Manual Channel Selector Switch: This
switch is used to select either Channel One or
Channel Two of the amplifier. (Note: The switch
must be in the Channel One position when
operating the amplifier using the foot switch to
change channels.)
3. Gain Mode 1: Controls the volume of the first
gain stage of Channel One. Rotating the control
clockwise will make the Channel One volume
louder and increase overall gain and harmonics.
4. Gain Mode 2: Controls the volume of the
second gain stage of Channel One. Rotating the
control clockwise will make the Channel One
volume louder and increase overall gain and
harmonics. An important item to understand
about the second gain stage of Channel One is
that it is stacked on top of the first gain stage.
When the amplifiers is in Mode 2 the Gain Mode 1
Control and the Gain Mode 2 Control work
together. (Note: The Mode 2 Gain Control has no
effect unless the mode switch on the back panel is
set to the Mode 2 position.)
5. Channel One Treble: Rotating the control
clockwise will increase the high end frequency
output of Channel One.
6. Channel One Middle: Rotating the control
clockwise will increase the mid frequency output
of Channel One.
7. Channel One Bass: Rotating the control
clockwise will increase the low end frequency
output of Channel One.
8. Channel Two Gain: Controls the volume of
Channel Two. Rotating the control clockwise will
make the Channel Two volume louder and
increase overall gain and harmonics.
9. Channel Two Treble: Rotating the control
clockwise will increase the high end frequency
output of Channel Two.
10. Channel Two Middle: Rotating the control
clockwise will increase the mid frequency output
of Channel Two.
11. Channel Two Bass: Rotating the control
clockwise will increase the low end frequency
output of Channel Two.
12. Master: Rotating the control clockwise will
increase the overall volume of the amplifier.
13. Presence: Rotating the control clockwise will
increase the overall top end frequency of the
tone and slightly decrease negative feedback.
14. Indicator Light: On when the amplifier is
receiving electrical power.
15. Off/Standby/Play: When the switch is in the
Off position the amplifier is totally shut down.
With the switch in the middle position the
amplifier is turned on and in Standby mode. With
the switch in the up position the amplifier is ready
to play. When turning the amplifier on it is
recommended that the operator leave the switch
in the Standby position for at least 30 seconds
before moving the switch into the play position.
16. Channel One Mid Boost: When in the ON
position this switch will boost the mid frequencies
of Channel One (Note: The switch must be in the
ON position when operating the amplifier using
the foot switch to control the Channel One Mid
Boost.).
17. Channel Two Mid Boost: When in the ON
position this switch will boost the mid frequencies
of Channel Two (Note: The switch must be in the
ON position when operating the amplifier using
the foot switch to control the Channel Two Mid
Boost.).

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Rear Panel: Controls And Features
(Reference the front panel viewing left to right)
1. Fuse: Replace only with a 3A slo-blo
fuse. Never install a larger fuse than specified.
Failure to install the properly rated fuse could
result in damage to the amplifier. Fuses provide a
critical safeguard for the amplifier and a blown
fuse could be an indication of a much bigger
problem either with the amplifier or the power
source. See a service technician if the amplifier is
repeatedly blowing fuses.
2. Rectifier Selection Switch: Your amplifier
has the ability to operate on either a tube rectifier
or from a solid state rectifier and the Rectifier
Selection Switch determines the mode of
operation. The tube rectifier will be a bit warmer
with a softer feel while the solid state will provide
the player with a bit more volume and edge. The
amp must be in Standby mode before changing
the position of this switch.
3. Bias Adjust Control: This control allows either
the end user or a qualified technician to set the
idle current of the power tubes. Approximately
35ma should be used to set the bias.
4. Power Level: The power level switch will allow
the amplifier to operate in either Pentode or
Triode mode. While in Pentode mode the amp will
achieve full power. When operating in triode
mode the amp will produce roughly half of the full
power. It needs to be noted that while in Triode
Mode the amplifier tone is different than when
operated in full Pentode Mode and tone controls
will need to be adjusted accordingly. The amp
must be in Standby mode to select rectifier
operation.
5/6/7. EFFECTS LOOP: Send / Receive / Bypass
switch for the effects loop.
8. SPEAKER IMPEDANCE SELECTOR: Position
the selector switch to match the amplifier speaker
load.
9/10. Main And External Speaker Jacks:
Connect a speaker to either of these jacks. Both
jacks can be used at the same time to drive
multiple cabinets. Do not connect a combined
speaker load less than 4ohms or greater than
16ohms. IMPORTANT: A speaker load must be
connected to the amplifier at all times during
amplifier operation. Failure to do so will result in
output transformer failure very quickly and will
not be covered under warranty. It is a good
practice to get in the habit of listening for normal
amp noise as soon as the standby switch is
moved into the play position. If no noise is heard
the amplifier should be turned off immediately
and the speaker connections checked.
11. Channel One Mode Switch: Manually
selects Mode One to Mode Two for Channel One.
(Note: The switch must be in the Mode Two
position when operating the amplifier using the
foot switch to control the Channel One Mode.).
12. Footswitch Jack: Connect the foot switch
controller to this jack.

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Tube Layout
RECTIFIER TUBE: 5R4. "Replace only with high quality 5R4 (or compatible) tube.
POWER TUBES: EL34 (x2). "Replace only with a high quality matched duet of EL34 tubes. "The Dual 40 is a fixed
biased amplifier and therefore will need to be re-biased when changing output tubes.
PHASE INVERTER TUBE: Replace with any high quality 12AX7 tube.
PER-AMP GAIN TUBE Channel Two: Replace with any high quality 12AX7 tube.
CATHODE FOLLOWER TUBE Channel One: Replace with any high quality 12AX7 tube.
PER-AMP GAIN TUBE Channel One: Replace with any high quality 12AX7 tube.

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Footswitch Controller
1. Channel Selector: Stomp the Channel footswitch to switch the Dual 40 between channels. When the
amplifier is operating on channel one the indicator light is turned on. The amplifier panel switch must be
in the channel 2 position in order for the footswitch to work.
2. Mode Selector: Stomp the Mode footswitch to switch the Dual 40 between channel one modes.
When the amplifier is operating in channel one / mode two the indicator light is turned on. The amplifier
panel switch must be in the mode 2 position in order for the footswitch to work.
3. Boost 1 Selector: Stomp the Boost 1 footswitch to activate the boost function for channel one.
When the channel one boost mode is engaged the indicator light is turned on. The amplifier panel switch
must be in the + position in order for the footswitch to work.
4. Boost 2 Selector: Stomp the Boost 2 footswitch to activate the boost function for channel two.
When the channel two boost mode is engaged the indicator light is turned on. The amplifier panel switch
must be in the + position in order for the footswitch to work.
Connect the footswitch to the amplifier with a quality 5 pin midi cable.

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Warranty
The following warranties apply to the original owner of the amplifier. "All warranty work must be performed by Oldfield
or an authorized technician for the warranty to be in effect. "Warranties do not cover normal wear and tear or abuse.
Failure to comply with the safety precautions outlined earlier in the owner’s manual will void all warranties.
Rectifier and Power Tubes: Guaranteed for thirty days after date of purchase. "If a failure occurs Oldfield will replace
any rectifier or power tube during this period free of charge
Preamp Tubes: Guaranteed for ninety days after date of purchase. "If a failure occurs Oldfield will replace any
preamp tube during this period free of charge.
Power Transformer, Output Transformer And Choke: These items are guaranteed for one year after date of purchase
against manufacturer’s defects. "If a failure occurs due a defect in manufacturing Oldfield will replace any of these
items during this period free of charge. "Warranties on these items are void if the owner uses any type of power soak
or attenuator in conjunction with the operation of the amplifier or fails to connect a speaker load to the amplifier while
in operation.
Defects Due To Workmanship: Oldfield guarantees the amplifier to be free from workmanship defects for five years.
Circuit Components: Any failed circuit component will be replaced at Oldfield’s discretion for a period of five years
after the purchase date. "
In every case Oldfield guarantees to work with the customer to remedy any situation in a timely manner and to the
satisfaction of the amplifier owner.

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Operational Notes
The Oldfield Dual 40 amplifier offers the player a lot of functionality and at first glance can appear to be
somewhat complicated to operate. A little experimentation goes a long way to understanding all the
tones hidden inside your Dual 40 so don’t be afraid to flip some switches and twist some dials to
broaden your understanding.
Below are some suggested starting points:
JTM 45 / 67 Plexi / 59 Bassman
Channel Selector - 1
Mode Switch - 1
Mid + 1 Switch - Off
Channel One / Mode 1 Gain - 12 O’Clock
Master - 12 O’Clock
Tone Controls - 12 O’Clock
65 Blackface Bandmaster / Clean American
Tone
Channel Selector - 2
Mode Switch - N/A
Mid + 2 Switch - Off
Channel Two Gain - 12 O’Clock
Master - 12 O’Clock
Tone Controls - Treble 1 O’Clock, Middle 12
O’Clock, Bass 11 O’Clock
Brit Crunch
Channel Selector - 1
Mode Switch - 1
Mid + 1 Switch - On
Channel One / Mode 1 Gain - 2 O’Clock
Master - 10 O’Clock
Tone Controls - Treble 1 O’Clock, Middle 12
O’Clock, Bass 11 O’Clock
80’s Brit Tone
Channel Selector - 1
Mode Switch - 2
Mid + 1 Switch - Off
Channel One / Mode 1 Gain - 2 O’Clock
Channel One / Mode 2 Gain - 2 O’Clock
Master - 11 O’Clock
Tone Controls - Treble 1 O’Clock, Middle 12
O’Clock, Bass 11 O’Clock
80’s Hair Band Tone / 90’s Alt Rock Tone
Channel Selector - 1
Mode Switch - 2
Mid + 1 Switch - On
Channel One / Mode 1 Gain - 3 O’Clock
Channel One / Mode 2 Gain - 3 O’Clock
Master - 9 O’Clock
Tone Controls - Treble 1 O’Clock, Middle 1
O’Clock, Bass 11 O’Clock
Blues Tone
Channel Selector - 2
Mode Switch - N/A
Mid + 2 Switch - On
Channel Two Gain - 1 O’Clock
Master - 10 O’Clock
Tone Controls - Treble 1 O’Clock, Middle 12
O’Clock, Bass 11 O’Clock
Jimi Tone
Channel Selector - 1
Mode Switch - 1
Mid + 1 Switch - Off
Channel One / Mode 1 Gain - 2 O’Clock
Master - 12 O’Clock
Tone Controls - Treble 1 O’Clock, Middle 11:30
O’Clock, Bass 11 O’Clock
Sultans Of Swing Tone
Channel Selector - 2
Mode Switch - N/A
Mid + 2 Switch - Off
Channel Two Gain - 1 O’Clock
Master - 1 O’Clock
Tone Controls - Treble 1 O’Clock, Middle 11
O’Clock, Bass 12 O’Clock
Page Tone
Channel Selector - 1
Mode Switch - 2
Mid + 1 Switch - Off
Channel One / Mode 1 Gain - 2:30 O’Clock
Channel One / Mode 2 Gain - 8 O’Clock
Master - 1 O’Clock
Tone Controls - Treble 1 O’Clock, Middle 1
O’Clock, Bass 12 O’Clock