Using Power Scaling
When an amplifier is turned up to ‘full volume’ the tone will contain both pre-amp and power amp
distortion. The amount of each will depend on the output of the instrument and the design of the
amplifier. Breakup/distortion from the output tubes in the power amp is smoother and richer than
pre-amp breakup/distortion.
In many situations the amplifier can be too loud and Master Volume controls are typically used to
control the final speaker volume. In such a case the breakup/distortion you hear may just be from
the pre-amp.
Power Scaling allows the output tubes to distort when the output is reduced by the Master Volume
thereby allowing output distortion at any speaker volume.
As you turn the Power Scaling control down towards ‘1’ (anti-clockwise) it changes the response of
the power amp and the output tubes will become increasingly easy to distort by the signal from the
pre-amp. At a low Volume setting and high MV setting the distortion will be primarily output tube
but as you increase the Volume the pre-amp will begin to distort and so you add pre-amp distortion
to the output tube distortion.
If you consider that the equivalent of ‘full volume’ on the stock amp is:
Volume=12
MV=12
Power Scale=12
then to get ‘full volume’ distortion at a lower volume you would have:
Volume =12
MV set less than 12
Power Scale set less than 12.
However, varying the Volume, Master Volume and Power Scaling controls to balance the pre-amp
and output tube distortion can give you a wide variety of tones including the tone you would get if
everything was wide open (less any speaker distortion of course).
e.g. as with any Master Volume amplifier you can just turn up the volume to get a level of pre-amp
breakup/distortion and then vary the Master Volume to get the volume you need and this may or
may not create distortion in the output tubes i.e. if the MV is turned down to reduce the speaker
volume you may have no output tube distortion.
