twoBIAS Adjust and BIASFine Adj. potentiometersapply to allfour power tubes.Idle
currentvariesfromtubetotube.Selectedtubesetswithmatchingidlecurrentmustbe
installed to adjust bias properly. The permissible range for every tube is roughly 25
milliamperes(minimum)to33milliamperes(maximum),whichisequivalentto12to16
wattsanodedissipationpertube.
Beforeadjustingbias,thecorrecttubetype(6L6GCorEL34)mustfirstbeselected.The
selector must be used to do this before the power amp is activated via the Standby
switch. The secondstep isto adjust biascoarsely usingthe BIAS Adjust control. Tothis
end, the tube's idle current must be checked by pressing the corresponding button.
The LEDs light up only when one of the four buttons is pressed. If none of the three
LEDs illuminate despite having pressed a button, this tube's bias is well outside the
currently adjusted range. The Adjust BIAS control selects the correct range. To this
end, the button is pressed and held while the control is slowly rotated clockwise or
counterclockwise until the green LED lights up. The BIAS Fine Adj. control serves to
fine-tune the setting, if necessary. All four power tubes should operate within the
permissible range (as described in point 5 above), otherwise this can result in
unbalanced signals (when using unselected tubes with different characteristics),
transient distortion (when bias is too low), or anode plate overheating (when bias is
toohigh), which shortens tubelife.BecauseLEDscannotindicate idle current withthe
accuracy of a measuring device, I recommend that the technician checks bias by
measuringthe cathode resistor's voltage drop or at theindividualtubesocketsusinga
tubecheckadapterwhenservicingtheamp.
A great deal of effort went into tuning this tremendously versatile amp head; I
devoted particularly painstaking attention to the details: The Clean and Crunch
channels are matched so that their Gain rangesoverlap somewhat;the samegoes for
and . This is intentional, and serves very sensible sound-sculpting
purposes. For instance, higher Gain settings (in the 12-to-3 o'clock range, depending
on pickups) push the Clean channel into moderate overdrive, and activating Gain
Boostpropelsthischannelintothedirtzonethatmuchearlier.Thismeansyoucanuse
thischannelforultracleanchordwork,jazz-stylecompingandcluckingchicken-picked
lead lines. And courtesy of that typical tube overdrive, it means the same channel is
great grittier riffs and leads, with the amount of dirt hinging upon how hard you
attackthestrings.Ifyouaddtheguitar'svolumeknobtothesonicequation, yougeta
vast spectrumof fine tonal distinctions injust this one channel. The same goes for the
Crunchchannel:Itsspectrumrangesfromclean(whenGainissetnohigherthanabout
10 o'clock, depending on pickup) to fat, wooly, and warm tube overdrive at higher
Gain settings. High-output pickups such as humbuckers will even serve up enough
oomph for punchy leads. Though these application areas overlap somewhat, the
Crunch and Clean channels are voiced differently. Crunch features an additional
triode, making it a tad more dynamic and eliciting a slightly different frequency
response.Whenusedincombinationwithhigh-outputpickups,Irecommendthatyou
roll off the bottom-end (and give a wide berth) a touch to forestall
low-endmud.
A few words from the designer on your ENGL Special Edition Amp's sounds
andsettingsaswellassomepracticaltips:
Lead I Lead II
Mega Lo Punch
OntheSubjectofSoundsandSettings
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