Hey Anwar,
First, welcome to the family man....second, there's a massive, massive difference in the bias between 220 and 235 V. Huge, and yes, that will heat up the Sankens big time. The amp was certainly set up for optimum performance at 220 V. and needs to be rebiased for sure. This also minimizes the hum as well. The stereo amp is appr. 30 W on idle, yes, but you also have a center channel as well, and the heat is accumulative, which in turn brings up the bias again, etc. etc. etc.
Don't leave the amp on , and make arrangements for a rebias as soon as possible,
Klaus