Aiken Amplification Invader User manual

Invader
User's Manual
Aiken Amplification
1225 Montague Avenue
Greenwood, SC 29646
Tel: [phone]
http://www.aikenamps.com

Contents
Contents...............................................................................................................2
Getting Started.....................................................................................................3
Front Panel Controls and Switches...................................................................5
Rear Panel Controls and Switches....................................................................8
Tube layout and replace ent...........................................................................10
Biasing................................................................................................................11
Speakers.............................................................................................................12
Troubleshooting................................................................................................13
Specifications....................................................................................................16
InvaderManual.doc 12/08/11 Page 2 of 16
Copyright 2000 2011, Aiken Amplification, Inc.

Getting Started
Congratulations on purchasing your new
Aiken Invader amplifier!
The Invader is an all tube amplifier,
available in 18 or 30 watt versions. This
amplifier is truly touch sensitive, going from
clean to crunch to singing leads by just
adjusting the volume control on the guitar.
The 4 input design allows jumpering of the
two channels, which are independently
voiced, to provide a wide range of tones
from any guitar, using single coil or
humbucking pickups.
The amplifier was designed specifically to
capture those old plexi/ali/bassman tones at
less than ear shattering volumes, with the
addition of a 3 knob reverb, built in
attenuator, and speaker emulating,
transformer balanced, XLR direct out.
Features include:
All tube circuit, including tube rectifier. Preamp tubes are JJ/Tesla ECC83, reverb driver is a
NOS Jan/Philips 12AT7WC. Output tubes are JJ/Tesla EL84. Rectifier tube is Sino or
Russian 5AR4/GZ34.
Front panel controls/connections: Four input jacks, a high level and low level for each
channel. Volume 1 (bright), Volume 2 (dark), Bass, Mid, Treble, Presence, Dwell, Tone,
Reverb, Attenuator. Input channels can be jumpered by connecting a cable from the lower
channel 1 input to the upper channel 2 input. This allows a mix of the two volume controls to
provide a wide range of tones, allowing the amplifier to work well with any guitar, either
single coil or humbucker. Exclusive Plexi/Ali front panel switch to reconfigure the preamp
section to early "plexi" style for a full rich tone (great for warm clean tones) or the later
aluminum, or "ali" style preamp, which is voiced brighter and tighter in the low end (best for
distortion styles).
Rear panel controls/connections: AC mains input, impedance selector switch for 4, 8, or 16
ohm operation, two 1/4" speaker jacks, XLR output with ground lift switch, reverb footswitch
jack. Also includes locking mil style bias and balance pots and three tip jacks for easy bias
setting without having to remove the chassis from the cabinet.
Solid, finger jointed pine cabinet. The 2x10 and 1x12 combos are 25 1/2" wide, 21" tall, and
9 1/2" deep. The 2x12 combo is 29" wide, 21" tall, and 9 1/2" deep. The head is 25 1/2" wide,
10 1/4" tall, and 9" deep.
.090" aluminum chassis with welded seams, ground smooth for a flawless appearance.
White powder coated for durability.
Turret board construction, using silver plated Teflon wire and chassis mounted ceramic tube
sockets for ease of maintenance and reliability. Built to last.
Premium, tight tolerance parts are used for reliability, including 2W 1% metal film resistors,
630V axial leaded polypropylene film/foil capacitors, and low noise, sealed, 2W conductive
plastic mil style RV4 pots.
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Copyright 2000 2011, Aiken Amplification, Inc.

Massive, custom wound, high interleave transformers, rated for over twice the maximum
amplifier output power, allowing the amplifier to be run full power into an attenuator
continuously, without failures.
Output power (at onset of clipping): 18W (or 30W for 4 EL84 models) into 4, 8, or 16 ohms
resistive load.
Built in power attenuator with 0dB, 3dB, 6dB, 9dB, 12dB positions, as well as a REC (
15dB) position for low volume recording, or apartment/bedroom volume practicing. Perfect
for studio or club use. This is actually a true attenuator, working between the output
transformer and speakers, functionally similar to some of the current attenuators on the
market.
Reverb: 3 knob spring reverb with level, dwell, and tone controls. Footswitch jack for on/off
control accepts any standard grounding type footswitch (not included).
Available with two 12" speakers, a single 12" speaker, two 10" speakers, or in a head
configuration. A wide variety of speakers are available, including Celestion, WeberVST,
Jensen, Eminence, and others. Extension speaker cabinets are also available.
Speaker emulating, transformer balanced XLR direct out for recording or stage use.
Designed to emulate the frequency response of a 4x12 cabinet miked with an SM57.
Complete with ground lift switch to eliminate hum problems. Output level is approximately
20dBu at onset of clipping. Consumer type recording gear which only accepts 40dB mic
level inputs may require an inline 20dB or 30dB pad to properly interface and avoid input
overload. Output level is independent of attenuator setting, so the FOH mix level doesn't
change when changing attenuation settings, which means the sound man doesn't get mad at
you for changing stage volume with the attenuator!
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Copyright 2000 2011, Aiken Amplification, Inc.

Front Panel Controls and Switches
Input jacks:
Channel 1 is voiced bright, channel 2 is voiced much darker. The upper inputs are higher
gain than the lower inputs for each channel. You can jumper the channels by plugging
into channel 1 upper input and connecting a patch cord from channel 1 lower input to
channel 2 upper input. This allows you to mix the two volume controls for the desired
balance of bright/dark tones, and is very useful for tailoring the tone to your needs. The
two volumes act as a second set of pre preamp tone controls when used in this manner.
For cleanest tone, plug into the lower jacks of each channel.
Plexi/Ali switch:
This switch configures the preamp section to match either the warmer early
"plexi/Bassman" style preamp circuits or the later and brighter "aluminum panel" circuits.
For full volume output stage distortion/crunch tones, the plexi/ali switch is usually best put
in the "ali" position, as this cuts some of the low end and adds a bit more gain and
midrange boost on the second stage. Too much low end can sound "boomy" or "mushy"
when playing wide open. The plexi setting is warmer, with more low end, and excels for
clean tones or for fattening up bright single coil pickup guitars, such as Telecasters.
Because the plexi/ali switch completely reconfigures the preamp circuitry, it can produce
an audible "pop" or "thump" when switching. It is recommended that the volume controls
be turned down before changing modes.
Volume :
Volume 1 is the "bright" channel volume control.
Volume 2:
Volume 2 is the "dark" channel volume control.
Treble:
The treble control adjusts the high frequency equalization.
Middle:
The middle control adjusts the midrange frequency equalization.
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Copyright 2000 2011, Aiken Amplification, Inc.

Bass:
The bass control adjusts the low frequency equalization.
Dwell:
The dwell control adjusts the drive to the reverb tank. Higher dwell levels result in an
apparently "longer" decay time of the reverb. The dwell control also allows adjustment of
the proper drive level when playing clean or distorted. Distorted settings typically require
a much lower dwell level than clean settings, as there is more drive to the reverb tank
when the volume control is increased. A good "rule of thumb" is to back off on the dwell
as the volume is turned up, unless you want a very deep "surf" reverb.
Tone:
The tone control adjusts the tone of the reverb signal. Counter clockwise rotation
produces a darker tone, and clockwise rotation produces a brighter tone. It is best
adjusted by hitting a chord and quickly muting the strings to listen to the decay of the
reverb "tail". The tone control can then be adjusted to taste for a darker or brighter
reverb.
Reverb:
The reverb control adjusts the amount of reverb added to the main signal. The reverb
circuit is a parallel mix circuit, so the dry path is not affected by the signal, and the reverb
is completely out of the circuit when the control is turned fully off.
Presence:
The presence control adjusts the high frequency equalization in the output stage. It is a
"shelving" control that operates by cutting the amount of high frequencies in the global
negative feedback loop, which results in a boost in the output high frequency range and a
subjectively "brighter" and more "open" tone in the highs due to the lower negative
feedback at those frequencies. Note that a small amount of noise during rotation of the
presence control is normal, and is due to a small DC voltage present on the control. This
was deliberately done, in keeping with the "old style" presence control circuitry.
Attenuator:
The attenuator controls the overall output level, and allows turning the amplifier up to get
full volume overdrive tones at lower volumes, without sacrificing tone quality. This
approach avoids the "buzzy" sound characteristic of master volume amplifiers. The
attenuator features 0dB, 3dB, 6dB, 9dB, and 12dB positions, as well as a REC (
15dB) position for low volume recording or bedroom/apartment practicing. It is okay to
switch the attenuator to different settings with the amplifier on, but it is recommended to
not be playing while changing positions, because a rotary switch, such as that used in the
attenuator, will have a small fractional amount of time where there is no connection at all
during the switching process. While we have never seen an output transformer or tube
damaged by this, it is remotely possible that the transient may cause a problem, so it is
not recommended. Before changing positions, just stop playing for a second, change to
the different attenuation level, and continue playing.
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Copyright 2000 2011, Aiken Amplification, Inc.

Pilot lamp:
The pilot lamp lights when power is applied to the amplifier and the power switch is on.
Standby switch:
The standby switch allows muting of the amplifier output when not in use. When the
switch is in the up position, the amplifier is on, and when it is in the down position, the
amplifier is on standby. The tube filaments remain on and warmed up, so the amplifier is
ready to play as soon as it is taken off standby. The correct powerup sequence is to turn
the amplifier on with the power switch and then, after it has had time to warm up, the
standby switch is turned on. When turning the amplifier off, the standby switch should
first be turned off, then the power is turned off after a few seconds.
Power switch:
The power switch turns the amplifier on in the up position and off in the down position.
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Copyright 2000 2011, Aiken Amplification, Inc.

Rear Panel Controls and Switches
AC Mains:
Plug the supplied IEC mains cord into this outlet to provide power to the amplifier.
Mains Fuse:
18W amplifiers: 2A slo blo
30W amplifiers: 3A slo blo
Note: the silkscreen on the back of the amplifiers reflects the original 1A designation and
should be ignored – use the above recommended fuses to prevent “nuisance” fuse
blowing from turn on surges.
HT Fuse:
500mA fast acting fuse
Impedance Selector:
The impedance selector allows selection of 4, 8, or 16 ohm output impedance to match
the speaker in use. Be sure to set this switch to the appropriate setting for the speaker or
speakers connected to the amplifier. All amplifiers are shipped from the factory with a
single 16 ohm speaker or a pair of speakers wired in series to provide a 16 ohm load.
This allows connection of an external 16 ohm cabinet to be used simultaneously with the
internal speaker by setting the impedance selector to 8 ohms, or four 16 ohm cabinets
can be used by setting the impedance selector to 4 ohms.
Speaker Jacks:
Two speaker jacks are provided to allow use of the amplifier with either the internal
speaker (combo units only) or up to two external speaker cabinets. More than two
external cabinets may be safely used with the amplifier, but this will require the use of "Y"
cables for the extra two cabinet connections. Be sure to use only quality speaker cable
do NOT, under any circumstance, use guitar cable to connect the amplifier to a speaker
cabinet. Doing so may cause damage to the amplifier.
Balanced Line Out:
The balanced line out contains speaker emulation circuitry that is designed to emulate
the response of a miked 4x12 speaker cabinet. It allows direct to board operation in live
or recording settings without the use of a microphone. The emulator circuitry is tapped
off before the attenuator, so the attenuator level does not affect the line out level. The
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Copyright 2000 2011, Aiken Amplification, Inc.

speaker emulator usually sounds best at louder settings on the attenuator, because of
the interaction between the speaker and the amplifier, which results in a more natural
tone. A bit of equalization may be required on the board, typically a midrange cut or bass
boost, for the most natural tone, especially at lower attenuation settings. It may also be
necessary to cut frequencies above 4kHz –5kHz to tailor the high frequencies to your
liking.
The output level of the XLR at onset of clipping is around 20dBu. Some consumer
grade boards and recording devices won't handle line level balanced signals, and require
an inline line to mic level pad of approximately 25dB to avoid overloading the front end
and causing clipping distortion. These can usually be found at music stores or can be
ordered online.
Ground lift switch:
The ground lift switch disconnects the XLR out from the chassis ground, and is used
whenever there is a ground loop hum when the XLR output is connected to a mixing
board. The switch should be tried in both positions, and left in the position that has the
lower hum level.
Footswitch:
This jack allows connection of any standard footswitch to remotely turn on the reverb on
and off.
Bias Test Jacks:
Three standard tip jacks are available to allow easy bias current measurements without
removing the chassis. Refer to the section on biasing for instructions on the use of these
jacks.
Bias:
A locking mil style RV6 trimpot is provided to allow adjustment of bias current. The outer
locknut should be loosened before adjusting the screwdriver slot control. Refer to the
section on biasing for further instructions.
Balance:
A locking mil style RV6 trimpot is provided to allow adjustment of bias balance. The
outer locknut should be loosened before adjusting the screwdriver slot control. Refer to
the section on biasing for further instructions.
InvaderManual.doc 12/08/11 Page 9 of 16
Copyright 2000 2011, Aiken Amplification, Inc.

Tube layout and replacement
The Invader uses four ECC83/12AX7 tubes, one ECC81/12AT7 tube, and two 6BQ5/EL84 output
tubes (four EL84s in the 30W version). It also uses a single 5AR4/GZ34 rectifier tube.
The preamp tubes are housed in removable "bayonet" metal shields. The shields can be
removed by pushing down on them and rotating the shield to the left, then pulling it upwards off
the tube. The tube can then be pulled out of the socket. The output tubes have spring wire
retainers that can be slipped off to one side, allowing easy removal of the EL84 tubes.
The preamp tube function is as follows, starting at the side closest to the input jack: preamp 1
(12AX7), preamp 2/cathode follower (12AX7), reverb driver (12AT7), reverb recovery (12AX7),
and phase inverter(12AX7). The chassis top view layout is shown in the diagram above.
You may freely sub any 12xxx type tube in the two preamp and phase inverter positions. It won't
hurt anything, and you may find some different tones you like. The 12AU7 is a good lower gain
tube, as is the 5751. Other choices are 12AY7, 12AT7, or 12AZ7. In addition, different
manufacturer's tubes will sound different. Some people prefer the tone of various Ei, Sovtek, or
other tubes, and some insist on NOS tubes for a true vintage tone. Feel free to experiment!
The 30W model may be safely operated with either the two inner or the two outer EL84 tubes
removed for half power operation. It is recommended that the rear panel impedance selector be
set to the next lower setting (i.e. 8 ohms when using a 16 ohm speaker), but it won’t hurt anything
if you forget to do this.
Note: vacuum tubes, especially output tubes, can get very hot in normal operation, and may
cause burns if removed before they have a chance to cool down. Be sure to wait several minutes
before replacing tubes to allow them to cool down. Do not, under any circumstances, remove or
replace the tubes with the power on, as this could cause a deadly electrical shock should the
glass break, exposing the high voltage plate terminals. Also, be sure to pay attention to the
orientation of the tubes when putting them back in the socket. The tube pinout is keyed so it can
only be placed in the socket in one direction, and if the tube is forced in incorrectly, it can damage
the tube or the ceramic socket. The octal rectifier tube has a phenolic key that fits a
corresponding keyhole in the socket. If this key is broken off, it will allow incorrect placement of
the tube in the socket, which could result in damage to the amplifier. Be sure to carefully
examine the tube before replacing it.
InvaderManual.doc 12/08/11 Page 10 of 16
Copyright 2000 2011, Aiken Amplification, Inc.