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VAC PA80/80 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 PA80/80 is a single chassis wide-band low-feedback stereo amplifier
conservatively rated at 80 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 PA80/80 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.
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Summary of Contents for VAC PA80/80
- Page 1 80 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.
- Page 2 The chassis and power transformers will become hot in normal use. Do not allow the chassis of the VAC components to touch any metal parts, such as the frame of an equipment rack. This might create a parallel ground path that will degrade the sound of your system.
- Page 3 Any time that the VAC Power Amplifier has not been used for a few weeks the sound may be different. This is also normal for high resolution audio equipment. Optimum sound should return after a few hours of operation, preferably with an audio signal.
- Page 4 Installing New Output Tubes Replacement tubes are available from VAC and other sources. Output tubes are KT88 beam power Kinkless Tetrodes (6550 may also be used - see Tips & Advice, Output Tubes). It is not necessary that they be matched pairs, although a slight improvement in measured performance may be achieved in this way.
- Page 5 Care of Chassis & Face Plate VAC chassis are aluminum for superior electromagnetic performance. The finish is a tough textured powder coat paint. This finish is durable but can be scratched or chipped, just as that of a fine automobile may be damaged.
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Page 6: Registration Form
This amplifier is warranted for a period of thirty (30) days from the date of purchase. In addition, if the registration card(s) is received by VAC along with a copy of your sales receipt from an authorized VAC dealer within this thirty days, a service contract will be extended to cover your equipment for two (2) years (except tubes which are covered for 90 days). - Page 7 In normal use, output tubes will last at least 2 years and perhaps more than 10 years. VAC will be happy to test tubes for concerned customers. For appropriate fees we can provide transconductance, idle current and/or a photographic record of the tube's plate family curves.
- Page 8 As with interconnects and speaker cables, each tube manufacturer's KT88 tends to have a distinct sound when used in VAC amplifiers, and of course the 6550As sound different as well. Here is a brief summary of our experiences with currently available tubes from different sources.
- Page 9 A Word About Low Level Tubes The small tubes (Voltage Amplifier/Phase Splitter and Driver) in the VAC Amplifiers are type 12AU7. This tube is essentially the same as types 12AU7A, 5814, 6189, CV4003, ECC82, and E82CC. The quality of the tube used is by far more important than which of these (equivalent) types is used.
- Page 10 The VAC implementation of the ultra-linear circuit has been selected to achieve performance quality as close to pure triode as possible while still increasing power output and efficiency.
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Page 11: Specifications
SPECIFICATIONS The VAC System has been developed with the critical ear as the major arbiter of quality, with both conventional and unique measurements providing insight and guidance as necessary. The lack of emphasis on measurements is due to the fact that engineering's arsenal of equipment and techniques do not operate on the pattern recognition principals that control human perception of sound.