I have an old acoustic AS80R that I have been using with a semi acoustic electric guitar for a nice clean sound. I like the sound of the combo (it has Celestion speaker elements), but the amplifier makes a constant 100 Hz buzz as soon as I turn it on, even when no guitar is connected. The buzz is louder than what I consider normal. Two professional service shops have tried to repair it.

Could I use it as speaker cabinet and replace the amp with a separate amplifier & how to do it?