3. Even though you are using matched tubes, they are likely to have somewhat different bias voltages. By
rotating bias control adjust bias on the tube with higher reading. The bias should be adjusted to
approximately 350mV (0.35V), any value between 340 and 360mV (0.34 to 0.36V) is acceptable. For actual
bias current divide measured voltage by 10 to get current in mA (350mV=35mA). Check the bias reading
on the other tube and it may not be identical, but should not be lower than 290mV (0.29V). If it is, you are
likely to have poorly matched tubes - the amplifier will work, but performance may suffer a bit.
4. Repeat steps 2 and 3 for the other channel.
5. At this point you may allow the amplifier to work for a longer period of time (30 minutes or more) and then
check and readjust bias, if necessary.
Even though you may be tempted to check bias every so often, the practice will not give you meaningful
results - tube bias will depend on the input voltage value and even small variations of the AC line will make
bias voltage drift slightly causing your readings to differ and creating perception that tubes drifted more than
they actually do.
model i34
amplifier was designed with this in mind - tubes are run well below their
maximum ratings and normal variations of bias voltage will not affect their life nor performance. Checking
the bias every 200-300 hours of operation is acceptable, although not required.
Servicing
Because of its careful design and high manufacturing standards, your amplifier should normally require
only minimal service to maintain its high level of performance.
CAUTION: Lethal voltages are present inside the amplifier. Do not remove the amplifier’s bottom
cover and do not tamper with components inside the unit even with the power turned off. Servicing
should be left only to authorized and trained personnel.
9
We thank you for your confidence in Vista-Audio products. Our equipment has been
carefully assembled by highly skilled engineers and technicians. It will give you
many years of top-notch performance.
