Hi Roland,
Do not connect a cab or speaker or whatever to this amp if it's under 8
Ohms.
The amplifier in this AVT275 is a chip amp (TDA7293).
You'll blow the amp.
I have them fairly regular in repair because of exactly these
manipulations; connecting a 4 Ohm cabinet.
It's a dual amp combo and it needs both outputs to be loaded with
minimum 8 Ohms. (if you want sound from both amps off course...)
I found that it's one of the very few amps that can allmost reproduce
the sound of the Spotniks, a swedish guitar group from the sixties.
Try to play Johny Guitar on it.
Cheers and a lot of fun.
Zilog