VAC Renaissance 70-70 User Manual

RENAISSANCE SEVENTY/SEVENTY Mk. III

Dual Mono

Zero Feedback

All Triode

Power Amplifier

by

Valve Amplification Company

Operation & Maintenance

IMPORTANT INFORMATION

PLEASE READ CAREFULLY

Your Renaissance Seventy/Seventy has been fitted with a thermal sensor circuit. It
works in conjunction with the indicator lights located under the VAC logo on the front
panel, and has two functions:

1)If the idle current in a pair of 300B output tube should drop well below
acceptable limits, the light corresponding to that pair (left-most pair, left-center
pair, right-center pair, right-most pair) will light green. At least one of these
tubes should be replaced. Obtain a new tube, and replace one of the pair. If this
does not resolve the indication, return the original tube to its socket and replace
the other tube of the pair.

These lights will also be green when the amplifier is first switched on, and will
extinguish when the bias resistors have reached normal operating temperature
after several minutes. Note: a strong cool air current could cause the lights to
remain green even in normal operation.

2)Should any output tube draw excessive idle current (run away or internal
short) the light corresponding to that pair will glow red and the high
voltage supply to that channel will be shut down. The red light will stay
on until the power switch is turned off. One tube of the pair must be
replaced. Obtain a new tube, and replace one of the pair. If this does not
resolve the indication, return the original tube to its socket and replace
the other of the pair.

The lights for the other three pairs will show green after a few minutes...this
should be disregarded.

This protection feature normally will operate with much greater speed than the
AC line fuse, and provides a high degree of protection against elevated
temperature or fire due to a major failure in an output tube. However,
completely failsafe methods are not possible. As with any high power electrical
device, never leave the amplifier run unattended. Turn the amplifier off
immediately if you smell any strong odor, or if you see any parts glowing orange
through the gold vent grille.

To minimize difficulties, always source the highest quality tubes, avoiding inexpensive
or generic 300B tubes. We recommend obtaining replacement tubes from VAC, stating
that they are for use in the Renaissance Seventy/Seventy.

CAUTION

THESE UNITS CONTAIN NO USER SERVICEABLE PARTS. DO NOT REMOVE THE
BOTTOM PLATES OR TOP 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.

USE DUE CAUTION WHEN OPERATING THE AUDIO GROUND SWITCH. ALLOW THE
UNIT TO BE SWITCHED FULLY OFF FOR 5 MINUTES FOR THE TUBES TO COOL
DOWN. THE TUBES AROUND THIS SWITCH BECOME VERY HOT AND COULD CAUSE
SERIOUS BURNS IF TOUCHED.

THIS AMPLIFIER IS VERY HEAVY. IT MAY BE ADVISABLE TO HAVE ASSISTANCE IN
UNPACKING, MOVING, AND SETTING UP. BE SURE TO USE PROPER LIFTING
TECHNIQUES TO AVOID BACK STRAIN AND INJURY.

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Introduction
Unpacking
Installation
Operation
Installing New Output Tubes
Replacement of Low Level Tubes
Care Of Chassis
Tips and Advice

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

Tuning Your System
Specifications
Footnotes
Warranty & Registration Form

INDEX

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INTRODUCTION

The Renaissance Seventy/Seventy is a completely unique power amplifier. It allies purist amplifying devices
with the power and solidity required to control modern audiophile loudspeakers.

The most noticeable feature of this amplifier is the 300B filamentary triode output tube. Originally designed
by Western Electric in 1935 (Footnote 1), it has several extremely desirable features that have kept it in
continuous production since that time. An examination of its dynamic curves (Figure 1) reveals it to be a
naturally linear device, more so than triode connected pentodes or beam power tubes (ex: KT88, EL34), let
alone any transistor device. It gives this superb performance with voltages on the order of 450 VDC, not the
1000-1500 VDC required by other output triodes like the 211 or 845. This lower voltage and lower output
impedance allows superior output transformer design, control of the loudspeaker, and safety.

Each 300B tube has its own separate heater power supply and independent cathode self-bias network. This has
several major advantages. No user adjustment of any kind is necessary to maintain proper balance of the
amplifier. The stabilizing action of this technique upon the idle current (bias point) of each tube is exceptionally
strong, and self corrects for large mismatches among tubes or drift with age. This circuit also results in real­world output capability much greater than the test-bench rating would indicate (Footnotes 2,3,4).

A total of four 300B are used in each channel to reach 70 watts per channel in Class A.

The input circuitry of the Renaissance Seventy/Seventy is derivative of the unique Williamson circuit, which
provides pure, direct coupled, inherently balanced input amplification and phase splitting. Type 6SN7/5692
octal twin triodes do the honors.

The superb VAC output transformer provides superb voltage/current translation, allowing impedances from
eight ohms to as low as one ohm to be driven.

The 35 pound chassis is machined from quarter inch thick aluminum plate. This strong, resonance-resistent
structure houses two electrically independent channels of amplification. Each channel is separate, down to two
dedicated shielded power cords. A total of eight transformers are used, providing sixteen power supplies.

The units is completely hand wired in three dimensional space for the shortest possible lead lengths, allowing
passive components to perform much nearer to the theoretical ideal.

The Renaissance Seventy/Seventy 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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