I haven't owned these, but certainly the amp has to be turned on. It's not clear if you need to unhook the speaker cables and/or interconnects. FWIW, the parent company (Cary) suggests disconnecting the amps from speakers and sources before biasing, though on my Cary SLI-80 I have occasionally checked bias with everthing connected. I would caution that many amps require the speakers to be connected while in operation, so I would suggest contacting AES.
FWIW, here are the Cary intructions for their amps.
FWIW, here are the Cary intructions for their amps.
How do you correctly bias a Cary Audio vacuum tube amplifier?
Disconnect the speaker cables and the input RCA cable or XLR cable from the input jack.
Start with the amplifier warmed up for 5-10 minutes and then turn it off to connect the bias cable.
Connect the provided Bias Cord into the bias connection jack. It has a 1/4 inch mono 'phone plug' on one end and a pair of alligator clips on the other end. Plug the phone plug into the jack on the chassis. The red alligator clip is for positive electrical connections, the black one is for negative electrical connections on the milli ampere (mA) meter.
Set your meter to the milli amperes (mA) reading range. NOT to the Milli Volts (mV) range!
Turn the bias adjustment screw on the chassis all the way counterclockwise so that the meter will read zero when you turn the power on. Now, turn the AC power on. Wait for 60 seconds to warm up the tubes.
SLOWLY turn the bias adjustment screw clockwise while you watch the meter for a mA reading.