VAC Phi 300 User Manual

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The VAC Phi Three Hundred

Stereo/Mono Beam Power Amplifier

300

Operation & Maintenance Information

Valve Amplification Company

Manual issued 03/15/2006

Revised 11/14/2006

PLEASE READ CAREFULLY

Your Phi Beam Power amplifier is fitted with a unique output tube monitoring circuit. Rather than
directly contacting the audio path, and thus contaminating the pure sound, the temperature of a
small cathode resistance is sensed. The four bi-color LED’s on the front panel indicate the tubes’
conditions.

If the idle current of a KT88 output tube drops below nominal limits, the LED corresponding to that
tube will light green. This indicates that either the bias setting for that tube should be adjusted, or
the tube should be replaced at your convenience, but it is safe to continue operating the amplifier.

The exact idle current of each tube may be tested by means of the meter and the test switches
located on the front panel. The associated bias control should be adjusted so that the needle
points directly at the dot in the center of the meter. When no test switch is selected, the meter
indicates the incoming ac voltage (wall voltage).

Note: These LED’s will also be green when the amplifier is first switched on, and generally will
extinguish when the bias resistors have reached full operating temperature after approximately 30
minutes. The threshold between green and no illumination is not precise; do not be overly
concerned if some positions take longer to extinguish or fail to extinguish. The precise condition
of individual tubes may be checked with the built in meter.

Note: air currents could cause the lights to remain green even in normal operation.

In the event that any output tube draw excessive idle current (a “run away” tube or a tube not
biased correctly), the high voltage supply in the amplifier will shut down automatically and the LED
corresponding to the problematic KT88 tube will indicate red. The red light will stay on until the
power switch is turned off. This tube must be replaced. (Note: The LED’s for the other tubes will
show green after a few minutes...this should be disregarded.)

To minimize difficulties, always source genuine VAC Tested audio tubes for your Phi.

CAUTION

THE AMPLIFIER AND POWER SUPPLY CONTAIN NO USER SERVICEABLE PARTS. DO NOT REMOVE THE
BOTTOM PLATES OR CHASSIS COVERS. LETHAL VOLTAGES ARE PRESENT WITHIN THE CHASSIS. DO
NOT OPERATE THE UNITS IF THEY ARE 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. IT IS STRONGLY RECOMMENDED THAT THE TUBE COVERS BE LEFT IN PLACE AT ALL
TIMES.

THE TUBE COVERS WILL BECOME HOT IN NORMAL OPERATION. DO NOT SET OR SPRAY ANYTHING
ON THEM.

THE AMPLIFIER AND POWER SUPPLY ARE HEAVY. IT IS ADVISABLE TO HAVE ASSISTANCE IN
UNPACKING, MOVING, AND SETTING UP. BE SURE TO USE PROPER LIFTING TECHNIQUES TO AVOID
BACK STRAIN AND INJURY. BE CERTAIN TO INSTALL IT IN A SECURE LOCATION FROM WHICH IT CAN
NOT FALL OR TIP OVER.

INDEX

Introduction
Unpacking & Assembly
Installation
Input connectors
Operation
Feedback
Triode & Ultra-Linear Modes
Illuminated Logo
Installing New Output Tubes
Biasing & Checking Output Tube Condition
Replacement of Low Level Tubes
Care Of Chassis
Tips and Advice

A Word About Tubes in General
Output Tubes
Low Level Tubes
Impedance Matching
Grounding

Tuning Your System
Specifications
Footnotes
Warranty & Registration Form

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INTRODUCTION

The Phi 300 is a unique power amplifier, and the most power and detailed in VAC’s history.
Featuring a new direct-coupled input & driver circuit, extremely fast and vivid sound is achieved
from both single-ended and balanced sources.

The Phi 300 may be used as a 150 watt/channel stereo amplifier, or as a 300 watt monophonic
amplifier, as determined by the rear panel switch. In either mode, front panel level controls may be
selected or bypassed; these can be useful in balancing room acoustics or trimming level balance
in biamp applications.

The front panel mute control is useful when exchanging cables or making changes to your system.

Triode switches are provided for those who wish to explore that operating mode.

The chassis is machined from thick aluminum, finished in a metallic base coat/clear coat finish.

The Phi 300 is designed not to the latest fad but to substance, for the highest possible sound
quality. Time spent familiarizing yourself with this manual will be well rewarded.

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UNPACKING & ASSEMBLY

Your amplifier has been shipped with the side and front glass in place. The following steps show
how these are installed, in the event that you ever need to change them.

Remove the screws that secure the aluminum top frame to the chassis
pillars. Turn counterclockwise to remove.

Take care to prevent the tool from scratching the chassis.

Remove the top frame.

From each of the four columns remove the tape, which prevented the
nylon setscrews from coming loose during shipment.

Slide the side glass plates into the pillars’ channels.

The glass will not go all the way to the chassis top, but has a gap at the
bottom for air flow.
Take care not to scratch or break the glass.

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The front glass has the etched VAC logo. Install this between the front
pillars.
Take great care not to scratch this glass.
The front glass fits into a small channel in the front plate.

Tighten the white nylon setscrews that secure the side glasses. Turn
clockwise to tighten.

There are four setscrews for each glass plate.

Do not tighten the setscrews for the front glass yet.

Install the six aluminum blocks at the top of the side glasses.
If there is a ‘dimple’ in the block, it should face the outside of the amplifier.

Tighten the metal setscrews that secure each block using the allen key
supplied. Turn clockwise to tighten.

Replace the aluminum top frame.
Ensure that the front glass fits into the groove in the top frame.
Ensure that the top frame sits flush in the pillars.

Replace the four screws that secure the top frame. Turn clockwise to
tighten.

Tighten the four white nylon setscrews that secure the front glass using the
tool provided. Turn clockwise to tighten.

Do not over tighten.

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