andreus A-22 User manual

OPERATION MANUAL
Model A-22
Head and Combo
08/10

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Thank you for pur hasing an Andrews Amplifier. The Model A-22 is
built to the highest standards of raftsmanship and is finely tuned
for the ultimate tone. This amp is very simple to operate but we
suggest reading this short manual in order to get the most from your
new amp.

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FEATURES;
• ALL TUBE CIRCUITRY PURE WARM TUBE SOUND – Your guitar signal
does not pass through any transistors or integrated ir uits (ICs). We
have also avoided using any relays or other swit hing devi es so nothing
interrupts your pure guitar signal.
• ALL HAND-WIRED CONSTRUCTION – Also sometimes alled “point-to-
point” wiring, the A-22 utilizes a very high quality turret board made of
super-tough G10 omposite. This glass-epoxy laminate is spe ified for
its extremely high strength and high dimensional stability over
temperature . The extra-thi k board material will never warp, melt, or
absorb moisture and there are no opper tra es to peal away from the
board over time. All wiring and soldering is done by hand and quality
he ked to ensure many years of trouble free operation.
• CUSTOM-WOUND, AMERICAN-MADE TRANSFORMERS – These
transformers are built to our spe ifi ations spe ifi ally for the
requirements of this amp design. They are wound on paper bobbins like
in “the good old days” and are rated to withstand extreme heat for high
reliability. In addition, a spe ial type of steel ore is utilized for maximum
effi ien y, lighter weight and superior tone. The output transformer is
interleaved for optimum balan e. Output impedan e is swit hable to 4, 8
or 16 ohms and 2 speaker ja ks are provided.
• CUSTOM DESIGNED CHASSIS – Our hassis is designed spe ifi ally for
this amp model so that every part an be mounted in the optimal lo ation
for lowest noise and highest stability.
• CUSTOM DESIGNED CABINET – Our abinets are spe ially designed for
maximum durability and superior tone. We use very high-grade void-free
Balti Bir h ply for our abinets. The abinet omponents are pre ision
ut using high-te h equipment and are hand assembled with are.
Dovetail joints are used at the orners for maximum strength. The ombo
abinet features a 3-pie e ba k that an be onfigured as losed-ba k or
semi-open to allow for even more tonal versatility. Unlike most other
ombo amps, the speaker ompartment is isolated from the tubes. This
greatly redu es the han es of the tubes being vibrated by the sound
pressure waves oming off the ba k of the speaker therefore redu ing
tube mi rophoni s, rattling and premature failure.
• EXTERNAL BIAS TEST POINTS – The A-22 is equipped with external bias
test points and an externally a essible adjustment ontrol. This makes
output tube repla ement fast and e onomi al. In fa t, with a low ost
multi-meter you an adjust bias yourself. This an be a real advantage in
ase of a tube failure during a performan e or re ording session. See the
se tion about the rear panel for more information.

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Warnings and Pre autions
Va uum tubes generate a lot of heat. Do not tou h hot tubes. Insure plenty of
ventilation behind the amp. Keep away from urtains and other flammable
obje ts. Keep the amplifier away from hildren.
Do not expose your amplifier to rain. Never set any ups, glasses, bottles or
ans of liquid on your amplifier.
Do not use any solvents to lean your amplifier.
Never operate your amplifier without a proper speaker load or damage may
o ur. See the se tion about the rear panel features for more information.
Make sure the amplifier is always properly grounded. Never remove or defeat
the ground pin from your power ord. Always unplug the amplifier before
hanging tubes or fuses.
Use only orre tly rated fuses. See the rear panel of your amplifier and this
manual for proper fuse ratings.
This amplifier an reate high sound pressure levels. Please use proper
hearing prote tion and/or maintain an adequate distan e from the amplifier to
avoid hearing damage.
There are no fuses or other user servi eable parts inside your amplifier. Please
refer servi ing to qualified servi e personnel.
Never insert any tool or other obje t into ventilation holes, tube so kets or other
openings unless instru ted to do so in this manual. Otherwise, you may ome
in onta t with dangerous high voltages inside the hassis.

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Front Panel
1. INPUT JACKS – For maximum versatility, we have provided two input jacks
(labeled IG and LOW). For maximum overdrive, use the IG jack. For a
more usable range of clean and crunch tones, try the LOW jack, especially with
high output pickups or noisy pedal boards. The IG jack has 9db more gain
than the LOW jack.
2. VOLUME CONTROL – This control could also be labeled “Preamp Gain”
or “Input Volume”. It is used in conjunction with the MASTER VOLUME
CONTROL. When the MASTER VOLUME is turned to 10, the VOLUME
CONTROL acts as a standard volume control as if the amp did not have a
MASTER VOLUME CONTROL. That is, when the volume control is turned up,
the amp will give you a nice warm overdriven tone at its maximum volume.
When the MASTER VOLUME is turned lower, you can still get nice overdrive
tones at lower output volume. By using the IG or LOW input jack and
adjusting the VOLUME and MASTER VOLUME controls to various positions,
you can fine tune the amount of crunch and overdrive desired at different
volume levels. If you find that you are always setting this control below 5 or 6,
try changing the V1 preamp tube to a 12AU7 (ECC82). This will result in lower
gain and give you a wider range of clean and crunch tones on the VOLUME
control. See the section on Tube Replacement for more details.
3. TREBLE CONTROL - This control varies the amount of treble and upper
midrange frequencies. It is most effective when the input volume setting is low.
Use the PRESENCE control to dial in the treble content of overdriven signals
(when the Input VOLUME is turned up).
4. BASS CONTROL – This control varies the amount of bass and lower
midrange frequencies.
5. PRESENCE CONTROL – This control can be used to reduce unwanted
treble frequencies from your signal and is especially effective when the Input
VOLUME is turned up high and he Master Volume is set to a low level. Crank it
up for a little more bite or back it off for a warmer, smoother tone. By carefully
adjusting the TREBLE and PRESENCE controls, you can vary the balance of
high frequencies for both clean and overdriven tones.

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6. MASTER VOLUME CONTROL – This control is designed to be very
versatile. Used in conjunction with the VOLUME control and IG or LOW
inputs, you can obtain varying levels of overdrive at different volumes. Full
output power can be achieved with at a setting of 8.5 - 10 Try experimenting
within this range to get subtle tonal differences.
7. STANDBY SWITCH – This switch turns on the high voltage for the tubes.
When turning on the amp, make sure the STANDBY switch is in the off (down)
position. Turn on the POWER (UP position) switch first. The pilot light will light
up. Wait at least 30 seconds to allow time for the tubes to warm up completely
before turning on the STANDBY switch. After the tubes are warmed up, turn
on the STANDBY switch (UP position) to operate the amp. It is a good idea to
turn the STANDBY switch off when not using the amp for more than a few
minutes. This will quite the amp and the stop plate current from flowing in the
tubes, resulting in longer tube life.
8. POWER SWITCH – This switch turns on the main power to the amplifier.
Always turn off the POWER SWITC when not using the amp for several hours
or more.
9. PILOT LIGHT – This light indicates when the main power is turned on. For
bulb replacement, simply unscrew the red lens, grab the bulb with your fingers,
push in while turning counterclockwise and release. Replace with a standard #
47 bulb. For longest life a $755 bulb may also be used. The lens thread fits
many standard lamp lenses and “jewels” allowing you to customize the color if
you desire.

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Rear Panel
1. FUSES – Always use correctly rated fuses. The MAIN fuse should be replaced
only with a 1.5 Amp “Slow Blow” 250 volt type. The .V. fuse should be replaced
only with a 500mA (1/2 Amp) fast acting 250V type. Always unplug the AC cord
before changing fuses. When installing a new fuse, first insert it into the cap of the
fuse holder, then while holding only the cap, insert the fuse into the holder, push in
and turn clockwise to lock the cap and fuse in place.
2. BIAS TEST POINTS AND ADJUSTMENT CONTROL – These are
provided for ease of measurement and adjustment of the idle current of the output
tubes. Bias adjustment is necessary whenever the output tubes are replaced.
See page 9 for bias adjustment instructions and precautions. The adjustment
control is located on the underside of the chassis near the test points.
3. SPEAKER JACKS – Always use the jack labeled MAIN first. If an additional
cabinet is to be used, meaning that two cabinets will be connected at the same
time, connect the second cabinet to the jack labeled EXT. This amplifier produces
22 watts RMS output power before clipping. When the amp is driven into distortion
at high volume, the output power can exceed 40 watts. Make sure any speakers
you connect can handle the output power of the amp. Always set the impedance
selector switch to match the correct speaker load. See chart below. NEVER
OPERATE THE AMPLIFIER WITHOUT A SPEAKER CONNECTED OR DAMAGE
MAY OCCUR AND THE WARRANTY WILL BE VOID.
Speaker “Break-In” – New speaker cones are tight and stiff. This results in a
brighter tone with less bass and low mids and may even be considered “harsh” at
times. By the time your speaker has been played hard for 20 to 30 hours or more,
its true character and tone will become apparent. Until your speaker is fully
broken-in, you may find that you can achieve better tone by reducing the
PRESENCE and/or TREBLE controls.
4. IMPEDANCE SELECTOR – Always set this switch to the proper speaker load
according to the chart below. Note: The A-22 combo incorporates a built-in
8 ohm speaker so leave it set to 8 when not connecting another cabinet.
Setting For One Cabinet For Two abinets
4 One 4 ohm abinet Two 8 ohm abinets
8 One 8 ohm abinet Two 16 ohm abinets
16 One 16 ohm abinet

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Convertible Cabinet (spe ifi versions
only)
The cabinet back features a removable center-section to allow for more tonal
versatility. When the center-section is left in place, the cabinet will function as a
closed-back speaker enclosure. In this mode, the sound will be more focused or
directional and the bass response will be tighter. When the center section is removed,
the cabinet will function as a semi-open enclosure. The overall volume will be
increased, especially the bass response. In addition, the sound will become less
focused and the bass will sound looser.
As speakers are “broken in” they tend to become looser sounding. This condition will
continue to progress as the speaker is used more and more. Another advantage of
being able to close the back of the cabinet is that it may help to tighten the response
of an aging speaker.
To remove the center section, remove the 10 screws along the top and bottom the
removable portion, being very careful not to press too hard on the screw heads. The
screws are threaded into T-nuts which may push out if too much pressure is applied to
the screws when removing them. If this happens, you may need to hook a pair of
needle nose pliers under the head of the screw and pull outwards on the screw while
turning it to keep the nut from turning. The center panel is designed with gaps at the
ends that are big enough to insert a coin to aid in removing the panel. Also, the panel
is raised slightly so that it can be more easily removed by hand.
When re-installing the center panel, please follow the same precautions regarding
excessive pressure on the screws.
If the back panel is to be removed to replace the speaker, the best option is to remove
just the middle and upper or lower section. This will give you access to the speaker
and should create a big enough opening to allow the speaker to be removed. If the
entire rear panel is removed in one piece, it may be damaged.

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FOR TECHNICAL TYPES
We have provided this information for those who have a te hni al interest,
proper equipment and proper training in dealing with high voltage ir uits.
GUITAR AMPLIFIERS CONTAIN LETHAL VOLTAGES. If you have any doubt
about your ability to safely perform this pro edure, refer the job to a qualified
te hni ian!
Bias Adjustment Pro edure:
Pre autions:
• Lethal volta es are present inside the chassis and at the tube pins. Do not
open the chassis or insert any objects into any openin s other than where
directed by these instructions.
• Vacuum tubes et very hot. Always allow the tubes to cool completely before
touchin them.
• When replacin output tubes, use only the very hi hest quality tubes or the
amplifier may be dama ed. For more details, see the section below re ardin
tube replacement.
1) Unplug the amplifier and allow the tubes to cool. The output tubes are the two tall
tubes on the left side of the amp when viewed from behind.
2) Unsnap the retaining clips that hold the output tubes in place and remove the
tubes. Install a new matched pair of EL84 or 6BQ5 tubes taking care not to bend
any tube pins. Snap the retaining clips back into position.
3) Using a digital multi-meter, set for DC Volts measurement and select a range that
will show 0-100 mV. Insert the black meter lead into the black test point terminal.
Insert the red meter lead into the left red test point terminal.
4) Insert a small flat blade screwdriver into the adjustment control hole and gently
turn the control to its mid position. The adjustment control is located on the
underside of the chassis near the bias test points.
5) Plug in the AC cord and turn on the amplifier’s main power switch. After waiting at
least 30 seconds, turn on the standby switch. The meter should display a few
millivolts (mV).
6) While taking care not to touch any hot tubes, insert the screwdriver into the
adjustment control and very slowly turn the adjustment until the meter reads
20mV. Turning clockwise will increase the voltage, counterclockwise will reduce
the voltage.
7) Now remove the red meter lead from the test point and insert it into the ri ht red
test point terminal and take a reading. The two terminals are reading a voltage
which represents the idle current of the two output tubes. If you get readings
within 5mV of each other at each test point, the tubes are considered to be
matched. Be sure to adjust the bias so that neither tube idles at more than 20mV.
We have found that the optimum bias point is reached when the tubes test points
read 20mV each but it is ok to set to any voltage from 15mV to 20mV without
causing any damage. Allow the tubes to warm up for at least 5 minutes and
re- he k bias. Repeat the adjustment pro edure if ne essary.
8) It is a good idea to re-check the bias periodically (every 500 hours or so) as the
idle current can drift over time as the tubes age.