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So you’re band is going on in an hour.
You’re setting up your gear and something
is wrong with your amp…maybe? The fol-
lowing is a systematic troubleshooting guide
for when this happens.
1) DON’T PANIC!
Here are the items you should carry with
you in case of trouble.
1) Spare guitar cables
2) Spare speaker cables
3) Spare fuses for everything
a. Look at the fuse holders on
all your gear and get
replacement fuses for each one.
4) A spare preamp tube and
power tubes.
5) A new 9 volt battery even if
you don’t use pedals (you’ll see
why later)
6) A reliable digital multimeter.
Doesn’t need to be fancy or
expensive.
7) A small flat blade screwdriver
for bias adjustment.
8) Band Aids. In case of injury.
Has nothing to do with fixing
your gear but they sure come in
handy when you are bleeding.
9) A spare tire for your car. You
wouldn’t go anywhere without
a spare tire would you? Same
goes for your gear that you
count on to work every time.
Stuff goes wrong. If you are prepared,
you won’t need to freak out.
Your “rig” is just a combination of
“sub-systems” consisting of, but not limited
to, your guitar, cables, effects, amp and
speakers. The trick is to quickly and accu-
rately eliminate each component to narrow
the trouble down to one part of the “sys-
tem”. A systematic approach using process
of elimination will quickly tell you which
component in your “system” has failed.
SYMPTOM = NO SOUND:
1) The first quick check is obviously to
make sure everything is securely plugged in
and all power indicators are lit on every-
thing and the amp is not in STANDBY. I
can’t tell you how many times something
didn’t work simply because a plug was
not fully inserted. Also, many amps have a
MAIN and an EXTENSION speaker output.
Verify you are using the MAIN output first.
I’ve made that mistake myself.
2) Accurately verify if everything is abso-
lutely, 100% dead or can you near some tiny
sound (hum, hiss, a little guitar, anything
at all) coming from the speakers. This is
important information because there are two
different approaches to troubleshooting de-
pending on which symptom you encounter.
3) If you are sure there is
absolutely no
sound at all, do this:
a.
This tells you either the amp or
the speakers are dead. Here is a simple and
quick speaker test. Get your 9 volt battery
that you, of course, have in your emergency
kit. Pull the speaker cable end out of your
amp and hold it in one hand. Take the 9 volt
battery and touch the two battery terminals
to the tip and body of the plug simultane-
ously.
You will hear a fairly loud “thump”
noise from your speaker cabinet each
time you touch the battery. If you hear the
“thump”, you just verified the speakers and
speaker cable are good and can be removed
from the list of possible problem compo-
nents. If you don’t hear the “thump” either
your cable or your speaker cabinet is at
fault. By the way, you can use this same test
for your combo amp speakers.
b. A special note is in order here. If
you are having the “no or very little sound”,
do not…I repeat DO NOT just turn every-
thing up louder or, worse, full up and try to
play. This is not an acceptable repair tech-
nique. If your speaker cable or cabinet is
bad, doing this will quite possibly blow up
your tube amp that was probably not broken
until you did this. Plus, if you have every-
thing cranked and, by some chance things
suddenly start working, you will probably
damage your amp, speakers or hearing.
c. Next is the amp itself. First unplug
everything from the amp except for the
power cord. One very common failure is a
shorted power tube. Many amps have a fuse
that is dedicated to protecting the power
tubes and transformers.
It is usually on the rear panel labeled
something like HT or High Voltage or
Power Tubes. Remove and inspect this fuse.
If it looks burned inside, this is pretty much
a sure indication of a shorted power tube.
Often a fuse “looks” fine but can still be
open (blown).
Learn how to measure continuity with
your multitmeter and use it to verify if the
fuse is open or not. If the fuse reads just
a couple of ohms on your meter, it is not
blown and power tubes are not likely the
problem.. If you get no reading, infinite or a
very high ohm reading, it is blown.
If you do have the misfortune of blow-
ing a power tube, which of course will only
happen at the most importune time, there is
a way out. It does require you carry a couple
of extra power tubes and at least four of the
correct value HT fuse for your amp. If you
do find the fuse is open, your amp will not
produce any sound which is why we are
talking about this here.
Follow this procedure to get your self
out of trouble and back “up and running”:
1) Turn the amplifier power off.
2) Replace the blown HT/Power
tubes fuse.
3) Remove all the power tubes
4) Turn the amplifier power on and
wait 30 seconds.
5) Move the STANDBY switch to
the PLAY position.
6) Wait 30 seconds again and now
turn the amp off.
7) Remove and recheck the HT/
Powertubes fuse.
8) If the fuse is blown, you are
screwed. Nothing you can do
right now will make it work….
sorry. Hope you brought a
backup amp. If the fuse is not
blown, one of your power tubes
is shorted, which is good news.
9) Put one, and only one of the
power tubes back in.
10) Turn the POWER switch on,
wait 30 seconds and now turn
the STANDBY on.
11) Next POWER and
STANDBY off.
12) Recheck the HT/Powertubes
fuse. If it is not blown, that tube
is good. If it is blown, the tube
is bad so get rid of it.
13) If the fuse is good, leave that
tube in and install another one.
Same drill, blown fuse=Bad
tube, good fuse=Good tube.
See the pattern? If you install the tubes
one at a time like this, when you put the
shorted one in, the fuse will blow. Once you
determine that a tube is, in fact, shorted you
have options. If the amp only has two power
tubes, you will want to put one of your
spare tubes in. Of course you brought them
with you right? One note here, I suggest
you buy a matched set of four power tubes
for your amp. Use two and keep two for the
spares. If they are from the same set, you
won’t need to rebias them and you are good
to go. If your amp has four power tubes, you
have two choices.
You can get through the show with just
two power tubes with somewhat reduced
power and headroom and not worry about
replacing any tubes. To do this, simply leave
in only two of the known good tubes. Install
them as one on each end of the row of tubes
and leave the center pair out or, put the good
pair in the center sockets and leave each end
out. Doesn’t matter which way.
tech talk: identifying speaker or tube problems
