Ampeg Guitar Amplifier SJ12T user manual

							 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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							Table of Contents:
The Front Panel  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4,5
The Rear Panel  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
Important Information About Tubes and Tube Products
A Brief History Of The Tube  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
Tube Types And Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7,8
The Nature Of Tubes: Why (And When) To Replace Them . . . . .8,9
The Importance Of Proper Biasing  . . . . . . . . . . . . . . . . . . . . . . . .9
Survival Tips For Tube Amplifiers  . . . . . . . . . . . . . . . . . . . . . . . .10
System Block Diagram  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
Thank you for selecting the Ampeg Classic SuperJet guitar amplifier. Revived
from the sixties and ready for the nineties, this easy-to-use amplifier repre-
sents Ampeg’s quest to provide you the finest instrument amplification sys-
tems available. In order to get the most out of your new amplifier, please read
these instructions before its use.  
						

							3
IMPORTANT SAFETY INSTRUCTIONS•READ, FOLLOW, HEED, AND KEEP ALL INSTRUCTIONS AND WARNINGS.
•DO NOT OPERATE NEAR ANY HEAT SOURCE AND DO NOT BLOCK ANY VENTILATION OPENINGS ON THIS APPARATUS. FOR
PROPER OPERATION, THIS UNIT REQUIRES 3” (75mm) OF WELL VENTILATED SPACE AROUND HEATSINKS AND OTHER AIR
FLOW PROVISIONS IN THE CABINET.
•DO NOT USE THIS APPARATUS NEAR SPLASHING, FALLING, SPRAYING, OR STANDING LIQUIDS.
•CLEAN ONLY WITH LINT-FREE DAMP CLOTH AND DO NOT USE CLEANING AGENTS.
•ONLY CONNECT POWER CORD TO A POLARIZED, SAFETY GROUNDED OUTLET WIRED TO CURRENT ELECTRICAL CODES AND
COMPATIBLE WITH VOLTAGE, POWER, AND FREQUENCY REQUIREMENTS STATED ON THE REAR PANEL OF THE APPARATUS.
•PROTECT THE POWER CORD FROM DAMAGE DUE TO BEING WALKED ON, PINCHED, OR STRAINED.
•UNPLUG THE APPARATUS DURING LIGHTNING STORMS OR WHEN UNUSED FOR LONG PERIODS OF TIME.
•ONLY USE ATTACHMENTS, ACCESSORIES, STANDS, OR BRACKETS SPECIFIED BY THE MANUFACTURER FOR
SAFE  OPERATION AND TO AVOID  INJURY.
•WARNING: TO REDUCE THE RISK OF ELECTRIC SHOCK OR FIRE, DO NOT EXPOSE THIS UNIT TO RAIN OR MOISTURE.
•SERVICE MUST BE PERFORMED BY QUALIFIED PERSONNEL.
•OUR AMPLIFIERS ARE CAPABLE OF PRODUCING HIGH SOUND PRESSURE LEVELS. CONTINUED EXPOSURE TO HIGH SOUND
PRESSURE LEVELS CAN CAUSE PERMANENT HEARING IMPAIRMENT OR LOSS. USER CAUTION IS ADVISED AND EAR PRO-
TECTION IS RECOMMENDED IF UNIT IS OPERATED AT HIGH VOLUME.
CAUTIONRISK OF ELECTRIC SHOCK
DO NOT OPEN
WARNING: TO REDUCE THE RISK OF FIRE OR ELECTRIC
SHOCK, DO NOT EXPOSE THIS APPARATUS TO RAIN OR MOIS-
TURE. TO REDUCE THE RISK OF ELECTRIC SHOCK, DO NOT
REMOVE COVER. NO USER-SERVICEABLE PARTS INSIDE.
REFER SERVICING TO QUALIFIED SERVICE PERSONNEL.
IT IS NECESSARY FOR THE USER TO REFER TO THE INSTRUCTION MANUAL
“ES NECESARIO QUE EL USUARIO SE REFIERA AL MANUAL DE INSTRUCCIONES.”
REFERREZ-VOUS AU MANUAL DUTILISATIONEXPLANATION OF GRAPHICAL SYMBOLS:
EXPLICACION DE SIMBOLOS GRAFICOS:
EXPLICATION DES SYMBÔLES GRAPHIQUES:DANGEROUS VOLTAGE
“VOLTAJE PELIGROSO”
DANGER HAUTE TENSION==
PRECAUCIONRIESGO DE CORRIENTAZO
NO ABRA
PRECAUCION: PARA REDUCIR EL RIESGO DE INCENDIOS O DESCARGAS
ELECTRICAS, NO PERMITA QUE ESTE APARATO QUEDE EXPUESTO A LA
LLUVIA O LA HUMEDAD. PARA DISMINUOIR EL RIESGO DE CORRIENTAZO.
NO ABRA LA CUBIERTA. NO HAY PIEZAS ADENTRO QUE EL USARIO PUEDO
REPARAR DEJE TODO MANTENIMIENTO A LOS TECHNICOS CALIFICADOS.
ATTENTIONRISQUE DELECTROCUTION
NE PAS OUVRIR
ATTENTION: PROTÉGEZ CET APPAREIL DE LA PLUIE ET DE LHUMIDITÉ
AFIN DÉVITER TOUT RISQUE DINCENDIE OU DÉLECTROCUTION. POUR
REDUIRE DELECTROCUTION NE PAS ENLEVER LE COUVERCLE. AUCUNE
PIECE INTERNE NEST REPRABLE PAR LUTILISATEUR. POUR TOUTE
REPARATION, SADRESSER A UN TECHNICIEN QUALIFIE.
Declaration Of Conformity
#35, Effective 01-01-2001
Manufacturer’s Name:SLM Electronics 
Production Facility:11880 Borman Drive, St. Louis, MO 63146, USA
Production Facility:700 Hwy 202 W, Yellville, AR 72687, USA
Shipping Facility:1400 Ferguson Ave., St. Louis, MO 63133, USA
Office Facility:1400 Ferguson Ave., St. Louis, MO 63133, USA
Product Type:Audio Amplifier
Complies with the following Standards:
Safety:EN60065, E60065, C22.2, UL6500 and/or UL813
EMC:Directive 89/336/EEC, EN55103, EN55013, EN61000,
and/or FCC 47CFR 15B clA
Supplementary information provided by:
SLM Electronics - R & D Engineering 
1901 Congressional Drive, St Louis, MO 63146, USA
Tel.: 314-569-0141, Fax: 314-569-0175 
						

							4
1. Guitar Input accepts the output from
your instrument by means of a shielded
signal cable. This input signal to this jack
is not attenuated and accommodates
instruments with standard output signals.
If your instrument has a strong output
signal, use the Accordion Input (#2).
2. Accordion Inputaccepts the output
from your instrument by means of a
shielded signal cable. The signal to this
jack is attenuated 6dB to accommodate
instruments with stronger output signals.
3. Volumecontrols the overall output
level of the amplifier. At lower volume
settings the sound will be clean. As you
push the volume higher and crank your
guitar the sound becomes distorted.4. Tonecontrols the overall tonal charac-
ter of the amplifier. Rotating the knob
toward the “T” (“Treble”) increases the
higher frequencies, giving a brighter,
more “crisp” sound. Rotating the control
towards the “B” (“Bass”) reduces the
high frequencies, giving a darker, more
“muffled” sound. The Tone control offers
a cut or boost of 30dB at 4kHz.
5. Tremolo-Speedsets the rate at which
the tremolo effect “vibrates.” The
Tremolo-Intensity control (#6) must be
turned up to hear the effects of this
knob’s setting.
The Front Panel:
MODEL SJ-12T
GUITAR ACCORDION
VOLUME0 1 2345
6
7
8
9
10
TONEB0 1 2345
6
7
8
9
10SPEED
0 1 2345
6
7
8
9
10
TRESUPERJET
T
5 4 3 2 1 
						

							5
6. Tremolo-Intensity sets the depth of
the tremolo effect. For slow, smoother
vibrato effects try the Intensity control at
around 6 and the Speed control at 1. For
the really wild sounds, crank the
Intensity up towards 8 (or beyond) and
go from there.
7. Reverb-Dimension controls the
amount of reverberation applied to the
signal. With the control at the “0” position
there is no reverb applied; as the control
is turned towards “10” the amount of
reverb increases accordingly.8. Power lightilluminates (iridescent
blue) when the amplifier is turned on.
9. Power switchis used to turn the
amplifier on and off.
MODEL SJ-12T
ON OFF
INTENSITY OLO
0 1 2345
6
7
8
9
10
SUPERJET
DIMENSIONREVERB
0 1 2345
6
7
8
9
109 8 7 6 
						

							
6

(Reverb cables:
do not disturb)
(Reverb cables:
do not disturb)1314151011
12
10. Power cord connects the amplifier
to
 a  suitable  source of A.C.  voltage. This
is
 a  grounded, three-wire cord and must
be
  connected to a properly grounded
outlet.
DO NOT attempt to defeat the
ground
  connection of  the power cord!
If
  your amp was purchased outside  of
the
  United States, see the sticker next to
the
  A.C.  connector  for its power ratings.
Follow
  the above guidelines. 
1 1,12. Power T ubes: 6L6 (2)
13.
  Power Amp  Phase Splitter T ube:
12AX7
A/  7025  (1) 14.
 
Preamp T ube: 12AX7A/ 7025 (1)
Replace
  tubes ONLY with same types!
Refer
  to pages 7 through 10 for impor-
tant
  information about tubes and tube
products.
15:
  Footswitch Jack is located up  inside
the
  amplifier, just past the  cabinet’s cov-
ered
  back panel. Connect the supplied
footswitch
  here for remote control of the
Reverb
  and T remolo on/off.
The Rear Panel: 
						

							7
Important Information About Tubes and Tube Products:
ABrief History Of The Tube:
In 1883, Edison discovered that electrons would flow from a suspended filament when enclosed in an evac-
uated lamp. Years later, in 1905, Fleming expanded on Edisons discovery and created the Fleming Valve.
Then, in 1907, Dr. Lee de Forest added a third component – the grid – to the Flemings Valve and the vac-
uum tube was a fact of life. The door to electronic amplification was now open.
During World War II, data gleaned from their intensive research on the detectors used in radar systems led
Bell Telephone Laboratories to the invention of the transistor. This reliable little device gained quick support
as the new component for amplification. The death of the vacuum tube seemed imminent as designers, sci-
entists, and engineers reveled in the idea of replacing large, fragile glass tubes with these small, solid-state
devices.
However, there were (and still are) many serious listeners who realized that the sound produced by a tran-
sistor amplifier is significantly different from that produced by a tube amplifier with identical design specifica-
tions. They considered the sound produced by these new solid-state devices to be hard, brittle, and lifeless.
It was determined that solid-state devices produced a less musical set of harmonics than tubes. When pushed
past their limits, they tend to mute the tone and emphasize the distortion.
Tubes, on the other hand, produce a more musical set of harmonics, the intensity of which can be controlled
by the player. This characteristic adds warmth and definition to the sound which has become the hallmark of
tube amplifiers. When tubes are driven into clipping, the harmonic overtones can be both sweet and pleasing
or intense and penetrating, depending on the musician’s musical taste and playing technique.
Over the years, application engineers have designed a number of outstanding solid-state amplifiers that
sound very, very good. Some use special circuitry which enables them to simulate the distortion characteris-
tics of a tube amplifier. However, the tube amplifier, still held in the highest esteem by many musicians, offers
a classic vintage sound in a contemporary market. 
T
ube Types And Usage:
Tube amplifiers are based primarily on two types of tubes – preamplifier tubes and power tubes. The tubes
used in preamplifiers (12AX7, 12AU7, 12AT7, etc.) are smaller than the power tubes. These tubes amplify
the signal from your instrument and shape the sound. They are inherently microphonic (mechanically pick
up and transmit external noises). Since these tubes are used in the critical first stages of a tube amplifiers
circuitry, it is very important to use high-quality, low noise/low microphonic tubes for this application.
Although tubes of this quality may be difficult to find and typically cost more than off-the-shelf tubes, the
improvement in performance is worth the investment. 
Preamplifier tubes are also used to drive the power tubes. When used in this application, a 12AX7 will pro-
duce a more distorted tone than a 12AT7, which produces a clearer, sweeter sound. A 12AU7 is even
cleaner and brighter than a 12AT7, giving more definition to the sound. (In some cases it is possible to
change the sound by changing the type of preamp and/or driver tubes. When making any modification to
your equipment, it is highly recommended that you consult with a qualified service center.)
The power tubes are the largest tubes used in an amplifier. These tubes convert the low-level, conditioned
signal from the preamplifier into a level that is sufficient to drive the speakers. There are several types of
power tubes available, each of which offers a different performance/sound characteristic. For example, the
EL34 power tube produces a great Classic rock sound. When an EL34 is driven into distortion it produces a
unique sound (crunch). When compared to the 6L6, the EL34 distorts more quickly, exhibits a looser  
						

							8
Important Information About Tubes and Tube Products (Continued):
low-end response and produces more harmonics at mid and high frequencies (creamier sound). These
differences become more noticeable at higher volumes.
The 6L6 tubes produce a big low-end thump and have a very good dynamic range. They offer a more tradi-
tional American Rock sound. The 6V6 tubes produce a creamy sound with nice distortion. On the other
hand, the KT88 produces a big low-end but sounds more like an EL34 in the mid and high frequencies.
The 6550 power tubes are more rugged and stay cleaner sounding even at full power. When they do dis-
tort, the sound produced is more solid and has a tighter low end; more of a heavy metal type distortion
with lots of power.
Some tubes are available in matched sets. These tubes have been extensively tested for optimum perform-
ance and longevity.
The Nature Of T
ubes:Why (And When)To Replace Them:
Tubes are made up of a number of fragile mechanical components that are vacuum-sealed in a glass enve-
lope or bubble. The tubes longevity is based on a number of factors which include how hard and often the
amplifier is played, vibration from the speakers, road travel, repeated set up and tear down, etc.
Any time you notice a change in your amplifiers performance, check the tubes first.
If its been a while since the tubes were replaced and the sound from your amplifier lacks punch, fades in
and out, loses highs or lows or produces unusual sounds, the power tubes probably need to be replaced. If
your amplifier squeals, makes noise, loses gain, starts to hum, lacks sensitivity, or feels as if it is working
against you, the preamplifier tubes may need to be replaced. 
The power tubes are subjected to considerably more stress than the preamplifier tubes. Consequently, they
almost always fail/degrade first. If deteriorating power tubes arent replaced they will ultimately fail.
Depending on the failure mode, they may even cause severe damage to the audio output transformer
and/or other components in the amplifier. Replacing the tubes before they fail completely has the potential
to save you time, money and unwanted trouble. Since power tubes work together in an amplifier, it is cru-
cial that they (if there is more than one) be replaced by a matched set. If youre on the road a lot, we rec-
ommend that you carry a spare matched set of replacement power tubes and their associated driver tubes.
After turning off the power and disconnecting the amplifier from the power source, carefully check the tubes
(in bright light) for cracks or white spots inside the glass or any other apparent damage. Then, with the
power on, view the tubes in a dark room. Look for preamplifier tubes that do not glow at all or power tubes
that glow excessively red. 
Whenever you replace the power tube(s):
• Always have the amplifiers bias voltage checked by a qualified service center. Improper bias voltage will
cause degradation in performance and possibly damage the tubes and/or the amplifier. (See the section
below entitled, The Importance of Proper Biasing, for more information on this subject).
• We highly recommend that you replace the driver tube(s) as well. The driver tube determines the shape
and amplitude of the signal applied to the power tube(s) and has to work almost as hard as the power
tube(s). 
						

							9
Important Information About Tubes and Tube Products (Continued):
You can check your preamplifier tubes for microphonics by turning the amplifier on, turning up the gain and
tapping lightly on each tube with the end of a pencil or a chop stick (my favorite). You will be able to hear
the tapping through your speakers, which is normal. It is not normal for a tube to ring like a bell after it’s
tapped. If it does ring then it’s microphonic and should be replaced. Remember to use only high quality, low
microphonic tubes in the preamplifier section.
Even though power tubes are rarely microphonic, you should check them anyway. The power tubes can be
checked for microphonics just like pre-amp tubes. 
In the case of very high gain amps, you may be able to reduce the amount of noise generated by simply
swapping the preamp tubes around.
The Importance Of Proper Biasing:
For the best performance and longest tube life, proper biasing is imperative. Bias is the negative voltage
which is applied to the power tube’s control grid to set the level of idle current. We cannot over emphasize
the difference in warmth of tone and dynamic response that come with proper biasing. If the bias is set too
high (overbiased), the sound from the amp will be distorted at all levels. If the bias is set too low, (under
biased) the power tubes will run hot (the plates inside the tubes may glow red due to excessive heat) and
the sound from the amplifier will lack power and punch. The excessive heat greatly reduces tube life – from
a few days to as little as a few hours in extreme cases. Setting the bias on your amp is like setting the idle
on your car. If it’s too high or hot it’s running away with you and if it’s too low or cold it will choke when you
step on it.
The bias is adjusted at the factory in accordance with the type of power tube(s) installed in your amplifier. It
is important to point out that tubes of the same type and specification typically exhibit different performance
characteristics. Consequently, whenever power tubes are replaced, the bias voltage must be checked
(unless the amplifier is equipped with self-biasing circuitry) and readjusted to accommodate the operating
parameters of the replacement tubes.
Depending on the model and amplifier type, there may be hum balance controls, trim pots, or bias adjust-
ment controls on its rear panel. However, the bias adjustment should be performed only by qualified service
personnel with the proper, calibrated test equipment. 
						

							10
Important Information About Tubes and Tube Products (Continued):
Survival Tips For Tube Amplifiers:
To prolong tube life, observe these tips and recommendations:
• Match the impedance of your speaker cabinet(s) to your amplifier. Improper impedance matching will con-
tribute to early tube degradation and may cause premature tube failure.
• Make sure the speaker(s) are properly connected prior to turning on the amplifier.
• After playing the amplifier, allow sufficient time for it to properly cool down prior to moving it. A properly
cooled amplifier prolongs tube life due to the internal components being less susceptible to the damage
caused by vibration.
• Allow the amplifier to warm up to room temperature before turning it on. The heat generated by the tube
elements can crack a cold glass housing.
• Replace the output tube(s) before the performance degrades or the tubes fail completely. Replace the
tube(s) on a regular basis (at least once per year or as often as every 4 to 6 months if you play long and
hard every day).
• Always have the bias checked after replacing the output tubes (unless the amplifier is equipped with self-
biasing circuitry). This should be done ONLY at a qualified service center. Improper biasing could result
in the tubes running too hot, which greatly reduces the life of the tubes – or too cold, which results in dis-
torted sound regardless of level settings. Do not play the amplifier if it exhibits these symptoms – get the
bias checked/adjusted immediately to prevent tube failure and/or other damage.
• If the locating notch on the base of a power tube breaks off, replace the tube. This significantly reduces
the risk of damaging your amplifier by incorrectly inserting the tube.
• Protect the amplifier from dust and moisture. If liquid gets into the amplifier proper, or if the amplifier is
dropped or otherwise mechanically abused, have it checked out at an authorized service center before
using it.
• Proper maintenance and cleaning in combination with routine checkups by your authorized service center
will insure the best performance and longest life from your amplifier.
CAUTION: Tube replacement should be performed only by qualified service personnel who are
familiar with the dangers of hazardous voltages that are typically present in tube circuitry.