Linear Tube Audio ZOTL ULTRALINEAR User Manual page 5

Quick Start
Remove amplifier from the box.
Check that the MONO/STEREO switch on the back is in the correct
position for your setup (see Operating Modes for more information)
Attach the power cable to the IEC connector and plug into an
outlet. The ZOTL Ultralinear uses a Berning-designed auto-switching
power supply and can be used universally.
Hook up your source and speakers.
Once your system is set up and everything is plugged in, turn your
system on. The ZOTL Ultralinear is powered on and off via the
toggle switch in the center of the face plate.
When first powering on, the tubes can take 30-45 to warm up
before music starts playing. Sometimes there is a high-pitched or
distorted sound during this time. This is normal and will go away
once the amp is warmed up.