Page 2 of your user manual says it can be used from 100V to 240 V !
BUT it says that it's prewired for the US voltage ( in your case ) and will need to be 'reconnected' by a technician.
" Mains voltage is factory set and should only be
adjusted by ATC or your local dealer or distributor. "
This would mean that the transformer has taps on it for re-connection for 240 V operation. Look for a service manual and any good technician or good DIY techie could make the change in 1/2 an hour !
Before that , email ATC and ask them to send you the rewiring scheme for 240 V operation for your amp. Tell them you have a local technician to do it but don't have the service information ! Since they say it can be done I don't see why they wouldn't send you the info. Maybe also mention your serial number !
