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Tube-Amp First-Aid Kit Essentials
Every guitarist who plays a tube amp,
whether it’s a combo or a head and cab, should have
the following tools and spare parts on hand to address low
level first-aid needs:
• LED flashlight
• Small, inexpensive multimeter
• 1/4" female-to-female mono adapter
• Extra speaker cable
• Small flat-blade screwdriver
• Standard-size flat-blade screwdriver
• Philips screwdriver (for removing rear panel)
• Spare fuses
• Spare rectifier tube (if applicable)
• Spare set of matched power tubes
• At least one spare of each type of preamp-type tube
in your amp
• Oven mitt or ‘Ove’ Glove
• Electronic contact cleaner without lubricant (for
cleaning tube sockets)
• Electronic contact cleaner with lubricant (for cleaning
1/4" jacks)
• Spare amp, head, or power-amp pedal (for emergency
gig triage)
• 1' speaker-extension cable with 1/4" male and
female
• 1/4" connectors OR a 1/4" female-to-female
mono adapter
For a good percentage of 6-string guitarists
out there, a tube amp isn’t just the preferred way to
achieve the ultimate tone—it’s heresy to consider
playing anything that doesn’t have glowing valves around
back. And the longer you play, the more likely it is that
you’ve been through a bunch of brands, models, and output-tube
types in effort to find the sound(s) in your head. We all
tend to start out with what we can afford, and gradually we
graduate to something better—and better again—all
to achieve the next degree of tonal satisfaction.
But at some point, most of us tube-amp fans
also experience some sort of failure related to this arcane—yet
fantastic and sonically satisfying— technology from
the 1950s, and it’s often at the worst possible time.
Unfortunately, there’s no practical or accurate way
to predict when or where this will occur. But, as someone
who has been in the repair and modification business for more
than 25 years, I can tell you there’s a very good chance
it’ll happen to you sometime if it hasn’t already.
Sans a crystal ball and the ability to see into the future,
the best way to prepare is to practice preventive maintenance
and be prepared for the inevitable with a little bit of basic
knowledge and the proper contingent of tools and parts to
back it up. To that end, this article will furnish you with
must-know information that will help save the gig and allow
you to execute basic troubleshooting and repair on your amplifier.
Gig-Meltdown Triage
The first and most important tip I can give is to bring a
spare amp to every gig. If you notice, quite a few of the
players you see in television performances have two amps of
the same make. This is generally not for increased volume,
tonal variety, or to look cool—it’s life insurance.
There’s no time to change out or troubleshoot an amp
in that situation, and it would certainly be an epic fail
if you were performing on a latenight talk show and your one
and only amp failed during the performance of a lifetime.
If your tube combo dies on a gig, a pint-sized
solid-state head like the Orange Micro Terror or a small,
mic-able solid-state amp such as the Roland CUBE-80XL—perhaps
paired with your favorite overdrive/distortion pedal—will
get you through the gig and avoid the embarrassment of cancelling
mid-show.
Stompbox-sized amps like the Electro-Harmonix
Caliber 22 and Diago Little Smasher are an easy-as-pie lifesaver
when your tube amp melts down on the go.
Because fuses can often appear good to the
naked eye, it’s best to test them with a multimeter
set to read continuity in ohms.
Some fuse holders are integrated with the
line-cord receptacle and require a small flathead screwdriver.
I know some of you will say you either can’t afford
or don’t have room for another amp in your car, band
van, or on your stage, but your backup doesn’t have
to be the same model you normally prefer. If you don’t
have another tube amp that’ll suffice, many solid-state
options on the market offer an affordable solution. Remember,
your backup doesn’t have to blow minds with its peerless
tonal ecstasy—it just has to get you through the gig.
Whether you play a combo or a stack, you just
need a spare head or combo with a speaker out. Something like
an Orange Micro Terror head ($149 street) or a Roland CUBE-
80XL combo ($379 street) and an overdrive pedal will do—and
if the volume isn’t raging, you can just mic the cab.
Or, if most of your tone shaping comes from pedals and outboard
gear, something like the u¨berportable Electro-Harmonix
Magnum 44 ($150 street) or Diago Little Smasher ($190 street)
can be a godsend—even if you still need to mic your
cab. With most tube combos, you can use a 1/4" male-tofemale
speaker cable or female-to-female mono adapter (which costs
approximately $2 street) and another speaker cable to connect
the internal speaker to your backup power amp. (Note: Because
most cable adapters, whether male-to-female or female-to-female,
aren’t up to the same specs as quality speaker cable,
you should only resort to using them for short periods such
as during an emergency onstage meltdown.) All of the aforementioned
options are light, portable solutions that can be kept on
hand with minimal inconvenience so you can do a quick swap
and troubleshoot your main amp during a break or after your
gig—when you’re not under performance pressure.
That’s much more expedient than troubleshooting onstage—and
it will keep your bandmates and audience happy.
Troubleshooting After
the Gig
Now let’s move on to actual first-aid measures. It goes
without saying, that if you think your amp may have issues,
it’s probably either because it doesn’t sound
right or isn’t making sound at all. Although it’s
a bummer to deal with this at all, hopefully it happens at
home or during a rehearsal, so it doesn’t interrupt
a gig.
The first step to take when you think there’s
something wrong with your amp is to make sure it’s actually
the amp that’s faulty. To do so, first, plug directly
into your amp, bypassing any pedals or effects gear. If the
amp functions properly, look elsewhere in the signal chain
to pinpoint the problem. If it still won’t work, try
a different 1/4" cable, and if that doesn’t fix
the problem, use a different guitar. If the problem persists,
it’s probably your amp. The following sections detail
some of the most common issues that the average guitarist
should feel comfortable detecting and rectifying (forgive
the pun) without going to an experienced amp-repair tech.
Is the Indicator Lamp Illuminated?
If not, it’s probably because of a blown fuse. Usually
a fuse blows due to a failure in the amp, but occasionally
it’s due to something as simple as a power surge. Because
fuses can sometimes look good to the naked eye even when they’re
blown, the best way to check is to use a multimeter. Set the
meter to read continuity in ohms (O) and measure across the
fuse. If the meter indicates continuity or an almost zero
reading, the fuse is good. If not, you’ll need to replace
it.
To avoid buzzkill during a productive home
jam session or band rehearsal, I recommend you get to know
the fuses in all your amps and carry extras so you can pop
them in and keep rocking. Some fuse holders are easy to find
and as easy to operate as a push and a turn. Some require
use of a flat-blade screwdriver. Others are an integral part
of the line-cord receptacle and require you to remove the
cord and use a small flat-blade screwdriver to pry out the
fuse holder. Whichever type your amp uses, check the value
of the fuse currently installed—especially if you’re
not the original owner—and make sure it’s correct.
If your amp has multiple fuses, such as a high-tension (aka
“high-voltage” or “HT”) or output
fuse, make sure you have multiple replacements for each.
One point that’s crucial to keep in
mind is that you should never replace the fuse with a substantially
higher current rating just to keep the amp running. If a fuse
of the correct value continues to fail, the amp has a problem
that needs to be addressed. In such a scenario, possible causes
for repeated fuse failure could be:
Tube Tip
Whether they’re preamp or output tubes,
valves of the same type (e.g., EL84, EL34, GZ34, or 12AX7)
from different manufacturers do sound different. Whenever
possible, make sure the tubes in your spares kit are from
the same manufacturer as those currently installed in your
amp. This is especially true with regard to output tubes:
While preamp tubes from different companies can result in
differences in tone and gain, output tubes from different
manufacturers tend to bias up quite differently. So staying
with the same manufacturer—and, if the tubes are graded,
replacing with the same grade—should avoid having to
get the amp re-biased.
In a pinch, you can replace power tubes of
different brands or grades to get through a gig, but be sure
to have the bias checked and/or set as soon as you can for
optimal performance, tone, and lifespan.
• A faulty rectifier tube. If your amp
uses tube rectification in its power supply, a shorted rectifier
tube can cause a fuse to repeatedly blow. To see if this is
the case, locate the rectifier tube in the amp—it’s
usually the tube closest to the mains (AC) transformer, and
it’s typically a 5U4, 5Y3, 5AR4, GZ34, or 6X4. (Side
note: It’s a good idea to know what kind of rectifiers
are used in all your amps and to keep one of each necessary
type in your spares kit.) After you’ve located the rectifier,
install a new fuse and a new rectifier tube and try the amp
again. If it now functions properly, you’ve found the
cause of the failure. If not, replace the original rectifier
tube and continue troubleshooting.
• A faulty output tube. This is an especially likely
culprit if the fuse(s) failing is an HT or output fuse. If
you suspect this is a problem, install the new fuse(s) and
replace the full set of matched power tubes. If this corrects
the fuse-blowing issue, you’ve found the cause of the
failure. However, this unfortunately does not mean the amp
has a clean bill of health. Some tube failure can cause internal
components to fail. If you replace the power tubes and notice
lackluster performance, an increase in hum, or one or more
tubes glowing exceptionally red, the amp will need to be serviced
by an experienced tech, because more than likely the grid
or screen-grid resistor(s) have failed. If replacing the output
tubes has not alleviated the problem, re-install the original
tubes and have the amp serviced by an experienced tech.
An ‘Ove’ Glove or an everyday oven mitt is a handy
tool for dampening hot preamp and power tubes to determine
which is bad, as well as for removing them once you’ve
isolated the offending valve.
Is the amp making rumbling or glassy,
high-pitched noises?
If so, narrow down the source of the noise by turning down
any internal effects such as reverb or tremolo, as well as
all volume controls. With the amp in operating mode, hit the
top of the amp with your hand or fist using moderate force.
If this produces the noise in question, read the steps below:
• If the noise is of a rumbling nature: It could indicate
a faulty output tube. For a quick fix, replace the amp’s
power tubes with a full set of matched output tubes. If this
alleviates the noise, you’ve isolated and repaired the
problem. If the problem persists, replace the original tubes
and continue troubleshooting.
• If the noise is of a glassy or highpitched nature:
It is likely due to a faulty preamp-type tube. Starting with
the preamp-type tubes closest to the output tubes, tap each
one with your fingernail or the end of a pencil. If one in
particular produces the noise in question, replace that tube.
If this alleviates the noise, you’ve found the problem.
If not, replace the original and continue this process with
the remaining preamp tubes. If more than one tube produces
the noise during the tapping process, a trick to narrowing
down the possible offender is to attempt to dampen the adjoining
tubes while tapping. This can usually be done by placing your
hand on as many of the tubes as possible except the one you’re
tapping on. If they’re too hot to perform this barehanded,
use an oven mitt or ‘Ove’ Glove. This same technique
can be used to find an offending output tube.
If your amp is making loud, static-y sounds
when you play, you may need to clean its tube sockets with
electronic contact cleaner.
Before removing tubes to clean their sockets,
label the tubes and their sockets to ensure you replace them
in the spots that were producing satisfactory results prior
to the static problem. If tapping on the amp with all the
volume controls set to minimum produces no noise, set all
the volume controls to your typical settings and try again.
If the noise in question is now present, go through the preamp-tube
tap test once again, starting with the tubes closest to the
input(s) of the amp—you’ve most likely narrowed
it down to the first couple of gain stages.
If none of the above troubleshooting techniques
produce the noise in question and your amp has a mechanical
type reverb (i.e., a spring unit), turn up the reverb control.
If the noise is now present, the reverb drive and/or recovery
tube could be the cause. Unless you know the specific location
of these tubes, you may need to go through the tap test one
more time to find exactly which tube is at fault. (If your
amp is a blackface or silverface Fender style, looking at
the amp from the rear, the reverb-driver tube is generally
a 12AT7 and it’s usually third from the right, while
the 12AX7 reverb recovery tube is fourth from the right, just
past the small transformer.)
Is the amp making crackling
or popping noises when you’re not playing?
If so, this is can be caused by faulty preamp or power tubes.
The best course of action here is pure substitution. One by
one, replace each preamp tube and see if it alleviates the
noise. If none of the preamp tubes seem to be the cause, try
replacing the full set of output tubes with your set of matched
spares. If no tube substitution alleviates the problem, the
amp will need to be serviced, because there’s a good
chance it has a failing plate or cathode resistor in the preamp.
If your amp cuts in and out during
play, your effects-loop jacks may need cleaning with an electronic
contact cleaner that has lubricant.
If your amp isn’t making any sound,
it may have a bad speaker connection. You can test whether
the speaker is getting a proper signal by connecting one multimeter
lead to the sleeve (as shown with the black lead above) and
the other to the tip.
Is the amp making loud, static- like noises
when you play?
This could be due to dirty, oxidized, or compromised connections
in the tube sockets. To find out, while the amp is in operate
mode, wiggle each tube, starting with the output tubes—
which are usually the biggest offender. In order to avoid
blurting out expletives in front of children or others with
sensitive ears, be prepared for the amp to make a loud crackling
noise. If it does, there’s a good chance the sockets
are dirty or oxidized. More times than not, the fix is a good
cleaning—and that’s something anyone can do.
To clean the sockets, turn the amp off and remove the tubes
once they’re cool, being sure to take note of their
locations in the amp. I recommend marking each tube and its
associated socket with a Sharpie (“1,” “2,”
etc.) while you’re removing them. One by one, spray
a couple of shots of electronic contact cleaner, and then
insert and remove each tube in the socket 8 to 10 times. (Note:
Be sure your electronic contact cleaner is the type without
lubricant— lubricant can attract dust and debris, which
can become conductive.) Once you’ve cleaned all the
sockets, leave all of the tubes out for 5 to 10 minutes so
that the cleaner can evaporate. After the sockets are dry,
replace the tubes and try the amp again. If the symptom has
cleared up, you’ve taken care of the issue. If not,
try the socketcleaning procedure again—sometimes it
can take more than one cleaning to get the job done. If the
problem still persists after a couple of cleanings, the sockets
may need to be re-tensioned or replaced, which is probably
best left to a professional.
Does sound from the amp cut in and out
while you play?
This can be due to quite a few things, one of which can be
related to the tube sockets (see the previous section on cleaning
tube sockets).
If your amp has an effects loop, the problem could also be
that the contacts in its 1/4" jacks are dirty or oxidized—especially
if you don’t use the loop. To remedy this, spray electronic
contact cleaner—only this time use the type that does
have lubricant— into each jack, and then insert and
remove a cable 8 to 10 times. Afterward, leave the plugs inserted
for 15–30 minutes— or even overnight, if possible.
This will leave the jacks’ switching contacts open and
give the cleaner a chance to dry. You can then remove the
cable and try the amp again. (Note: As a preventive measure,
it’s not a bad idea to perform this type of jack cleaning
on your input and speaker jacks.)
Although they may require a bit of a tug, the quick connects
on many combo speakers can be removed to facilitate testing
of the speaker’s resistance—which can help you
determine whether the speaker cable has gone bad.
Does the amp not make sound at all?
This can be due to an open speaker connection. To check for
this, unplug the speaker cable from the head (leaving the
other end connected to the cab), and use your multimeter to
measure the resistance of the speaker load. Set the meter
to read resistance in ohms, connect one lead of the meter
to the body (sleeve) of the plug, and then connect the other
to the tip. A typical 16 O load will measure approximately
12–14 ohms, an 8 O load will measure approximately 6–7
O, and a 4 O load will measure approximately 3 O DC resistance
with the meter. If you can’t get a resistance measurement,
try again with a spare speaker cable. (Note: For testing purposes,
a 1/4" instrument cable can be used, but you should not
use one as a permanent substitute for a proper speaker cable.)
If you have a combo and you can’t get a reading at
the end of the combo speaker cable, perform the resistance
test right at the terminals on the speaker itself. I have
seen numerous instances where inexpensive combo speaker cables
with the molded plastic ends have failed, so it’s not
a bad idea to replace these with an upgraded cable as a preventive
measure—because an open speaker cable can cause substantial
damage to a tube amp. If you happen to have a combo where
the speaker is hardwired (i.e., it does not have a 1/4"
jack you can disconnect from the chassis) and you still wish
to check the speaker resistance, you will need to disconnect
one of the leads coming from the chassis to the speaker(s).
Luckily some amps use quick connects to attach the speaker
leads. If this is the case, simply remove one connector from
the speaker (this may take some force, but it will come off)
and measure the speaker resistance by connecting the meter
leads directly to the speaker terminals. If your hardwired
speaker doesn’t have quick connects, you’ll need
to unsolder one of the leads. (Note: Checking speaker resistance
with the speakers still connected to the amplifier will result
in a false reading. Because the amp’s output-transformer
resistance is extremely low, it will cause your reading to
look like the speaker(s) are shorted, which is almost never
the case.)
Be Prepared—and Don’t Get
in Too Deep
A number of issues with tube amps can be alleviated by even
the most risk-averse and electrically un-inclined guitarist
using the tools and methods discussed here. The most important
thing is to have the proper instruments and supplies on hand
and to follow the right processes. We recommend keeping this
story handy (you can access it for free online or get the
Premier Guitar app for Android or iPhone) so you can follow
the steps outlined here precisely every time.
Hopefully your amp woes never become so great that these
fixes don’t solve the problem, but if they do, be sure
to document the problem well and get in touch with a qualified
amp-repair person so they can help you get up and wailing
again with minimal downtime.
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