Andrews Amplification AC25 Operation Manual

AC25

OPERATION MANUAL

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Thank you for purchasing an Andrews Amplifier. The AC25 is
designed to deliver classic British “Class A” tones while providing
greater versatility and improved reliability.

As with all Andrews amps, these models are built to the highest
standards of craftsmanship and are finely tuned for the ultimate
tone. This manual will help you to get the most from your new amp.
Please feel free to contact us with any questions at
andrewsamps.com

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FEATURES;

• HAND-WIRED CONSTRUCTION – Also sometimes called “point-to-point” wiring,

the Spectraverb amps utilize a very high-quality turret board made of super­tough G10 composite. This glass-epoxy laminate is specified for its extremely
high strength and dimensional stability over temperature. The extra-thick board
material will never warp or melt, and there are no copper traces to peal away
from the board over time. All wiring and soldering is done by hand and quality­checked to ensure many years of trouble free operation.

• AMERICAN-MADE TRANSFORMERS – We utilize only the best transformers to

meet our specifications. They are chosen for superior tone and are rated to
withstand extreme heat for high reliability. Output impedance is available at 4, 8
or 16 ohms. The custom wound power transformer is designed for optimal
voltage to allow the EL84 output tubes to operate within their design parameters
which extends tube life and reduces tube failures.

• CUSTOM DESIGNED CHASSIS – Our durable light-weight welded aluminum

chassis is designed specifically for our amp models so that every part can be
mounted in the optimal location for lowest noise and highest stability.

• CUSTOM DESIGNED CABINET – Our cabinets are specially designed for

maximum durability and superior tone. The cabinet components are precision
cut and are hand assembled with care. Finger joints are used at the edges for
maximum strength. Tube ventilation is improved compared to vintage designs.

• CUSTOMIZABLE GAIN - The AC25 contains a “trim pot” to alter the range of the

gain of the amp. For those who prefer a cleaner tone or for those who prefer
more overdrive, in internal adjustment is provided. It comes from our shop
preset to a medium setting. Please refer this adjustment to qualified technician.

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Warnings and Precautions

During operation, vacuum tubes can reach temperatures over 400 degrees F. Do
not touch hot tubes. Insure plenty of ventilation behind the amp. Keep the amp
away from children as well as curtains and other flammable objects.

Do not expose your amplifier to rain. Never set any cups, glasses, bottles or
cans of liquid on your amplifier.

Do not use any solvents to clean your amplifier.
Never operate your amplifier without a proper speaker load or damage may

occur. See the section 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 cord. Always unplug the amplifier before
changing tubes or fuses.

Use only correctly rated fuses. See the rear panel description of this manual for
proper fuse ratings.

This amplifier can create high sound pressure levels. Please use proper hearing
protection and/or maintain an adequate distance from the amplifier to avoid
hearing damage.

Tube amps contain lethal voltages (even when unplugged). There are no fuses
or other user serviceable parts inside. Please refer servicing to qualified service
personnel.

Never insert any tool or other object into ventilation holes, tube sockets or other
openings unless instructed to do so in this manual. Otherwise, you may come
in contact with dangerous high voltages inside the chassis.

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Front Panel

1. INPUT JACKS – For maximum versatility, we have provided two input jacks

(labeled High and Low). The HI jack provides a bit more drive and sensitivity. The
LO jack provides a slight (6dB) attenuation and is useful when a cleaner and
slightly darker tone is desired, especially with high output pickups.

2. VOLUME CONTROL – Use this control to adjust the volume and gain of the

amp. Try using the other input jack to widen the range of the Volume control

3. TREBLE CONTROL - This control varies the amount of treble. At high

settings, it also decreases the amount of bass.

4. MIDRANGE CONTROL – The Midrange control adjusts the midrange level.

5. BASS CONTROL – This control varies the amount of bass. In general, it is

suggested to increase the bass setting as the master volume is turned down to
compensate for the way the human ear hears bass at different volume levels.

6. HIGH CUT CONTROL – This acts as an additional treble control and is placed

in the power amp circuit rather than the preamp. Turning the control
counterclockwise will filter highs from the power amp. Try various combinations of
treble and high cut settings to achieve the desired tone at various volume and gain
settings and various guitars.

7. MASTER VOLUME CONTROL – This controls the overall output
volume of the amp. Use this in conjunction with the Volume Control to
dial in the desired amount of crunch at the overall volume to fit your
situation. For even more flexibility, switch the output power to allow
your favorite Master Volume setting at the correct sound level for your
situation. For the cleanest tone, it’s recommended to keep the Master
Volume setting high and the power on High while dialing down the
Volume Control.

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8. OUTPUT POWER SWITCH – The high-power setting selects all four EL84

output tubes and produces about 25 watts. Switching to low power turns off two of
the output tubes and produces 10 or 14 watts. Turning off two tubes actually

changes the output impedance of the amp. To compensate, it is recommended to
move the speaker plug from the 8 ohm jack to the 4 ohm jack. Doing so will allow
the amp run most efficiently in the low power setting and will produce about 14
watts. If the low power mode is selected without changing the speaker plug
position, the amp will produce around 10 watts. Also, the output tubes may run a
little hotter and could have a reduced lifespan. Using the amp in the 10 watt mode
is generally safe for the amp but we recommend against long term use at that
setting for the sake of the tubes.

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 or #755
bulb or LED equivalent. The lens thread fits many standard lamp lenses and

“jewels” allowing you to customize the color if you desire.

10. STANDBY SWITCH – This switch turns on the high voltage for the tubes

amp in the standby mode. It is a good idea to place the amp in standby when
taking a break to extend the life of the tubes and to allow the amp to cool.

11. POWER SWITCH – This switch turns on the main power to the amplifier.

Always turn off the POWER switch when not using the amp for a couple of hours
or more.

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Rear Panel

1. POWER CONNECTOR & FUSE – Always use correctly rated 3 amp slow

blow fuse or severe damage to the amp may occur. Always unplug the amp
before replacing any fuses. The main AC fuse is located in the AC cord jack.
Use a small screwdriver to remove the fuse holder.

2. SPEAKER JACKS – Three speaker jacks are provided. One each for 4, 8

and 16 ohms. The built-in speaker is rated at 8 ohms so it should normally be
plugged into the 8 ohm jack but can be plugged into the 4 ohm jack when
operating the amp in the low power mode. See instructions for Front Panel. The
wiring of these three jacks can be customized for other combinations. For
example, the 16 ohm jack can be converted to an additional 4 ohm jack so the
amp can be used with it’s built-in speaker and an additional 8 ohm speaker
cabinet at the same time. NEVER OPERATE THE AMPLIFIER WITHOUT A

SPEAKER CONNECTED OR DAMAGE MAY OCCUR AND THE WARRANTY
WILL BE VOID.

In the chart below, keep in mind that the built-in speaker is 8 ohms and is
considered to be one cabinet.

Connection

For One Cabinet

For Two cabinets

4 ohm jack

One 4 ohm cabinet

Two 8 ohm cabinets

8 ohm jack

One 8 ohm cabinet

Two 16 ohm cabinets

16 ohm jack

One 16 ohm cabinet

3. OUTPUT TUBES – Matched set of EL84 tubes

4. PREAMP TUBES – 12AX7/ECC83 tubes

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TUBE REPLACEMENT

Precautions:
Always unplug the amplifier and allow the tubes to cool completely before
touching them.

The AC25 is designed with cathode biasing. This means bias adjustments are
not necessary when replacing tubes. When purchasing EL84 output tubes, be
sure to purchase matched quads and replace all four together. Also, for
maximum tube life, request a set with “lower plate current”.

When to replace tubes:

Preamp tubes such as 12AX7 will generally last for many thousands of hours but
occasionally problems can development before they “wear out”. If you hear crackling,
popping, humming, ringing, or other strange noises, try replacing your preamp tubes
one at a time. This may resolve the problem. Preamp tubes can be replaced
individually at any time without any adjustment.

Output tubes usually have a shorter life. They will often start to sound bad long before
they fail. If you notice that your amp is gradually losing volume, headroom or “punch”,
or if you notice that low notes are sounding a little “flabby”, it might be time for a new
matched set of high-quality output tubes. This could happen after a several months or
it might take several years depending on how much the amp is played.
Similar symptoms can be caused by a worn-out speaker so be sure to try the amp on
another cabinet to be sure.

Sometimes an output tube will fail before it “wears out”. A tube failure will usually
result in blown fuse. If you find a blown fuse in your amp, the most likely cause is a
bad output tube. If your amp is blowing fuses, try a new matched set of output tubes.
Always use the correct fuse rating.

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LIMITED WARRANTY – Valid in USA and Canada only

Andrews Amp Lab Inc. warrants this product to be free of defects in materials and
workmanship for a period of five (5) years from the original date of purchase to the
original purchaser. For subsequent owners, the length of warranty shall be for a
period of 1 year from the original date of purchase. During the warranty period, in the
unlikely event that a defect occurs, Andrews Amp Lab will at its discretion, repair or
replace the product at no charge to you for parts or labor. You must provide a copy of
the original purchase receipt in order to receive warranty service.

What is covered:

• All components other than vacuum tubes and footswitches are covered for the

periods listed above.

• Vacuum tubes and footswitches are covered for a period of 90 days from the

original date of purchase.

What is not covered:

• Any damage due to abuse, accident, improper AC power, lightening, AC power

surge, flood, moisture, rain, solvents and other liquids, fire, smoke, improper
connections, improper bias adjustment, improper service, defective tubes not
installed Andrews Amp Lab or it’s authorized agent or normal wear and tear

• Any amp with altered, defaced or removed serial numbers

• Any product that has been altered or modified in any way not authorized in

writing by Andrews Amp Lab Inc.

• Andrews Amp Lab Inc. shall not be liable for any consequential and/or

incidental damages.

How to obtain warranty service: Contact Andrews Amp Lab to arrange for service by
calling 770-671-0485 or e-mailing [e-mail] or check the web at
andrewsamplab.com or andrewsamps.com for the latest contact information. After
confirming warranty status, send or bring your amp to the location specified. If
shipping, you are responsible for the cost of getting the amp to us and we will pay the
return shipping costs.

Copyright 2018 Andrews Amp Lab Inc. All Rights Reserved