andrews Para-Dyne 20 User manual

OPERATION MANUAL
Head and Combo
11/03/2012

2

3
Thank you for purchasin an Andrews Amplifier. The Para-Dyne
TM
name is derived from the two-channel dynamic tone of the amp. As
with all Andrews amps, these models are built to the hi hest
standards of craftsmanship and are finely tuned for the ultimate
tone. This manual will help you to et the most from your new amp.
Please feel free to contact us with any questions at
andrewsamps.com

4
FEATURES;
• 2 CHANNELS OF ALL-TUBE TONE - Selectable by front panel or footswitch,
Channel One provides those classic warm yet sparklin clean tones and is a
perfect platform for pedal boards while Channel Two ives you a wide ran e of
smooth, sustainin overdrive lead tones.
• OPTIONAL BUFFERED SERIAL EFFECTS LOOP – See the rear panel explanation
for more information. If effects are to be used on the lead channel at hi h ain
settin s, the optional effects loop is recommended.
• HAND-WIRED CONSTRUCTION – Also sometimes called “point-to-point” wirin ,
the Para-Dyne amps utilize a very hi h quality turret board made of super-tou h
G10 composite. This lass-epoxy laminate is specified for its extremely hi h
stren th and hi h 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 wirin and solderin is done by hand and quality-
checked 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 hi h reliability. Output impedance is switchable to 4,
8 or 16 ohms and 2 speaker jacks are provided.
• CUSTOM DESIGNED CHASSIS – Our durable welded steel chassis is desi ned
specifically for our amp models so that every part can be mounted in the optimal
location for lowest noise and hi hest stability.
• CUSTOM DESIGNED CABINET – Our cabinets are specially desi ned for
maximum durability and superior tone. We use hi h- rade birch ply for our
cabinets. The cabinet components are precision cut usin hi h-tech equipment
and are hand assembled with care. Dovetail or fin er joints are used at the
corners for maximum stren th.
• SELECTABLE OUTPUT POWER LEVELS – A “triode/pentode” switch is provided
to allow the output power to be reduced about half the rated output for those
situations when you want a little less volume without sacrificin tone.
• EXTERNAL BIAS TEST POINTS – The Para-Dyne amps are equipped with
external bias test points and an externally accessible adjustment control. This
makes output tube replacement fast and economical. In fact, with a low cost
multi-meter you can adjust bias yourself. This can be a real advanta e in case of
a tube failure durin a performance or recordin session. See the section about
the rear panel for more information.

5
Warnin s and Precautions
Durin operation, vacuum tubes can reach temperatures over 400 de rees F. Do
not touch hot tubes. Insure plenty of ventilation behind the amp. Keep the amp
away from curtains and other flammable objects and children.
Do not expose your amplifier to rain. Never set any cups, lasses, 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 dama e may
occur. See the section about the rear panel features for more information.
Make sure the amplifier is always properly rounded. Never remove or defeat
the round pin from your power cord. Always unplu the amplifier before
chan in tubes or fuses.
Use only correctly rated fuses. See the rear panel and this manual for proper
fuse ratin s.
This amplifier can create hi h sound pressure levels. Please use proper hearin
protection and/or maintain an adequate distance from the amplifier to avoid
hearin dama e.
Tube amps contain lethal volta es (even when unplu ed). There are no fuses
or other user serviceable parts inside. Please refer servicin to qualified service
personnel.
Never insert any tool or other object into ventilation holes, tube sockets or other
openin s unless instructed to do so in this manual. Otherwise, you may come
in contact with dan erous hi h volta es inside the chassis.

6
Front Panel
1. INPUT JACKS – For maximum versatility, we have provided two input jacks
(labeled I and LO). The I jack provides a bit more drive and sensitivity. The LO
jack provides a slight 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 of the clean
channel. When not using the footswitch, pull this knob to select the clean channel.
When using the footswitch, keep this knob pushed in.
3. BRIGHT SWITCH – This three position switch is used to adjust the balance of
brightness (treble) between the clean channel and the overdrive channel. Moving
the switch to the down position will remove brightness from the clean channel
without affecting the overdrive channel. The middle position provides a more
neutral brightness balance and the upper position will add additional brightness to
the clean channel.
4. DEPTH CONTROL – The DEPT control adjusts the depth of the bass for the
clean channel. Use it in conjunction with the bass control to balance the bass
response of the clean channel vs. the lead channel. In general bass and/or depth
should be turned up for playing at lower volumes and down for higher volumes.
5. GAIN CONTROL – This is for adjusting the gain or overdrive of the lead
channel. It is used in conjunction with the MASTER VOLUME control.
6. TREBLE CONTROL - This control varies the amount of treble and is effective
on both channels. Note that the tone controls are interactive. The treble control’s
adjustment range is widest when the MIDRANGE control is not turned up too high.
7. MID CONTROL – The MID control adjusts the midrange frequency levels for
both channels. Keep the setting low for vintage American tones. Turn it up for a
warmer tone with increased sustain.
8. BASS CONTROL – This control varies the amount of bass on both channels.
Use in conjunction with the DEPT control to balance between the two channels.
In general, it is suggested to increase the bass setting as volume is decreased to
compensate for the way the human ear hears bass at different volume levels.
Bass is generally turned down at high volume settings to keep the low end “tight”.

7
9. MASTER VOLUME CONTROL – Use the MASTER VOLUME control to
adjust the loudness of the amp when using the lead channel. Try setting it a little
louder than the clean channel and switching to the lead channel for solos. For
practicing at low volume, the control is designed to maintain a great overdrive tone
when turned down. See additional notes below.
10. 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 one minute 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 quiet the amp and stop the plate current from flowing in the tubes, resulting in
longer tube life.
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 several hours or
more.
12. 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. The lens thread fits many standard lamp lenses and “jewels” allowing you to
customize the color if you desire.
Adjustment su estions –
• Try adjusting the tone controls on the overdrive channel first. After achieving
your desired settings, switch to the clean channel. Use the BRIG T and
DEPT switches to balance the lows and highs with the overdrive channel
depending on your guitar, effects and volume settings.
• When playing the amp at high volume, for example when the MASTER
VOLUME is turned up high or when the clean volume is turned up high, a richer
sound is achieved with more apparent bass. It is normal for the tone controls to
be a bit less responsive in this state since additional harmonics are created in
the output stage after the tone controls. The TRIODE/PENTODE switch on the
rear panel can be used to drive the output tubes at slightly less volume.

8
Rear Panel
1. FUSES – Always use correctly rated fuses or severe damage to the amp may
occur. Refer to the rear panel for fuse ratings. Always unplug the amp before
replacing any fuses. When installing a new V 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. The main AC fuse is located
in the AC cord jack. Use a small screwdriver to remove the fuse holder.
2. TRIODE/PENTODE SWITCH – In the PENTODE position, the amp will
operate normally with full output power. In the TRIODE mode, the output power will
be reduced roughly by half. This will allow the volume controls be set higher for a
more “cranked up” tone while slightly reducing the actual volume of the amp.
Always be sure to stop playing before switching. Operating this switch while
playing could cause damage to the amp or tubes.
3. BIAS TEST POINTS AND ADJUSTMENT CONTROL – These are
provided to simplify measurement and adjustment of the idle current of the output
tubes. Bias adjustment is necessary whenever the output tubes are replaced.
See page 10 for bias adjustment instructions and precautions. The adjustment
control is located on the underside of the chassis near the test points.
4. 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. Make sure any speakers
you connect can handle more than 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 may be tight and stiff. This results in a
brighter tone with less bass 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 TREBLE control slightly.

9
5. IMPEDANCE SELECTOR – Always set this switch to the proper speaker load
according to the chart below. Note: The Para-Dyne combos incorporates built-in 8
ohm speaker loads so leave it set to 8 when not connecting another cabinet.
Settin For One Cabinet For Two cabinets
4 One 4 ohm cabinet Two 8 ohm cabinets
8 One 8 ohm cabinet Two 16 ohm cabinets
16 One 16 ohm cabinet
6. FOOTSWITCH JACK – Insert the plug from the footswitch cable here. The red
LED on the footswitch will glow when in the lead channel mode. For proper
operation, make sure the clean channel volume knob is pushed in when using the
footswitch.
7. OPTIONAL BUFFERED SERIAL EFFECTS LOOP – Use the loop for
connecting effect units such as reverb, delay, tremolo and chorus to avoid the
noise and distortion that sometimes occurs when connecting the certain effects in
the input jack if using high gain settings on the amp. Effect loops are generally not
recommended for overdrive and distortion effects.
a) Send – Connect the input of your effects chain here.
b) Return – Connect the output of your effect chain here.
c) Level – Adjusts the level of the loop signal. For best results, first try the
LOW level setting. The LOW will work best for most applications. The IG
setting may produce slightly less background hiss but is only usable for “line
level” effects and may cause distortion or volume reduction under certain
conditions, especially when the clean channel volume or overdrive channel
gain is set very high. See notes belo .
d) Bypass – To completely bypass the loop circuit and maintain a 100% tube
signal path, set this switch to the “out” position.
Notes on the effects loop – Some 9 volt “stomp box” type effects are not designed
to be used in effect loops and can not handle the levels present in the loop ithout
distortion. If your effect distorts even hen the loop is s itched to the LOW level
setting, your effect unit may not be compatible. Try upgrading to an effect that can
handle higher levels or one that runs on a higher supply voltage.

10
FOR TECHNICAL TYPES
We have provided this information for those who have a technical interest,
proper equipment and a DYI attitude. CAUTION! GUITAR AMPLIFIERS
CONTAIN LETHAL VOLTAGES. If you have any doubt about your ability to
safely perform this procedure, refer the job to a qualified technician!
Bias Adjustment Procedure:
Precautions:
• Lethal voltages are present inside the chassis and at the tube pins. Do not
open the chassis or insert any objects into any openings other than here
directed by these instructions. The entire procedure can be accomplished
ithout opening the amp.
• Vacuum tubes get very hot. Al ays allo the tubes to cool completely before
touching them.
• When replacing output tubes, use only the very highest quality tubes or the
amplifier may be damaged. For more details, see the section belo regarding
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 or spread open the retaining clips that hold the output tubes in place and
remove the tubes. Install a new matched pair of the same type of output tubes that
came installed in your amp. i.e. EL34, 6V6 or 6L6
3) Utilizing a digital multi-meter, set for DC Volts or millivolts measurement and select
a range that will show 0-100 millivolts. Insert the black meter lead into the black
test point terminal and insert the red meter lead into the 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 one minute, 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 slot and very slowly turn the adjustment until the meter reads
65mV for EL34 amps, 75mV for 6L6 amps, 44mV for 6V6 amps and 40mV for
EL84 amps. The test point shows the combined reading for both output tubes.
7) It’s a good idea to re-check the bias periodically (every 500 hours of use) as the
idle current can drift over time as the tubes age.