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 Hi,Lim
Usually the operating manual comes with the amp with diagrams and descriptions for how
to adjust bias for the power tubes. If not provided, look at the top panel where you can see the two bias meters with 2 switches. The switches are for on or off the bias meters. Near
to these meters you'll also find two screws which are used for bias adjustment.
When you have the new EL34 or 6CA7 power tubes plugged in already, switch on the amp
and wait for 5 minutes. Then turn the bias meter switches to ON position. Look at the meters you can see them being activated, check whether it points before or after the red
mark on the meters and both sides are balanced or not.
Use screw driver to move the bias screws, do it slowly and sightly towards clock-wise and
then anti-clock-wise as a test. You'll rightaway know the clock-wise and anti-clock directions for adjusting the bias and the results can be seen on the meters. Usually, set
both meters to point to the position right before the red mark. Make sure both sides are balanced.
When the bias adjustment is done, turn the two bias switches to OFF position.
Hope the above info is helpful to you, and enjoy music. Best regards.
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