Power
Scaling allows you to produce a cranked amp sound
at much lower volumes, and also extends power tube
life and amp reliability. It even saves your hearing,
allowing you to enjoy compressed or distorted amp
tones for your entire life without disturbing
your neighbours! For more information on Power
Scaling, see
our Power Scaling FAQ
and the description of the other PSK
Power Scaling Kits.
The
Power Scaling Box (PS-Box) provides
all of the performance benefits of PSK
Power Scaling Kits in a convenient, easy to install,
pre-assembled, pre-tested form. It is intended
as an add-on to existing amps where no drilling is
preferred. For new construction, the original PSKs
should be used.
This
pre-assembled unit requires the same skill to install
as the PSKs. Installation
time is about the same as the PSKPC, but a
bit shorter than the PSK-1 where you make your
own cards.
PS-Box
can be added to any cathode-biased or fixed-biased
guitar amp up to 160W, with a supply voltage less
than 600Vdc, with or without a tube rectifier. In
cathode-biased amps, i.e., AC-30s and similar, PS-Box
provides a bias supply of its own, making it possible
to add fixed-to-cathode-bias switching using the techniques
from TUT2.
To
allow for individual bias adjustments for each output
tube, install the appropriate BMK
Bias Mod Kit to the amp, using the PS-Box
violet lead as the bias source. In higher-power amps
(100W+) and hot-running amps, it is recommended that
a 12Vdc fan be added, which can be powered from the
fan power supply jack on the PS-Box. Note:
the fan supply is filtered adequately for a fan and
is NOT intended to power pedals or other devices.
PS-Box
is designed for a "no holes" installation in vintage
amps or any stock amp head or combo. The box mounts
on an inner wall of the amp cabinet, wired into the
amp through any existing grommeted hole. A small board
is mounted inside the amp, to provide filtering for
non-Power Scaled circuits.
Lead-out
from either end of the PS-Box is possible,
as each end has a wire entry point. For example, in
a Marshall-style head, PS-Box is mounted on
the roof of the wooden amp sleeve, with the leads
coming out the right-hand end (left-hand upside down)
looking from the rear. In a Fender amp, PS-Box
will mount on the left-hand wall (combo amps) or on
the floor (heads) of the wooden amp sleeve, with the
leads coming out the left-hand end, looking from the
rear. A piece of split-extrusion cable covering is
included, which is easily cut to length, to protect
the wires running between the amp and PS-Box.
The
single Power Scale control is on the box, so
PS-Box becomes your "secret weapon" concealed
in the back of your amp.
In some applications, it is advantageous to incorporate
the Drive Compensation control (included) to keep
the output stage from distorting excessively. This
control is best added to the amplifier chassis as
it handles audio signals. This two-control approach
to Power Scaling affords the greatest versatility
of tone and distortion textures.
Some automatic limiting of output stage distortion
occurs if more than just the output stage is Power
Scaled. In this case, the Drive Compensation control
can be wired like a conventional master volume for
fine adjustment of compression/distortion effects.
Scaling more circuitry allows single-control over
power and loudness, but ultimately reduces the amount
of distortion possible - the counter-intuitive result
also obtained using a "variac".
The PS-Box notes outline all of these options,
and the Drive Compensation control is provided as
a loose part.
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