VAC Vintage Mk II - Manual (Page 3)

either 2, 4, or 8. The "G" terminal is at ground potential, and the amplifier does not
invert phase.
4) Do not connect two amplifier outputs to each other.
5) Connect the AC cord to the power source indicated on the rear panel (100 volts AC,
120 volts AC, 220 volts AC, or 240 volts AC at 50 or 60 Hertz).
6) Follow the BIAS/BALANCE procedure described in this manual to set the idle
current. Check the idle current at 1 minute, 30 minutes, 1 hour, and 2 hours. Also,
read the section entitled INSTALLING NEW OUTPUT TUBES.
Operation
Continuous operation is not recommended. If the amplifier will not be auditioned for a few
hours it is best to turn them off. This avoids undue stress to the EL34 output tubes.
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 15 minutes of operation, with
subtle changes occurring for up to one hour. 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 2,000 and 5,000 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.
Please note that although your VAC amplifiers have been run for 48 hours at the factory,
they will continue to "break in" for approximately 150 hours. Also be aware that many
components display the need for a new break in period after being transported in unheated
cargo aircraft.
Bias and Balance Adjustment
Your VAC Power Amplifier has been shipped with output tube bias preset. This should be
checked when you install your amplifier, and approximately every month thereafter. It must
also be set whenever an output tube is changed.
Monitoring and adjustment of the output tubes is quite easy, and requires a voltmeter
capable of reading in the millivolt range. To start, place the black test lead in the center test
point (TP2) and the red lead in TP1. Adjust the bias control to obtain a reading of 325
millivolts DC (.325 volts).