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15
Maintenance
Adjusting Vacuum Tube Bias
As shipped from the factory, the output "bias" adjustments are set for a
nominal 65mA per KT120 tube. Under these idle conditions the tubes are
each dissipating a conservative amount of power of their total capacity.
This point of operation provides "enriched" Class AB 1, and will satisfy the
most critical listener.
For best results, operate and adjust the VSi75 at 120V AC. Adjustment
must be made under zero-signal conditions after at least 15-20 minutes of
uninterrupted stabilization time.
Pressing the "BIAS" button on the remote or front panel enters the VSi75 into
bias mode, beginning with tube V1. Using the included plastic alignment
tool, adjust the bias via the labeled adjustment port located in front of each
tube which corresponds with the "V" number shown on the LCD display
until the bias reads 65mA. Pressing the "BIAS" button again will advance
the unit to V2, V3, V4 and back to the main operation screen.
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