VAC PA100/100 POWER AMPLIFIER
Operating Instructions
DO NOT OPEN THIS UNIT - NO USER SERVICEABLE PARTS INSIDE. DO NOT
REMOVE THE BOTTOM PLATE. LETHAL VOLTAGES ARE PRESENT WITHIN
THE CHASSIS. DO NOT EXPOSE TO MOISTURE OR OPERATE IT IF WET.
VACUUM TUBES BECOME HOT ENOUGH TO CAUSE SERIOUS BURNS. NEVER
TOUCH A TUBE WHEN THE UNIT IS ON. IT MAY TAKE SEVERAL MINUTES
FOR THE TUBES TO COOL DOWN AFTER THE UNIT IS SWITCHED OFF.
DO NOT PLUG INTO AC UNTIL ALL CONNECTIONS ARE COMPLETED.
Introduction
The VAC PA100/100 is a single chassis wide-band low-feedback stereo
amplifier conservatively rated at 100 watts per channel. It is to be operated only
from the voltage visible on the configuration card located under the fuse. Please
contact VAC or your dealer if the voltage in your area does not agree with the
label. The fuse is a slow blow type of the size noted on the back of the chassis.
A tube cage is available as an option.
The input circuit of the PA100/100 is derivative of the Williamson design, which
was first published in England in 1947, and was the mainstay of the original
high fidelity movement. Notable features of this circuit include a direct-coupled
input amplifier and phase splitter, resulting in low phase shift, and inherent
precise balance of the phase splitter (if properly executed) at all frequencies and
levels, resulting in excellent push-pull balance, stability, and low distortion.
The output stage is derived from the renowned PA90C, featuring individually
adjustable "fixed-bias" and partial-triode ("ultra-linear") operation.
Premium parts are employed throughout, including 14 pound 22 section bifilar-
wound ultra-wideband output transformers, polypropylene and polystyrene
signal capacitors, high current rectifiers, low ESR power supply, and
proprietary wiring. The quality of parts and careful layout allows the use of very
little feedback for high sonic purity and low distortion.
