Invader MKII User's Manual Aiken Amplification, Inc. 1225 Montague Avenue Greenwood, SC Tel: 864-993-8383 http://www.aikenamps.
Contents Getting Started.....................................................................................................3 Front Panel Controls and Switches...................................................................5 Rear Panel Controls and Switches....................................................................8 Tube layout and replacement...........................................................................10 Biasing.....................................................................
Getting Started Congratulations on purchasing your new Aiken Invader MKII amplifier! The Invader MKII 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. to provide a wide range of tones from any guitar, using single-coil or humbucking pickups.
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 (2-EL84 model) or 30W (2-EL34 model) into 4, 8, or 16 ohms resistive load.
Front Panel Controls and Switches Input jack: Plug your guitar in here and you are ready to rock! 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.
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.
Power switch: The Power switch turns the amplifier on in the up position and off in the down position. Glory switch: What good is power without the glory? The Glory 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.
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: operation. 2A slo-blo for 100V/120V operation, 1A slo-blo for 200V-240V 30W amplifiers: 3A slo-blo for 100V/120V operation, 1½ A slo-blo for 200V-240V operation. AC Mains voltage selector: Set this switch to the appropriate position to match the mains voltage in the country in which you are using the amplifier.
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 must be loosened before adjusting the screwdriver-slot control.
Tube layout and replacement The Invader uses four ECC83/12AX7 tubes, one ECC81/12AT7 tube, and two 6BQ5/EL84 output tubes (or two EL34 tubes in the 30W version). 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.
Output power reduction by using 6V6 tubes (30W models only): It is possible to reduce the power of the 30W Invader to around 18W to 20W by changing the two EL34 output tubes to 6V6 tubes. The amplifier will need to be rebiased before using, to insure the tubes are running at a safe idle current . In order to familiarize yourself with the biasing procedure, you should read the next section on biasing before making this change.
Biasing Biasing is very easy, and doesn't require removing the chassis from the cabinet. You simply use a voltmeter (any inexpensive digital multimeter will do), set it for the smallest DC voltage range (typically 200mV). Then: (1) Unplug any guitar cords going into the input jack. Turn the two volume controls all the way down (other control positions don’t matter). Unscrew the lock nut on the bias pot on the rear panel, and turn the bias control all the way down (counterclockwise).
Speakers Changing speakers is like getting a whole new amp. Every model sounds completely different, some sounding quite good and some amazingly bad. The amplifier is particularly suited for use with Celestion loudspeakers, which give the characteristic "British" sound this amplifier is designed to create. Celestion Greenbacks have less volume and a dip in the mids, which makes them nice and smooth.
Troubleshooting Pilot lamp not lit: Is the amplifier plugged into a functional outlet of the appropriate voltage? Is the mains fuse blown? If so, replace with the appropriately rated fuse. If the fuse again blows, the amplifier may have a shorted output tube or rectifier tube. Replace the tubes and fuse, and power the amplifier up again. If the fuse still blows, the amplifier will need to be serviced. Pilot lamp lit, but no sound: Is the HT fuse blown? If so, replace with the appropriately rated fuse.
Humming or buzzing noise: Unplug the guitar cord from the input and unplug any cable used for jumpering the two inputs. If the buzzing stops, try replacing the cord. Be sure to use only guitar cables, not unshielded speaker cables! If in doubt, unscrew the connector and look to see if there is a shield around the center connector. Some smaller speaker cables are easily mistaken for guitar cables. Fluorescent lights and light dimmers can be a source of hum/buzz, as can computer monitors.
Ringing noise or feedback that occurs with no guitar plugged in: If the amplifier exhibits a "ringing" noise, especially when tapping on the chassis, or if it makes a howling or whistling feedback noise when the volume is turned up but no guitar is plugged in, there is probably a microphonic tube in the amplifier, likely in the first position (the small tube closest to the input jacks), or in the reverb recovery position. Remove the shield and lightly tap on the tube with the volume turned up.
Specifications Output Power: 18W for the 2-EL84 model or 30W for the 2EL34 model, at onset of clipping into resistive load at rated impedance. Input Impedance: 1Megohm Input sensitivity: 10mV for output clipping, all volume/tone controls fully up, ali mode. Tube complement: Four ECC83/12AX7, one 12AT7, two EL84 (18W model), or two EL34 (30W model).
