VAC PA90 - Manual (Page 6)

6
OPERATION
Set the STANDBY switch on the PS90 to on. This provides power to the filaments (heaters) of
the PA90 tubes and charges the bias supply. After a delay of 2 minutes the OPERATE switch
may be set on, providing full voltage (approximately 480 volts) to the plates of the tubes. The
amplifier is now on and ready for listening.
Following the turn on procedure described above will help ensure long tube life. Having two
power switches provides additional control over the amplifier.
To turn the unit off, first turn the OPERATE switch to off, followed by the STANDBY switch.
(Actually, they may be thrown simultaneously. In addition, switching off STANDBY alone will
cut both supplies, but OPERATE must be switched off before the next turn-on.) Sound
(distorted) will continue for several seconds after the power is switched off. The slow sound
decay is caused by the slow discharge of the large energy storage capacitors in the power
supply and power amplifier. (The sound would continue for much longer except for the bleeder
resistors in the PS90.)
To mute the unit for a short time (15 minutes maximum advisable), turn the OPERATE switch
to off but leave the STANDBY switch on. The unit will play immediately when OPERATE is
again switched on.
Do not use the STANDBY mode for periods exceeding 15 minutes.
Before disconnecting your amplifiers from their power supplies allow them to sit with power
off for five minutes. This allows energy stored in the amplifier chassis to drain back in to the
power supplies. Failure to do so may result in damage to the regulators when the units are
reconnected.
As with all high fidelity products, the sound characteristics of the VAC amplifiers change
somewhat as they warm up. Best sound will be achieved after one hour of operation, with
subtle changes occurring for up to two hours. However, we advise against leaving the
equipment on at all times because of the attendant acceleration of output tube wear. Life of the
output tubes averages between 3,000 and 10,000 hours depending upon brand fitted and
random variations within the tubes themselves.
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. Refer to the discussion
of break in contained in the INTRODUCTION section of this manual for further information.
Please note that although your VAC System has been run for 48 hours at the factory, they will
continue to "break in" for approximately 150 hours. The break in is most pronounced on the 90
Watt Amplifiers, particularly in the ultralinear mode. Note that the triode and ultra-linear modes
do not require separate break in periods, and that the ultra-linear mode will improve even if you
only operate the amplifiers in the triode mode (this is in most cases the most listenable way
to break in the PA90).
Also be aware that many components display the need for a new break in period after being
transported in unheated cargo aircraft.