Absolare Push-Pull User Manual - Page 12

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6.2.2.  EL34  Bias  Levels  
There is no separate bias adjustments for EL34 tubes, but the push-pull symmetry is
important. With a multimeter at lowest DC volt measurement setting, insert black and
red probes into blue sockets. The adjustment point is in between the EL34 sockets.
You should try to get 0.0V or near by turning the adjustment pot with a small flat
screwdriver. If you cannot cross the zero value (i.e. you only get positive or negative
values in entire adjustment range) you should turn off the unit, wait until tubes are
cooled down, swap EL34's and repeat the adjustment procedure above. This
happens when one of the EL34 tube gain is very different than the other one. If
swapping the tubes does not solve the issue then you should replace at least one of
the tubes or install a gain matched pair.
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ABSOLARE Push-Pull Amplifier User Manual 0.9