Absolare Push-Pull User Manual page 7

The large 845 output tubes must be installed in correct orientation. The small
indicator pin on the lower side of the tube base must be aligned with the small hole
on the right-side of the tube socket, as illustrated in the figure below.
CAUTION: Incorrect positioning of 845 tube may seriously damage the amplifier!
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ABSOLARE Push-Pull Mono Amplifier User Manual 1.2