Peavey ReValver MK III - Page 41

The couplingcapacitor removes the high voltage DC oset from the output signal of the tube
stage. This high-pass frequency is usually between 5-10 Hz, but if it is set higher then a user can
change the tonal and dynamic properes of the stage.
The gridresistor value is an all-in-one resistor used to calculate the eects of the stage’s band pass
limitaon. Inside each tube there is an internal capacitance called “Miller capacitance.” The
greater the resistor, the lower the bandwidth. The bandwidth can be calculated at 1/(6.28*RC)
where R is the “grid resistor” and C is the Miller capacitance (usually around 150pF). In a normal
triode stage with a 12AX7 tube, the bandwidth is around 15 kHz if the grid resistor is 68 kOhm.
The slider for ClassA/B is used for pentodes in push-pull conguraon only. (The Bias voltage
slider can be used as an alternave.) This sets the bias of the tube stage such that it corresponds
more to a Class A or B stage.
Some of the non-physical tweaks:
Normally, a tube’s output swing is determined by the VPP, along with the various loads in the
cir cuit. Seng ClipLimit to something higher than 1.0 gives the circuit a greater dynamic range.
The output gets higher and the distoron on one side decreases. Clipsoness is used to smooth
out the sharp dynamic edge and gives the distoron a smooth sound.
The default value of the DynamicBiasosetamount is 1.0, and scaling this value changes the
dynamics of the signal. The signal is usually not enrely free to move through the tube, and strong
transients and high volumes aect the bias of the tube, moving up and down, as a funcon of
volume.
Cathodebiasedtrebleboost (where applicable) changes the “lter eect” that the cathode
resistor & capacitor has on the frequency response.
The Biasadjust slider simply adds or subtracts a certain voltage to or from the tube’s bias. Other-
wise, this bias is dened by the tube and its surrounding components.
Extrainputheadroom gives the stage more dynamic headroom, making the tube distort later if
given a greater headroom. For a triode this means the signal is “aenuated” before the input and
“amplied” aer the output, thus restoring the signal strength to the following tube.
The tube Tweak GUI features the following graphical displays: A “bode plot” (frequency& phase
response) an oscilloscope (with input and output signal display overlaid) and “transfer funcon”
(a snapshot of the stac input-to-output relaonship).
The whole tube component can be disabled via the Disablecircuit checkbox.
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