User Manual for the Diezel
Herbert Amplifier
Table of Contents
Chapter One: Safety and Warranty
1.1 Safety Warnings
1.2 Warranty Information
Chapter Two: Using Your Herbert
2.1 Mains Connections, Power and Standby
2.1.1 Mains/connect to power outlet
2.1.2 Power up, Warm up, Standby off
2.1.3 Power tube caution
2.1.4 Operating Temperature
2.1.5 Power Tube Information
Chapter Three: Peripheral Connections
3.1 Front Panel Connections
3.1.1 Signal In
3.1.2 Connection Information
3.1.3 Cable Selection
3.2 Rear Panel Connections
3.2.1 Send/Return Loop
3.2.2 Parallel and Serial Return
3.2.3 Switch-able Loop as additional Volume Control
3.2.4 Switch-able Loop for external Pre-Amp
3.2.5 Switch-able Loop as switch for parallel Loop
3.2.6 Tuner Out
3.2.7 Compensated Out
3.2.8 Speaker Connections
3.2.9 Reasons for Dynamic Losses in the Effects Loop
3.3 MIDI Connections
3.3.1 MIDI In
3.3.2 MIDI Thru
Chapter Four: The Three Pre-Amplifiers
4.1 Pre-Amplifier Duties
4.1.1 Channel One
4.1.2 Channel Two
4.1.3 Channel Three
4.2 Pre-Amplifier Tubes
4.3 Noise and Microphonics
Chapter Five: Power Amplifier
5.1 Tone and Volume of the Power Amplifier
5.1.1 Master Volume
5.1.2 Presence
5.1.3 Deep
5.2 Power Amplifier Tubes
5.2.1 Function
5.2.2 Selection
5.2.3 Life Span
Chapter Six: Functions and Switches
6.1 Programming Herbert
6.2 Manual Channel Selection
6.3 Mid Cut on/off
6.4 Loop on/off
6.5 Mute on/off
6.6 Master 2
6.7 Store
Chapter Seven: Midi
7.1 MIDI
7.2 MIDI In
7.3 MIDI Thru
7.4 MIDI Communication
7.4.1 Omni Mode
7.4.2 Single Channel Mode – automatic Channel Recognition
7.4.3 Single Channel Mode – manual Channel selection
7.5 Program Information
7.6 Phantom Power
Chapter Eight: Remote Switch
Chapter Nine: Maintenance and Cleaning
9.1 Cleaning
9.2 Care
9.3 Tube Change
Chapter One: Safety and Warranty
1.1 Safety Warnings
We would like to stress the importance of the following points , for reasons of your
personal safety, product longevity and product liability.
Do not use the amplifier in or near wet locations
Do not store the amplifier in damp or wet locations
Do not operate the Amplifier on voltages other than those designated on the rear panel of
the amplifier.
Do not open the panels of the amplifier. No user serviceable part s inside.
Your Herbert operates on very high internal voltages, which may still be present after the
Amplifier has been turned off and disconnected for a while.
Do not use the Amplifier for anything other than its design purpose: To Amplify Electric
Guitar Signals!
Do not use fuses other than those intended and specified for the amplifier
Do not use 2-conductor extension cords or anything other than 3-pole g rounded outlets for
this Appliance. Your life may depend on it!
Please observe the following points when transporting your Herbert:
Herbert is a Tube Powered Amplifier; therefore it is sensitive to shock, especially after
playing the amplifier for a while. Please store and transport your amplifier gently, and try
and avoid temperature extremes in storage, which might cause condensation resulting in
moisture on internal components. Usually a 60 Minute acclimatization period is sufficient to
ensure safe operation.
The Amplifier should be stored in a controlled environment, and it should be transported in
a suitable flight case. Make sure the Amplifier gets transported in its normal operating
position, not upside down or on its side.
The Herbert’s Design incorporates a very potent power amplifier. It is configured to deliver
satisfying guitar tone at most volume levels, from a small bedroom to a large arena. In its
normal operational volume level (75-80dB) it will prov ide beautiful tones with very little
coloration. For reasons of your own personal health, please do not run the amplifier above
these levels for extended periods of time without wearing hearing protection. Hearing Loss
is a long -term problem, and is normally not curable.
1.2 Warranty
5 years to the original owner with proof of purchase. Power Tubes and Pre Amp tubes are
covered for 3 months to the original owner. The amps will be tracked via both Diezel USA
and Diezel Germany recorded sales beginning 1/20/2009. ALL REPAIR WORK MUST BE
DONE BY A DIEZEL CERTIFIED TECHNICIAN. Not following this procedure will VOID
WARRANTY. This will ensure the the original owner and us at Diezel Amplification that the
work is done correctly and that there is knowledge of what is going on out there with each
amp. To any second owners or more, there is no warranty coverage nor is a warranty
transferable. (This policy is no different then before). Of course we at Diezel are happy to
serve people who purchase their amplifier on the used market should your amp ever need
servicing. Parts and labor charges will occur for our work on your amplifier as usual.
If you purchased your amp before 1/20/2009 you are categorized under the same
guidelines as when you purchased your amp (Lifetime warranty fo r the original owner, 1
year transferrable warranty).
Chapter Two: Using Your Herbert
2.1 Mains Connections, Power and Standby
2.1.1 Mains/Connection to Power Outlet
Please make sure that both switches (Power and Standby) are in the off position before
connecting to the Mains circuit. Verify line voltage before connecting the power cord.
Never start Herbert without speakers being connected to the proper terminals. (See 3.2.8)
2.1.2 Power up, Warm up, Standby off
First turn the Power switch to on (facing up). The indicator will light up. This starts the tube
heating process. After about 40 seconds, the tubes have sufficiently heated for normal
operation. Your Herbert is now ready for operation and the standby switch can be turned to
“run” (also facing up). Premature activation of the stan dby switch will lead to unnecessary
tube stress and subsequent reduction of the power tube’s life span.
2.1.3 Power Tube Caution
Tubes are electronic components that only function with vacuum intact and under very high
operating temperatures. Each tube has one or more heating filament s, much like a light
bulb. These filaments heat up the Anode of the tube. If you switch the standby switch
before these Anodes have reached their operating temperature then the Anode surfaces are
not heated evenly yet; the “operating temperature” of the tube is not reached yet. This
causes undue stress on the tubes and their related components inside the amp. One should
therefore always give the amp it’s much needed warm-up time, even if musical inspiration
hits with full force.
2.1.4 Operating Temperature
It will take a little more time after warm-up until everything inside the amp is working in
sync and to it’s fullest potential. A trained ear will n otice a slightly warmer tone and better
complexity in tone after playing the amp for a short while. It’s like warming up before
running a marathon. Get it?
2.1.5 Power Tube Life
The power tubes of your amplifier are subject to a certain aging process. Once one of the
tubes shows signs of aging, unreliability or unus ual noise, then we suggest that you
replace all power tubes. Matched tube sets wear relatively even, or so our experience
suggests. This means if one goes, the others are not far from meeting the same fate.
The aging process manifests itself by a depletion of a thin layer of Wolfram on the Anodes.
This can take anywhere from 6 month to 3 years, depending on the amount of use of the
amplifier. The amount of wear is determined by the amount of performance that is asked
from the tube.
Chapter Three: Peripheral Connections
3.1 Front Panel Connections
3.1.1 The input jack (“IN”)
The input jack receives your Electric Guitar signal by means of a shielded guitar cord with
1/4” mono style plug.
Your guitar cord is an important part of your signal chain and its quality and construction
type clearly affect the overall tone of your rig. Try and buy the best quality guitar cord
that you can or want to afford. Call us if you have doubts and need recommendations.
This is where the smart “weak link” comment comes in. Get it?
3.1.2 Cable ABC
Some cords and cables sound very neutral; others color the sound spectrum and/or
attenuate high frequencies due to capacitance inside the wire and shield. What are we
talking about? OK. A capacitor is used in electronic crossovers, amongst other things, to
divide low and high frequencies. Capacitance in a cable therefore cuts your guitar’s high end
to a certain degree. Generally, the longer of a cord you use, the more of the cords inherent
characteristics will be audible.
3.1.3 Cable Selection
In certain instances it is desirable to match a guitar cord to a specific instrument. One can
use the otherwise undesirable qualities of a cord to one’s advantage, if one has the time
and patience to experiment with different cords and guitars. You should do this when
playing with a band or when you are recording. Sometimes it is difficult to tell a
component’s true advantages until it is used in the right context. A guitar that has very
piercing highs could theoretically be tamed down somewhat by the use of a long guitar cord
that offers some high-end attenuation. The loops of your Diezel Herbert send signals at
higher levels and impedances, which makes this section of wiring less sensitive. You should
still use reliable and good quality wiring for all loops and inserts.
3.2 Rear Panel Connections
3.2.1 Send/Return Loop
The System consists of 3 separate Loops. It allows creation of effects path in either serial,
parallel, or switched configurations. The individual channel volume controls det ermine the
signal strength at the send jacks. The range is - ... to +10dB. The output impedance is 4.7
kOhm. If you want to use the loops, then connect the “Send” to the input of the Effects
unit. Be sure and adjust the input level of the effects unit to the amplifiers level. Most
effects units have led bar or other level control devices. The Output of the effects unit
must be connected to one of the return jacks, parallel, switched, or serial. If you use the
parallel return, then the signal can be mixed to the original signal via the rear panel
mounted “Volume” control.
3.2.2 Parallel or Serial
Which is better for you? Read on.
There are 2 ways to handle effects signals. If you use the serial return, then the signal path
of your Herbert is interrupted, the signal is sent to the processor, gets more or less
processed, then sent back to the serial return into the power amp. Digital effects units often
digitize this signal, then process it, then convert it back to analog, then send it to the amp.
This is called ADA conversion. It is necessary for digital effects units to do this to your
guitar signal, so that it becomes a digital code, which the processor can read and
understand. Your tubes, however, need an old fashioned analog signal, so the processor
needs to convert the signal back to analog before it goes back to the amp. Generally, even
in highest quality effects processors, this causes a change in the original signal, typically a
loss of tonality and warmth, also noticeable as a “harder” sound.
When you use the serial loop for an effects unit like this, then your signal will h a ve been
ADA converted at least once. Tone junkies and vintage freaks alike will more than likely
have hives developing by now. But, as always, there is a better wa y. Using the Parallel loop
and the mix (labeled “Volume”) control on the back determines how much effect signal is
being added to the original signal, which now still flows throu g h the amplifier. There is
always an analog connection between the send and return jacks: a parallel loop!
Important: You must set the mix control on the effects unit to 100% wet when using the
parallel loop. Otherwise there will be nasty phasing problems resulting in unsatisfactory
tone. The signal portion that is unaffected by the mix control in the effects unit would
reach the amplifier at a different time due to the cabling, and cause phasing cancellations.
3.2.3 Switch-able Loop as additional Volume Control
Those of you who can live without processors in the parallel loop can use this loop for a
second master volume for each channel.
To do this, just loop a short 1/4” cable from the switch-able send to parallel loop return.
Now you can choose a second master volume by turning the mix control past 1:00 PM to
full open, and push the ‘ Loop” button to activate your second master volume. Now, with
the loop activated, the mix control can act as another way to control volume.
3.2.4 Switch-able Loop for external pre-amp
One might extend one’s tonal variety by hooking up an external guitar pre-amp to the
switch-able return jack. Now the external preamp, once selected via the “Loop” function,
can feed the Herbert’s power amp.
3.2.5 Switch-able Parallel Loop
To route your effects signal parallel to the original signal, connect the switch-able send to
the input of your effects unit and go from the output of your effects unit to the parallel
return. Now you can switch the send to the effects unit on and off via midi, with the effects
signal decaying naturally when the loop is turned off.
3.2.6 Tuner Out
You guessed it – it’s for a guitar tuner. Stays lit while mut e is activated. So you can tune
without annoying your band members, or the audience. Elegant, no?
3.2.7 Compensated Out
A frequency corrected signal will leave this jack if you connect it to a mixer or recording
device. Use it to quietly compose or send an auxiliary signal to a console etc. Always make
sure that your amp is connected to either a loudspeaker or a load (i.e. THD HotPlate).
3.2.8 Speaker Connections
Herbert has 5 speaker jacks: 1 for a 16-Ohm load, 2 for 2 16-Ohm loads or 1 8Ohm load,
and 2 for 2 8-Ohm loads or 1 4-Ohm load. Confusing? Oh, yes! Just do what it says on
the jacks, and you’ll be fine
3.2.9 Top 5 Reasons for dynamic losses in the effects loop
Many different factors can be responsible for loss of dynamics, aside from those mentioned
in 3.2.2 (ADA conversion). A vital point that oft en leads to frustration is a maladjusted
output level of an effects unit. If the out pu t level is too high, then unwanted distortion is
caused in the power amp. If it is too low, then the rig will not sound punchy and might get
lost easily in the band sound. When used in the serial loop, the output of the effects unit
determines the ultimate drive signal strength of the power amp. The output level should be
matched to give the best possible sound with all 3 channels without over driving the power
amp section. Headroom adjustments of 10% are usually sufficient.
3.3 MIDI Connections
3.3.1 MIDI In
Midi in receives “program change” orders from commonly available midi pedals and control
systems. The Herbert is able to supply phantom power to your midi pedal via a 7-prong
DIN midi cable. This can help unclutter your stage system and rids the artist of these
pesky power supplies.
Pin 1 and 6 is ground (-) Pin 3 and 7 is hot (+)
The voltage is 9-12V AC or DC, which is acceptable for 98% of all midi pedals. Maximum
power usage of the pedal cannot exceed 800mA (0.8A) Please observe proper polarity to
avoid damage to the MIDI pedal.
3.3.2 MIDI Thru
This jack routes the midi signal to other midi partners. MIDI data not addressed to the
Herbert gets looped through this jack.
See chapter 7 for MIDI programming instructions
Chapter Four: Three Pre-Amplifiers
4.1 Pre-Amplifiers and their Functions
The Diezel Herbert comes equipped with 3 different and totally independent preamps. This
allows the artist to play every conceivable musical style without having to make major
changes to his or her amplifier. The preamps are voiced to deliver the 3 most wanted
guitar tone flavors: 1-Clean, 2-Crunch/Heavy 3- Lead.
This concept delivers 3 stellar guitar sounds with excellent playability, warm dynamics and
razor sharp equalization possibilities. The ton e controls work in an unusually wide range, so
a little adjustment goes a long way. As with so many other thin gs - less is often more. We
suggest you start exploring the channels with all controls set to 12:00 o’clock, and the
master volume just slightly cracked open. (To avoid hearing damage)
4.1.1 Channel One (Clean Tone)
Clean Tone is a very sensitive subject, because there are so many different ideas on how
a clean amp should sound like. Clean tonal textures require much higher dynamic range
than distorted sounds. From hard and percussive sounds to soft and warm blossoming
tones. Herbert was designed to offer as many of the clean variety as possible. Your choice
of guitars and pickups will have a large part in this equation.
4.1.2 Channel Two (Crunch)
This channel’s main objective is to cover soft and heavy overdrive and distortion sounds. It
features a voicing switch, with -/+ settings. With the (-) setting selected, blues and classic
rock sounds can easily be realized. The (+) setting kicks everything up a few notches and
offers crunch with a good bite, allowing you to dial in punchy heavy rhythm and searing
solo tones.
4.1.3 Channel Three (Lead)
This channel is voiced for highly articulate single not e lines or for very heavy and massive
rhythm guitar. Due to its slight midrange accent and very high gain structure, it possesses
good punch and will, with ease and authority, rule any stage or studio. The “less is often
more” rule applies here also.
4.1.4 Mid Cut
The section Mid Cut incorporates controls for Intensity and Level. Designed for
friends of Heavy or Nu-Metal type musical styles, the Intensity control attenuates
low midrange at approximately 400Hz. To compensate for the inevitable volume
loss when activating this feature, one can bring the volume level back up with the
Level Control.
This Mid Cut function is MIDI assignable and can therefore be assigned to any or all
of the three channels. If you don’t want to use the Mid Cut function, then it can be
used as an additional programmable volume control with the Intensity control set
to 0 or off. This gives your Herbert 8 programmable volume options!
4.2 Pre-amp Tubes
The pre-amps are equipped with 12AX7 tubes in all positions. The pre-amp tubes are not
used to make big power, but merely as pre-amplifiers. Therefore their life expectancy is
much higher than that of the power amplifier tubes.
This is not to undermine their utter importance in ov erall sound and response of the
amplifier. Also, many nuisance defects like crackling noises and low dynamics are direct ly
related to defective pre-amp tubes. Like all other tubes, 12AX7 tubes come in many
different gain stages, and offer a wide variety of tonal behavior. Our choice for production
was made to ensure a wide variety of tones, with low noise and, hopefully, excellent
reliability.
4.3 Microphonics and Bad Noises
The overall performance of pre-amp tubes is easily influenced by mechanical factors from
the outside. This would manifest itself by a sudden feedback sound with high pitch. The
input stage is especially suspect to this phenomenon. If one encounters microphonic tube
behavior, then the first tube should be checked as a rule. Pre-Amplifier tubes can also cause
hum or other bad noises, like crackling or ticking.
Chapter Five: Power Amplifier
5.1 Tone and Volume of the Power Amplifier
5.1.1 Master Volume
As the name suggests, this controls the overall, global volume of the amplif ier. For your
enjoyment, there is also a second programmable master volume control, which allows
volume adjustments via remote control while you are playing. Both controls are l aid out so
that even a low-performance effects unit can be used and amplified in the loops.
5.1.2 Presence
This knob controls frequencies over 3KHz. Treble is produc ed and dispersed in a very small
beam from the speaker, so be sure to position yourself in the projection area of the speaker
when making adjustments.
5.1.3 Deep
The Deep control is an active bass control, contrary to conventional bass controls. It
controls the frequencies around 120Hz without influencing the overall dynamic range of the
power amplifier. Diezel Co. is not responsible for disintegrating speaker cabinets.
5.2 Power Amplifier Tubes
5.2.1 Function
As the name suggests, the power amp section is the part of the amplifier that produces
output power, measured in watts. Preamp signals are sent to the power amp(s), which
amplifies this signal to a level that is acceptable for loudspeakers. Guitar amplifiers utilize
several different types of power amps, which differ in output power and tone. We chose
the tube type power amplifier for its tried-andtrue performance and familiar tonal
behavior.
5.2.2 Selection
Diezel Co. installs the most reliable and best sounding tubes that are currently available in
sufficient quantities. So it is possible that tube brand and tube type will change during
production. You can fine-tune your Herbert by having different type and brands of tubes
installed, however, it is imperative that the amp is biased properly. Herbert utili zes 6 power
tubes, organized in 3 pairs with triple bias possibility. This allows use of 3 different pairs of
power tubes, either the same or different types.
5.2.3 Life Span
Power tubes last 1 to 3 years, depending on care, volume and frequency of use of the
amplifier. If you use your amp only once a month, then the tubes will obviously last longer.
Really… We have heard tubes that are over 10 years old, but it was not a good thing. Tubes
age in a very slow manner, slow enough for the artist to get used to the changing tone. To
keep things fresh and to keep your tube dealer in business, we recommend re-tubing,
cleaning and biasing once a year if the amp is used frequently.
Chapter Six: Functions and Switches
6.1 Programming the Herbert
It is quite easy to program your Diezel Herbert and, also, easy to explain. Pushing the
“Store” toggle switch twice must follow each change in the MIDI program. After the first
click, the selected blue LED lights will blink. Click on the switch again and your program is in
memory. Each of the 128 programs (patches, program changes) can be changed as often as
is desired.
6.2 Manual Channel Selection
The 3 channels of the Herbert can be selected manually by activating the red button above
each channel strip, or can be programmed via the midi control system. If you assign the
Channel one switch function to a MIDI program (for example “01”), then you can initiate
this channel’s switching via your MIDI pedal. Push “01” on your MIDI pedal after
programming, and the pedal will send digital information to the amplifier. The amp will read
this information and decide whether or not it is supposed to respond. When properly
programmed, it will then switch on channel one.
OK, here it is again:
Select 01 on your MIDI pedal. Select channel one of the Herbert. Now pu sh “Store” twice.
Voila, it’s a MIDI program! Now select program change “02” on your pedal, switch the amp
to channel two, hit “Store” twice, and suddenly you have a MIDI pedal controller with 2
program changes. Continue on until you run out of channels, about 1 more time.
All the other functions of the amp can be programmed in the same exact way. Remember:
push “Store” twice to finalize a MIDI program procedure. Select the program on the pedal
to recall the setting from the amp.
6.3 Mid Cut On/Off
The switching function “Mid Cut” is applicable to all channels. The Mid Cut is active when
the corresponding LED is lit.
6.4 Loop On/Off
This function activates a device that is connected to the switch-able loop.
6.5 Mute On/Off
“Mute” silences the beast. “Tuner Out” stays active. Makes sense, no?
6.6 Master 2 On/Off
Master 2 can be used for all channels, much like the Mid Cut function.
6.7 Store
As discussed earlier, this is the universal programming button. Activating this button twice
will verify an intended program procedure. In case you have pushed this button once by
accident, or if you have started to program and don’t want to anymore for whatever reason,
then you can push any other switch (any switch but the “Store” switch) to cancel the
programming procedure. The previously established program will be preserved. On models
equipped with GPS, this will call out the quickest way to a near by music store.
Chapter Seven: MIDI
7.1 MIDI
MIDI is an acronym for Musical Instruments Digital Interface and is an internationally
accepted communications system between musical instruments (and processors and
computers) of all kinds. We will only need to learn a small portion of this “lan guage” to use
the Herbert and its peripheral MIDI partners. We are going to learn only about “program
change”.
7.2 MIDI In
MIDI In is a 7-pole DIN jack. It must be connected to the MIDI Out jack of your foot
controller (or MIDI pedal), or the MIDI Out of any effects unit connected to the pedal
directly.
7.3 MIDI Thru
Connect this port to the midi in of other units to continue the MIDI chain
7.4 MIDI Communication
7.4.1 Omni Mode
The Omni mode will allow reading of MIDI information on all 7 channels. It is an easy way
to get into the MIDI system but it is not advisable if more MIDI partners on different
channels are in the same system. Then a certain MIDI channel should be assigned to the
Herbert and its program changes should be restricted to this channel (See 7.4.2). To put
the amp into the Omni mode, hold the “Mute” switch down and activate the “Master 2”
switch quickly and then release the mute switch. The Mid Cut, Master 2, Loop and Store
LED’s will now blink to verify that the Omni mode is being accepted. This function needs to
be disabled under some circumstances in order to use single mode automatic or single
mode manual.
7.4.2 Single Channel Mode – Automatic Channel Recognition
Your Herbert can automatically recognize the pedal’s send/receive channel. To get your
amp into the mood (or mode) for this, push and hold “Mute” and then activate any program
change button on your MIDI pedal. The amp will look for a program change and recognize
the channel it is being sent on. Then it will switch to this channel and stay there as soon as
you let go of “Mute”.
7.4.3 Single Channel Mode – Manual Channel Selection
If you would like to have your Herbert on a certain MIDI channel, then we can
accommodate you here as well. Here is how this works:
Push and hold “Mute” and then turn on the preamp channels in the order that corresponds
to your midi channel preference. For example: if you want to have your Herbert to respond
only to MIDI information that is being sent on channel 7, then you must hold the “Mute”
button down and turn the Preamp channel one selector off, channel two selector on,
channel 3 selector on. If you let go of “Mute” now, then your Herbert is set to respond to
MIDI channel 7 only. Get it? The table below gives you the sequence for all 7 MIDI
channels.
Midi Channel Ch1 Ch2 Ch3
1 off off off
2 on off off
3 off on off
4 on on off
5 off off on
6 on off on
7 off on on
7.5 Program Information
Herbert can remember up to 128 program changes.
7.6 Phantom Power
Several of the pins in the MIDI jack can supply phantom power to your MIDI pedal, as
explained in chapter 3.3.1
Chapter Eight: Footswitch
The optional Columbus footswitch can be connected via the rear panel mounted XLR jack.
The Columbus will not recognize functions selected f rom the front panel.
Chapter Nine: Maintenance and Cleaning
9.1 Cleaning
Never use a wet method of cleaning the amplifier, i. e. any amplifier. Usually it is sufficient
to wipe down the outside of the amp with a slightly moist cleaning rag. Do not use abrasive
cleaning chemicals. Sometimes a vacuum cleaner can be used to remove dust and dirt from
nooks and crevices. Do not remove the chassis from the housing to clean the amp. The
inside of your amp carries dangerous voltages.
9.2 Care
Be gentle with this amplifier. Any mechanical shocks and wide temperature changes,
moisture-rich environments and extreme conditions (dust, wind, heat, cold, moisture) can
substantially shorten tube life, in some cases, even amplifier life.
Do not block the air circulation grilles in the front and in the back of the amp. Do not push
the amp right up against objects that would interfere with its normal airflow. The top of the
amplifier might get warm after prolonged use, this is normal, but will melt your ice cream
and definitely ruin your beer. Never put beverages on top of the amp where they could spill
and flow inside the amplifier. You’ll hate it if this happens, guaranteed!
9.3 Tube Change
Tube changes are only to be undertaken by authorized service personnel. If power tubes
with different values then the original ones are to be installed, then the amplifier must be
re-biased before operation can be resumed. The amplifier uses a three circuit bias
system. It is quick and easy to accomplish biasing, but involves removing the chassis and
use of specialized equipment for measuring currents inside the amplifier. Only trained
professionals should attempt this procedure.
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