Mesa/Boogie F-50 Owner`s manual

Mesa/Boogie F-50 Owner`s manual
MESA BOOGIE
Series
Owner's Manual
Hello from the Tone Farm...
YOU, the smart player and all around intuitive human, have put your trust in us to be your
amplifier company. This is something we do not take lightly. Our reward is that we've made
a classic amplifier and by choosing this amplifier, you have become part of the MESA
family...Welcome! Our goal is to never let you down. Your reward is that you are now the
owner of an archetypal guitar amp bred of fine all tube amp heritage...benefiting from the
many patented pioneering MESA/Boogie circuits that led to the refinement of your new
instrument. Feel confident, as we do, that this amp will inspire many hours of musical
satisfaction and lasting enjoyment. It was built with you in mind, by players who know the
value of a fine musical instrument and the commitment it takes to make great music. The
same commitment to quality, value and support we make to you...our new friend.
Series
Table of Contents
Precautions
Overview
Instant Gratification
0
1-2-3
2
FRONT PANEL: Controls & Switches
GAIN
TREBLE
MID
BASS
REVERB
MASTER
CH 1 & 2: CONTOUR SELECT SWITCH
ON/STANDBY & POWER ON SWITCHES
4
4
4-5
5
5
5-6
6
5
REAR PANEL: Controls / Switches / Connection Jacks
FUSE
RECORD & PHONES
FX: SEND & RETURN
FX MIX CONTROL
SPEAKER MUTE SWITCH
SPEAKERS
FACTORY SAMPLE SETTINGS
PERSONAL SETTINGS PAGE
TUBE TASK CHART
TUBE NOISE & DIAGNOSING PRE-AMP PROBLEMS
Feature Article by RandallSmith
"Bias Adjustment"
SPEAKER IMPEDANCE & SPEAKER HOOK-UPS GUIDE
Feature Article by Randall Smith
"Triodes, Pentodes & Irishmen"
PARTS SHEEET
7
7
7
8
8
8
9
10
11-12-13
14-15
16-17-18
19 thru 24
25-26-27
28
PRECAUTIONS & WARNINGS
Your MESA/Boogie Amplifier is a professional instrument. Please treat it with respect and operate it properly.
USE COMMON SENSE AND ALWAYS OBSERVE THESE PRECAUTIONS:
WARNING: EU: permission from the Supply Authority is needed before connection.
WARNING: Vacuum tube amplifiers generate heat. To insure proper ventilation always make
certain there is at least four inches (100mm) of space behind the rear of the amplifier cabinet.
Keep away from curtains or any flammable objects.
WARNING: Do not block any ventilation openings on the rear or top of the amplifier. Do not
impede ventilation by placing objects on top of the amplifier which extend past the rear edge of its
cabinet.
WARNING: Do not expose the amplifier to rain, moisture, dripping or splashing water. Do not
place objects filled with liquids on or nearby the amplifier.
WARNING: Always make certain proper load is connected before operating the amplifier. Failure
to do so could pose a shock hazard and may result in damage to the amplifier.
Do not expose amplifier to direct sunlight or extremely high temperatures.
Always insure that amplifier is properly grounded. Always unplug AC power cord before changing
fuse or any tubes. When replacing fuse, use only same type and rating.
Avoid direct contact with heated tubes. Keep amplifier away from children.
Be sure to connect to an AC power supply that meets the power supply specifications listed on
the rear of the unit. Remove the power plug from the AC mains socket if the unit is to be stored
for an extended period of time. If there is any danger of lightning occurring nearby, remove the
power plug from the wall socket in advance.
To avoid damaging your speakers and other playback equipment, turn off the power of all related
equipment before
making the connections.
Do not use excessive force in handling control buttons, switches and controls. Do not use
solvents such as benzene or paint thinner to clean the unit. Wipe off the exterior with soft cloth.
Be sure to have the warranty card filled out by the store at which it was purchased and return to
Mesa/Boogie.
YOUR AMPLIFIER IS LOUD! EXPOSURE TO HIGH SOUND VOLUMES MAY CAUSE PERMANENT HEARING DAMAGE !
No user serviceable parts inside. Refer service to qualified personnel. Always unplug AC power before removing chassis.
EXPORT MODELS: Always insure that unit is wired for proper voltage. Make certain grounding conforms with local standards.
READ AND FOLLOW INSTRUCTIONS OF PROPER USAGE.
Series
Operating Instructions
OVERVIEW:
Congratulations on choosing the F Series as your amplifier and welcome to the Mesa/Boogie family! The new F Series amplifiers
combines high gain lead performance, an amazing mid-gain crunch or blues sound and a bold and beautiful clean sound in a simple
2 Channel, Three Mode, all-tube, hand-built package that begs to rock. This tidy format is available in three power versions, the F-30,
F-50 and F-100, and in both head and self-contained combo platforms.
The bright and bouncy F-30 with its 2xEL84 power string operating in our patented Dyna-Watt circuit is housed in the original
Boogie 1x12 size and powers the legendary Celestion Vintage 30. This is perfect as a super portable, lightweight and surprisingly
powerful combo. As a short head powering a 2x12 or 4x12, this little wolf in sheep’s clothing shows its fangs and becomes a viable gig
rig for mid size venues where its power clip can add a unique and dynamic personality. Like its forefathers, this little dynamo stays true
to the little giant-killer tradition that won the first Boogies worldwide acclaim 30 years ago.
The F-50 holds the title as middleweight champion of the line with its robust and balanced 2x6L6 power section and this rich, pristine
blend speaks from our popular Wide-Body 1x12 combo or head. The combo features our favorite custom designed, proprietary
Celestion C90 speaker and sounds twice its size as it envelopes you with its 3D magic, while the head through a big cab is absolutely
over the top with a tight top end snap and aggressive mid-power urgency.
The big daddy F-100 is the power broker of this clan with the undeniable authority of 4x6L6’s working for your tone. This big block bad
boy produces stunning clean headroom and can push some serious air in its 2x12 combo format featuring two Celestion Vintage 30’s
or, when punishment is required, the Long Chassis head pumping a 4x12…it’s the final word in loud. The voice is fatter and a little
FRONT VIEW:
INPUT
ON
ON
STANDBY
POWER
CH1
TREBLE
GAIN
MID
BASS
REVERB
MASTER
.FT
SW
CH
2
CH
CONTOUR
REAR VIEW:
WARNING:
Unplug power
before replacing
fuse or removing
bolts mounting
chassis.
POWER
120 V~
60 Hz
2A
FUSE
2A
SLO
BLO
FOOTSWITCH
SOCKET
BELOW
F-Series All Tube Amplifiers
MESA BOOGIE
Handbuilt in Petaluma, CA
SPEAKERS
FUSE
10%
100%
FX MIX
RCORD / PHONES
FX SEND
RETURN
STEREO / MONO
8 OHM
COMBO
WARNING: To reduce risk of fire or
MUTE SPKR ON
electric shock, replace fuse with
same type and rating only. Do not
expose this unit to rain or moisture.
SILENT RECORDING
PAGE 1
WARNING: To reduce risk of fire or electric
shock, Do not remove cover. No userserviceable parts inside. Refer
servicing to qualified personnel.
4 OHM
4 OHM
USE WITH 8 OHM SPEAKERS
OVERVIEW: (Continued) darker than that of its lower power family members but posses a depth and punch found only in amps of
this serious-gigging horsepower range. Our legendary 60/100 switch has been included and allows you to detune the power section
to achieve the brighter, more clippable feel of the F-Series.
F-Series amplifiers are crafted with the same custom quality, chassis, cabinet and tight tolerance parts found in our top of the line
multi-channel amplifiers. They become the deal of the century by focusing on maximum performance derived from a more straightforward layout that defines their stripped, business like personality. Yet make no mistake, these three over the top, footswitchable
sounds stand proud against any amp at any price.
Features include 2 Channels which are divided into a separate Rhythm Channel (top) and a Two-Mode Lead Channel (bottom) which
shares a set of Tone controls to produce the more vintage, warm sauce of Lead 1 and the huge, aggressive spread of Lead 2 Contour.
Add to this a long tank, 3-spring, pure analog Reverb, a Parallel Effects Loop and a dedicated Recording Output and the F-Series
preamp shines with old world luster as it delivers modern high gain performance.
All this preamp versatility is powered by feeding our dynamic dual differential driver first seen in our popular Strategy 400 Stereo
power amp, which lends an explosive nature to the sound and gives the impression of headroom far beyond the rated wattage. We
then send this super-buffed signal to the output section that responds to every nuance of your playing style.
All this performance is controlled via the included 3 button footswitch and this rounds out the package to achieve a performance
minded instrument of ultimate expression. So before we get to the specific controls and features, take a spin around the world of tone
found in the 3 Modes using the sample setting below as a guide.
INSTANT GRATIFICATION:
INPUT
ON
ON
STANDBY
POWER
CH1
GAIN
TREBLE
MID
BASS
REVERB
MASTER
FT.
SW
CH
2
CH
CONTOUR
NOTE: To audition the 3 modes using the Footswitch, toggle between Channel 1(top) and Channel 2 (bottom) using the left button
and toggle between Lead 1 and Lead 2 Contour with the middle button.
PAGE 2
OVERVIEW: (Continued)
REAR VIEWF-30
:
Handbuilt in Petaluma, CA
SPEAKERS
FUSE
10%
100%
FX MIX
RCORD / PHONES
FX SEND
RETURN
STEREO / MONO
8 OHM
COMBO
FOOTSWITCH
SOCKET
BELOW
WARNING: To reduce risk of fire or
MUTE SPKR ON
4 OHM
4 OHM
USE WITH 8 OHM SPEAKERS
WARNING: To reduce risk of fire or electric
electric shock, replace fuse with
same type and rating only. Do not
expose this unit to rain or moisture.
shock, Do not remove cover. No userserviceable parts inside. Refer
servicing to qualified personnel.
SILENT RECORDING
EL84
MESA
FUSE
2A
SLO
BLO
MESA BOOGIE
EL84
POWER
120 V~
60 Hz
2A
F-30 All Tube Amplifier
MESA
WARNING:
Unplug power
before replacing
fuse or removing
bolts mounting
chassis.
REAR VIEWF-50
:
POWER
120 V~
60 Hz
2A
FUSE
2A
SLO
BLO
F-50 All Tube Amplifier
MESA BOOGIE
Handbuilt in Petaluma, CA
SPEAKERS
FUSE
10%
100%
FX MIX
RCORD / PHONES
FX SEND
RETURN
STEREO / MONO
8 OHM
COMBO
FOOTSWITCH
SOCKET
BELOW
WARNING: To reduce risk of fire or
MUTE SPKR ON
4 OHM
4 OHM
USE WITH 8 OHM SPEAKERS
WARNING: To reduce risk of fire or electric
electric shock, replace fuse with
same type and rating only. Do not
expose this unit to rain or moisture.
shock, Do not remove cover. No userserviceable parts inside. Refer
servicing to qualified personnel.
SILENT RECORDING
6L6 GC
WARNING:
Unplug power
before replacing
fuse or removing
bolts mounting
chassis.
6L6 GC
REAR VIEWF-100
:
10%
100%
FX MIX
RCORD / PHONES
FX SEND
RETURN
STEREO / MONO
8 OHM
COMBO
WARNING: To reduce risk of fire or
MUTE SPKR ON
WARNING: To reduce risk of fire or electric
shock, Do not remove cover. No userserviceable parts inside. Refer
servicing to qualified personnel.
electric shock, replace fuse with
same type and rating only. Do not
expose this unit to rain or moisture.
SILENT RECORDING
6L6 GC
FOOTSWITCH
SOCKET
BELOW
SPEAKERS
FUSE
6L6 GC
FUSE
2A
SLO
BLO
MESA BOOGIE Handbuilt in Petaluma, CA
PAGE 3
6L6 GC
POWER
120 V~
60 Hz
2A
F-100 All Tube Amplifier
6L6 GC
WARNING:
Unplug power
before replacing
fuse or removing
bolts mounting
chassis.
4 OHM
4 OHM
USE WITH 8 OHM SPEAKERS
CONTROLS:
GAIN:
This is by far the most powerful control in each of the three different Modes that are activated by the Mode switch. It not only
determines the overall gain amount, shape and sensitivity of the Mode selected...but it is also a powerful Tone control. Generally
speaking, whatever is dialed up here ultimately determines the Modes’ personality. Set low, it allows cleaner and brighter sounds with
enhanced dynamic response, especially in the higher frequencies. Set high, the whole personality of the Mode becomes darker,
fatter and more overdriven.
INPUT
GAIN
We worked hard to make sure that the entire range of Gain available is usable in the F-Series and
more importantly, musical. Don’t think for a moment that this simple layout limits you in any way in
regards to the amount and texture of Gain that is available. Long neurotic hours were spent to
ensure that the ranges of Gain were stylistically accurate. It’s probably a good time to mention that
most of the great sounds can be found in the F-Series by setting the GAIN control moderately in the
Lead 2 - Contour mode.
In the Channel 1 Mode, try setting this control somewhere between ( 11:00 through 1:00 ). Use of
moderation here will reduce the likelihood of pesky tube microphonic problems ever occurring,
while at the same time making all three Modes easier to balance in volume and FX send strength.
TREBLE:
As in most tube guitar amplifiers, the TREBLE control ( in all three Modes of your F-Series amplifier ) is the most powerful of the rotary
controls and is next in line only to the GAIN control as a shaping tool. Because it is first in the signal path of the tone controls - and
from here the Middle and Bass receive their signal - it is by far the dominant tone control.
For this reason the setting of the TREBLE control is very important for equal representation of the three frequency regions to appear at their respective controls.
INPUT
GAIN
TREBLE
Like most of the controls on your F-Series amplifier there is an optimum region of the
TREBLE control where ample top end is mixed in and yet enough signal is still passed on
to the MIDDLE and BASS controls. As you might surmise, here is the sweet spot. There
are definitely great sounds above and below this middle region ( 11:00 through 1:30 ), but
the balance between the TREBLE control and the other two tone controls is compromised.
The one place you may want to throw caution to the wind and set the TREBLE control
above this median zone presents itself in Channel 1 of your new F-Series amplifier. The TREBLE control can be used to dump extra
gain into the mix. As you might surmise, the BASS Controls’ effectiveness will be reduced, so you may have to run a much higher
setting than you are used to seeing to achieve a balance. This said, keep in mind that the TREBLE control in Channel 1 should not
be set much above ( 3:30 ) to avoid unwanted microphonic tube problems.
MID:
The MID control is responsible for the blend of midrange frequencies in the mix and though its effect is not as dramatic as that of the
TREBLE control, it plays an integral part in achieving any sound in your F-Series amplifier. It is capable of changing the feel dramatically as it blends in a group of frequencies that tend to soften or stiffen the way a sound feels to play.
Most players tend to lean in the direction of lower MID control settings ( 7:00
through 11:00 ) where a scoop in this region produces girth ( by letting the
Bass become a little more dominant ) and a lack of punch lends a more com
INPUT
GAIN
TREBLE
MID
PAGE 4
CONTROLS:
MID: (Continued) pressed, even feel to the strings and therefore less apparent resistance to the pick. As the MID control is increased,
( 11:00 through 11:30 ), the sound is rounded-out and filled-in with a focused mid attack appearing rather quickly. As you would guess,
the feel starts to change - becoming more resistant. Above this region the MID control could be used to compensate for either weaker
pick-ups or for times when a specific deficiency is produced by either an extremely high setting of other tone controls, or a physical
anomaly in the room. While these MID control settings ( 2:00 - 5:00 )can introduce added gain and create enhanced focus, the tradeoff will be a stiffer, more forward, less compressed feel.
BASS:
This control blends in the lower frequencies and its effectiveness, again, depends on the setting of the TREBLE control. It should also
be set with moderation, as extreme settings in either low or high directions can produce an unbalanced tone. In any one of the three
Modes, be especially careful using higher Gain settings. Too
much Bass will cause a flabby unfocused sound that can’t be
dialed out because excessive Bass has been introduced to the
pre-amp in the early stages.
INPUT
GAIN
TREBLE
MID
BASS
Try setting the BASS control to (7:00 ) for clean sounds in the
CLEAN Mode and ( 4:00 ) or below when dialing up High Gain
overdriven sounds in this Mode. In the Channel 2 / CONTOUR
Mode, try setting the BASS somewhere between ( 10:00 through
2:00 ). These settings will depend upon the amount of Gain and
Treble that you have dialed up.
REVERB:
Your new F-Series amplifier is equipped with a rich, natural sounding analog Reverb circuit. The REVERB control enables you to
dial-in just the right amount of Reverb to be mixed with the dry signal. It is normal for extreme settings of the REVERB control to
slightly alter the character of the amplifier as the voicing of the Reverb circuit becomes more dominant in the mix.
CH1
BASS
REVERB
MASTER
.FT
SW
CH
2
NOTE: Avoid using high setting the REVERB control when High Gain and Treble
settings are in use. This reduces the likelihood of annoying microphonic problems
occurring.
CH
CONTOUR
MASTER:
The individual MASTER controls serve three purposes in the layout of the F-Series. FIRST: They serve as level balancing controls
for each of the two channels. This enables a wide range of front end Gain settings to be matched to a given listening level and the
level of the other Modes.
SECOND: They act as Effect Send controls for each Mode in the Effects Loop. As with
many of the controls on the F-Series, the best results for balance and tone are usually
found in the medium range of this control.
CH1
BASS
REVERB
MASTER
.FT
SW
CH
2
CH
CONTOUR
THIRD: The MASTER control is the Record / Phones Send Level control. When using
the direct RECORD / PHONES jack found on the Rear Panel to interface di PAGE 5
CONTROLS:
MASTER: (Continued) -rectly to a mixing board or recorder, this control will determine the amount of signal you will be sending via
this jack. In this application it is usually best to start with the MASTER controls set to ( 7:00 ) and gradually increase them to the
proper level. This minimizes the possibility of blowing speakers or eardrums in the event the engineer has an extremely sensitive
input headroom setting in place at the console.
CH.1 / CH.2 / CONTOUR SELECT SWITCH:
Use this mini-toggle to select one of the three Modes - CHANNEL 1, CHANNEL 2 or CONTOUR. In order for the channel select
Footswitch to operate when connected to your new F-Series amplifier, the channel select mini-toggle switch
must be in its middle position - FT . SW.
CH1
MASTER
.FT
SW
CH
2
CH
CONTOUR
ON / STANDBY:
Perfect for set breaks...this toggle switch also serves an even more important purpose. In the STANDBY position (switch up), the
tubes are at idle so that during power up they may warm up before being put to use.
ON
ON
STANDBY
POWER
Before the power is switched on, make sure the STANDBY switch is in the
STANDBY position. Wait at least 30 seconds and then flip the STANDBY
switch to its ON position. Following this simple warm up procedure helps
in preventing tube problems and increase their toneful life substantially.
POWER / ON:
This switch delivers the A.C. power to the F-Series. Make sure the unit is properly grounded ( all three terminals of the A.C. power cord
must be connected whenever possible and that the proper voltage is present. Follow the cold start procedure described in the ON/
STANDBY section above when powering up your new F-Series amplifier.
NOTE: Never alter the A.C. power cord in any way.
ON
ON
STANDBY
POWER
PAGE 6
REAR PANEL:
REAR VIEW:
WARNING:
Unplug power
before replacing
fuse or removing
bolts mounting
chassis.
POWER
120 V~
60 Hz
2A
FUSE
2A
SLO
BLO
F-Series All Tube Amplifiers
MESA BOOGIE
Handbuilt in Petaluma, CA
SPEAKERS
FUSE
100%
10%
FX MIX
RCORD / PHONES
FX SEND
RETURN
STEREO / MONO
8 OHM
COMBO
FOOTSWITCH
SOCKET
BELOW
WARNING: To reduce risk of fire or
MUTE SPKR ON
electric shock, replace fuse with
same type and rating only. Do not
expose this unit to rain or moisture.
SILENT RECORDING
4 OHM
4 OHM
USE WITH 8 OHM SPEAKERS
WARNING: To reduce risk of fire or electric
shock, Do not remove cover. No userserviceable parts inside. Refer
servicing to qualified personnel.
FUSE:
This is the A.C.’s ( Alternating Current ) main fuse and provides protection from outside A.C. fluctuations,
FUSE
as well as power tube failure damage. Should the FUSE blow, replace it with the same rating in a sloblo type package. The domestic U.S. version requires a 2 Amp SLO-BLO FUSE. A power tube short or
POWER FUSE
RECORD / PHONES
120 V~ 2 A
failure is often the cause of a blown fuse...Follow the cold start procedure mentioned earlier in the ON
STEREO OR MONO
50-60 Hz SLO
2A
BLO
/ STANDBY switch section and watch the power tubes as you flip the STANDBY to the ON position. If a
FOOTSWITCH
power tube is going bad or is arcing you will see it! Flip the STANDBY switch to STANDBY immediately
SOCKET
BELOW
and replace the faulty power tube and the fuse if necessary. If you see nothing abnormal as you lift the
STANDBY switch, it is possible that a power tube shorted temporarily and blew the FUSE. If this is the
case it may work again normally. To be extra safe you may want to replace all power tubes in the troubleshooting tradition and save
the replaced set as spares. Carry along a few extra fuses for they too could be worth their weight in gold some day.
WARNING:
2A S.B.
WARNING:
2A S.B.
POWER
120 V~
50-60 Hz
2A
FUSE
2A
SLO
BLO
FUSE
FUSE
Unplug power
before replacing
fuse or removing
bolts mounting
chassis.
FUSE
Unplug power
before replacing
fuse or removing
bolts mounting
chassis.
RECORD / PHONES
STEREO OR MONO
FOOTSWITCH
SOCKET
BELOW
Unplug power
before replacing
fuse or removing
bolts mounting
chassis.
POWER
120 V~
50-60 Hz
2A
FUSE
2A
SLO
BLO
FOOTSWITCH
SOCKET
BELOW
The send level strength is determined by the GAIN and MASTER controls. From this jack, adequate
signal level will be available to you for most of your recording needs and live direct performances.
2A S.B.
FUSE
FUSE
WARNING:
RECORD / PHONES:
This jack provides direct-to-console interfacing for recording or sound reinforcement applications. It
can also be used to power a set of personal headphones which is a convenient way to practice day or
night privately. It is a circuit dedicated to reproducing the roll off that occurs in the output section with a
speaker connected.
RECORD / PHONES
STEREO OR MONO
F-50
PREAMP PATENT
4,701,957
FX
SEND
10%
100 %
FX MIX
RETURN
FX LOOP: SEND & RETURN
These two 1/4" jacks are the patch point for external effects. The Effects Loop is
wired in parallel with the normal signal. Connect the SEND jack of the F-Series to
your Effects Input jack. Connect the RETURN jack of the F-Series to the Output jack
of your effect unit. The Effects Loop is a patch point between the pre-amp and power
section. Therefore, the RETURN jack can double as a “Power Amp Input” jack.
When the RETURN is used as an input, the F-Series FX MIX control is the only
control being utilized regardless of the mode selected and should be set to 100%. While the RETURN is being used in this manner,
all other controls are inactive.
PAGE 7
REAR PANEL:
10 0%
10%
FX MIX
FX MIX:
This control determines the dry/wet blend of the FX Loop signal in relation to the unaffected signal. Set to 10%
you will experience only the dry signal (no noticeable FX) and at a setting of 90% the entire signal will be wet (total
effect.)
RETURN
For the best results...Set the mix of your effect to 100% wet. Then dial in the amount of effect that you wish to hear,
starting at 10% with the FX LOOP MIX control. The drier (closer to 10%) signal you use, the better your tone
should be. This parallel type FX Loop allows the amplifier to retain its purity with the smallest amount of degredation
due to possible effect impedance mismatching.
SILENT RECORDING:
This rocker switch which is located down under the chassis and selects between the live “Speaker
On” setting and the silent “Speaker Mute” setting. This is a perfect solution for all-nighters! This
switch mutes all of the signal at the power section driver stage, removing the need for a speaker load
IN THIS POSITION ONLY!
10 0 %
MIX
TURN
MUTE SPKR ON
SILENT RECORDING
SPEAKERS
8 OHM
4 OHM
4 OHM
NOTE: When this switch is set to the “ON” position, a speaker load must be maintained by either a
load resistor of some type or a speaker itself. Failure to follow this instruction could result in major
damage to the amplifier. Leave your speaker connected.
SPEAKERS:
Sensitivity to speaker mismatching in regards to ohmage differences is low, hence no damage to
the amplifier will occur. However, very low ohmage loads will cause the power tubes to wear faster.
The F-Series are equipped with a single 12 inch 8 Ohm speaker, but as you can see, other speaker
configurations may be used. When using two 8 Ohm speakers, connect each of them to the 4 Ohm
speaker jacks that are provided, this will equal a 4 Ohm load which is the proper impedance
required when using this particular speaker configuration.
4x12 cabinets may be 4, 8 or 16 Ohms. If you are not sure of the impedance of your cabinet, you may need to remove the Rear Panel
in order to verify the impedance rating of the individual speaker or speakers. Mesa/Boogie 4x12 and 4x10 cabinets come
standard wired to 8 Ohms, and are wired in series-parallel.
Some Non-Mesa 4x12 cabinets are wired 16 Ohms using four 16 Ohm speakers. By wiring all four speakers in parallel, you can
reduce the cabinet to an impedance load of 4 Ohms (assuming the speakers are 16 Ohms each.) No matter how unusual your
speaker setup, it is always possible to get good performance.
PAGE 8
FACTORY SAMPLE SETTINGS
Sample #1 Fat Clean: Channel 1
ON
INPUT
ON
CH1
GAIN
TREBLE
MID
BASS
REVERB
MASTER
.FT
SW
CH
2
CH
CONTOUR
STANDBY POWER
Sample #2 Squeaky Channel 1
ON
INPUT
ON
CH1
GAIN
TREBLE
MID
BASS
REVERB
MASTER
.FT
SW
CH
2
CH
CONTOUR
STANDBY POWER
Sample #3 Blues Power: Channel 2
ON
INPUT
ON
CH1
GAIN
TREBLE
MID
BASS
REVERB
MASTER
.FT
SW
CH
2
CH
CONTOUR
STANDBY POWER
Sample #4 Liguid Solo: Channel 2
ON
ON
CH1
INPUT
GAIN
TREBLE
MID
BASS
REVERB
MASTER
.FT
SW
CH
2
CH
CONTOUR
STANDBY POWER
Sample #5 Huge Crunch: Channel 2 Contour
ON
INPUT
ON
CH1
GAIN
TREBLE
MID
BASS
REVERB
MASTER
.FT
SW
CH
2
CH
CONTOUR
STANDBY POWER
Sample #6 Insane Lead: Channel 2 Contour
ON
INPUT
ON
CH1
GAIN
TREBLE
MID
BASS
REVERB
MASTER
.FT
SW
CH
2
CH
CONTOUR
PAGE 9
STANDBY POWER
PERSONAL SETTINGS
Sample #1
ON
INPUT
ON
CH1
GAIN
TREBLE
MID
BASS
REVERB
MASTER
.FT
SW
CH
2
CH
CONTOUR
STANDBY POWER
Sample #2
ON
INPUT
ON
CH1
GAIN
TREBLE
MID
BASS
REVERB
MASTER
.FT
SW
CH
2
CH
CONTOUR
STANDBY POWER
Sample #3 l
ON
INPUT
ON
CH1
GAIN
TREBLE
MID
BASS
REVERB
MASTER
.FT
SW
CH
2
CH
CONTOUR
STANDBY POWER
Sample #4
ON
ON
CH1
INPUT
GAIN
TREBLE
MID
BASS
REVERB
MASTER
.FT
SW
CH
2
CH
CONTOUR
STANDBY POWER
Sample #5
ON
INPUT
ON
CH1
GAIN
TREBLE
MID
BASS
REVERB
MASTER
.FT
SW
CH
2
CH
CONTOUR
STANDBY POWER
Sample #6
ON
INPUT
ON
CH1
GAIN
TREBLE
MID
BASS
REVERB
MASTER
.FT
SW
CH
2
CH
CONTOUR
PAGE 10
STANDBY POWER
F-30
TUBE TASK CHART
MUTE SWITCH
PARTIAL VIEW OF CHASSIS
B A
V 1
B A
BACK EDGE OF CHASSIS
B A
V 2
EL84
B A
V 3
EL84
V 4
(4)
12AX7
(Each 12AX7 contains two separate Triodes)
V3 B= FX Return
Phase Splitter /
V4 A=
Output
V4 B=
Description of Tube Functions
V1 A= Input Stage both Channels
V1 B= Clean Channel
V2 A= 2nd Input Stage bothChannels
V2 B=Channels 2 & 3 Boost Stage
V3 A=Channels FX Send
PAGE 11
F-50
TUBE TASK CHART
MUTE SWITCH
PARTIAL VIEW OF CHASSIS
B A
V 1
B A
BACK EDGE OF CHASSIS
B A
V 2
6L6
B A
V 3
6L6
V 4
(4)
12AX7
(Each 12AX7 contains two separate Triodes)
V3 B= FX Return
Phase Splitter /
V4 A=
Output
V4 B=
Description of Tube Functions
V1 A= Input Stage both Channels
V1 B= Clean Channel
V2 A= 2nd Input Stage bothChannels
V2 B=Channels 2 & 3 Boost Stage
V3 A=Channels FX Send
PAGE 12
F-100
TUBE TASK CHART
MUTE SWITCH
PARTIAL VIEW OF CHASSIS
B A
6L6
V 1
B A
6L6
BACK EDGE OF CHASSIS
B A
V 2
6L6
B A
V 3
6L6
V 4
(4)
12AX7
(Each 12AX7 contains two separate Triodes)
V3 B= FX Return
Phase Splitter /
V4 A=
Output
V4 B=
Description of Tube Functions
V1 A= Input Stage both Channels
V1 B= Clean Channel
V2 A= 2nd Input Stage bothChannels
V2 B=Channels 2 & 3 Boost Stage
V3 A=Channels FX Send
PAGE 13
TUBE NOISE & MICROPHONICS:
You may occasionally experience some form of tube noise or microphonics. Certainly no cause for alarm, this quirky behavior
comes with the territory and the Tone. Much like changing a light bulb, you don’t need a technician to cure these types of minor user
serviceable annoyances and in fact, you’ll be amazed at how easy it is to cure tube problems...by simply swapping out a pre-amp or
power tube!
First may we suggest that you set the amplifier up on something so that you can get to the tubes comfortably without having to bend
down. It also helps to have adequate lighting as you will need to see the tube sockets clearly to swap tubes. Use caution and common
sense when touching the tubes after the amplifier has been on as they may be extremely hot! If they are hot and you don’t want
to wait for them to cool off, try grasping them with a rag and also note that the glass down around the bulbous silvery tip is
considerably less hot which makes it easier to handle. Gently rock the tube back and forth as you pull it away from its socket.
DIAGNOSING POWER TUBE FAILURES:
There are two main types of tube faults: shorts and noise. Both large and small tubes may fall prey to either of these problems but
diagnosis and remedy is usually simple.
If a fuse blows, the problem is most likely a shorted power tube and shorts can either be mild or severe. In a mildly shorted tube the
electron flow has overcome the control grid and excess current flows to the plate. You will usually hear the amp become distorted and
begin to hum slightly. If this occurs, quickly look at the power tubes as you switch the amp to STANDBY and try to identify one as
glowing red hot. It is likely that two of a pair will be glowing since the “shorted” tube will pull down the bias for its adjacent mates, but
one tube may be glowing hotter — and that one is the culprit. The other two are often fine — unless they’ve been glowing bright red
for several minutes.
Because there is no physical short inside the tube (just electrons rioting out of control) merely switching to STANDBY for a few
moments then back to ON will usually cure the problem...at least temporarily. Watch the tubes carefully now. Should the problem
recur, the intermittent tube will visibly start to over heat before the others and thus it can be identified. It should be replaced with one
from the same color batch, shown on its label. Call us and we will send one out to you. The severe short is not nearly so benign. In
the worst cases, a major arcing short occurs between the plate and the cathode with visible lightning inside the glass and a major
noise through the speaker. If this is seen to happen, IMMEDIATELY turn the amp to STANDBY. By this time the fuse probably will have
blown. Such a short is usually caused by a physical breakdown inside the tube including contaminate coming loose or physical
contact (or near contact) between the elements. Replace it and the fuse with the proper slo-blo type and power up the amp using the
power up procedure as we described earlier in this manual.
TUBE NOISE:
Often caused by contamination within in a tube, the culprit can usually be identified, and by lightly tapping on the glass, you will
probably hear the noise change. Hearing some noise through the speakers while tapping on the 12AX7’s is normal however. And the
one nearer the INPUT will always sound louder because its output is being further amplified by the second 12AX7.
The power tubes should be all but quiet when they are tapped. If crackling or hissing changes with the tapping, you have probably
found the problem. To confirm a noisy power tube, merely put your F-Series amplifier on Standby, remove it from its socket and turn
it back on. It will cause no damage to run your amplifier briefly with one power tube missing. You may notice a slight background hum,
however, as the push-pull becomes unbalanced. Whenever you are trying to diagnose a suspect tube, keep your other hand on the
POWER and STANDBY switches ready to shut them off instantly in the unlikely case you provoke a major short.
If you think you’ve located a problem tube but aren’t sure, we recommend substituting the suspect with a new one just to be sure of
your diagnoses. You will be doing yourself and us a big favor by just following the simple guidelines previously mentioned regarding
tube replacement. You’ll probably be successful with much less effort than is required to disconnect everything and haul the unit to a
technician who will basically perform the same simple tests. If the tubes are still within their six-month warranty period, we will
happily send you a replacement. Just note the color designation on the tube label so that we can send you the appropriate match.
PAGE 14
DIAGNOSING PREAMP TUBE PROBLEMS:
Because your amplifier is an all tube design, it is quite possible that you will at some point experience minor pre-amp tube noise.
Rest assured - this is no cause for alarm and you can take care of the problem yourself in a matter of minutes by simply swapping
tubes.
Let us begin by saying; It is a “very good” idea to keep at least a couple of spare pre-amp tubes on hand at all times to insure
uninterrupted performance. These minor pre-amp tube problems can take many forms but can generally be described in two categories: Noise and Microphonics. Noise can be in the form of crackling, sputtering, white noise/hiss and/or hum. Microphonic problems
usually appear in the form of a ringing or high pitched squealing that gets worse as the gain or volume is increased thus are more
noticeable in the higher gain “HI” modes. Microphonic problems are easily identified because the problem is still present even with
the instruments’ volume off or unplugged altogether - unlike pick-up feedback which ceases as the instrument is turned down.
Microphonic noise is caused by mechanical vibration and shock: think of banging a microphone around and you’ll understand where
the word came from.
The best way to approach a pre-amp tube problem is to see if it occurs only in one specific mode or channel. Then refer back to the
TUBE TASK and DESCRIPTION CHART and it should lead you to the tube needing replacement. Then all that remains is to swap the
suspect tube for a known good performer.
If you cannot narrow down the trouble to a specific mode or channel, the problem may be the small tube that drives the power tubes
which is operational in all modes and channels. Though rare, a problem with the driver tube would show up in all aspects of performance - so if you can’t narrow the problem down to being mode or channel specific, you may want to try replacing the driver tube.
Driver problems generally show themselves in the form of crackling or hum in all modes of performance and/or weak overall output
from the amplifier. Occasionally an anemic driver tube will cause the amplifier to sound flat and lifeless, but this is somewhat uncommon, as worn power tubes are a more likely suspect for this type of problem.
Sometimes making the diagnosis is more trouble than it’s worth and it’s faster and easier to merely replace the small pre-amp tubes
ONE AT A TIME with a replacement known to be good. But MAKE SURE you keep returning the tubes to their original socket until you
hit the one that cures the problem. You’ll notice that tubes located nearer to the INPUT jack always sound noisier...but this is because
they are at the start of the chain and their noise gets amplified over and over by the tubes that follow. The tube that goes into this
“input socket” (usually labeled V1) needs to be the least noisy of the bunch. The tube that goes at the end of the preamp chain - just
ahead of the power tubes - can be quite noisy without causing any problem at all. The tubes in your amp have already been located
in the most appropriate sockets and this is why you should NEVER pull them all out at once and ALWAYS swap them one at a time.
ALWAYS return a perfectly good tube to its original socket. Also it’s a good idea to put the amp on STANDBY when swapping tubes to
reduce the heat build up in the tubes themselves and to prevent explosive noises (which can still occur even if you are pulling the
tubes away from their sockets gently) from coming through the speaker.
Remember, take your time, be patient and chances are real good that you can fix your amp yourself by finding and replacing the bad
tube. It kills us to see someone who has shipped their amp back to us...and all it needed was a simple tube replacement! If you must
send back your amp, unplug the power cord, speaker and reverb cables then remove the chassis from the cabinet by unscrewing the
four mounting bolts on top. The chassis then slides back like a drawer and comes out. Remove the big power tubes and mark them
according to their location from left to right 1, 2 etc. They need to be wrapped separately with plenty of wadded up newspaper around
them and put in a smaller box within the larger carton. To wrap the chassis, use plenty of tightly wadded up newspaper so there is at
least six inches of “crush space” between the chassis and the cardboard box. Bubble wrap also works well, but please DON’T use
styrene peanuts - they will shift during transit and get lodged inside your electronics as well as allowing your amp to end up at the
bottom of the box unprotected and possibly damaged. Pre-amp tubes don’t normally wear out as a rule. Therefore, it is not a good
idea to change them just for the sake of changing them. If there isn’t a problem - don’t fix it. If there is no result from your
substitutions, it may be possible that you have more than one problematic tube. Though rare, this does happen and though it makes
the troubleshooting process a little more intimidating, it is still possible to cure the problem yourself.
NOTE: It is normal to hear a slight metallic ringing sound when tapping on the preamp tubes. As long as the tube does not break
PAGE 15
into oscillation or start crackling or any other form of bizzare noise, it is considered normal and functional.
BIAS ADJUSTMENT: (a continuing series)
CATHODE ( )
GRID ( , )
SCREEN
GRID ( )
NOTE: An article written by Randall Smith that
we thought you might find interesting.
BEAMCONFINING
ELECTRODE ( )
..
.....
....
.
...
.
....
PLATE
( , )
Here’s a question we often hear:
Structure of a 6L6 / 5881
Beam Power Pentode.
“Why doesn’t Mesa put bias adjustments
in their amplifiers?”
Well, there’s a short answer and a long answer to this question.
The short answer is that during my 12 years of repairing Fenders, one of the most frequent problems I saw was bias controls that were
either set wrong or that had wandered out of adjustment due to vibration. As any honest tech will tell you, there’s lot’s of easy money
to be made by sprinkling “holy water” on amplifiers ... uh, what I meant to say is “Your amp needed biasing.” See what I mean? What
customer is going to argue with that?
It only takes a moment and a volt meter: The Fender diagram shows how: “Adjust this trim pot for - 52 volts.” That’s it. Nothing more.
Now don’t be fooled into thinking that tubes “draw” more or less bias, they don’t. The way a bias supply is connected to a tube is akin
to a dead end road, it just trails off to nowhere without really completing a circuit. It’s a static voltage and regardless of what tube is in
the socket — or even if the tubes aren’t plugged in at all, it doesn’t change the bias voltage a bit.
So the end of the short answer is this: Since a bias supply needs to put out the right voltage and never vary, I wanted to build
amplifiers that were individually hard wired to the correct values and NEVER needed adjustment. And for 25 years, that’s how Mesa/
Boogies have been built.
Time to change tubes? Just plug our tubes into any one of our amps and you’re DONE. No tech needed. NO bills and no BS about
biasing. And most important: The bias is RIGHT because it can’t change!
Now, you want the long answer? Here’s more information on how our hard-wired bias avoids trouble. Please read on.
But first, let’s make an important distinction. Our business is designing and building high performance amplifiers. And for this we need
tubes whose variance is within a narrow range. Our warehouse is full of rejects ...oh, they work — they just don’t perform within our
tolerance range. We have a very sophisticated computer - based tube testing system (nicknamed “Robotube”) that matches and
measures tubes over seven important parameters. It can even predict which tubes are likely to have a shortened lifetime — even
though they work perfectly during the test.
Because our business is building quality amps, we can afford to reject a lot of wayward tubes. The guys you hear complaining
because Boogies don’t have bias adjusters are primarily in the business of selling tubes - not amps. They don’t want to throw away 30
percent of their inventory, so they promote the idea that tubes outside our parameters can be used to “customize” amplifiers and they
criticize us because our amps can’t be adjusted to accommodate their out-of-Mesa tolerance tubes.
Now you might be thinking, “But I thought you just said that tubes don’t “draw” bias, therefore they don’t effect the bias supply and thus
PAGE 16
it doesn’t need to be adjustable.”
BIAS ADJUSTMENT: (Continued) When you set the bias (whether it’s by selecting the right resistors, as we do, or adjusting a
trimmer — which is quicker) what you are doing is establishing the correct amount of idle CURRENT that flows through the power
tubes. But you can’t adjust the current directly, you can only change it by adjusting the amount of bias VOLTAGE that goes onto the
tubes’ control grids.
Voltage and current are NOT the same. Current is the AMOUNT of electricity, the “quantity” — and is measured in amperes. Voltage
is the degree of electric charge — like the “pressure” to use the old water analogy. Let me illustrate how different voltage and current
are:
When you scrape your feet across a carpetted floor in dry, wintery conditions, your body can become charged with 50,000 to 100,000
volts of static electricity. And when you reach for the door knob, a spark jumps and you feel it! The voltage is super high but the
current (measured in micro-amps) is tiny - otherwise you would die from electrocution.
Contrast this with your car battery, which puts out a mere 12 volts. You can lay your hands right across the terminals and not feel a
thing. Yet the amount of current available can run to several hundred amperes .. enough to turn over a cold engine and get it started.
So current and voltage are two totally separate electrical parameters — though when you multiply them together, you get POWER,
which is measured in watts.
When you set the bias of an amplifier, you are adjusting the static VOLTAGE at the control grid of the tube in order to produce a
desired amount of idle CURRENT flowing to the tube’s plate. A small change in grid voltage, produces a large change in the amount
of current flowing — and that’s basically how a tube works. Say that again because it’s super important: A small change in voltage at
the grid causes a large change in current flowing to the plate. See, that’s the essence of amplification: A small change causing a large
change. And here it’s a small voltage change causing a large current change.
The bias conditions are what determines how much current flows through the big power tubes when you’re not playing. And what
drives your speakers is flucuations in that current flow when are ARE playing. If the amount of current increases and decreases 440
times per second, then you’ll hear an A note. If the fluctions in current flow are large and still at 440 per second, you’ll hear an A that
is LOUD!
But for purposes of biasing, it’s the amount of “plate current” flowing with no signal applied that’s important. Unfortunately current is
hard to measure because the circuit must be interuppted — as in “cut the wire” — and the meter spliced “in series” with the broken
circuit. But measuring VOLTAGE is easy. It is not necessary to interrupt the circuit because a voltage reading can be taken in
PARALLEL with the circuit intact.
Thus, as a matter of convenience, most bias settings are given in volts at the grid ... even though current through the plate is the
important factor. In fact plate current is so inconvenient (and dangerous) to measure that Fender doesn’t even state what the correct
value should be. They only give the grid voltage that will produce that current. (That’s the minus 52.) But that only happens if the
tubes being used are “in spec.”
As long as the tubes ARE “in spec”, the right bias voltage will always give the correct plate “CURRENT” — but then there’s no need
for the bias voltage to be adjustable!
If the tubes are NOT in spec, then the only proper way to re-set the bias is to cut the circuit and measure the current while adjusting
the bias ... but no manufacturer I know even STATES the desired current value! Be that as it may, when the original bias voltage is
altered far enough, it will compensate for the tube’s abnormal performance and the correct amount of idle current flow may then be
restored. Clearly this is something most repair techs should not attempt.
Some newer amps have LED indicators connected to the circuit which will turn on when the right threshold of current flow has been
reached. This is an improvement, and almost worthy if you’re willing to except resistors and lights added into your amplifier’s audio
path — which we aren’t. The other “advantage” of this system is that it allows some amp manufacturers to avoid matching their
power
tubes. The thinking is that adjusting the bias to each tube separately
PAGE 17 eradicates the inherent differences between the tubes by
insuring that the same current flows through each one.
“
BIAS ADJUSTMENT: (Continued) tubes. The thinking is that adjusting the bias to each tube separately eradicates the inherent
differences between the tubes by insuring that the same current flows through each oneAgain, this has some merit .. but it’s still not
as good as using tubes that are matched in the first place because compensating for the mis-match causes the push-pull circuit itself
to become unbalanced. Two wrongs don’t really make a right.
Some of the other recommended biasing, “methods” — such as -”.. tubes running red hot, increase the bias .. sounds harsh and runs
too cool, turn it down ...” are guesswork at best. Luckily, one of the great things about tube amps is that they can usually stand some
abuse without causing any real harm ... at least not immediately.
But don’t these alterations imply that you are second-guessing the amp designer and that there’s a better set of operating conditions
that the designer missed but the tube sellers have discovered?
Now some players may like the sound of their amp altered by tubes with extreme characteristics and with the bias set to help
compensate. But often it is the mere novelty of change that they’re really responding to and when the amp goes back to the proper
original way, we’ve seen them be far happier still!
Because every part in every one of our designs has been meticulously evaluated, compared and stressed over — no matter how
seemingly insignificant it might be. And with every design we look for a “sweet spot” where all the parameters — including the bias —
come together to give the best sonic performance, consistently and reliably. Every part and voltage is important — yet no one
complains that these other parameters aren’t available for tinkering.
Consider our patented Simul-Class circuitry where there are two different bias voltages used for separate pairs of power tubes ... and
changing one voltage also changes the other. Great care goes into getting this just right and we think we’d be asking for trouble to
have it adjustable for the world to play with ... unless you like paying to have your amp messed up. Sorry, I meant to say, “Uh, ... your
amp needed biasing.”
If that doesn’t appeal to you, then merely plug a matched set of Mesa tubes into one of our amps and you’re ready for tone. Guaranteed. You’d be amazed at the number of service calls we field every day that lead to a diagnosis of out-of-tolerance, non-spec tube
problems. To think these would be prevented by including a bias adjustment is something of an insult to you and us. If you put the
wrong size tires on your car, do you think changing the pressure will make them right?
Please, don’t think this is a blanket indictment of the other guys selling tubes — it isn’t. And their tubes aren’t all bad either. It just
doesn’t make sense to pay more of your hard earned cash for tubes that were probably made in the same Russian or Chinese factory
and which have the possibility of being outside the performance window we select for your amp. And it pains us to hear the hype and
mystique built up around biasing when twenty-five years of evidence affirms our decision to make bias circuits that “never need
adjustment”. How much money and trouble that has saved Mesa/Boogie players you couldn’t estimate.
Our rigorously tested and hand selected tubes are available at your nearest Mesa/Boogie Pro Center or from us directly. Nobody
offers better price, quality or warranty than we do ... so why swerve?
Next time we’ll talk about our part in developing the great Sylvania STR 415 type 6 6 and how we’re on the verge of seeing something
fairly close reappear on the market. Remember, we still have some of these super rugged mondo-bottles available for older amps —
Boogies only please! Until then, Relax, Breathe and Nourish your soul!
Cheers!
Mesa/Boogie Ltd.
Randall Smith
Designer & President
PAGE 18
SPEAKER IMPEDANCE MATCHING & HOOK-UP GUIDE:
IMPEDANCE:
Wiring up speakers to provide the most effective load and making sure that all of them are in phase will help in creating the best sound
possible. This is not too difficult, as long as you understand a few things about loading and how to connect your speakers to provide
an optimal resistive load.
Mesa Boogie amplifiers can handle 4 and 8 ohms effectively. Never run below 4 ohms in a tube amplifier unless you are absolutely
certain that the system can handle it properly; this can cause damage to the Output transformer. A few amplifiers can handle 2 ohms
effectively without damaging them ( for example the Mesa’s Bass 400+ ). You can always have a higher resistance ( 16 ohms, for
example ) without damaging results, but too low of a resistance will likely cause problems.
MIS-MATCHING:
When running a higher resistance ( for example: 8 ohm output into 16 ohm cabinet ), a slightly different feel and response will be
eminent. A slight mismatch can provide a darker smoother tone with a little less output and attack. This response is a result of the
amplifier running a bit cooler. Sometimes when using more than one cabinet a mismatch will be the only option.
WHAT IS MY CABINETS IMPEDANCE:
If you have only a single speaker, you just match that single speakers impedance to the amplifier, and you are done. In many cases,
you will have a number of speakers, and then you must calculate the “load” that the amplifier will need to support. There are generally
three ways to wire multiple speakers together. They are as follows:
SERIES:
When you wire ( hook-up ) speakers in Series, the speakers resistance ( as measured in ohms ) is additive - i.e. putting two 8 ohm
speakers in Series results in a 16 ohm load.
NEGATIVE =
POSITIVE =
BLA
BLA
DOW
Made by
Speaker A = 8 Ohms
Made by
DOW
SHA
CK
Electro-Voice
SHA
CK
Electro-Voice
Speaker B = 8 Ohms
SERIES: Connect the Negative side of Speaker A
to the Positive side of Speaker B
PAGE 19
SPEAKER IMPEDANCE MATCHING & HOOK-UP GUIDE: (Continued)
PARALLEL:
When wiring in parallel, the resistance of the speakers decreases. Two 8 ohm speakers wired in ( hooked-up ) Parallel results in a 4
ohm load. It’s easy to calculate the effect of a resistive load when all the speakers are all the same resistance. It is really not suggested
to wire different resistive load values in Parallel ( 8 and 4, 16 and 8 etc. ) The formula for figuring the total impedance in Parallel is the
multiplication of the two loads divided by the sum of the two loads - i.e. putting two 8 ohm speakers in Parallel results in a 4 ohm load.
Connect the Positive side of Speaker A to the Positive side of Speaker B - Connect the Negative side of Speaker A to the Negative
side of Speaker B.
Speaker B
8 Ohms
Speaker A
8 Ohms
BLA
BLA
DOW
Made by
Made by
DOW
SHA
CK
Electro-Voice
SHA
CK
Electro-Voice
NEGATIVE
POSITIVE
Total Load = 4 Ohms
COMBINATION SERIES & PARALLEL:
This is really just two sets of Parallel wired speakers connected in series. This is how you maintain a consistent load with multiple
speakers. The importance of this is more evident when you have more than one cabinet to connect to your amplifier.
This is when you need to figure out the loads and how to
wire them up without applying too low of a resistance on the
All 4 Spkrs.are 8 Ohms
amplifier.
SPEAKER A
SPEAKER B
BLA
BLA
Made by
DOW
DOW
Made by
Simply connect the Positive side of Speaker A to the Positive side of Speaker C.
SHA
CK
Electro-Voice
SHA
CK
Electro-Voice
Connect the Negative side of Speaker A to the Positive side
of Speaker B, then on to the Positive side of Speaker D and
finally on to the Negative side of Speaker C.
And lastly, connect the Negative side of Speaker B to the
Negative side of Speaker D.
SPEAKER D
BLA
POSITIVE
4 Eight ( 8 ) Ohm speakers wired in Series Parallel = a Total
Load of 8 Ohms.
K SHA
CElectro-Voice
Made by
DOW
Made by
DOW
SHA
CK
Electro-Voice
BLA
SPEAKER C
NEGATIVE
PAGE 20
WIRING SCHEMES...Amplifier to Speaker Cabinets
1
Partial back view of amplifier
8 OHM
4 OHM
2
Partial back view of amplifier
4 OHM
8 OHM
4 OHM
4 OHM
8 Ohm Cabinet
3
Partial back view of
some Mesa amp
84Ohm
Ohm Cabinet
Cabinet
8 OHM
4 OHM
4 OHM
4 Ohm Cabinet
4
5
Partial back view of amplifier
4 OHM
8 OHM
16 OHM
Partial back view of amplifier
8 Ohm Cabinet
4 OHM
8 OHM
16 OHM
SAFE MISMATCH
16 Ohm Cabinet
16 Ohm Cabinet
SAFE MISMATCH
PAGE 21
6
WIRING SCHEMES...Amplifier to Speaker Cabinets
Partial back view of amplifier
Partial back view of amplifier
8 OHM
4 OHM
4 OHM
4 OHM
4 OHM
8 OHM
16 Ohm Cabinet
8 Ohm Cabinet
8 Ohm Cabinet
8 Ohm Cabinet
7
SAFE MISMATCH
CORRECT MATCH
8
9
Partial back view of amplifier
8 OHM
4 OHM
Partial back view of amplifier
4 OHM
8 OHM
8 Ohm
4 Ohm Cabinet
4 OHM
8 Ohm
SERIES BOX
4 Ohm
4 OHM
PARALLEL BOX
4 Ohm
CORRECT
MATCH
16 Ohm
4 Ohm Cabinet
16 Ohm Cabinet
PAGE 22
16 Ohm
CORRECT
MATCH
16 Ohm Cabinet
WIRING SCHEMES...Amplifier to Speaker Cabinets
10
Partial back view of amplifier
4 OHM
4 OHM
16 Ohm
8 OHM
SERIES BOX
8 Ohm
8 Ohm
8 Ohm Cabinet
8 Ohm Cabinet
8 Ohm Cabinet
SAFE MISMATCH
11
12
Partial back view of amplifier
4 OHM
4 OHM
CORRECT MATCH
8 OHM
Partial back view of amp
8 OHM
4 OHM
4 OHM
8 Ohm
PARALLEL BOX
16 Ohm
16 Ohm
8 Ohm Cabinet
16 Ohm Cabinet
16 Ohm Cabinet
SAFE MISMATCH
16 Ohm Cabinet
PAGE 23
16 Ohm Cabinet
WIRING SCHEMES...Amplifier to Speaker Cabinets
13
Partial back view of amplifier
16 Ohm
4 OHM
4 OHM
8 OHM
SERIES BOX
8 Ohm
8 Ohm
8 Ohm Cabinet
8 Ohm Cabinet
16 Ohm Cabinet
SAFE MISMATCH
14
Partial back view of amplifier
8 OHM
4 OHM
4 OHM
8 Ohm
PARALLEL BOX
16 Ohm
16 Ohm Cabinet
16 Ohm Cabinet
SAFE MISMATCH
PAGE 24
16 Ohm
16 Ohm Cabinet
ON TRIODES, PENTODES & IRISHMEN:
With apologies to Friends and Relatives from the Emerald Isle - who will make their appearance soon enough - the humor which
follows is dedicated to the memories of Spec McAuliff and Fae (Rafael) McNally, two of the True Greats.
As their numerical references suggest, the terms Diode, Triode and Pentode indicate the number of elements within the vacuum tube
i.e. two, three or five. All tubes also require a filament or heater which is not included in the count. Its purpose is to excite electrons
from the cathode coating by raising the temperature such that they are able to boil out of the electron-rich coating material and form
a cloud of free electrons in the vacuum space surrounding the cathode.
Although the term filament and heater are often used interchangeably, there are specific differences: A filament is a directly heated
cathode where cathode coating is applied directly to the heating element. Examples are 5U4 twin diode rectifier and 300B triode
amplifier tubes.
A heater, on the other hand, is a heating element which is separate from the cathode and is usually inserted within the tubular cathode
sleeve. Examples are 12AX7 twin triode amplifier and 6V6 or EL84 beam power pentode tubes. In all cases this fundamental aspect
of each tube\’d5s construction is clearly visible, especially when the heating element is glowing red hot.
The cathode, then, would be considered the first numbered element because it is the source of the electrons. The word itself is from
the Greek literally meaning completely down, which implies a sense of central origin - like the center of the earth where Tone begins.
It might be said that an ecstatic audiophile experiences a positive catharsis, his soul being purified when his system transports him to
Audio Nirvana. The only trouble with taking this positive imagery too far is that the cathode is, unfortunately, negative... at least
electrically speaking. However this is easily remembered since virtually all musicians and audiophiles have also experienced the
more common negative catharsis when they emerge from the emotional rebirth kicking and screaming in rage and frustration.
Once heated, the intrinsically negative electrons are energetic little fellows of almost no mass. Thus they may be accelerated almost
instantaneously and will travel through a vacuum a nearly the speed of light. Being of like, negative charge, they tend to repel one
another and thus within the electron cloud surrounding the cathode, there is much jostling and elbowing as each one tries to maintain
his distance from all the others... unless there is a strong and universal attraction from an outside influence.
Visualize, if you will, a group of sub-atomic Irishmen milling about and in a repellent, negative state of mind. All are scowling and none
wants to have anything to do with the other. Now introduce a strong attraction say, a public bar, and you can easily picture an orderly,
if rapid movement of the lot in a single direction. This is what happens when a positively charged element called the anode or plate is
introduced into the vacuum.
The plate is the large metal element most prominently visible through the glass of an electron tube. It is the outermost element of a
tube’s structure and it surrounds all the others. The cathode is at the center radiating electrons outwards. As higher and higher
positive voltage is applied to the plate, the attraction for the electrons surrounding the cathode is increased and with nothing standing
in the way, full uninhibited flow to the plate occurs...sort of like removing the doors and offering free drinks to the crowd of surly
Irishmen milling around outside. As electrons flow to the plate, the space charge will continually be replenished by further ‘boiling’ of
the hot, electron-rich cathode as you can easily imagine other Irishmen impatiently taking up the places of those who’ve gone inside
- until the entire village is deserted.
Now, where do they come from and how do they emerge? Well, a grand and elegant lady once showed me how to revive flat
champagne: She dropped a raisin into the glass. There was a dramatic and immediate increase in effervescence with the introduction
of a cathoding surface. Thousands of tiny bubbles suddenly appeared - and continued to flow from the raisin. Of course the bubbles
were made up of gas dissolved in the beverage, but the analogy makes it easy to visualize the loosely bound electrons dissolved in
the rich cathode coating as they effervesce from its heated surface.
But back to the electron flow. If the electrons are strongly attracted to a positively charged plate, then it follows that they are strongly
repelled by a negatively charged plate and they are. Thus, if an alternating current - such as comes from a transformer - is applied to
PAGE 25
the plate, electrons will flow only during the times when the plate is positively charged. During periods of negative plate charge,
ON TRIODES, PENTODES & IRISHMEN: (Continued) electron flow is stopped and the space charge of electrons remains compressed in the area around the cathode.
Thus a diode tube - one with a cathode and an anode - is mostly used to rectify alternating current into direct current by passing it
without restriction, but in one direction only. This also explains why closing time is stricly enforced at Irish pubs: During normal
operation, the traffic flow is similarily unimpeded and uni-directional toward the bar and this process rectifies the work-day negativity.
It goes without saying that no one leaves as long as the atmosphere around the bar remains positively charged.
TRIODES:
This section is a continuing technical treatise on the workings of Irish Pubs but to make it easier for the layman to understand, it is
explained in terms of vacuum tube technology. Enter the original bar - free beer and no doors. Well, it turns out that some control over
the flow can be a necessary and useful advantage. This led to the invention of those swinging louvered saloon doors which are open
at the top and bottom. They are patterned after the control grid of the vacuum tube, which is a loosely wound coil of thin wire located
between the cathode and the plate.
In a Triode the plate is always positively charged with high voltage D.C. and even though the grid is blocking the path, those negative
electrons can still FEEL the strong attraction - just as the Irishmen can see in through the louvers of the bar doors. They know what
pleasures lie beyond, but to get there requires overcoming the negative influences controlling the access. This negative influence is
typically called a Bias. In electronic terms that means the grid is supplied with a voltage which is slightly MORE NEGATIVE than the
already negative electrons. The more negative the Bias, the more it tends to neutralize the attraction of the plate and repel the
electrons back toward the cathode.
The Irish can be similarily charged with Bias, but unless you are Irish yourself, this type of Biasing may be more difficult to understand.
The effect is similar though: The more negative the Bias, the more it impedes forward progress. Generally speaking though, the
electronic Bias of the grid is easiert to overcome, and for two main reasons: First, the Bias is set - like the bar doors - to allow some
passage. Second, the grid is mostly NOT THERE, like the louvered doors which are mostly open spaces. Unlike the plate which is
solid, the grid is like a coiled bed spring. It can create a repelling field but mostly it’s empty space in between widely seperated
windings of wire. It’s very easy to control the electrons as they pass through the grid’s force field: Changing the grid voltage only
slightly will have an enormous effect on how much current flows through... and that’s what AMPLIFICATION is: a small change in
voltage at the grid causing a large change in current flowing to the plate.
The purpose of the louvered bar doors is similar to that of the grid, namely, to give momentary pause while still revealing the promise
within. Hesitation mostly gives way to temptation, but there are those few stalwart Irishmen who think twice and decide to come back
later. Most just pause slightly then go on through. That is the purpose of the bar doors: to prevent everyone from crowding in all at
once - and as the door is made less of a barrier, wider spaces between the louvers, more of the bar’s attractive influence is felt outside
thus amplifying the customer flow and increasing the crowd at the bar.
PENTODES:
Occasionally though, bar doors - even the louvered type - were found to be too effective, and too many customers turned away.
Something further was needed to increase the attraction of the bar and overcome the resistance created by the door. Thus the cocktail
waitress was invented.
Once again the idea was inspired by the vacuum tube. It had been discovered in some tubes, often large power types, that the
distance to the plate was too great to attract enough electrons past the negative influence of the control grid. So another grid coil of
fine wire was inserted between the first grid and the plate. This was called the screen grid and carrying a highly positive charge, it
functioned as a bait for the plate.
In a properly designed power tube such as an EL84 or a 6V6, the windings of the screen grid are precisely aligned to fall in the shadow
of the control grid. This way the electrons responding to the pull of the screen grid are lined up in sheets as they pass between
windings of the inner control grid... only to find that they have been fooled! Once past the control grid and drawn toward the screen
PAGE 26
grid, they discover...there’s almost nothing there. The path they’re on has them aligned to zing straight through the spaces BETWEEN
ON TRIODES, PENTODES & IRISHMEN: (Continued) screen grid windings. So rather than a close and personal encounter, they
just fly on past - and once they’re out that far, there’s no stopping them. The influence of the plate takes over and - being solid metal
and of the highest positive attraction - it is at this final destination that the electrons congregate.
Thus the proper cocktail waitress - visible through the louvers - is scantily clad so as to be all the more effective at reinforcing the
attractive influence of her bar and by being located in between the door and the bar, she serves as bait to lure customers past the
door’s negative influence. Once through the door however, it is the rare Irishman who actually comes in personal contact with the
cocktail waitress as, for all intents and purposes, she - like the screen grid - turns out to be a vanishing illusion. Yet, having come this
far, the solid influence of the bar itself now takes over and attracts the customers to congregate, having happily reached their destination.
If you’re still following this and haven’t lost track of the count, you’ll know we’re still one element short of the five needed to make a
Pentode. This last part is a pair of beam-confining shields which being negatively charged, serve to direct the flow right toward the
plate. This is much the way a short entrance hall to the bar prevents wandering accidentally into the Men’s room on the way.
Once at the bar though, the circuit is complete and the process of soul-nourishing works its ritual magic. Biases having been overcome, illusory nightingales having vanished, the spirits truly soar and the once surly Irishmen now are filled with warmth, wit and
kindred friendship, enjoying the music and glowing nicely with their heaters on.
With appreciative thanks to the inhabitants of the Land of the Leprechaun, we have now concluded our little diversion into the
mechanics of proper bar lay-out.
A feature article by Randall Smith
Designer / President
PAGE 27
POT pt#
593150
MASTER
408115
POT pt#
593148
REVERB
POT pt#
ALL FRONT PANEL KNOBS
POT pt#
593736
BASS
POT pt#
593150
POT pt#
POT pt#
593148
MID
POT pt#
593739
408004
MUTE SPKR ON
SILENT RECORDING
or
electric shock, replace fuse with
same type and rating only. Do not
SWITCH
pt# 600115
WARNING: To reduce risk of fire
CH
2
CH1
CH
CONTOUR
.FT
SW
MESA BOOGIE
592794
592738
591842
TREBLE
POT pt#
593737
POT pt#
FRONT VIEW F SERIES
INPUT
GAIN
592738
POT pt#
593737
10 0%
FX MIX
RETURN
KNOB pt#
593739
FX
SEND
POT pt#
POT pt#
JACK pt# 610120
2A S.B.
FUSE
FUSE
STEREO OR MONO
RECORD / PHONES
PREAMP PATENT 10%
4,701,957
F-Series
Amplifiers
FUSE HOLDER pt# 790347
REAR VIEW F SERIES
WARNING:
FUSE
2A
SLO
BLO
Unplug power
before replacing
fuse or removing
bolts mounting
chassis.
POWER
120 V~
50-60 Hz
2A
FOOTSWITCH
SOCKET
BELOW
JACK pt# 618100
JACK pt# 618100
JACK pt# 618100
8 OHM
LENS pt# 703782
PILOT LIGHT
BULB pt# 703110
SWITCH pt# 607303
CAUTION: To reduce risk of fire or electric
shock, do not remove cover. No userserviceable parts inside. Refer
servicing to qualified personnel.
ON
601073
SWITCHES pt#
ON
POWER
4 OHM
STANDBY
618100
JACK pt#
(all three)
SPEAKERS
4 OHM
USE WITH 8 OHM SPEAKERS
PAGE 28
MESA BOOGIE
The Spirit of Art in Technology
Thank you
for trusting MESA/Boogie to be your amplifier
company. We wish you many years of toneful enjoyment from
this handbuilt all tube instrument.
The Spirit of Art in Technology
1317 Ross Street Petaluma, CA 94954
USA
Phone No. (707) 778-6565 Fax No. (707) 765-1503
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